No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Biochemical Characterization and Enzymatic Hydrolysis of Different Commercial Soybean Protein Isolates
Abstract
Thirteen commercial soybean protein isolates (SPIs) were characterized and submitted to the same conditions of hydrolysis with pancreatin to the same degree of hydrolysis (DH). The 13 SPIs differed with respect to their phytate contents (7.41−15.62 mg/g of protein), presence of trypsin inhibitor (5.17−94.72 UTI/mg of protein), protein dispersibility index (PDI) (11.7−88.7%), and relative compositions of the 7S subunits and 11S polypeptides present in the soluble fraction: α‘ (0−100%); α (0−26%); β (0−44%); acid polypeptide (50−100%); basic polypeptide (0−50%). The reaction time necessary for the hydrolysis to attain a DH of 21.5% varied from 48 to 252 min and was longer for isolates with complete 7S and 11S globulin fractions and higher PDI values. The 10% TCA soluble nitrogen index of the hydrolysates varied from 61.5 to 100%. The total free amino acids varied between 7.5 and 31.0%, with basic and hydrophobic amino acids being present in greater amounts. Electrophoresis indicated differences in the molecular weight profiles of the hydrolysates. The 13 SPIs analyzed were shown to be different, resulting in different products when submitted to the same conditions of hydrolysis. Keywords: Protein hydrolysis; soy protein hydrolysates; pancreatin; peptides
... Enzymatic synthesis has potential application in the food industry to remove bitterness of protein hydrolysates, to improve amino acids composition, or to modify some functional property (Lozano and Combes 1992). Soy protein is widely used as the nitrogen source in infant and adult formulas, both in the intact and hydrolyzed form (Henn and Netto 1998; Lahl and Braun 1994 ; Zhao and others 1997). Although soy hydrolysates present unique functional characteristics , their low methionine content is a limiting factor in the nutritional quality of the final product, especially for infants and patients on medical diets receiving it as the only protein source. ...
... Additionally in Mexico, the porcine pancreas is an enzyme source completely underutilized. Recently other authors (Henn and Netto 1998; Hettiarachchy and Kalapathy 1997) using commercial pancretin to hydrolyse soy protein isolates obtained good results respect to protein functionality. Soy flour. ...
... H values were higher in the high molecular weight and hydrolysis fractions than those for low molecular weight and synthesis fractions , as it corresponds to the degree of denaturation. According to Henn and Netto (1998), there is a decreasing in the proportion of the basic peptide of 11S from soy protein isolates with an increasing of degree of denaturation. Additionally, the areas of endotherms correlated directly to the surface hydrophobicity values . ...
: Soy protein was enzymatically modified and ultrafiltred, and functional properties were evaluated. After enzymatic hydrolysis, hydrolysate (20 g/100 mL) was incubated with chymotrypsin and glycerol at 37°C. Different methionine methyl-ester concentrations, pHs, and time were tested. Amino acid composition and functional properties of ultrafiltrated fractions (FI>10, 10>FII>3, and 3>FII>1 kDa) were evaluated. Optimum hydrolysis conditions were 12 h and 50°C, and those of synthesis were 0.07585 g Met/g, pH 7, and 3 h, binding 2.2% to 5% methionine. Fractions under 10 kDa presented 100% solubility and the best clarity. High-methionine fractions had higher foam volume, lower emulsifying capacity and hydrophobicity. Modified hydrolysates have a potential for use in soluble high nutritional products.
... Os resultados relativos à análise centesimal do IPS Samprosoy 90-NB encontram-se na Tabela 1. Para os cálculos de conversão do nitrogênio em proteína foram utilizados os fatores 6,25, que são utilizados na legislação bromatológica brasileira e também pelas indústrias de alimentos; e 5,71, que é o mais adequado, por representar o conteúdo nitrogenado específico da soja [48]. Os valores obtidos (90,2% para o fator 6,25 e 82,4% para o fator 5,71) estão de acordo com os recomendados pela legislação [5] e encontrados por MARTINS [20], HENN & NETTO [16], NETTO & GALEAZZI [21] e SALADO [25], todos considerando o fator de conversão de 6,25. Valores superiores a 96,9% (N x 6,25) em base seca foram obtidos por SOUZA [27] no IPS produzido a partir de farinha desengordurada de soja, sob diferentes temperaturas e com rendimento médio de 26,57%. ...
... Valores superiores a 96,9% (N x 6,25) em base seca foram obtidos por SOUZA [27] no IPS produzido a partir de farinha desengordurada de soja, sob diferentes temperaturas e com rendimento médio de 26,57%. O conteúdo de umidade e cinzas está de acordo com os encontrados por MARTINS [20], SALADO [25], HENN & NETTO [16] e SOUZA [27]. Quanto ao conteúdo de lipídeos, o valor obtido está semelhante ao descrito por MARTINS [20] e SALADO [25] e abaixo dos valores encontrados por HENN & NETTO [16] e SOUZA [27]. ...
... O conteúdo de umidade e cinzas está de acordo com os encontrados por MARTINS [20], SALADO [25], HENN & NETTO [16] e SOUZA [27]. Quanto ao conteúdo de lipídeos, o valor obtido está semelhante ao descrito por MARTINS [20] e SALADO [25] e abaixo dos valores encontrados por HENN & NETTO [16] e SOUZA [27]. HENN & NETTO [16] avaliaram 13 IPSs comerciais de diferentes marcas e obtiveram diferentes valores quanto ao conteúdo de proteína, lipídeos, umidade e cinzas. ...
O presente trabalho teve como objetivo realizar a caracterização química e nutricional da plasteína produzida a partir de isolado protéico de soja (IPS). O hidrolisado de IPS foi produzido em sistema descontínuo, 5% de substrato, relação enzima/substrato 1/20, 6 h, 37°C, sob agitação. A plasteína foi produzida com 40% de substrato em solução aquosa, pH 7, 24 h a 37°C, sob repouso. Na caracterização química, foi verificada a distribuição dos pesos moleculares por meio de eletroforese (SDS-PAGE) e cromatografia de exclusão molecular (CEM). A SDS-PAGE não permitiu a visualização das bandas tanto no hidrolisado quanto na plasteína. Na CEM o hidrolisado apresentou 5 frações de PM na faixa de 5,4 a 66,2 kDa e a plasteína com 2 frações de PM na faixa de 9,6 e 58,7 kDa. O escore químico de aminoácidos essenciais confirmou a presença dos aminoácidos sulfurados como limitantes, sendo obtidos os valores de 93,2 e 96,4% para o hidrolisado e plasteína, respectivamente. A modificação enzimática através da reação de síntese de plasteína mostrou ser um processo viável na produção de matéria-prima para formulações alimentares de uso em nutrição clínica e em outros sistemas, sendo necessária a suplementação de metionina quando utilizada como fonte exclusiva de proteína.
... To improve the nutritional value of the unheated meal, soybeans are subjected to thermal treatments such as toasting and extrusion (1,(6)(7)(8). Depending on temperature and humidity conditions during heat treatment, the components of the soybean matrix may interact resulting in a reduced enzymatic degradability and extractability of the proteins (9,10). Generally, the effects of heat treatment on solubility and the proteolytic degradation of pure soy proteins, concentrates, and isolates are well described in the literature (7,(11)(12)(13)(14)(15). ...
... Depending on temperature and humidity conditions during heat treatment, the components of the soybean matrix may interact resulting in a reduced enzymatic degradability and extractability of the proteins (9,10). Generally, the effects of heat treatment on solubility and the proteolytic degradation of pure soy proteins, concentrates, and isolates are well described in the literature (7,(11)(12)(13)(14)(15). Purified native proteins may show some resistance toward proteolytic degradation, but the enzymatic degradability of most proteins improves by appropriate heat treatment at high humidity followed by proteolysis (16,17). ...
... The residues contained 15-20% protein. The amino acid compositions of the meals were comparable to those reported in the literature (7). Enzymatic extraction of NN caused an increase in the proportion of the hydrophobic amino acids (34) in the residue. ...
To study the incomplete enzymatic extractability of proteins and carbohydrates of thermally treated soybean meals, one unheated and three heat-treated soybean meals were produced. To obtain truly enzyme-resistant material, the meals were extracted by a repeated hydrolysis procedure using excessive concentrations of different combinations of commercial protease and carbohydrase preparations. The water extractability of protein from the different meals varied considerably (13−67%). For all soybean meals, enzymatic treatment extracted most of the original protein (89−94%). Carbohydrase preparations did not improve protein extraction. High-humidity heat treatment led to a more effective enzymatic extraction, which seemed to correlate with the extent of protein denaturation. Results with purified proteins indicated that the soybean meal matrix affects the enzymatic extraction of protein from the meals. Interactions between protein and other components (e.g., cellulose) may explain the incomplete enzymatic extractability of protein from the meals. Keywords: Soybean meal; heat treatment; hydrolysis; extraction; enzymatic residue; protease; carbohydrase; composition; protein; carbohydrate; amino acid
... Limited proteolysis exposes hydrophobic and hydrophilic residues, enhances the amphiphilic characteristics of proteins, and improves emulsification (Tavano, 2013). However, previous studies found that soy proteins were generally resistant to proteolysis (Govindaraju & Srinivas, 2007;Henn & Netto, 1998;Qi et al., 1997). The intrinsic difficulty is that globular soy proteins have compact quaternary and tertiary structures that protect many of the peptide bonds (Govindaraju & Srinivas, 2007). ...
... The intrinsic difficulty is that globular soy proteins have compact quaternary and tertiary structures that protect many of the peptide bonds (Govindaraju & Srinivas, 2007). Moreover, protein aggregation during the processing of SPI may result in the burying of cleavage sites (Henn & Netto, 1998). Therefore, pre-treatment is necessary to modify the structural characteristics of soy proteins, in order to increase their accessibility to protease and obtain enhanced functionalities. ...
Soy protein isolate (SPI) was treated by high-pressure microfluidization and pancreatin hydrolysis in this work. Results showed that microfluidization substantially enhanced pancreatin hydrolysis of SPI in terms of degree of hydrolysis (DH), with a preferable treatment condition at 120 MPa and 30 g/L SPI concentration. SDS-PAGE conducted under reducing conditions showed that microfluidization increased the accessibility of some subunits (α’-7S, A-11S and B-11S) in SPI to pancreatin hydrolysis, resulting in changes in protein solubility (PS), surface hydrophobicity (H0), and molecular weight distributions for hydrolysates. Emulsion systems (20 vol.% oil, 20 g/L protein samples, pH 7.0) formed by control SPI and SPIH (SPI hydrolysates) were unstable due to fast coalescence and bridging flocculation during homogenization, while that formed by MSPIH (microfluidization pretreated SPIH) with 5.8 % DH was more stable and showed smaller mean droplet size (d43). Compared with SPIH, MSPIH showed a stronger increase in PS and a more moderate change in H0 during pancreatin hydrolysis, suggesting the production of more surface-active soluble peptides, which may explain their markedly improved emulsifying capabilities. This work showed that modified SPI could be an effective food emulsifier with microfluidization pre-treatment and limited proteolysis leading to desirable functional modifications of globular proteins.
... Hal ini dduga disebabkan oleh beberapa hal, yaitu penurunan ikatan peptida yang spesifik bagi enzim (sesuai untuk aksi enzirn tersebut), inhibisi produk dan inaktifasi e~m , kompetisi antara substrat asli atau protein yang tidak terhidrolisis &ngan peptida yang terbentuk selama hidrolisis. Gb 3. Penga~h lama waktu hidrolisis bungkil kedelai terhadap protein Waktu hidrolisis rata-rata dari berbagai isolat protein kedelai dengan pankreatir~ dilaporkan berkisar dari 0,8 sampai 4,2 jam (Henn & Netto, 1998). Dilaporkan pula bahwa isolat protein kedelai &ngan indeks dispersi protein lebih tinggi dan mengandung semua sub unit fraksi polipeptida yang larut air, memiliki protein native. ...
... Rendemen pepton kharnir lebih besar bila dibandingkan dengan pepton dari bungkil kedelai, ha1 ini diduga karena bentuk atau struktur protein dari kedua bahan tersebut berbeda. Netto & Galeazzi (1998) menyebutkan seringkali sulit bagi protein dalarn bentuk alami (native) seperti protein kedelai untuk mengalami dekomposisi dengan enzim hidrolitik seperti protease. Disebutkan pula bahwa denaturasi protein dengan panas, alkohol, d l umumnya dlakukan l&h dahulu sebdum I Waktu (jam) I Gb. 4. Pengaruh lama waktu hidrolisis khamir terhadap protein terlarut diperlakukan dengan hidrolisis proteolitik. ...
... Hal ini dduga disebabkan oleh beberapa hal, yaitu penurunan ikatan peptida yang spesifik bagi enzim (sesuai untuk aksi enzirn tersebut), inhibisi produk dan inaktifasi e~m , kompetisi antara substrat asli atau protein yang tidak terhidrolisis &ngan peptida yang terbentuk selama hidrolisis. Gb 3. Penga~h lama waktu hidrolisis bungkil kedelai terhadap protein Waktu hidrolisis rata-rata dari berbagai isolat protein kedelai dengan pankreatir~ dilaporkan berkisar dari 0,8 sampai 4,2 jam (Henn & Netto, 1998). Dilaporkan pula bahwa isolat protein kedelai &ngan indeks dispersi protein lebih tinggi dan mengandung semua sub unit fraksi polipeptida yang larut air, memiliki protein native. ...
... Rendemen pepton kharnir lebih besar bila dibandingkan dengan pepton dari bungkil kedelai, ha1 ini diduga karena bentuk atau struktur protein dari kedua bahan tersebut berbeda. Netto & Galeazzi (1998) menyebutkan seringkali sulit bagi protein dalarn bentuk alami (native) seperti protein kedelai untuk mengalami dekomposisi dengan enzim hidrolitik seperti protease. Disebutkan pula bahwa denaturasi protein dengan panas, alkohol, d l umumnya dlakukan leb~h dahulu sebdum I Waktu (jam) I Gb. 4. Pengaruh lama waktu hidrolisis khamir terhadap protein terlarut diperlakukan dengan hidrolisis proteolitik. ...
... Sin embargo, las mejoras más recientes en la preparación de concentrados proteicos son las que conciernen a la mejora de sus características organolépticas mediante el procedimiento del triple disolvente, que consiste en extraer sucesivamente la harina con hexano, hexano-etanol y etanol-agua (Hayes y Simms, 1973;Howard et al., 1980). ...
... Actualmente los aislados proteicos más extendidos son los de soja, ya que ofrecen ventajas económicas, nutricionales y funcionales manteniendo las cualidades sensoriales deseables necesarias para la aceptación por el consumidor (Wagner et al., 1990, Nagano et al., 1996, Henn et al., 1998. Hoy día existen una gran variedad de aislados de soja disponibles comercialmente, diseñados específicamente para proporcionar las características deseadas según el alimento de que se trate. ...
A review on the production of protein concentrates and isolates and their use in human foods has been carried out. The three methods usually used in the obtention of protein concentrates are described: extraction with water, with thermic treatment or with hydroalcoholic solutions. Also the most common methods used for the obtention of protein isolates are described, including isoelectric precipitation or protein recovery by Ultrafiltration. Applications of protein isolates in human foods, such as nutritionals or functionals, are also described.
... Hubungan antara konsentrasi substrat dan enzim pada proses hidrolisis kedua substrat di atas dapat dilihat pada Gambar 1 dan 2. Rasio konsentrasi enzim papain terhadap substrat bungkil kedelai masih dapat dilakukan pada 1 : 20 sedangkan untuk khamir masih dapat dilakukan pada rasio 1 : 30. Netto & Galeazzi (1998) melaporkan rasio enzim/substrat untuk hidrolisis isolat protein kedelai dengan pankreatin adalah 1/35 sementara Henn & Netto (1998) mengamati hidrolisis isolat protein kedelai dengan pankreatin pada rasio enzim/substrat 1/15. Perlakuan pada beberapa kondisi suhu (40 -80 0 C) menunjukkan laju hidrolisis optimum untuk bungkil kedelai dapat dicapai pada suhu 70 0 C sedangkan laju optimum untuk khamir adalah 60-70 0 C. Dapat disimpulkan bahwa suhu 60 0 C adalah optimum untuk kedua substrat tersebut. ...
... Netto & Galeazzi (1998) menyebutkan seringkali sulit bagi protein dalam bentuk alami (native) seperti protein kedelai untuk mengalami dekomposisi dengan enzim hidrolitik seperti protease. Disebutkan pula bahwa denaturasi protein dengan panas, alkohol, dll umumnya dilakukan lebih dahulu sebelum Waktu hidrolisis rata-rata dari berbagai isolat protein kedelai dengan pankreatin dilaporkan berkisar dari 0,8 sampai 4,2 jam (Henn & Netto, 1998). Dilaporkan pula bahwa isolat protein kedelai dengan indeks dispersi protein lebih tinggi dan mengandung semua sub unit fraksi polipeptida yang larut air, memiliki protein native. ...
... The proximate composition of the SPIs is shown in Table 1. In general, the mean values of the analyzed parameters (protein, lipid, moisture, ash and protein composition) are in accordance with the range of values described in literature [30,31]. ...
The objectives of the present study were to assess how structural and gelation properties of soy protein isolates (SPIs) are affected by the characteristics of the soybean meal starting material used for protein extraction. The different degree of denaturation and aggregation due to processing treatments undergone by the soybean meals significantly affect the soy protein structural organization and functional properties. The main type of interaction responsible for the aggregates differed in the commercial and laboratory isolates, thus impacting on the protein composition of the soluble fraction of the different isolates. Spectroscopy analysis revealed that the commercial SPIs differ from the lab samples essentially due to the degree of protein aggregation and to differences in the tertiary structure (amide II). At the structural level, the lab-prepared SPIs obtained from the raw soy meal subjected to more extensive processing treatments is the one closest to the commercial samples, differentiating itself from the other laboratory isolates by the aggregation state. However, some extent of pre-denaturation may be beneficial for the gelation performance of the soy protein samples, decreasing the gelation temperature and producing gels with higher stiffness and elastic character. On the contrary, extensive protein denaturation originate thermodynamically stable aggregates, water insoluble macro-aggregates less unfolded and dissociated by the heat treatment, being less available to integrate the three-dimensional network.
... As shown in Fig. 1(a), the WISC of all samples decreased as pH was increased and then decreased sharply at pH of about 5.8 and beyond. This could be ascribed to the higher acidic amino acid residue (glutamic acid residue, aspartic acid residue, etc.) content in the soy protein, because the acidic amino acid residue is readily reactive with base to give carboxylate structures, and in water media the solubility of soy protein is increased (Henn and Netto 1998). The WISCs of SBA also decreased with pH, and were significantly lower than the control samples when the pH was lower than 5.8, indicating that the water-solubility components of SBA were enhanced as a result of polysaccharides in DSF being hydrolyzed during the Viscozyme L treatment process (Qu 2011). ...
To evaluate the effects of preparation conditions of a 'green' soy-based adhesive(SBA), Viscozyme L was employed to hydrolyze the polysaccharides in defatted soy flour (DSF) for preparing SBAs, and plywood bonded by SBAs with Pinus massoniana veneer was then produced. Effects of enzymolysis pH, temperature, time, and additive amount of the Viscozyme L on water-insoluble substances content (WISC) and bonding strength (boiling-water test) of SBAs were investigated. Results showed that bonding strength increased first then decreased as enzymolysis pH and temperature were increased. WISC decreased with increasing pH and decreased first then increased as temperature increased. WISC decreased and bonding strength improved slowly with the increasing time. Bonding strength improved slowly as additive amount of Viscozyme L increased. WISC decreased as the added amount of Viscozyme L increased and then decreased slowly at the added amount of Viscozyme L of about 50 FBG and beyond. SBAs prepared by Viscozyme L action on soy flour slurry decreased WISC and improved bonding strength. The suitable preparation conditions of SBA for plywood are as follows: enzymolysis pH 5.2, temperature 50°C, and time 20 min, and the additive amount of Viscozyme L depended on the application condition.
... Lo and co-workers studied the effects of a 4 wt% solution of trypsin (Sigma-Aldrich P7545) on SPI at pH 7.5 and 37ºC for 2 hours and found that the hydrolysis slowed considerably in the second hour and produced positively charged C-terminal peptides (Lo et al., 2006, Lo et al., 2005. Henn and Netto studied the digestion of 13 SPI with pancreatin (unknown type) at a 1:15 enzyme to substrate w/w ratio at pH 8 and 40ºC for a range of times from 48 to 252 minutes to obtain the desired degree of hydrolysis (Henn & Netto, 1998). ...
... Previous work has tended to concentrate on measuring the extent of hydrolysis of soy protein isolates (Henn and Netto, 1998;Netto and Galeazzi, 1998) rather than soymilk. ...
... these meals are well suited to animal nutrition, due to their poor solubility, inhomogeneity, and intermingling with non‐ protein components (Garcia and Phillips, 2009), they are dif‐ ficult to utilize for other non‐feed applications (Garcia et al., 2006). Hydrolysis has been used to improve the solubility and functionality of many bulk protein materials including wheat gluten (Wang et al., 2006), fish (Gildberg et al., 1989), animal hair (Coward‐Kelly et al., 2006a), and soy protein isolate (Henn and Netto, 1998). Practical scale protein hydrolysis is usually achieved by catalysis with enzymes, acid, or alkali. ...
Rendered proteins are well suited for animal nutrition applications, but due to their insolubility, inhomogeneity, and the presence of non-protein substances, they are difficult to utilize in other applications. In an attempt to overcome these obstacles to utilization, three types of rendered proteins [meat and bone meal (MBM), feather meal (FM), and blood meal (BM)] were partially defatted and then hydrolyzed to varying extents using calcium hydroxide or one of three enzymatic treatments, in 4- or 6-L batches. After centrifugation, filtration, and spray drying, these hydrolysates were analyzed for changes in physical and chemical properties that relate to their potential utility. In all cases, the proportion of organic matter solubilized increased along with hydrolysis duration, although the molar mass distribution of the hydrolysis product only had a weak dependence on hydrolysis duration; the soluble material consisted of very small peptides at all time points. Alkalihydrolysis was not effective in yielding a product low in ash; although the insoluble ash in MBM and FM appears not to have been carried over into the product, it was replaced by significant amounts of calcium salts; corresponding enzymaticallyhydrolyzed batches contained approximately 40% less ash. Alkali-hydrolysis in particular had effects on the amino acid composition of the products, destroying some amino acids and creating others, including the cross-linked amino acids lysinoalanine and lanthionine; enzymatic hydrolysis effects on amino acid composition were different in type and generally lesser in magnitude. It is concluded that hydrolysis is a promising treatment for increasing the non-feed utility of rendered animal proteins. © 2011 American Society of Agricultural and Biological Engineers.
... Small molecular weight (MW) proteins in the SCN and MSCN were analysed by the method described by Henn and Netto (1998). The SCN or MSCN (2% w/v) was dispersed in distilled water and stirred until no sedimentation was observed. ...
The mozzarella cheese market has been growing considerably in recent years, due to the increasing demand for pizzas. Owing to the high cost of traditional mozzarella cheese and consumer preference towards healthier products, cheese analogs containing low levels of saturated fatty acid and cholesterol can be used to make additional varieties of mozzarella cheese. The current study attempted to use rice bran oil (RBO) and rice flours in the production of milk fat-free mozzarella cheese analogs made with sodium caseinate (SCN). The SCN was physicochemically modified by lactic acid hydrolysis with limited water content (30-50%). It was found that mozzarella cheese analogs retained similar stretchability and meltability characteristics to those of commercial cheese and could be prepared by emulsifying 20% RBO in an aqueous suspension containing 16% SCN, 7.75% MSCN (4.12 mg TCA soluble peptide/g SCN), 1.25% waxy rice flour and 51% aqueous phase. Confocal laser scanning microscopy showed dispersed strands of gelatinised waxy rice starch separated from the protein phase after cheese melting. The multi-phase structure thus helped control the meltability and stretchability of the mozzarella cheese analogs containing RBO. Consequently, RBO could be used to replace milk fat in cheese products.
... 3 Many physical, chemical and enzymatic modi®cations have been used to expand the range of functional properties in soy proteins. 2,4,5 These modi-®cations can be costly in terms of the process itself as well as losing some other properties at the expense of improving the targeted ones. Chemical modi®cation also poses the problem of removing any unreacted reagents from the ®nal product. ...
Soy protein isolate (SPI) fractions were produced using two different pore size microfiltration membranes. Microfiltration was carried out on SPI produced by isoelectric precipitation of a crude protein extract. Five fractions were obtained: two retentates and two permeates from the two membranes plus an intermediate fraction obtained as the retentate on the small‐pore‐size membrane using the permeate from the larger‐pore‐size membrane. Emulsions stabilised by the retentate fractions exhibited higher values (P < 0.01) of emulsion stability index (ESI) and emulsifying activity index (EAI) than those stabilised with fractions made from the permeates. The intermediate fraction gave intermediate ESI values, while the EAI values were not significantly different from those for SPI and one of the retentates. SDS‐PAGE profiles indicated that the fractions exhibiting high functionality in terms of ESI and EAI were also richer in 7S globulin soy protein subunits.
© 2002 Society of Chemical Industry
... It was also lower than protein contents reported for soy protein isolates (87.9-94.1%; Henn & Netto, 1998) and for chickpea (83.4%) and sunflower (97.0%) protein isolates (Vioque et al., 2001). Final protein content is the result of a raw material's original composition and the preparation method employed; it influences both protein and carbohydrate content (NFE). ...
Use of low degree of hydrolysis (DH < 10%) with enzymatic treatment can produce protein hydrolysates with functional properties superior to the raw material. Suspensions of Phaseolus lunatus protein isolate (PPI) were treated with one of two commercial enzymes (Alcalase or Flavourzyme) at 50 °C and pH 8.0. DH with Alcalase was greater than Flavourzyme at 5 or 15 min of reaction. Alcalase-prepared hydrolysates had more peptides than those prepared with Flavourzyme. All the hydrolysates had higher solubility than the PPI, the highest being for the Alcalase-prepared hydrolysate at 15 min reaction time. Overall, the Alcalase-prepared hydrolysates had better solubility characteristics, whereas the Flavourzyme-prepared hydrolysates had better film properties (maximum emulsifying capacity and the highest foam formation values). This is probably because of the greater ease of movement toward the interface as shown by their high surface hydrophobicity values. The Alcalase-prepared hydrolysates had generally low or nonexistent film properties.
... Schofield et al. (1983) indicated that molecular weights of wheat gluten were shifted to higher values at a certain temperature, and at 100 C, glutenins and gliadins in wheat gluten appeared to crosslink respectively or together. Henn and Netto (1998) and Lavelli et al. (1996) suggested that proteins with a compact structure submitted to the acid deamidation resulted in the rupture of tertiary structure and unfolding molecular conformations; however, excessive denaturation was often accompanied by a different degree of aggregation. Actually, in present case, the samples of soluble fractions of acid deamidated wheat gluten with or without moisture-heating were subjected to electrophoretic analysis (see Section 2.2). ...
Background:
The number and surface nature of amino acids (AAs) in substrate proteins available to hydrolytic enzymes are critical. Among them, the micro-environmental properties of specific AAs in substrates before hydrolysis would probably dominate the susceptibility of substrates to enzymatic hydrolysis. Fundamental knowledge concerning this regard is lacking. The objective of this work was to investigate the relationship between the exposure level of AAs in acid-deamidated wheat gluten and their susceptibilities to in vitro enzymatic hydrolysis by pancreatin through both high-performance liquid chromatography and Raman spectra. Wheat gluten deamidated with HCl (HDWG), citric acid (CDWG), succinic acid (SDWG) and acetic acid (ADWG) at the same degree of deamidation under the same heat treatment were chosen as the substrates. Substrate characterisations including degree of hydrolysis, surface hydrophobicity and structural characteristics before hydrolysis, together with analysis of free AAs of the corresponding hydrolysates during hydrolysis, were investigated.
Results:
Hydrolysates from SDWG had the highest value for the degree of hydrolysis. The susceptibility of CDWG to pancreatin hydrolysis was the lowest, lower than native wheat gluten (CK) after the initial 36 h. Compared with free AAs, the mole increase profiles of CK, Arg production levelled off in HDWG after 12 h whereas it was inhibited in ADWG. For SDWG, Arg release was dramatically inhibited after 12 h and was replaced by Trp. Investigations using Raman spectra of the micro-environment of Cys, Trp, Tyr and His and the mole increase trend of them indicated that the exposure level of these amino acids in substrates was positively related to their susceptibilities to pancreatin hydrolysis especially after 24 h of hydrolysis.
Conclusion:
Deamidation by four acids has a distinct influence on the structural characteristics of wheat gluten substrates. Although the substrates were selected at the same level of deamidation by the same heat treatment, their resultant conformational differences significantly influenced the exposure level of amino acids for binding to enzymes and the susceptibility of substrates to in vitro enzymatic hydrolysis. Therefore, it had an influence on changing enzyme cutting sites of pancreatin. This information will provide a better understanding of specific behaviour of AAs in wheat gluten during enzymatic hydrolysis from a new perspective.
... Many physical, chemical and enzymatic modifications have been used to expand the range of functional properties in soy proteins. (Campbell, Shih, & Marshall, 1992;Henn & Netto, 1998;L'hocine, Boye, & Arcand, 2006;Qi, Hettiarachchy, & Kalapathy, 1997;Wu, Hettiarachchy, & Qi, 1998). These modifications can be costly in terms of the process itself as well as losing some other properties at the expense of improving the targeted ones. ...
Five soy proteins isolate (SPI) fractions were produced using two microfiltration membranes with different pore sizes. Fractionation was carried out on SPI produced by isoelectric precipitation of a crude protein extract. The five fractions were two retentates and two permeates from the two membranes, the fifth fraction was obtained as the retentate on the smaller-pore-sized membrane fed with the permeate from the larger-pore-sized membrane. Solubility, foaming and emulsifying properties of the collected fractionates were investigated. It was observed that in the pH range 3–8 the retentates featured superior solubility compared with permeates. There was no significant difference (p>0.01) in solubility between the retentates and SPI at pH⩾6. Foaming characteristics of the fractions followed the same trend as solubility with regard to foam expansion. There was, however, no particular trend observed with regards to foam stability. Emulsions stabilised by the retentates exhibited higher values (p<0.01) of emulsion stability index (ESI) and emulsifying activity index (EAI) than those stabilised with permeates. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) profiles indicated that the fractions exhibiting high functionality in terms of solubility, foaming and emulsifying properties were also richer in 7S globulin soy protein subunits.Isoelectric focussing (IEF) profiles showed that retentates were richer in species with isoelectric points (pI) between 5.2 and 5.6 while permeates featured more prominently at pIs between 4.5 and 4.8.
... Schofield et al. (1983) indicated that molecular weights of wheat gluten were shifted to higher values at a certain temperature, and at 100 C, glutenins and gliadins in wheat gluten appeared to crosslink respectively or together. Henn and Netto (1998) and Lavelli et al. (1996) suggested that proteins with a compact structure submitted to the acid deamidation resulted in the rupture of tertiary structure and unfolding molecular conformations; however, excessive denaturation was often accompanied by a different degree of aggregation. Actually, in present case, the samples of soluble fractions of acid deamidated wheat gluten with or without moisture-heating were subjected to electrophoretic analysis (see Section 2.2). ...
The effect of acetic acid and hydrochloric acid (HCl) deamidation pretreatment on the susceptibility of wheat gluten to enzymatic hydrolysis by Pancreatin and sensory characteristics of the resultant hydrolysates was investigated. At two degrees of deamidation (24% and 60%, with or without moisture-heating, respectively), wheat gluten pretreated by acetic acid deamidation was more susceptible to be hydrolyzed as evaluated by the hydrolysis degree, nitrogen solubility index, titratable acid amount and free carbohydrate content of the hydrolysates. Wheat gluten pretreated by acetic acid deamidation at a degree of 24% exhibited the highest susceptibility to enzymatic hydrolysis. Moisture-heating (121 °C, 10 min) in the deamidation pretreatment decreased the susceptibility of wheat gluten to enzymatic hydrolysis and the peptide factions of ≤3000 Da in the hydrolysates due to the formation of larger molecule weight aggregates. The hydrolysates prepared from acetic acid deamidated wheat gluten showed more intense glutamate-like and sauce-scented taste and better nutritional characteristics.
... Digestibility of these amino acids (and His and Tyr) appears to be high in the three tested diets (but the soybean diet was supplemented with free Met; Table1). It is known that these amino acids largely appear as free amino acids in casein (Savoie, 1994) and soybean (Henn and Netto, 1998) hydrolysates. No major disparity was found in the amino acid composition of the squid and fish hydrolysates. ...
The effects of pelleted diets with different protein composition (fish, squid or soybean meals as main protein sources) on trypsin secretion and expression were studied in the lobster Panulirus argus. Trypsin secretion was shown to be maximal 4 h after ingestion. At this time, fish- and squid-based diets induced trypsin secretion, as well as up-regulation of the major trypsin isoform at the transcription level. While fish- and squid-based diets elicited a prandial response, soybean-based diet failed to stimulate the digestive gland to secrete trypsin into the gastric fluid or induce trypsin expression above the levels observed in fasting lobsters. In vitro assays showed that intact proteins rather than protein hydrolysates stimulate trypsin secretion in the lobster. However, the signal for trypsin transcription appears to be different to that for secretion and is probably mediated by the appearance of free amino acids in the digestive gland, suggesting a stepwise regulation of trypsin enzymes during digestion. We conclude that trypsin enzymes in P. argus are regulated at the transcription and secretion level by the quality of dietary proteins through two distinct signaling pathways. Our results indicate that protein digestion efficiency in spiny lobsters can be improved by selecting appropriated protein sources. However, other factors like the poor solubility of dietary proteins in dry diets could hamper further enhancement of digestion efficiency.
... Partial denaturation improved rehydration of protein and increased the accessibility of cleavage sites to enzymes. This observation was consistent with previous research on soy protein modification (Nielson 1997; Henn and Netto 1998; Jung et al 2005). However, these pretreatments (homogenization, sonication, or thermal pretreatments) did not alter the total soluble fraction of rice protein hydrolysate. ...
Rice endosperm protein was modified to enhance solubility and emulsifying properties by controlled enzymatic hydrolysis. The optimum degree of hydrolysis (DH) was determined for acid, neutral, and alkaline type proteases. Solubility and emulsifying properties of the hydrolysates were compared and correlated with DH and surface hydrophobicity. DH was positively associated with solubility of resulting protein hydrolysate regardless of the hydrolyzing enzyme, but enzyme specificity and DH interactively determined the emulsifying properties of the protein hydrolysate. The optimum DH was 6-10% for good emulsifying properties of rice protein, depending on enzyme specificity. High hydrophobic and sulfhydryl disulfide (SH-SS) interactions contributed to protein insolubility even at high DH. The exposure of buried hydrophobic regions of protein that accompanied high-temperature enzyme inactivation promoted aggregation and cross-linking of partially hydrolyzed proteins, thus decreasing the solubility and emulsifying properties of the resulting hydrolysate. Due to the highly insoluble nature of rice protein, surface hydrophobicity was not a reliable indicator for predicting protein solubility and emulsifying properties. Solubility and molecular flexibility are the essential factors in achieving good emulsifying properties of rice endosperm protein isolates.
... 3 Many physical, chemical and enzymatic modi®cations have been used to expand the range of functional properties in soy proteins. 2,4,5 These modi-®cations can be costly in terms of the process itself as well as losing some other properties at the expense of improving the targeted ones. Chemical modi®cation also poses the problem of removing any unreacted reagents from the ®nal product. ...
Thesis (Ph. D.)--University of Reading, 2001.
... Actualmente los aislados proteicos más extendidos son los de soja, ya que ofrecen ventajas económicas , nutricionales y funcionales manteniendo las cualidades sensoriales deseables necesarias para la aceptación por el consumidor (Wagner et al., 1990, Nagano et al., 1996, Henn et al., 1998). Hoy día existen una gran variedad de aislados de soja disponibles comercialmente, diseñados específicamente para proporcionar las características deseadas según el alimento de que se trate. ...
A review on the production of protein concentrates and isolates and their use in human foods has been carried out. The three methods usually used in the obtent ion of protein concentrates are described: extraction with water, with thermic treatment or with hydroalcoholic solutions. Also the most common methods used for the obtention of protein isolates are described, including isoelectric precipitation or protein recovery by ultrafiltration. Applications of protein isolates in human foods, such as nutritionals or functionals, are also described.
Se ha real izado una revisión sobre la obtención de concentrados y aislados proteicos vegetales y sus aplicaciones en alimentación humana. Se describen los tres métodos más comunes para la obtención de concentrados proteicos: extracción con agua, con tratamiento térmico o con soluciones hidroalcoholicas. También se describe los métodos más frecuentes de obtención de aislados proteicos, que incluyen en su segunda fase la precipitación isoelectrica de las proteínas o la recuperación mediante ultrafiltración de las mismas. Por último se citan las aplicaciones más importantes de los aislados en alimentación humana, como pueden ser nutricionales o funcionales.
Summary This research describes the extraction of both a protein concentrate and isolate from the seeds of cupuassu (Theobroma grandiflorum Schum) using a mild extraction procedure, and provides the amino acid and electrophoretic profiles of the proteins of this Amazonian product. The pH of minimum solubility, considered as the isoelectric point representative of the proteins was 3.5. The mild extraction system was not capable of producing a protein concentrate and protein isolate containing more than 31.18 and 64.33% protein, respectively. From the electrophoretic profiles of the defatted flour, protein concentrate and protein isolate, three major bands were observed with approximate molecular weights between 20.03 and 39.79 kDa. Six additional weak bands were evident in the profiles of the defatted flour and the concentrate, but two of these were absent from the isolate. As inferred from the amino acid profiles of the flour, concentrate and isolate, the cupuassu seed proteins contain a composition nutritionally superior to that of cocoa for most of the amino acids.
A soja constitui excelente fonte de proteína para a alimentação humana e animal, porém contém alguns componentes de ação antinutricional, como os inibidores de proteases, lectinas, fitatos e saponinas. Neste trabalho foram avaliados os efeitos do tratamento sob alta pressão isostática, considerado brando em relação ao tratamento térmico, sobre os fatores antinutricionais como teor de fitato e inibidor de tripsina de solução com 5% de isolado proteico de soja, processada na faixa de 200 a 700 MPa. Foram realizadas duas extrações de fitato e inibidor de tripsina de bateladas diferentes, sendo as amostras analisadas em triplicata. Há indícios que o tratamento sob alta pressão isostática seja eficiente para eliminar o fitato presente nas amostras de isolado proteico de soja, mas não se mostrou efetivo para alterar os teores de inibidor de tripsina. PALAVRAS-CHAVE: ISOLADO PROTEICO DE SOJA; FITATO; INIBIDOR DE TRIPSINA; ALTA PRESSÃO ISOSTÁTICA.
Peanut protein concentrate (PPC) was extracted from commercial defatted peanut flour (DPF) after protease pretreatment. The effect of proteolysis by Alcalase 2.4 L, papain and Protamex at various degrees of hydrolysis (DHs; 1–8%) on the yield and functional properties of PPC were investigated. Proteolysis remarkably increased the nitrogen solubility of DPF in acidic and basic conditions. Enzymatic degradation of denatured and insoluble proteins in DPF was mainly responsible for the increase of nitrogen solubility index. Compared with the control, the yield of PPC was significantly increased by enzymatic pretreatment. In terms of the functional properties, PPCs prepared by papain and Protamex at 4% or 8% DH had high emulsifying activity index. For all three enzymatic treatments, foaming capacity and foaming stability were significantly improved at various DH ( P < 0.05). This study demonstrated that protease pretreatment was a highly effective way to extract PPC with good functional properties from DPF.
PRACTICAL APPLICATIONS
Peanut is an important oilseed crop and a well‐accepted food. After oil production through thermal treatment, the defatted peanut flour is the main by‐product, which possesses large amount of proteins. However, due to the low extraction yield and poor functional properties of these proteins, they are not well utilised in industry till now. In this work, protease was used to pretreat defatted peanut flour. The results indicated that this pretreatment could improve the yield and functional properties of peanut proteins. Functional properties of food proteins are important in food processing and food product formulation. Peanut protein with good emulsifying and foaming properties would have a potential application in some food system, such as salad dressing, sausages, bologna, soups, confectionery, frozen desserts and cakes and so on. Therefore, this work is helpful for extensive utilisation of peanut proteins.
O presente trabalho teve como objetivo realizar a caracterização química e nutricional da plasteína produzida a partir de isolado protéico de soja (IPS). O hidrolisado de IPS foi produzido em sistema descontínuo, 5% de substrato, relação enzima/substrato 1/20, 6 h, 37°C, sob agitação. A plasteína foi produzida com 40% de substrato em solução aquosa, pH 7, 24 h a 37°C, sob repouso. Na caracterização química, foi verificada a distribuição dos pesos moleculares por meio de eletroforese (SDS-PAGE) e cromatografia de exclusão molecular (CEM). A SDS-PAGE não permitiu a visualização das bandas tanto no hidrolisado quanto na plasteína. Na CEM o hidrolisado apresentou 5 frações de PM na faixa de 5,4 a 66,2 kDa e a plasteína com 2 frações de PM na faixa de 9,6 e 58,7 kDa. O escore químico de aminoácidos essenciais confirmou a presença dos aminoácidos sulfurados como limitantes, sendo obtidos os valores de 93,2 e 96,4% para o hidrolisado e plasteína, respectivamente. A modificação enzimática através da reação de síntese de plasteína mostrou ser um processo viável na produção de matéria-prima para formulações alimentares de uso em nutrição clínica e em outros sistemas, sendo necessária a suplementação de metionina quando utilizada como fonte exclusiva de proteína.
Soybean is an excellent protein source for human and animal consumption but it has as well some antinutritional factors such as protease inhibitors, lectins, phytate and sapponin. In this work, the effects of isostatic high-pressure treatment (200-700 MPa), an alternative to thermal treatment, on antinutritional factors phytate and trypsin inhibitor content in 5% soy protein isolate (SPI) solution were evaluated. Two extractions of phytate and trypsin inhibitor of different batch were carried out and the analyses were repeated three times. There is an indication that high-pressure treatment was efficient to eliminate the phytate but could not change trypsin inhibitor content.
In this study, modified rancimat method was used to determine the antioxidative effect of Thymbra spicata oil on the oxidative stability of corn and palm oils at various concentrations of Thymbra spicata (1.39–5.49 mg mL) and temperatures (90, 100, and 120°C). For a comparison, butylated hydroxyltoluene was used as a standard antioxidant. Thymbra spicata oil was significantly effective on oxidation of both corn and palm oils at concentrations used in this study. Specifically, the induction period of corn and palm oils was significantly elongated in the presence of Thymbra spicata oil. However, butylated hydroxyltoluene was more effective against oxidation of oils than Thymbra spicata oil. Thymbra spicata oil could be used as an easily accessible source of natural antioxidant for use in fats and oils.
Graft copolymers of soybean protein isolate (SPI) and methacrylic acid (MAA) were prepared in an 8 mol/L urea aqueous solution with ammonium persulfate (APS) as an initiator, β-mercaptoethanol as an unfolding agent for SPI, and a chain-transfer agent. Evidence of grafting was obtained by the comparison of the Fourier transform infrared and NMR spectra of SPI with those of the SPI-grafted MAA copolymer [SPI-g-poly(methacrylic acid) (PMAA)]. A possible copolymerization mechanism of SPI and MAA was determined, and the copolymerization rate equation was derived. The effect of β-mercaptoethanol content, APS content, and reaction temperature on the graft copolymerization was studied by the determination of the grafting parameters, including grafting percentage and grafting efficiency. Dynamic laser light scattering was used to investigate the effect of the pH value on the hydrodynamic radius of SPI and the grafted SPI aggregate in aqueous solution. The average hydrodynamic radius of SPI-g-PMAA aggregate was much smaller than that of the SPI aggregate at about the isoelectric point of SPI and a high pH value, and the hydrodynamic radius distribution of the SPI-g-PMAA aggregate was narrower than that of the SPI aggregate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4023–4029, 2006
Glutaminase (EC 3.2.1.5) was applied in the present work to deamidate soybean protein isolates with limited extent, and some reaction conditions were selected. Three deamidated soybean protein isolates products with degree of deamidation of 3.5, 5.6, and 6.6% were prepared with reaction conditions as follows: soybean protein isolates concentration of 5% (w/v), glutaminase addition level of 400 U/kg soybean protein isolates, reaction temperature of 37°C, and reaction times of 12, 24, and 36 h, respectively. SDS-PAGE and size exclusion chromatography analysis showed that glutaminase exhibited weak ability to catalyze the hydrolysis of the peptide bonds in soybean protein isolates. The results indicated that the deamidated soybean protein isolates prepared showed improved solubility in a pH range of 3 to 10, and had higher emulsion stability on the oil-in-water dispersions when compared to the original soybean protein isolates, but had poor emulsifying activity. Rheological assay revealed that the suspensions prepared by the deamidated soybean protein isolates products showed higher apparent viscosity, and the values of apparent viscosity depended on the degree of deamidation of the deamidated soybean protein isolates product and the addition level of Ca2+ in the suspensions. The storage modulus G′ and viscous modulus G′′ of the prepared suspensions gave similar behaviors as apparent viscosity. Three deamidated soybean protein isolates products prepared contained better iron (II)-chelating activity than the original soybean protein isolates as the evaluated index showed an increase of 19 to 30%. Limited deamidation of soybean protein isolates by glutaminase showed beneficial impacts on the selected properties of deamidated soybean protein isolates totally, and might be served as a practical approach to prepare multifunctional ingredients for the food industry.
We examined the thermal stability of yeast hydrolysates before and after ultrafiltration (UF) in vitro, and the anti-obesity activity of yeast hydrolysates before and after heat treatment in vivo. Yeast hydrolysate after UF showed significantly higher thermal stability than before UF. Yeast hydrolysates before and after UF showed 3 and 4 thermal transition peaks in their thermograms, respectively, and the total thermal denaturation enthalpies of yeast hydrolysates before and after UF were 69.5 and 36.5J/g, respectively. For the anti-obesity activity study, yeast hydrolysates before and after heating were administered ad libitum with water to 7-week-old male SD rats. The administration of yeast hydrolysate (YH-control; no heat treatment, YH-1; heat treatment at 140°C, and YH-2; heat treatment at 160°C) significantly increased mRNA expression of cocaine- and amphetamine-regulated transcript (CART) compared with control rats (saline administration). However, there was no significant difference between the heat-treated groups and YH-control and there was no significant difference in neuropeptide Y expression between the heat-treated groups and YH-control. These results suggest that yeast hydrolysate can be use an anti-obesity material after heat treatment.
The charges and sizes of peptides released during in vitro casein digestion were investigated. Casein was hydrolysed sequentially by pepsin and pancreatin and, during hydrolysis, the products of digestion were removed by dialysis. The undigested residues were separated by ion-exchange chromatography into basic–neutral (BN), lightly acid (LA) and acid (A) fractions. Each of these fractions was further resolved by sequential ultrafiltration (MWCO 10 and 1 kDa) into two retentates (>10 and 10–1 kDa) and one permeate (<1 kDa). The polypeptides (>10 kDa) produced by pepsin hydrolysis were degraded into small molecules during the first 2 h of pancreatin hydrolysis; less than 100 mg g−1 of the total N remained undigested. Most of the material produced was in the BN10-1 (ie basic–neutral, 10–1 kDa) fraction, with three times as much N as the A10-1 fractions. As digestion progressed a decrease in the proportion of N in the residues retained by the dialysis membrane was observed. This decrease was particularly rapid in the BN10-1 fraction. Large proportions of leucine (Leu), lysine (Lys), arginine (Arg), phenylalanine (Phe) and tyrosine (Tyr) were found as peptides smaller than 1 kDa, both in the dialysates and retentates, while glutamine (Glu), threonine (Thr), serine (Ser) and asparagine (Asp) appeared mostly in the A10-1 and A > 10 fractions. After 6 h of pancreatin hydrolysis most of the proline (Pro) content was in the BN10-1 fractions. The mechanisms behind and the implications of these results are discussed. Copyright © 2004 Society of Chemical Industry
Endo-protease treatments achieving low degrees of hydrolysis (DH 2% and 4%) were used to improve functional properties of hexane-extracted soy flour (HESF), extruded-expelled partially defatted soy flour (EESF), ethanol-washed soy protein concentrate (SPC), and soy protein isolate (SPI). These substrates had protein dispersibility indices ranging from 11% to 89%. Functional properties, including solubility profile (pH 3 to 7), emul-sification capacity and stability, foaming capacity and stability, and apparent viscosity were determined and related to surface hydrophobicity and peptide profiles of the hydrolysates. Protein solubilities of all substrates increased as DH increased. Emulsification capacity and hydrophobicity values of the enzyme-modified HESF and EESF decreased after hydrolysis, whereas these values increased for SPC and SPI. Emulsion stability was improved for all 4% DH hydrolysates. Hydrolyzed SPC had lower foaming capacity and stability. For substrates other than SPC, foaming properties were different depending on DH. Hydrolysis significantly decreased the apparent viscosities regardless of substrate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated differences in the molecular weight profiles of the hydrolysates. HESF and EESF, which had high proportions of native-state proteins, showed minor changes in the peptide profile due to hydrolysis compared with SPC and SPI.
Effect of limited proteolysis of extruded soy flour on rheological properties and microstructure of the obtained hydrolysates was investigated. Flow curves with a controlled shear rate and time-dependent curves with a constant shear rate were determined. The surface of investigated material was studied with atomic force microscope Quesant "Nomad" model. Rheological characteristics have been studied using a Cheng and Evans structural theory. Multiple exponential flow law was used to calculate non-Newtonian equilibrium viscosity. The shear stress was modified using structural parameter accounting for time-dependent effect. These studies have shown a significant influence of the enzyme used upon the rheological properties and structure of suspensions of hydrolysis products.
The mixed protein gels were prepared adding soy protein isolate (SPI), 7S globulin, enzyme-hydrolyzed soy proteins, 10- to
100-kDa ultrafiltration fraction and 0.5- to 10-kDa ultrafiltration fraction to myofibril protein isolate (MPI) gels, and
five chemical interactions namely nonspecific associations, ionic bonds, hydrogen bonds, hydrophobic interactions and disulfide
bonds in these gels were investigated by means of determining gel solubility within 20–75°C. Furthermore, correlations between
gel strength and different chemical interactions were evaluated statistically by Pearson’s correlation test. The gels with
0.5- to 10-kDa fraction presented the biggest gel strength below 60°C, and the gels with SPI had better gel strength above
65°C. At different endpoint temperatures, nonspecific associations decreased in order of MPI mixed with 0.5- to 10-kDa fraction,
10- to 100-kDa fraction, enzyme-hydrolyzed soy proteins, 7S globulin and SPI. Gels with ultrafiltration fractions had higher
ionic bonds. Hydrogen bonds fluctuated in small scale below 55°C and reduced at higher temperature. Hydrophobic interactions
increased to maximum before decreasing slowly as the temperature went on. In short, both hydrophobic interactions and ionic
bonds had significantly positive correlation with gel strength for mixed gels with enzyme-hydrolyzed soy proteins, whereas
for the other four mixed gels, it was hydrophobic interactions and nonspecific associations.
KeywordsMyofibrillar-Soy protein-Ionic bonds-Hydrogen bonds-Hydrophobic interactions-Disulfide bonds
In recent years, soy protein isolate (SPI) has attracted great attention due to its biodegradability, biocompatibility, and
wide availability. It has been used in food and pharmaceutical industry such as edible films and drug delivery systems. In
this study, we report the synthesis and self-assembly behavior in aqueous solution of thermally responsive graft copolymer
(SPI-g-poly(N-isopropylacrylamide) (PNIPA)) of soy protein isolate and N-isopropylacrylamide in aqueous solution. SPI-g-PNIPA was synthesized in the 8mol/l urea cushioning solution, by using ammonium
persulfate as the initiator and mercaptoacetic acid as the protein unfolding agent. Laser light scattering, transmission electron
microscopy, and fluorescence spectroscopy have been used to study the self-assembly behavior of SPI-g-PNIPA in aqueous solution.
Above the critical micelle concentration (cmc), SPI-g-PNIPA aggregates could assemble into different structures including
the simple spherical structure, spherical core–shell structure, and random coil structure, depending on the graft copolymer
concentration. The graft copolymer concentration, temperature, pH value, and ionic strength were found to influence the aggregate
size and morphology of SPI-g-PNIPA in aqueous solution. With increasing ionic strength, the aggregate size increases. However,
pH value, SPI-g-PNIPA concentration, and temperature have complicated influences on the aggregate size. The lower critical
solution temperature of the SPI-g-PNIPA at pH8.5 is 36°C. The method of intrinsic fluorescence spectroscopy was used for
the first time to determine the cmc value of SPI-g-PNIPA in aqueous solution.
KeywordsSoy protein isolate-
N-isopropylacrylamide-Self-assembly
Soy protein products hexane-defatted soy flour, extruded-expelled soy flour, soy protein concentrate and soy protein isolate, were modified by using the enzyme bromelain to 2% and 4% degrees of hydrolysis (DH). Peptide profiles, water solubility, and rheological properties including dynamic shear, large deformation, and apparent viscosities of resulting hydrolysates were determined. Protein subunits profiles for the hydrolysed isolates and concentrates were extensively altered by the treatment while only minor changes were observed for the hydrolysed flours. Water solubility profiles of all hydrolysates in the pH range of 3.0–7.0 were enhanced by hydrolysis. For the unhydrolysed controls, the isolate had the highest storage modulus (G′), followed by the concentrate, the extruded-expelled flour and the hexane-defatted flour. The hydrolysates retained some of their gelling ability even though the losses in storage modulus (G′) were substantial. After heating step to 95 °C, the G′ values of all substrates at 25 °C decreased with increase in DH. Texture profile analyses of the soy protein gels were also lower in hardness after hydrolysis. The Power Law model provided excellent fit to hydrolysate dispersions flow (R2>0.99). Hydrolysis decreased the consistency coefficients of dispersion and increased flow behavior index resulting in thinner dispersions. These results suggest that limited protease hydrolysis of various soy protein meals with bromelain produce soy protein ingredients with modified rheological properties.
Coeliac disease (CD) is a long-life intolerance to gluten proteins, with prevalence of 1–2% worldwide and health consequences if not treated. Currently, the treatment is the dietary gluten withdrawal, but commercial gluten-free foodstuffs present undesirable properties. Therefore, attempts are being made to modify the immunogenic sequences of gluten to avoid recognition by the immune system and to prepare safe and acceptable foods. These include long-time fermentation by sourdough and enzymic modification. The present article reviews our current knowledge of the pathogenesis of CD and the advantages and limitations of the current approaches to gluten modification and to develop safer foods for CD patients.
Oil, protein and solid extraction yields obtained during aqueous extraction processing (AEP) of full fat soybean flakes (FFSF), FFSF extruded at a die temperature of 100 °C and FFSF pressurised at 200 and 500 MPa for 15 min at 25 °C, were compared to those obtained during enzyme-assisted aqueous extraction processing (EAEP) using 0.5% of protease Protex 7L. Without enzyme addition, pretreatment of the FFSF with extrusion and 500 MPa increased and decreased, respectively, the oil extraction yield while protein extraction yield was significantly decreased after both treatments. The best treatment in terms of oil and protein recovery was EAEP of extruded flakes with 90% and 82% of oil and protein extraction yield, respectively, and 17% of free oil. Addition of protease during extraction significantly decreased the yield of isolated soy protein (ISP) due to an increased solubility of the proteins at pH 4.5. ISP from extruded EAEP had higher solubility at pH 7.0 and better functionality. The DSC results, combined with the protein extraction yields, showed that a proportion of the proteins became insoluble after extrusion and 500 MPa treatment, while only those extracted from 500 MPa FFSF had a reduced native state.
With the purpose of analysing the molecular size and composition, proteinaceous material was extracted from the insoluble components of a digesta sample obtained from pigs fed a feed consisting of only soybean meal. Gel permeation chromatography indicated that the alkali-extractable fraction of the proteinaceous material from the residue was of relatively high apparent molecular weight. However, the combined results from gel electrophoresis, RPLC-MS, and MALDI-ToF MS showed that the extracted protein material was in fact, to a high extent, composed of aggregated peptides. To our knowledge this has not previously been described. Aggregates extracted by dilute alkali were fully degraded upon subsequent proteolytic treatment. N-terminal sequencing of selected protein bands from SDS-PAGE gels indicated the presence of partly degraded -conglycinin alpha subunits in the residue
Membrane processes are increasingly reported for various applications in both upstream and downstream technology, such as microfiltration, ultrafiltration, emerging processes as membrane chromatography, high performance tangential flow filtration and electrophoretic membrane contactor. Membrane-based processes are playing critical role in the field of separation/purification of biotechnological products. Membranes became an integral part of biotechnology and improvements in membrane technology are now focused on high resolution of bioproduct. In bioseparation, applications of membrane technologies include protein production/purification, protein-virus separation. This manuscript provides an overview of recent developments and published literature in membrane technology, focusing on special characteristics of the membranes and membrane-based processes that are now used for the production and purification of proteins.
Different combinations of pHs (2 to 12) and temperatures (25, 30 and 35 degrees C) were tested to obtain a protein isolate from ebony (Pithecellobium flexicaule, Benth) seeds. Seed proteins contained 54.6% albumins, 32% globulins, 5.7% glutelins and 1.3% prolamins. The isoelectric points for albumins, globulins and glutelins were in the pH range of 2.3-2.7. The average molecular weight of albumins ranged from 92 to 100 kDa and for the four globulin subunits in the range of 28.4 to 57.3 kDa. For isolate production, proteins were sequentially extracted with distilled water and a 5% NaCl solution. The resulting supernatants were mixed. The best extraction was achieved at pH 11 and 25 degrees C. 45.6% of the total seed protein was precipitated at pH 2.6 yielding an isolate with 90% protein (N x 6.25). The isolate contained high quantities of lysine, leucine, threonine and phenylalanine but were low in sulfur containing amino acids methionine and cysteine. The extraction process reduced tannins, phytates and trypsin inhibitor in 53, 70 and 70%, respectively. In vivo protein digestibility of the protein isolate was 85.4% and the corrected digestibility essential amino acid score was of 44% due to the lack of sulfur containing amino acids. In order to upgrade the protein quality of ebony isolate it is recommend to supplement with methionine or sulfur containing rich foods.
Soybean protein is used in a number of food products but unfortunately is also a common cause of food allergy. Upon ingestion of soy protein, healthy mice like other animals and humans generate a soy-specific antibody response in the absence of signs of illness. Not much is known about the relationship between the immunogenic proteins involved in this nondeleterious antibody response and the pathological response associated with food allergy. The objective of the present study was to characterize the antigenic specificity of the soy protein-specific antibody response generated in healthy mice ingesting soy protein.
Blood from mice fed a soy-containing diet was analyzed using ELISA and immunoblot for antibody reactivity towards various soy protein fractions and pure soy proteins/subunits. Mice bred on a soy-free diet were used as controls.
The detectable antigenic specificity of the serum antibodies of soy-consuming mice comprised glycinin and beta-conglycinin. Immunoblots with soy protein extract demonstrated antibody reactivity towards both the basic and the acidic chains of glycinin and the beta-conglycinin subunits with an individual response pattern among mice. Moreover, antibody reactivity was found towards the native quaternary structure of glycinin.
Mice ingesting soy protein generate an antibody response with reactivity towards glycinin and beta-conglycinin. Antibody reactivity found towards the native quaternary structure of glycinin indicates an oral immunogenicity of the highly processing-resistant oligomerized glycinin.
Several tests for the detection of soy proteins in foods have been described in the literature, and some are commercially available. This article gives an overview of these methods and discusses the advantages and disadvantages of each individual method. Based on the conclusions of this inventory, an experimental approach was designed to improve the sensitivity of measuring soy protein in processed foods. The aimed sensitivity is 10 ppm (10 microg soy protein in 1 g solid sample), which is over 100-fold lower than presently available tests. The aimed sensitivity is this low because levels of food allergens at 10 ppm and above may provoke reactions in food allergic persons. Native soybean meal, soy protein isolate, soy protein concentrate, and textured soy flakes were used as test materials. Several extraction procedures were compared and a new method using high pH was selected. Polyclonal antibodies were raised in rabbits and goats, and immunopurified antibodies were used in sandwich and inhibition enzyme-linked immunosorbent assay (ELISA). Extraction at pH 12 resulted in good yields for all tested samples, both quantitatively (Bradford) and qualitatively by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Immunopurified rabbit antibodies against this extract used in a competition ELISA format resulted in a sensitive test with a detection limit of 0.02 microg/mL, corresponding to 0.4 microg/g (0.4 ppm) in food samples. Cross-reactivity with some main food ingredients was measured and appeared to be negative in all cases. The presently developed test is applicable for soy ingredients and soy-containing foods that are processed in different ways. The limit of quantitation is 1 ppm, which is an enormous improvement over earlier described methods.
The kinetics of peptide release during in vitro digestion of 4 protein sources (casein, cod protein, soy protein, and gluten) were investigated. Samples were sequentially hydrolyzed with pepsin (30 min) and pancreatin (2, 4, or 6 h) in a dialysis cell with continuous removal of digestion products. Nondialyzed digests were fractionated by ion-exchange chromatography and ultrafiltration. Animal proteins were digested at a greater rate than plant proteins. Target amino acids of specific enzymes appeared more rapidly in the dialyzed fractions when compared to other amino acids. Throughout the hydrolysis, nondialyzed digests contained a higher proportion of peptide mixtures with basic-neutral properties. Except for gluten, peptide fractions with molecular weights that exceeded 10 kDa (basic-neutral, BN > 10) were rapidly hydrolyzed during the first 2 h of pancreatin digestion. The kinetics of release and the composition of peptide fractions were different when the protein sources were compared. The analysis of amino acids revealed that threonine and proline proportions were relatively high in BN > 10 and in peptide fractions with molecular weight between 10-1 kDa (BN 10-1), while tyrosine, phenylalanine, lysine, and arginine predominated in the low molecular weight (<1 kDa) fractions. More resistant peptides were generally rich in proline and glutamic acid. The role of in vitro digestion assays in dietary protein quality evaluation is discussed.
Structure-digestibility relationship was investigated in in vitro model systems for phaseolin and vicilin, the major 7S storage proteins of dry bean and green peas, respectively. Native phaseolin was more resistant to trypsinolysis than vicilin, while heating caused a reversal of proteolysis rates. Conformational studies using far-uv and near-uv CD spcctroscopy suggested the native conformatin of vicilin to be far more flexible to thermal treatment and SDS-induced environmental changes; however, neither the thermal treatment nor the anionic detergent caused a complete randomization of structure in either proteins studied. Ironically, the flexible native conformation of vicilin seemed to induce greater undesirable changes upon heating so as to confer resistance to proteolysis. The possible role of secondary and quarternary structures of these two proteins is descussed in relation to their digestibility.
Intestinal perfusion studies performed in man have suggested that amino acid nitrogen may be absorbed more rapidly from peptides than free amino acids. The aim of the present study was to compare the effects of the oral administration of peptides and free amino acids. Two isonitrogenous liquid test meals, one containing 50 g of a partial enzymic hydrolysate of fish protein in which approximately 80% of the nitrogen content was present as small peptides (peptide meal), and the other a mixture of free amino acids (amino acid meal) the composition and molar pattern of which simulated that of the peptide meal, were administered on separate occasions to six normal subjects intubated with a triple lumen tube. Both meals contained the reference marker polyethylene glycol. Fractional absorption of amino acid residues one and two hours after ingestion of the two meals was similar at three intestinal locations situated 120, 160, and 200 cm from the mouth of each subject, and at two hours 73.8% and 72.0% of the amino acid residues had been absorbed respectively by the time the contents of the peptide and amino acid meals reached the middle sampling port of the tube. The total sum of individual amino acid increments in plasma was significantly greater 30 minutes (p < 0.025) and one hour (p < 0.05) after ingestion of the peptide than amino acid meals. By three hours the total area under the two plasma curves was similar. Normal human subjects thus appeared to be capable of assimilating orally administered mixtures of peptides and free amino acids with equal efficiency. Secretion of fluid into the lumen of the upper small intestine, assessed by reference to dilution of the polyethylene glycol, was less after ingestion of the peptide meal. In clinical situations characterised by fluid and electrolyte malabsorption consideration might be given to using small peptides rather than free amino acids as the nitrogen source in nutritional diets.
An accurate, reproducible and generally applicable procedure for determining the degree of hydrolysis of food protein hydrolysates has been developed. The protein hydrolysate is dissolved/dispersed in hot 1% sodium dodecyl sulfate to a concentration of 0.25-2.5 × 10-3 amino equivalents/L. A sample solution (0.250 mL) is mixed with 2.00 mL of 0.2125 M sodium phosphate buffer (pH 8.2) and 2.00 mL of 0.10% trinitrobenzenesulfonic acid, followed by incubation in the dark for 60 min at 50 °C. The reaction is quenched by adding 4.00 mL of 0.100 N HCl, and the absorbance is read at 340 nm. A 1.500 mM L-leucine solution is used as the standard. Transformation of the measured leucine amino equivalents to degree of hydrolysis is carried out by means of a standard curve for each particular protein substrate.
This study was conducted to determine the P and phytate contents of the major soy protein fractions prepared from defatted Bragg soybeans and commercial defatted soy flakes. The 11S, 7S, and soy whey precipitate fractions from defatted Bragg soybeans and commercial defatted soy flakes contained 0.08%, 0.63-0.68%, and 10.49-15.20% P (dry basis), respectively. These same fractions from commercial defatted soy flakes contained 0.07%, 1.40%, and 45.37% phytate (dry basis), respectively. It was concluded that most of the P of 11S protein is non-phytate, whereas phytate accounts for a major portion of the P content of 7S and soy whey precipitate fractions.
The electrophoretic behavior of a soy protein isolate was analyzed in both nonreducing and reducing SDS-PAGE. Aggregates formed by α and α′ subunits of β-conglycinin exhibited both ionic interactions and disulfide bonds. Higher molecular weight aggregates (180 000-190 000) consisted of trimers or dimers of α′ and α subunits, whereas those of intermediate molecular weight (115 000-120 000) were formed by α′,α subunits of β-conglycinin and A polypeptides of glycinin. The latter exhibited a higher sensitivity toward changes of ionic strength and thermal treatments. The proportion of α′ and α subunits of the isolate which was included in these aggregates is highly dependant on the freeze-drying conditions. These aggregates were readily reduced in the presence of Na2SO3, even at low concentrations and in the absence of denaturing agents, thus suggesting that the disulfide bonds involved were accessible. These aggregates were stable at different pH values, in the presence of both SDS and urea.
Protein hydrolysates possess a number of functional properties, which make them attractive as a protein source in human nutrition, both in products for special medical use and in consumer products for more general use. Discussed here are the properties and possible application of hydrolysates for protein supplementation in market segments outside the medical field-i.e., diets for the elderly, sports nutrition, and weight-control diets. The physiological effects of protein hydrolysates are also reviewed.
Proteins for foods, in addition to providing nutrition, should also possess specific functional properties that facilitate processing and serve as the basis of product performance. Functional properties of proteins for foods connote the physicochemical properties which govern the behavior of protein in foods. This general article collates the published information concerning the major functional properties of food proteins, e.g., solubility, binding properties, surfactant properties, viscogenic texturizing characteristics, etc. The effects of extraction and processing on functional properties and possible correlations between structure and function are discussed, in relation to practical performance in food systems. Modification of proteins to improve functional characteristics is briefly mentioned.
Immunostimulative peptides were isolated from the pepsin digest of soybean by ion exchange, gel filtration, and reversed-phase high-performance chromatography. The peptides formed blastoids against the splenocytes of CSH/HeN mice. The amino acid sequences of these peptides were: Ala-Glu-lle-Asn-Met-Pro-Asp-Tyr, Ile-Gln-Gln-Gly-Asn, and Ser-Gly-Phe-Ala-Pro, respectively.
A rapid colorimetric procedure is described for determination of phytate based on the reaction between ferric ion and sulfosalicylic acid. Determination of the phytate content of a variety of cereals, legumes, and oilseeds demonstrates the simplicity of this method compared to the cumbersome digestion and colorimetric method for measuring liberated phosphorus.
In vitro activity of the proteolytic enzyme trypsin using casein as the substrate was substantially inhibited by low levels of phytic acid (myo-inositol hexaphosphate). The possible significance of this finding for protein availability in nutrition is discussed.
The nootkatone content in grapefruit peel oil extracted from flavedo and the peel oil content of fruit receiving preharvest treatment with 20 or 50 ppm gibberellic acid (GA) and/or 50, 125, or 250 ppm 2-(3,4-dichlorophenoxy)triethylamine (DCPTA) were determined. Treatment by GA reduced the rate of increase in nootkatone concentration observed in control fruit with maturation, and the effect was dose-dependent. When DCPTA was used alone as the growth regulator, nootkatone content increased significantly. When 50 ppm GA followed DCPTA treatment at the three levels used above, the effect of GA predominated and nootkatone content was significantly lower than that found in untreated fruit. Treatment by GA generally increased peel oil concentration.
The effects of proteolytic enzyme modification of soy protein isolate (SPI) on its molecular and functional properties were evaluated by treating a commercial SPI, Ardex F, with Alcalase, α-chymotrypsin, trypsin, Liquozyme, and rennet. Trypsin effectively decreased the molecular size of SPI followed by Alcalase and α-chymotrypsin. Hydrolytic breakdown occurred more extensively in the α′, α, and β subunits of 7S globulins than in the acidic and basic polypeptides of 11S globulins. Partial hydrolysis of SPI contributed to improving its solubility at pH 7.0 and 4.5, emulsifying capacity, and ability to undergo thermal aggregation. The extent of contribution was dependent upon the enzymes used, duration of proteolytic treatment, and functional properties sought after.
Nineteen samples originating from 14 types of feedstuffs were analyzed for tryptophan according to three procedures: The first required barytic hydrolysis at 105°C under vacuum, chromatography over Sephadex G 10, and ninhydrin colorimetry. The second and the third involved barytic hydrolysis at 125°C in the absence of air, reversed-phase liquid chromatography, and ultraviolet spectrophotometry or fluorometry. The values obtained with the three procedures for a given sample were identical. Tryptophan from lysozyme added to 11 samples was recovered in a mean yield of 99.7 ± 1.0% as measured by the second procedure.
The structure of soyasapogenol B1, previously shown to be an artifact of hydrolysis, was elucidated by X-ray crystallography and confirmed by mass spectrometry as 3β,22β,24-trihydroxyolean-13(18)-ene.
The effect of various concentrations of sodium chloride on the extractability of sesame seed proteins has been investigated. The extractability of total protein increases to nearly 80% until 5% sodium chloride concentration after which it remains constant. The extractability is also investigated as a function of pH in all the sodium chloride concentrations. The results indicate that the pH of minimum extractability drifts toward acidic pH as the sodium chloride concentration increases from 0.05 to 2.0 M. The observed results are explained due to preferential extractability of the various protein fractions with increasing concentration of sodium chloride and also due to the binding of sodium ions to these protein fractions.
The effect of disulfide bond cleavage on the solubility, surface hydrophobicity, and pepsin and pancreatin digestibility of glycinin and its components was studied by turbidity, 1,8-anilinonaphthalenesulfonate extrinsic fluorescence, ultraviolet absorbance, and polyacrylamide gel electrophoresis measurements. Disulfide bond cleavage increased the solubility of glycinin and its basic and acidic polypeptide components. It increased the surface hydrophobicity of acidic polypeptides and decreased that of glycinin and basic polypeptides. The digestibility of the acidic subunits with pepsin and pancreatin was enhanced whereas glycinin and basic polypeptides showed decreased digestibility following disulfide reduction. The decrease in the surface hydrophobicity and protein digestibility of glycinin might be due to the aggregation of the basic polypeptides primarily through hydrophobic interactions.
The effect of protein composition and degree of protein denaturation on the solubility, water-imbibing capacity (WIC), viscosity, and gelation capacity of commercial soy protein isolates was studied. It was found that the degree of denaturation may affect protein solubility, but very denatured proteins with high solubility were also detected. Isolates containing completely denatured proteins showed low gelation capacity. This characteristic is closely related to the relative amounts of the 7S and 11S proteins, since beta-7S subunit and basic 11S polypeptide were present in decreased concentrations in the soluble protein fraction. Isolates with a high degree of denaturation and intermediate solubility values presented the maximal WIC. Results confirmed that the apparent viscosity of soy protein dispersions is intimately related to WIC.
ABSTRACTA combination cation/anion exchange process was developed to remove 96–97% of the phytate and 97–99% of the Ca and Mg from soy protein isolates. Application of either of the ion exchange treatments alone failed to effectively remove phytate from soy protein extracts and also failed to convert the remaining phytate to a dialyzable form. Effective removal of phytate was only achieved by the combination ion exchange treatment. Consideration of these findings led to a proposed mechanism for the sequential disruption of the protein-Ca/Mg-phytate complex by the ion exchange treatment.
Solubility and water absorbing capacity of commercial soy protein isolates were correlated with structural parameters. The physico-chemical properties studied were degree of protein denaturation, surface hydrophobicity and sulfhydryl groups. The results indicated that solubility and water absorption were affected differently as the parameters were varied. These functional properties depended on more than one structural parameter. Solubility in 0.2M NaCl solution provided information about the degree of denaturation of soybean protein isolates. Isolates with highly denatured proteins, high surface hydrophobicity, low solubility in 0.2M NaCl solution and low SH exhibited the highest water absorbing capacity.
Three protein sources, casein, soya bean and rapeseed concentrates, were subjected to alkali treatment (0.2 M, 60° C) for 2 or 6 h. The impact of these treatments on protein digestibility and on release of amino acids, especially lysinoalanine, was evaluated by an in-vitro enzymic digestion method with simultaneous dialysis of digestion products. The impairment of digestibility was higher for casein and soya bean concentrate than for rapeseed concentrate. Whatever the amount of lysinoalanine produced in each protein, it was poorly released by proteolytic enzymes. The rate of release of other amino acids was reduced by the treatments, but to different levels for each protein. Arginine and lysine were particularly affected. As can be inferred from the release of the target amino acids, the hydrolytic capacity of chymotrypsin was not specifically impaired, in contrast to that of trypsin for casein and of elastase for all protein sources. This technique was useful to evaluate quickly the effects of processing on the digestibility of proteins.
The effects of sodium phytate and partially hydrolyzed sodium phytate (0 - 82% hydrolyzed) on pepsin digestion of casein and bovine serum albumin were evaluated by an in vitro procedure using dialy-sates of pepsin digestion over a period of 0 – 23 hr. The inhibitory effect of phytate differed with substrate and increased with dose level. At the highest phytate level, the digestion of casein and bovine serum albumin was reduced by 14% and 7%, respectively. The inhibitory effect of the phytate was inversely correlated with the degree of phytate hydrolysis. Hydrolysis for 16 hr almost eleminated the inhibitory effect of phytate.
Enteral feeding has been recognized as the preferred modality of nutritional support for patients in whom the gastrointestinal tract is either totally or partially functional.
Inactivation of lipoxygenase, trypsin inhibitor, urease and retention of protein solubility during water blanching of dehulled soybeans at 90°, 95° and 100°C were investigated. Lipoxygenase was the most heat labile, followed by urease and then trypsin inhibitor. Processing time based on “acceptable inactivation time” (AI) was proposed. AI value was longest for trypsin inhibitor, followed by urease and then lipoxygenase. The combined effect of heat on protein solubility and biologically active components inactivation was expressed as “PDI at acceptable inactivation time” (PDIAI). PDIAI value for the processing “limiting factor,” trypsin inhibitor inactivation, at the three temperatures were 36.7%, 42.5%, and 34.8%, respectively.
Proteins are increasingly being utilized to perform functional roles in food formulations. Common food proteins possess good functional properties including solubility, gelation, emulsification and foaming. The functional properties of proteins are impaired near their pl (isoelectric point), as is the case in most acidic foods. Enzymatic modification of food proteins by controlled proteolysis can enhance their functional properties over a wide pH range, and other processing conditions. Choosing the right proteolytic enzyme, environmental conditions for hydrolysis and degree of hydrolysis is crucial for enhancing the functional properties of proteins. Understanding the molecular properties required for protein functionality and the development of strategies to achieve them are critical for developing and utilizing modified protein ingredients. Numerous reports on enhancing the functionality of food proteins by limited proteolysis have been published, some of which are reviewed in this article.
Angiotensin-converting enzyme (ACE) acts in blood pressure regulation, converting angiotensin I to the potent vasoconstrictor angiotensin II and inactivating the vasodilator bradykinin to raise blood pressure. Various synthetic ACE inhibitors are currently in use as antihypertensive agents. Recently, ACE-inhibitory peptides have been isolated from enzymatic digests of food proteins. The possible roles of these food-derived ACE inhibitors are discussed.
Partial reduction of disulfide bonds of soy protein isolates was followed electrophoretically. Isolates treated with Na2SO3 under different conditions showed disappearance of high molecular weight aggregates. Acidic and basic 11S polypeptides and some whey proteins that remain in the isolates were also affected; reduction of the AB-11S subunit was very limited. The sulfitolysis method was also studied. The addition of a catalyst (Cu) and oxygen showed a similar effect in the sulfitolysis of soy proteins with Na2SO3. To achieve complete sulfitolysis, the presence of a denaturing and an oxidizing agent were needed. Mainly AB subunits of glycinin were reduced when urea was used, while mostly components other than AB-11S subunits were reduced when Na2SO3 was used in the presence of Cu and/or oxygen. © 1995 American Chemical Society.
Thermal behavior of soy protein isolates under different conditions of temperature, time, pH, protein concentration, and presence of reducing agents was studied. Thermal treatments above 85°C showed a decrease in concentration of the AB-11S subunit and of the two protein species of 20 and 29 kDa, and a gradual increase in the concentration of the A and B polypeptides of glycinin. None of the thermal treatments tested led to modifications of the relative proportions either of the high molecular weight aggregates (100-200 kDa) observed in the electrophoretic profiles or of the ?? and ? subunits of ?-conglycinin. Increasing the pH to 9 or 10 and increasing the protein isolate concentration enhanced AB-11S aggregation during the thermal treatment. Either the presence of Na2SO3 or the pH 9-10 favored the ?-?-conglycinin/B-glycinin aggregation. This interaction requires an increase of SH groups. Initially the ?-?-conglycinin/B-glycinin aggregates were stabilized by hydrophobic interactions and later by SS bonds. © 1995 American Chemical Society.
Soy protein isolates exhibit heterogeneous protein subunit compositions; their structural and functional properties are determined by the processing conditions. Drastic thermal conditions at pH 7 and 9 result in protein denaturation and polymerization, as evidenced by increased water retention capacity and lower solubility, surface hydrophobicity, and a higher level of AB-11S aggregates. Treatments of glycmin with urea and Na2SO3 at pH 7 incorporated 20% of sulfonate groups, resulted in no solubility losses of 11S protein A and B polypeptides, but increased their surface hydrophobicity. The increase of 7S fraction leads to an increase of aliphatic hydrophobicity. Thermal treatments at pH 7 and lower protein content lead to high solubility and high surface hydrophobicity isolates. 7S globulin was completely denatured, while 11S denaturation depended on the treatment conditions; different proportions of AB-11S, ?-7S, and B-11S aggregates were formed. Thermal treatments at pH 9 favored dissociation and denaturation of AB-11S protein. © 1994 American Chemical Society.
Protein isolates were prepared from water extracts of defatted soybean flour or flakes by acid precipitation at pH's from 3.5 to 5.2 with or without added 0.1 N NaCl. The resulting wheys and precipitates were analyzed for trypsin inhibitor (TI) activity (TIA), phytic acid, and minerals. TIA varied from 70 mg of trypsin inhibited/g of protein in an isolate precipitated at pH 4.5 from an extract with no added NaCl to 8 mg/g at pH 5.2 with added NaCl. Protein isolate yields varied from 85% of extract proteins at pH 4.5 with no added salt to 59% at pH 5.2 with added salt. The TIA was concentrated to 450 mg/g of freeze-dried permeate by ultrafiltration and dialysis. Retention of the TIA was 50% or more by an ultrafiltration membrane with a 100-kDa cutoff. Since TI's have a molecular weight of 20K or less, their retention indicates they were aggregated to a higher molecular weight. The phytic acid level was highest and zinc level lowest in the pH 3.5 protein precipitate compared to levels in the pH 4.5 and 5.2 precipitates. Levels of Ca, Mg, K, Na, Fe, Mn, and Cu in isolates, wheys, and a TI concentrate were also determined. Extent of removal of minerals and phytic acid from an acid-soluble TI concentrate at pH 2.4 was in the order K > Mn > Zn > Mg > phytic acid > P > Ca > Fe > Cu.
Various protein fractions were prepared from defatted soybean flour based on solubility differences and size on Sephadex G-200. The in vitro digestibility of these fractions by trypsin and by successive pepsin-trypsin treatment was affected by the presence of trypsin inhibitors, native structure of the proteins, and the presence of starch (shown to be present in soybeans). The trypsin inhibitors were destroyed by heating at 100°C for 30 min at pH 1 but not at neutrality. The native structure of the proteins could be destroyed by heating, particularly at low pH, digestion with pepsin at pH 1, or by cleavage of the disulfide bonds. Cleavage of disulfide bonds increased the in vitro digestibility of the proteins. Prior amylase treatment increased the trypsin digestibility of most of the protein fractions.
Twenty ambulatory, weight-losing patients with advanced cancer of the lung, breast, or ovary were randomized to supplement their diet for 2 months with either of two commercial complete liquid diets, one containing intact milk proteins and the other partially hydrolyzed soy proteins. Both products were prescribed as sip feeds in addition to normal food. The patients consumed more of the hydrolysate-containing product than of that with intact (milk) protein. The difference was significant and was maintained during both months of the study. An increase in total energy and protein was obtained in both groups, but was significant only with the hydrolysate product. At the end of the study there was no group difference in measures of nutritional status, but weight loss was halted in both groups.
The nutritional value of processed soy protein (isolated soy proteins and soy-protein concentrates) in human protein and amino acid nutrition is evaluated on the basis of a review of studies of growth and nitrogen balance in infants, children, adolescents, and adults. Findings show that well-processed soy-protein isolates and soy-protein concentrates can serve as the major, or even sole, source of protein intake and that their protein value is essentially equivalent to that of food proteins of animal origin. The importance of the sulfur amino acid content of soy protein for practical human nutrition is also examined from nitrogen-balance data. Under conditions of an anticipated normal usage of soy protein, methionine supplementation is not only unnecessary but may even be undesirable for young children and adults. However, for newborns, the data suggest that modest supplementation of soy-based formulas with methionine may be beneficial. Soy proteins have also been found to be of good quality to include in hypocaloric diets for weight reduction in obese subjects. Finally, the data indicate that soy proteins are well-tolerated and of good acceptability.
This article surveys the knowledge in the area of protein structure and chemistry of denaturation prior to an indepth review of the effects of heat on soy, milk, and egg proteins. It also reviews the methods available to assess denaturation of proteins. Protein denaturation is an ambiguous phenomenon and the consequences of denaturation on the functional properties of proteins is further confounded by this ambiguity. For each of the three food proteins, the known chemistry of individual proteins is reviewed followed by observations made on changes induced by heat in each protein group. Food proteins are not pure entities and purification and physicochemical characterization of various components of the food proteins have not been thoroughly investigated. Further, food is a complex milieu of water, fat, carbohydrate, vitamin, minerals, etc. along with proteins, and processing affects not only each individual component in the food but also the nature and intensity of intercomponent interactions in a food.
An amino acid analyzer operated essentially as described by Spackman, Stein, and Moore (11) has been equipped with provisions for automated injection of samples. As many as 8 samples (4 complete analyses) are stored in a sample changes of the type described by Murdock, Grist, and Hirs (10), and when required are displaced into the columns with a separate pump. The sample solutions are directed to the column surfaces through eapillary tubing and a system of check-valves; the valves isolate the injection system from the pressures developed during elution of the columns. Alternation of sample injection between the two columns is attained with motorized slide-valves. The analyzer is programmed with a control unit in which stepping switches, appropriately connected to relays, are incremented by pulses generated with the aid of a synchronous timing mechanism. The relays control the various operations requisite for the repetitive function of the analyzer, including regeneration of the columns, and action of the recorder and a digital integrator. The machine provides analyses in the range from 0.01 to 0.20 μmole of an individual amino acid with a precision of ±2%.
A comparative study was carried out in order to determine which of the most commonly used alkalies for protein hydrolysis in tryptophan determination gave the best results. Hydrolyses were performed with 2.5 and 4 n Ba (OH)2, 4 and 10 n NaOH, 5 n NaOH containing 5% SnCl2, and with 4 n LiOH, not previously reported for use. The effect of temperature and hydrolysis time on the measured tryptophan content was also determined. Based on results obtained with lysozyme and with seven high protein preparations 4 n LiOH gave the best results. A temperature of 145°C was selected as the most convenient temperature since maximum tryptophan values were obtained with 4–8 h. The hydrolysis time required was inversely related to the protein content of the preparation. Lysozyme, casein, bovine plasma protein, and dehydrated whole egg gave maximum tryptophan content after 4 h hydrolysis while skimmed milk powder, rice flour, wheat flour, and wild legume flour required 8 h hydrolysis.
Quantitative determination of amino acids is made simpler and more rapid by an instrument for automatically recording the ninhydrin color value of the effluent from ion exchange columns. The influent buffer, freed of air, is pumped at a constant rate through a column of sulfonated polystyrene resin. The effluent is met by a capillary stream of ninhydrin reagent delivered by a second pump. The color is developed by passing the mixture of reagent and effluent through a spiral of capillary Teflon tubing immersed in a boiling water bath. The absorbance of the resulting solution is measured continuously at 570 and 440 mμ as it flows through a cylindrical glass cell of 2-mm. bore. The peaks on the recorded curves can be integrated with a precision of 100 ± 3% for loads from 0.1 to 3.0 μmoles of each amino acid. A hydrolyzate of a protein or peptide may be analyzed in less than 24 hours. The more complex mixtures characteristic of blood plasma, urine, and mammalian tissues can be analyzed in 2 days. The instrument is applicable in principle to detection of ninhydrin-positive constituents in the effluent from various types of Chromatograph columns.
Lipid decomposition studies in frozen fish have led to the development of a simple and rapid method for the extraction and purification of lipids from biological materials. The entire procedure can be carried out in approximately 10 minutes; it is efficient, reproducible, and free from deleterious manipulations. The wet tissue is homogenized with a mixture of chloroform and methanol in such proportions that a miscible system is formed with the water in the tissue. Dilution with chloroform and water separates the homogenate into two layers, the chloroform layer containing all the lipids and the methanolic layer containing all the non-lipids. A purified lipid extract is obtained merely by isolating the chloroform layer. The method has been applied to fish muscle and may easily be adapted to use with other tissues.Lipid decomposition studies in frozen fish have led to the development of a simple and rapid method for the extraction and purification of lipids from biological materials. The entire procedure can be carried out in approximately 10 minutes; it is efficient, reproducible, and free from deleterious manipulations. The wet tissue is homogenized with a mixture of chloroform and methanol in such proportions that a miscible system is formed with the water in the tissue. Dilution with chloroform and water separates the homogenate into two layers, the chloroform layer containing all the lipids and the methanolic layer containing all the non-lipids. A purified lipid extract is obtained merely by isolating the chloroform layer. The method has been applied to fish muscle and may easily be adapted to use with other tissues.