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The effect of high humidity hot air impingement blanching on the changes in cell wall polysaccharides and phytochemicals of okra pods

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Journal of The Science of Food and Agriculture
Authors:
Sara Zielinska at Wroclaw University of Science and Technology
Sara Zielinska
Izabela Staniszewska
Izabela Staniszewska
Izabela Staniszewska
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Justyna Cybulska at Polish Academy of Sciences
Justyna Cybulska
Artur Zdunek at Polish Academy of Sciences
Artur Zdunek
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Abstract and Figures

BACKGROUND Okra pods contain heat‐sensitive substances, such as phenolic compounds and other phytochemicals that can be degraded when okra pods are subjected to heat treatment. The understanding of the impact of high humidity hot air impingement blanching (HHAIB) on the changes in physicochemical properties of polysaccharides and phytochemicals of okra pods is of great importance because over‐blanching may result in cell membrane disruption and changes in biologically active compounds under prolonged exposure to the thermal treatment. Therefore, the present study aimed to investigate the effect of HHAIB on the changes in physicochemical properties of pectins and phytochemicals extracted from okra pods. RESULTS Both the HHAIB time and method of extraction influenced their physicochemical characteristics and biological activity. Pectin fractions subjected to HHAIB were composed of polygalacturonic acid, rhamnogalacturonan, glucomannan, galactan, mannose, arabinose, rhamnose, calcium pectate and arabinogalactan. The contents of total phenolics, total flavonoids and antioxidant activity of extracts mostly increased during HHAIB (i.e. up to 19.0%, 13.2% and 35.3%, respectively). However, HHAIB reduced the chlorophyll‐a (up to 55.7%) and lycopene (up to 52.6%) contents of okra pods. CONCLUSION The acquired knowledge may be useful for better understanding and optimization of technologies based on HHAIB treatment. The HHAIB treated okra can be a promising natural alternative in different applications, including its use as a replacement of some ingredients in food or non‐food systems as a result of richness in polysaccharides and polyphenols, as well as high antioxidant properties. © 2022 Society of Chemical Industry.
Schematic diagram of high humidity hot air impingement blanching (HHAIB) equipment: (1) superheated steam generator; (2) flow regulation valve; (3) centrifugal fan; (4) blanching chamber; (5) series of round nozzles; (6) electric heater; (7) humidity sensor; (8) temperature sensor; (9) stainless steel mesh; (10) samples spread on a stainless steel mesh; and (11) control unit.
Schematic diagram of high humidity hot air impingement blanching (HHAIB) equipment: (1) superheated steam generator; (2) flow regulation valve; (3) centrifugal fan; (4) blanching chamber; (5) series of round nozzles; (6) electric heater; (7) humidity sensor; (8) temperature sensor; (9) stainless steel mesh; (10) samples spread on a stainless steel mesh; and (11) control unit.
… 
The FTIR spectra with highlighted the most important wavenumbers and PCA of the first derivative of FTIR spectra of (a) WSP, (b) CSP and (c) DASP fractions isolated from okra control sample and after different time of HHAIB (15–120 s) in the range of (4000–650 cm⁻¹). The PC2 × PC3 and PC3 × PC4 scatter of scores of WSP, CSP and DASP, as well as the related loading profiles of components PC2, PC3 and PC4, are presented. The wavenumber range 2750–1800 cm⁻¹ is not shown because of a lack of significant spectral information. Symbols: C – control sample (non‐treated); HHAIB 15, HHAIB 30, HHAIB 60, HHAIB 90 and HHAIB 120 – high‐humidity hot air impingement blanching for 15, 30, 60, 90 and 120 s; WSP – water‐soluble pectin; CSP – chelator‐soluble pectin; DASP – diluted alkali‐soluble pectin.
The FTIR spectra with highlighted the most important wavenumbers and PCA of the first derivative of FTIR spectra of (a) WSP, (b) CSP and (c) DASP fractions isolated from okra control sample and after different time of HHAIB (15–120 s) in the range of (4000–650 cm⁻¹). The PC2 × PC3 and PC3 × PC4 scatter of scores of WSP, CSP and DASP, as well as the related loading profiles of components PC2, PC3 and PC4, are presented. The wavenumber range 2750–1800 cm⁻¹ is not shown because of a lack of significant spectral information. Symbols: C – control sample (non‐treated); HHAIB 15, HHAIB 30, HHAIB 60, HHAIB 90 and HHAIB 120 – high‐humidity hot air impingement blanching for 15, 30, 60, 90 and 120 s; WSP – water‐soluble pectin; CSP – chelator‐soluble pectin; DASP – diluted alkali‐soluble pectin.
… 
The total polyphenols, flavonoids and antioxidant activity determined by the FRAP, DPPH and ABTS assays of okra pods subjected to high‐humidity hot air impingement blanching (HHAIB). The values are the mean ± SD averaged over three measurements. a,b Letters in different columns indicate no statistical differences between differently treated samples (P < 0.05). Symbols: C – control sample (non‐treated); HHAIB 15 s, 30s, 60s, 90s and 120 s – okra pods subjected to high‐humidity hot air impingement blanching at 15, 30, 60, 90 and 120 s, respectively; TP – total polyphenols, mg GAE g⁻¹ DM; TF – total flavonoids, mg RU g⁻¹ DM; FRAP – ferric‐reducing antioxidant power (mg AA g⁻¹ DM); DPPH ‐ 2,2′‐diphenyl‐1‐picrylhydrazyl (mg AA g⁻¹ DM); ABTS ‐ 2,2‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) (mg AA g⁻¹ DM).
The total polyphenols, flavonoids and antioxidant activity determined by the FRAP, DPPH and ABTS assays of okra pods subjected to high‐humidity hot air impingement blanching (HHAIB). The values are the mean ± SD averaged over three measurements. a,b Letters in different columns indicate no statistical differences between differently treated samples (P < 0.05). Symbols: C – control sample (non‐treated); HHAIB 15 s, 30s, 60s, 90s and 120 s – okra pods subjected to high‐humidity hot air impingement blanching at 15, 30, 60, 90 and 120 s, respectively; TP – total polyphenols, mg GAE g⁻¹ DM; TF – total flavonoids, mg RU g⁻¹ DM; FRAP – ferric‐reducing antioxidant power (mg AA g⁻¹ DM); DPPH ‐ 2,2′‐diphenyl‐1‐picrylhydrazyl (mg AA g⁻¹ DM); ABTS ‐ 2,2‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) (mg AA g⁻¹ DM).
… 
Surface microstructure of differently treated okra pods at magnification of 100×: control (a); sample subjected to HHAIB for 15 s (b); sample subjected to HHAIB for 30s (c); sample subjected to HHAIB for 60s (d); sample subjected to HHAIB for 90s (e); and sample subjected to HHAIB for 120 s (f). Symbols: C – control sample (non‐treated); HHAIB 15 s, HHAIB 30s, HHAIB 60s, HHAIB 90s and HHAIB 120 s – high‐humidity hot air impingement blanching for 15, 30, 60, 90 and 120 s.
Surface microstructure of differently treated okra pods at magnification of 100×: control (a); sample subjected to HHAIB for 15 s (b); sample subjected to HHAIB for 30s (c); sample subjected to HHAIB for 60s (d); sample subjected to HHAIB for 90s (e); and sample subjected to HHAIB for 120 s (f). Symbols: C – control sample (non‐treated); HHAIB 15 s, HHAIB 30s, HHAIB 60s, HHAIB 90s and HHAIB 120 s – high‐humidity hot air impingement blanching for 15, 30, 60, 90 and 120 s.
… 
The contents of chlorophyll a and b and lycopene of okra pods subjected to high‐humidity hot air impingement blanching (HHAIB). The values are the mean ± SD averaged over three measurements. a,b Letters in different columns indicate no statistical differences between differently treated samples (P < 0.05). Symbols: C – control sample (without any treatment); HHAIB 15, 30, 60, 90 and 120 s – okra pods subjected to high‐humidity hot air impingement blanching at 15, 30, 60, 90 and 120 s, respectively.
The contents of chlorophyll a and b and lycopene of okra pods subjected to high‐humidity hot air impingement blanching (HHAIB). The values are the mean ± SD averaged over three measurements. a,b Letters in different columns indicate no statistical differences between differently treated samples (P < 0.05). Symbols: C – control sample (without any treatment); HHAIB 15, 30, 60, 90 and 120 s – okra pods subjected to high‐humidity hot air impingement blanching at 15, 30, 60, 90 and 120 s, respectively.
… 
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Research Article
Received: 8 December 2021 Revised: 9 April 2022 Accepted article published: 21 April 2022 Published online in Wiley Online Library: 4 May 2022
(wileyonlinelibrary.com) DOI 10.1002/jsfa.11949
The effect of high humidity hot air
impingement blanching on the changes in cell
wall polysaccharides and phytochemicals of
okra pods
Sara Zielinska,aIzabela Staniszewska,bJustyna Cybulska,c
Artur Zdunek,cMonika Szymanska-Chargot,cDanuta Zielinska,d
Zi-Liang Liu,eHong-Wei Xiao,eZhongli Panfand Magdalena Zielinskab
*
Abstract
BACKGROUND: Okra pods contain heat-sensitive substances, such as phenolic compounds and other phytochemicals that can
be degraded when okra pods are subjected to heat treatment. The understanding of the impact of high humidity hot air
impingement blanching (HHAIB) on the changes in physicochemical properties of polysaccharides and phytochemicals of okra
pods is of great importance because over-blanching may result in cell membrane disruption and changes in biologically active
compounds under prolonged exposure to the thermal treatment. Therefore, the present study aimed to investigate the effect
of HHAIB on the changes in physicochemical properties of pectins and phytochemicals extracted from okra pods.
RESULTS: Both the HHAIB time and method of extraction influenced their physicochemical characteristics and biological activ-
ity. Pectin fractions subjected to HHAIB were composed of polygalacturonic acid, rhamnogalacturonan, glucomannan, galac-
tan, mannose, arabinose, rhamnose, calcium pectate and arabinogalactan. The contents of total phenolics, total flavonoids
and antioxidant activity of extracts mostly increased during HHAIB (i.e. up to 19.0%, 13.2% and 35.3%, respectively). However,
HHAIB reduced the chlorophyll-a (up to 55.7%) and lycopene (up to 52.6%) contents of okra pods.
CONCLUSION: The acquired knowledge may be useful for better understanding and optimization of technologies based on
HHAIB treatment. The HHAIB treated okra can be a promising natural alternative in different applications, including its use
as a replacement of some ingredients in food or non-food systems as a result of richness in polysaccharides and polyphenols,
as well as high antioxidant properties.
© 2022 Society of Chemical Industry.
Keywords: okra pods; high-humidity hot air impingement blanching; Fourier-transform infrared spectroscopy; principal component
analysis
INTRODUCTION
Abelmoschus esculentus (L.) Moench, generally called okra, is an
annual plant belonging to the Malvaceae family. Polysaccharides
are the major bioactive constituents of okra pods.
1
Besides of
polysaccharides (pectins), phytochemical compounds, such as
phenols, pigments (chlorophyll-a and chlorophyll-b), are available
natural antioxidants in okra pods.
1,2
Because the consumable period of okra pods is ≤1 week, dry-
ing can be used to prevent spoilage and extend their shelf-life.
To improve the drying rate and reduce the negative effect of dry-
ing on the quality of biological materials, it is essential to find an
effective pretreatment method.
3
A common method such us
hot water blanching has been used to prevent quality deteriora-
tion by inactivating the enzymes, destroying microorganisms or
expelling intercellular air from the tissues.
4
However, okra pods
contain heat-sensitive substances, such as phenolic compounds
and other phytochemicals that are unstable and can be degraded
*Correspondence to: M Zielinska, Department of Systems Engineering, Univer-
sity of Warmia and Mazury in Olsztyn, 11 Heweliusza 14, 10-718 Olsztyn,
Poland. E-mail: m.zielinska@uwm.edu.pl
aFaculty of Mechanical and Power Engineering, Wroclaw University of Science
and Technology, Wroclaw, Poland
bDepartment of Systems Engineering, University of Warmia and Mazury in Olsz-
tyn, Olsztyn, Poland
cInstitute of Agrophysics, Polish Academy of Sciences, Lublin, Poland
dDepartment of Chemistry, University of Warmia and Mazury in Olsztyn, Olsz-
tyn, Poland
eCollege of Engineering, China Agricultural University, Beijing, China
fDepartment of Biological and Agricultural Engineering, University of California,
Davis, Davis, CA, USA
J Sci Food Agric 2022; 102: 5965–5973 www.soci.org © 2022 Society of Chemical Industry.
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