The proteolytic activity of selected lactic acid bacteria in fermenting cow's and camel's milk and the resultant sensory characteristics of the products

Abstract

The aim of this study was to evaluate the proteolytic activities of 14 strains of lactic acid bacteria and their impact on sensory characteristics of the resultant fermented cow and camel milk. The results showed that Lactobacillus rhamnosus PTCC 1637 and Lactobacillus fermentum PTCC 1638 had high protease activity and high mean values for sensory quality in fermented cow's and camel's milk. Lactobacillus plantarum PTCC 1058 revealed high protease activity and sensory scores in camel milk. Consequently, milk fermentation using such strains might be recommended for the development of dairy products containing bioactive peptides.

Full text

ORIGINAL
RESEARCH The proteolytic activity of selected lactic acid bacteria
in fermenting cow’s and camel’s milk and the resultant
sensory characteristics of the products
MARYAM MOSLEHISHAD,
1
SAEED MIRDAMADI,
2
*
†
MOHAMAD
REZA EHSANI,
1
*
†
HAMID EZZATPANAH
1
and ALI AKBAR MOOSAVI-
MOVAHEDI
3
1
Food Science and Technology Department, Faculty of Agriculture and Natural Resources, Science and Research
Branch, Islamic Azad University, Tehran, Iran,
2
Department of Biotechnology, Iranian Research Organization for
Science & Technology (IROST), Tehran, Iran, and
3
Institute of Biochemistry and Biophysics, University of Tehran,
Tehran, Iran
The aim of this study was to evaluate the proteolytic activities of 14 strains of lactic acid bacteria
and their impact on sensory characteristics of the resultant fermented cow and camel milk. The
results showed that Lactobacillus rhamnosus PTCC 1637 and Lactobacillus fermentum PTCC 1638
had high protease activity and high mean values for sensory quality in fermented cow’s and
camel’s milk. Lactobacillus plantarum PTCC 1058 revealed high protease activity and sensory
scores in camel milk. Consequently, milk fermentation using such strains might be recommended
for the development of dairy products containing bioactive peptides.
Keywords Fermented milk, Lactic acid bacteria, Sensory evaluation, Protease activity.
INTRODUCTION
Camel’s milk, which is consumed as fresh, raw
milk or in the form of soured milk, has an
essential role in the human diet in the world’s
arid areas (Hassa€
ıne et al. 2007). Historically,
cultured milk has been consumed as an impor-
tant part of the traditional diet. Fermentation can
preserve milk under hot conditions in dry
regions for a considerable time (Farah and
Atkins 1992; Hassa€
ıne et al. 2007). Chemical
composition of camel milk is different from that
of cow’s milk, which can influence the func-
tional, biological and organoleptic characteristics
of milk and dairy products (Eshraga et al.
2011). Camel’s milk is characterised by a differ-
ent protein structure, different lipids and mineral
balance and higher amounts of free amino acids
and peptides (Abu-Taraboush et al. 1998; Sal-
ami et al. 2010; Boudjenah-Haroun et al. 2011).
Spontaneous fermentation of milk, which is
traditionally used by domestic producers, results
in variable product flavour as well as poor
hygienic quality. Controlled fermentation using
some strains of lactic acid bacteria (LAB)
improves fermented milk, especially traditional
camel’s milk products (Hassa
€
ıne et al. 2007;
Panesar 2011).
The benefits of LAB are well recognised due
to their health and nutritional effects of the live
micro-organisms, probiotics or indirect effects of
the metabolites with health-promoting character-
istics (Hayes et al. 2007). These micro-organ-
isms are capable to produce several substances
such as organic acids, diacetyl, hydrogen perox-
ide, bacteriocins and bioactive peptides (Moraes
et al. 2010). Their proteolytic system lets them
use milk protein as a source of nitrogen, which
has an essential role in the production of differ-
ent types of metabolites in fermented food prod-
ucts (Shihata and Shah 2000; Liu et al. 2010).
This ability can also cause the release of a wide
range of biologically active peptides such as
hypotensive peptides, opioid agonists, antagonist
peptides, antibacterial and immunomodulatory
peptides (Donkor et al. 2007). Recently, the
application of proteolytic food-grade LAB has
been considered as a new strategy for producing
novel functional food rich in bioactive peptides
(Hayes et al. 2007).
*Authors for
correspondence. E-mails:
mirdamadi@irost.ir;
mehsani@ut.ac.ir
†
These authors contribute
to this work equally.
© 2013 Society of
Dairy Technology
Vol 66, No 2 May 2013 International Journal of Dairy Technology 279
doi: 10.1111/1471-0307.12017

The proteolytic system of LAB contributes to the libera-
tion of milk-derived bioactive peptides in a variety of
fermented functional dairy products including cheese,
yoghurt, buttermilk and cultured milk. These peptides can
affect milk products’nutritional properties, beneficial health
effects and sensory attributes (Hugenholtz et al. 2000;
Fitzgerald and Murray 2006; Savijoki et al. 2006). Sensory
evaluation of dairy products is crucial for consumer accep-
tance and quality control (Karagul-Yuceer and Drake
2006).
Hence, the aim of the present study was to assess the prote-
olytic activities of some LAB and sensory evaluation of their
resulting fermented cow’s and camel’s milk products to
selecting specific bacterial strains for further study in the
development of dairy products containing bioactive peptides.
MATERIALS AND METHODS
Milk collection
Cow’s milk samples were collected from a commercial
dairy farm with approximately 500 lactating cows in Tehran
province, Iran. Camel’s milk was obtained from local camel
producers in Torkaman Sahra, Gorgan province, Iran. All
milk samples were collected aseptically in sterile bottles and
kept cold (4–5°C) during transportation to laboratory
according to Association of Official Analytical Chemists
(AOAC, 2002).
Milk analysis
Raw cow’s and camel’s milk samples were analysed for
total nitrogen (TN), crude protein (CP), noncasein nitrogen
(NCN) using AOAC method No. 998.05 (AOAC 2002),
casein nitrogen (CN), Non protein nitrogen (NPN) using
AOAC method No. 991.21 (AOAC 2002), ratio of casein
nitrogen to total nitrogen (CN/TN) by Kjeldal method, milk
urea nitrogen (MUN), milk fat, lactose and solid-non-fat
(SNF) concentration by a mid-infrared analyzer (Milko-Scan
S50; Foss Electric, Hillerød, Denmark), according to AOAC
No. 972.16 (AOAC 2002) total solids (TS) by calculation
(fat +SNF), pH with a potentiometer; and titratable acidity
(TA) according to the titrimetric method of AOAC No.
947.05 (AOAC, 2002).
Bacterial strains
The 14 different generally recognised as safe (GRAS)
LAB were obtained from Persian Type Culture Collection
of the Iranian Research Organization for Science and
Technology (IROST): Pediococcus pentosaceus PTCC
1426, Pediococcus acidilactici PTCC 1424, Pediococcus
acidilactici PTCC 1602, Lactobacillus fermentum PTCC
1638, Lactobacillus leichmannii PTCC 1057, Lactobacillus
delbrueckii subsp. delbrueckii PTCC 1333 and PTCC 1737,
Lactobacillus casei subsp. casei PTCC 1608, Lactococcus
lactis subsp. lactis PTCC 1403, Lactobacillus acidophilus
PTCC 1643, Lactobacillus rhamnosus PTCC 1637, Lactobacil-
lus reuteri PTCC 1655, Lactobacillus plantarum PTCC 1058,
Lactobacillus delbrueckii subsp. bulgaricus PTCC 1737, Strep-
tococcus thermophilus PTCC 1738. The organisms were main-
tained in skim milk (Merck, Darmstadt, Germany) plus
glycerol sterilised at 70 °C.
Preparation of fermented milk
The LAB (1% v/v) were cultivated in sterile 10 mL aliquots
of de Man Rogosa and Sharpe (MRS) broth and incubated
for 24 h at 37 °C. The cultures were centrifuged at 5000 g
for 15 min to separate bacteria. Biomass washed twice with
sterile distilled water. The bacteria were then inoculated into
skim milk (12% w/v) and incubated at 37 °C for 24 h as a
pre-culture to obtain approximately 10
8
colony forming units
(CFU)/mL. Fresh whole cow’s and camel’s milk were pas-
teurised at 80 °C for 20 min in a water bath, and then cooled
to 43 °C. The pre-cultures (2% v/v) were inoculated into
cow’s and camel’s milk and incubated at 37 °C for 24 h.
Determination of proteolytic activity
The proteolytic activity of selected LAB was determined
using three methods: a spot cultivation test in enriched CO
2
conditions; a spot cultivation test in anaerobic conditions;
and a well-diffusion test.
10% w/v skim milk was reconstituted with 250 ml of dis-
tilled water and 500 ml of 2.5% agar solution was sterilized.
They were mixed aseptically at 50 °C and poured into 9cm
diameter petri dishes.
Spot cultivation tests were conducted in enriched CO
2
(candle jar) and anaerobic conditions: 10 lL of selected
bacteria were spotted on skim milk agar medium and incu-
bated at 37 °C for 48 h in enriched CO
2
and under an
anaerobic environment with a GasPack system (Merck An-
aerocult type A). After 48 h, they were placed at 4 °C for
3 days, and the diameter of the clear zone surrounding each
culture was measured using a digital micrometre (Pailin
et al. 2001).
For the well-diffusion test, 50 lL of the supernatant of
centrifuged (5000 g) bacterial cultures in MRS broth med-
ium was loaded into the 6.5-mm-diameter wells of skim
milk agar plates. Protease activity was determined by esti-
mating the diameter of clear zone area after 24 h.
Preparation of fermented milk
The LAB (1% v/v) were cultivated in sterile 10 mL aliquots
of de MRS broth and incubated for 24 h at 37 °C. The cul-
tures were centrifuged at 5000 gfor 15 min to separate bac-
teria. Biomass washed twice with sterile distilled water. The
bacteria were then inoculated into skim milk (12% w/v) and
incubated at 37 °C for 24 h as a pre-culture to obtain
approximately 10
8
CFU/mL. Fresh whole bovine and camel
milk were pasteurised at 80 °C for 20 min in a water bath,
and then cooled to 43 °C. The pre-cultures (2% v/v) were
280 ©2013 Society of Dairy Technology
Vol 66, No 2 May 2013

inoculated into cow’s and camel’s milk and incubated at
37 °C for 24 h.
Sensory evaluation
A panel of 30 untrained assessors evaluated the sensory
attributes of the fermented milk for flavour, appearance and
overall acceptance based on the method developed by Inter-
national Dairy Federation (Karagul-Yuceer and Drake
2006). The samples, each of which was given a three-digit
code, were served in plastic containers under normal light.
The panellists received the samples randomly. They were
asked to rinse their mouth with water between each sample
testing. The test was accomplished based on 5-point hedonic
scale by panellists and scaled as 1 =dislike extremely,
2=dislike moderately, 3 =neither like nor dislike, 4 =like
moderately and 5 =like extremely.
Statistical analysis
All data were subjected to one-way analysis of variance
(ANOVA) using SPSS 12.0 software (SPSS Inc., Chicago, IL,
USA, 2002). Significant treatment means were separated by
Duncan’s new multiple range test. Correlation analysis
based on two-tailed Pearson correlations was performed.
RESULTS AND DISCUSSION
Determination of proteolytic activity of lactic acid
bacteria
Bacterial protease activity was assessed based on the ability
to produce clear zone on skim milk agar (Pailin et al. 2001;
Nemeckova et al. 2009). In all cases, except P. acidilactici
PTCC 1424 and PTCC 1602, the protease activity of the
cell-free supernatant was lower than that obtained in bacte-
rial cells (Table 1). This may be due to the spontaneous
production of extracellular and intracellular proteases in spot
cultivation assay in comparison with cell-released extracellu-
lar proteases of supernatant fluid in well-diffusion test. The
data were in line with those found by Percival et al. (1999),
which showed a wide clear zone for the whole culture com-
pared with supernatant fluid on skim milk agar.
As shown in Table 1, Lb. rhamnosus PTCC 1637,
Lb. fermentum PTCC 1638 and Lb. plantarum PTCC 1058
revealed a high level of proteolytic activity when examined
with all three methods. In previous studies, El-Ghaish et al.
(2010) and Kholif et al. (2011) also reported that
Lb. rhamnosus NRRL B-445, Lb. helveticus CNRZ32,
Lb. plantarum NRRL B-404 and Lb. delbrueckii subsp
bulgaricus CNRZ397 were the highest protease producers
among the tested strains.
Streptococcus thermophilus PTCC 1738 and Lac. lactis
subsp. lactis PTCC 1403 exhibited weak proteolytic activity
in spot cultivation test. No protease activity was detected in
their cell-free supernatants. Additionally, Lb. leichmannii
PTCC 1057 and Lb. reuteri PTCC 1655 had no proteolytic
activity under enriched CO
2
conditions, whereas proteolytic
activity was observed with the other methods. The data sug-
gested that the release of protease in a medium is influenced
by culture conditions. It has been previously reported that
culture conditions such as incubation period, pH and envi-
ronmental temperature are detrimental to the protease activ-
ity of bacteria (de Giori et al. 1985; Percival et al. 1999).
As shown in Table 5, most strains achieved approxi-
mately coordinated responses for protease activity in three
different situations. Correlation analysis indicated a
Table 1 Proteolytic activity of lactic acid bacteria was noted as diameter (mm SE) of clearing zone on skim milk agar
Lactic acid bacteria
Proteolytic activity
Supernatant Anaerobic Enriched CO
2
Lactococcus lactis subsp. PTCC 1403 10.66 0.89
deA
6.71 1.16
deB
Pediococcus pentosaceus PTCC 1426 4.12 0.62
bcA
5.79 0.64
fgB
6.08 0.07
deB
Pediococcus acidilactici PTCC 1602 4.69 0.29
abA
4.21 0.15
fgA
4.43 0.35
eA
Pediococcus acidilactici PTCC 1424 5.53 0.38
aA
4.11 0.09
gB
4.57 0.26
eB
Lactobacillus fermentum PTCC 1638 3.11 0.08
cdA
19.96 2.26
bcB
24.26 4.79
abB
Lactobacillus reuteri PTCC 1655 2.58 0.31
deA
8.26 0.06
efB

Lactobacillus leichmannii PTCC 1057 0.76 0.07
fA
12.02 0.49
deB

Lactobacillus plantarum PTCC 1058 4.43 0.32
abA
23.87 1.63
bB
20.35 1.91
bcC
Lactobacillus acidophilus PTCC 1643 2.93 0.43
deA
12.47 2.23
dB
8.04 0.21
deC
Lactobacillus delbrueckii subsp. delbrueckii PTCC 1333 4.31 0.26
bcA
18.69 2.31
cB
23.00 1.85
bB
Lactobacillus rhamnosus PTCC 1637 4.50 0.21
abA
28.79 2.25
aB
28.58 0.88
aC
Lactobacillus casei PTCC 1608 2.84 0.78
deA
23.30 0.36
bB
17.14 3.24
cB
Streptococcus thermophilus PTCC 1738 9.67 0.80
defB
9.69 1.26
dB
Lactobacillus delbrueckii subsp. bulgaricus PTCC 1737 1.90 0.04
eA
18.32 2.01
cB
8.55 0.07
deC
Negative (), no proteolytic activity was detected.
Values with different small letters in a column and with different capital letters in a row are statistically significant at P<0.05.
©2013 Society of Dairy Technology 281
Vol 66, No 2 May 2013

significant and positive correlation between protease activity
of bacteria under enriched CO
2
and anaerobic environments
using the spot cultivation method (Pearson’s correlation;
r=+0.859; P<0.01). As well, all strains showed proteo-
lytic activity under anaerobic conditions; therefore, it
appears that anaerobic growth conditions were more favour-
able for the assessment of protease activity.
Chemical composition of milk
Table 2 presents the chemical components of raw cow’s and
camel’s milk. Mean values for pH and lactose content in
camel milk were significantly (P<0.05) lower than those
observed in cow’s milk. The results were in line with those
obtained by Mehaia et al. (1995). In contrast, camel’s milk
contained higher average values (P<0.05) for fat content
and TA. The obtained data were in agreement with those
reported by Yagil et al. (1984) and Abu-Taraboush et al.
(1998). No significant difference (P0.05) was observed
between other milk components of raw cow’s and camel’s
milk, including TS, SNF and CP. As shown in Table 3, nitro-
gen compounds in camel’s milk were characterised by lower
CN/TN and higher NCN, non-protein nitrogen (NPN) and
MUN contents; these values were significantly (P<0.05)
different from those obtained for bovine milk. The literature
shows variations in camel’s milk composition; this could be
due to the differences in factors, such as stage of lactation,
age, calving number, breed, seasonal variations, geographical
origin and feeding conditions (Al haj and Al Kanhal 2010).
Sensory evaluation of fermented cow’s and camel’s milk
The results indicated that flavour acceptance of fermented
cow milk were in the range of 1.05 0.23 to 3.28 0.12
(Table 4). Fermentation of cow milk by Lb. acidophilus
PTCC 1643, Lb. rhamnosus PTCC 1637 and Lb. fermentum
PTCC 1638 had the highest score, while Lb. reuteri PTCC
1655 and Lb. delbrueckii subsp. delbrueckii PTCC 1333
had the lowest. The mean values for flavour analysis of fer-
mented camel milk were lower than 3.47 0.15 (Table 4).
Fermentation of camel milk by Lb. acidophilus PTCC 1643
and Lb. casei subsp. casei PTCC 1608 were recorded with
the highest score, while fermentation by Lac. lactis subsp.
lactis PTCC 1403 had the lowest score for flavour accep-
tance.
The flavour scores of fermented cow’s and camel’s milk
differed significantly (P<0.05), except for those of
Lb. acidophilus PTCC 1643, Lb. rhamnosus PTCC 1637,
Lb. fermentum PTCC 1638 and P. acidilactici PTCC 1602.
This might be attributed to several factors such as lower lac-
tose content, higher level of salts, vitamin C and polyunsat-
urated fatty acids; and the presence of microbial inhibitors,
as well as low protein concentrations in camel’s milk
(Elamin and Wilcox 1992; Eshraga et al. 2011).
The appearance values for all fermented cow’s milk sam-
ples (<3.20 0.58) were lower (P<0.05) those for camel
milk samples (>3.76 0.16). This is probably due to the
compositional and structural differences between cow’s and
camel’s milk (Tables 2 and 3). The relatively broad size dis-
tribution of casein micelles and small size of fat globules in
camel milk may explain the favourable colour and appear-
ance of fermented camel’s milk (Farah and R€
uegg 1985;
El-Agamy 2009). Compared with cow’s milk, camel’s milk
fat has a lower b-carotene content, which might influence
the whiter colour of fermented camel’s milk (Al haj and Al
Kanhal 2010).
The results confirmed that acid production in cow milk
after fermentation leads to coagulation of milk samples.
Table 2 Chemical composition (Mean SE) of raw cow’s and camel’s milk
TS
(g/100)
Lactose
(g/100)
Fat
(g/100)
CP
(g/100)
SNF
(g/100) pH TA (
°
D)
Cow 11.77 0.13
A
4.79 0.02
A
2.88 0.05
A
2.67 0.23
A
8.85 0.14
A
6.67 0.02
A
13.96 0.08
A
Camel 11.98 0.23
A
4.26 0.08
B
4.06 0.16
B
2.44 0.15
A
7.92 0.14
B
6.43 0.01
B
15.50 0.20
B
TS, total solid; CP, crude protein; SNF, solid-non-fat; TA, titratable acidity.
Values with different capital letters (A, B) within the same column are significantly different at P<0.05.
Table 3 Nitrogen component (Mean SE) of raw cow’s and camel’s milk
TN
(g/100)
CN
(g/100)
NCN
(g/100)
NPN
(g/100)
CN/TN
(g/100)
MUN
(mg/100)
Cow 0.42 0.037
A
0.38 0.036
A
0.04 0.001
A
0.01 0.003
A
0.91 0.006
A
18.00 1.633
A
Camel 0.38 0.024
A
0.33 0.025
A
0.05 0.001
B
0.03 0.002
B
0.88 0.002
B
49.50 2.780
B
TN, total nitrogen; CN, casein nitrogen; NCN, noncasein nitrogen; NPN, non-protein nitrogen; CN/TN, casein nitrogen in total nitrogen; MUN,
milk urea nitrogen.
Values with different capital letters (A, B) within the same column are significantly different at P < 0.05.
282 ©2013 Society of Dairy Technology
Vol 66, No 2 May 2013

Acid production reduces electrostatic repulsion on casein
micelles, and the hairs of casein may curl up somewhat as
the pH drops. Colloidal calcium phosphate is also dissolved
by milk acidification, which results in gel formation (Robin-
son et al. 2006).
Although the results (unpublished data) revealed that the
final pH in some fermented camel’s milk was lower than
4.6 (isoelectric pH value for bovine milk caseins), unlike
cow’s milk, camel’s milk samples showed no coagulation.
Our findings are consistent with those from Abdel Rahman
et al. (2009). This may explain the lower isoelectric pH val-
ues for camel’s milk compared with cow’s milk, as previ-
ously reported by Wangoh et al. (1998). In contrast, some
researchers have found that the isoelectric pH value for
cow’s and camel’s caseins are the same (El-Agamy 2009).
From a biochemical point of view, another important reason
might be due to the casein micelle size (Attia et al. 2001;
Faye and Esenov 2005), lower content of TS, minerals and
the small size of the camel’s milk fat globules: 1.2–4.2 lm,
instead of the 1–10 lm in cow’s milk (Ramet 2001).
Fermentation of cow’s milk by Lb. rhamnosus PTCC 1637
(3.30 0.16) had the highest overall preference score, and
Table 5 Pearson correlation matrix for proteolytic activity of lactic acid bacteria and sensory evaluation scores
Proteolytic activity
Sensory evaluation
Fermented cow’s milk Fermented camel’s milk
Supernatant Anaerobic Enriched CO
2
Flavour Overall acceptance Flavour Overall acceptance
Proteolytic activity
Supernatant 1 0.21 0.28 0.26 0.26 0.01 0.01
Anaerobic 1 0.86** 0.04 0.05 0.37 0.46
Enriched CO
2
1 0.04 0.04 0.14 0.24
Fermented cow’s milk
Flavour 1 0.99** 0.08 0.07
Overall acceptance 1 0.16 0.15
Fermented camel’s milk
Flavour 1 0.96**
Overall acceptance 1
**Correlation is significant at P<0.01 (two-tailed).
Table 4 Sensory evaluation scores (Mean SE) of fermented camel and cow milk after 24 h at 37 °C
Culture
Fermented
cow’s milk
Fermented
camel’s milk
Fermented
cow’s milk
Fermented
camel’s milk
Fermented
cow’s milk
Fermented
camel’s milk
Flavour Appearance Overall acceptance
Lactococcus lactis subsp. lactis
PTCC 1403
2.76 0.15
cdB
1.59 0.12
fA
3.20 0.58
aB
4.12 0.08
aA
2.78 0.16
bcB
2.33 0.18
fA
Pediococcus pentosaceus PTCC 1426 2.85 0.16
bcdB
1.75 0.19
efA
2.60 0.24
abB
3.87 0.15
aA
2.78 0.15
bcA
2.49 0.17
fA
Pediococcus acidilactici PTCC 1602 2.68 0.28
cdA
1.82 0.23
efA
2.20 0.37
bcB
4.06 0.10
aA
2.79 0.24
bcA
2.64 0.19
efA
Pediococcus acidilactici PTCC 1424 1.17 0.39
fgB
2.18 0.26
deA
1.12 0.08
dB
4.12 0.15
aA
1.09 0.05
eB
2.73 0.23
defA
Lactobacillus fermentum PTCC 1638 3.03 0.15
acA
2.65 0.17
cdA
2.80 0.66
aB
4.00 0.12
aA
3.09 0.12
abB
3.10 0.12
bceA
Lactobacillus reuteri PTCC 1655 1.04 0.21
gB
2.61 0.16
cdA
1.06 0.06
dB
4.06 0.10
aA
1.04 0.05
eB
3.08 0.14
ceA
Lactobacillus leichmannii PTCC 1057 2.52 0.21
dB
3.28 0.23
abA
2.60 0.24
abB
3.94 0.13
aA
2.61 0.19
cB
3.60 0.13
abA
Lactobacillus plantarum PTCC 1058 1.55 0.14
feB
3.31 0.22
abA
1.11 0.06
dB
4.00 0.18
aA
1.43 0.12
deB
3.50 0.19
abcA
Lactobacillus acidophilus PTCC 1643 3.28 0.12
aA
3.47 0.15
aA
3.00 0.40
aB
4.06 0.13
aA
3.18 0.08
abB
3.70 0.09
aA
Lactobacillus delbrueckii
subsp. delbrueckii PTCC 1333
1.05 0.23
gB
2.82 0.81
bcA
1.11 0.08
dB
4.00 0.10
aA
1.05 0.06
eB
3.33 0.13
abA
Lactobacillus rhamnosus PTCC 1637 3.24 0.17
abA
2.46 0.17
cdA
3.13 0.13
aB
4.08 0.06
aA
3.30 0.16
aB
3.43 0.12
abcA
Lactobacillus casei PTCC 1608 2.84 0.11
bcdB
3.41 0.15
aA
2.83 0.11
aB
4.06 0.16
aA
2.90 0.10
abcB
3.57 0.14
abcA
Streptococcus thermophilus PTCC 1738 2.60 0.19
dB
3.14 019
abA
3.20 0.20
aB
4.06 0.10
aA
2.57 0.17
cB
3.60 0.17
abA
Lactobacillus delbrueckii
subsp. bulgaricus PTCC 1737
1.88 0.22
eB
2.53 0.24
cdA
2.00 0.32
cB
3.76 0.16
aA
1.75 0.17
dB
3.15 0.15
bceA
Values with different small letters in a column and with different capital letters in a row are statistically significant at P<0.05.
©2013 Society of Dairy Technology 283
Vol 66, No 2 May 2013

fermentation by Lb. reuteri PTCC 1655 (1.04 0.21) the
lowest (Table 4). Camel’s milk fermented by Lb. acidophilus
PTCC 1643 (3.70 0.09) achieved the highest average over-
all acceptance scores, while camel milk fermented by
Lac. lactis subsp. lactis PTCC 1403 (2.33 0.18) achieved
the lowest. There was a statistically significant correlation
between overall acceptance and flavour scores of fermented
cow (Pearson’s coefficient; r = +0.996; P<0.01) and camel
(Pearson’s coefficient; r = +0.957; P<0.01) milk (Table 5).
Therefore, the results indicate that the most important compo-
nent of the sensory evaluation of fermented cow’s and
camel’s milk is flavour, which can influence overall consumer
acceptance.
Pearson’s correlation data indicated that contrary to previ-
ous studies, some of the proteolytic LAB may lead to the
formation of bitter peptides and flavour defects in dairy
products (Arvanitoyannis et al. 2009). The results of the
current study, showed that there is no specific correlation
between protease activity and either flavour defects or over-
all acceptance of fermented cow’s and camel’s milk
(Table 5).
CONCLUSION
The results showed that some strains such as Lb. rhamnosus
PTCC 1637 and Lb. fermentum PTCC 1638 had high prote-
ase activity and a high mean for sensory quality in fer-
mented cow and camel milk. Lb. plantarum PTCC 1058
had high protease activity level and sensory quality rating
for camel milk. Consequently, milk fermentation using such
strains might be recommended for development of fer-
mented cow and camel milk containing bioactive peptides.
Further studies should confirm the possibility of applying
these proteolytic LAB as a new approach for generating fer-
mented milk products rich in bioactive peptides.
ACKNOWLEDGEMENTS
This work has been supported by Iranian Research Organization
for Science and Technology (IROST), University of Tehran, Iran,
Iran National Science Foundation (INSF), Dairy Industries
Company (Pegah), Islamic Azad University, Science and
Research Branch of Tehran, Center for International Research
and Collaboration (ISMO) and French Embassy in Tehran.
Assistance of Dr. Behrouz Ehsani-Moghaddam in English editing
of this paper is also highly appreciated.
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