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العنوان
IMPROVEMENT OF FUNCTIONAL PROPERTIES OF BUFFALO’S MILK PROTEINS BY ENZYMATIC MODIFICATION /
المؤلف
ABDALLAH, MANAR SALAH SALAMA.
هيئة الاعداد
باحث / منار صلاح سلامة عبد الله
مشرف / عزة محمود فرحات
مناقش / مجدي محمد عبد المنعم عثمان
مناقش / عبد المنعم البدوي هجرس
تاريخ النشر
2023.
عدد الصفحات
154 P. :
اللغة
الإنجليزية
الدرجة
ماجستير
التخصص
علوم وتكنولوجيا الأغذية
تاريخ الإجازة
1/1/2023
مكان الإجازة
جامعة عين شمس - كلية الزراعة - قسم علوم الأغذية
الفهرس
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Abstract

Since, it may result from the partially enzymatic proteolysis of
milk proteins in peptides that have a role in improving the matrix
consistency a product such as the cow’s set yoghurt, especially if it is
available in the medium that helps it to do so.
Objectively, the aim of this study was to experiment the impact of
partially enzymatic proteolysis of certain buffalo’s milk proteinous
ingredients to choose the most appropriate one for the supplementation of
cow’s set yoghurt milk in relation to compositional, bacterial, biochemical,
rheological and organoleptic attributes of the resultant product.
Technically, to achieve this goal, the thesis was divided into two
main parts as follow:
Part I: Partial proteolysis of some buffalo’s proteinous ingredients by
different enzymes in relation to properties of the resultant
products
In this part, four buffalo’s proteinous ingredients were prepared
and poteolyzed as following:
1- Acid casein (ACn) was prepared by acidifying skimmed milk at
40°C to pH 4.6 with lactic acid. The casein precipitate was
washed, in native whey and with warm distilled water acidified to
pH 4.6 at 37- 40°C with the acid. After being properly cleaned, the
casein precipitate was pressed after the final wash and blended
with tiny particles. The precipitate was dried under at 60 °C for 6-
8 h.
2- Rennet casein (RCn) was made by adding rennet powder at the
rate of 5 g / 100 kg of skimmed milk at 37 °C. After complete
coagulation, chopping, and draining of the whey the coagulant
was treated as previously described in ACn preparation.
3- To prepare casein coprecipitate (CnCo), skimmed milk was
exposed to 90 °C for 30 min, followed by cooling to 40°C. The
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SUMMARY AND CONCLUSION
Manar S. S. Abdallah (2023), M.Sc., Fac. of Agric., Ain Shams Univ.
denatured protein complex was precipitated with lactic acid at pH
4.6. The CnCo was treated through steps similar to those applied
in the case of ACn.
4- For preparation the total milk proteinate (TMP), skimmed milk
was alkalized by 1N NaOH to pH 10 and heated to 70°C for 10
min. The pH was then adjusted to pH 3.5 using 1N HCl at the
room temperature to complex the whey proteins and casein. Again
the pH was raised to pH 4.6 by 1N NaOH to precipitate the
complexed proteins. Proteins precipitate was drained using a
cheese cloth. The precipitate was washed and dried as before
mentioned.
5- Enzymatic proteolyzed milk protein products were prepared by
dissolved isolated milk protein products in buffer solution and
agitated by an overhead mixer to a final concentration of 5 g
protein 100 g-1
. Mixing ceased and stored it overnight at 4 °C then
was sized to 4-L in erlenmeyer shake flasks at room temperature,
and adjusted into pH degree of 2 for pepsin, 8 for trypsin and 6.6
for chymosin (using hydrochloric acid and sodium hydroxide).
The proteinous ingredients were equilibrated to 37 °C for trypsin
or pepsin and to 42°C for chymosin. Thereafter, enzymatic
proteolysis was carried out by added 1 g enzyme for every 100 g
protein at different hydrolysis time (0.0,4.0, 8.0) h. At the end of
proteolysis, the reactions were stopped by placing the flasks in a
90 water bath for 2 min followed by an ice bath.
The obtained results of the 1st part could be summarized as follow:
1- Compositionally, the dried preparation of TMP kept moisture as
well as ash contents lower than those of the others preparation,
namely RCn which held the highest moisture content followed by
ACn came in the 2nd order and CnCo ,which came in the last
order. The protein contents behaved trending opposite to those of
moisture contents.
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SUMMARY AND CONCLUSION
Manar S. S. Abdallah (2023), M.Sc., Fac. of Agric., Ain Shams Univ.
2- Specificationally, the trypsin enzyme possessed the highest
activity followed by pepsin and chymosin, respectively.
Nevertheless, the protein contents mg per g enzyme were nearly
the same, therefore the specific activity of enzyme take trending
similar to those of absolute activities. The chymosin enzyme was
characterized with its higher clotting and lower proteolysis power
in comparison with either pepsin or rather trypsin.
3- Rheologically, the proteolysate of ACn possessed the highest
viscosity followed by RCn, CnCo and TMP, respectively. The
pepsin proteolysate had the highest viscosity followed by those of
chymosin and trypsin. The viscosity of protein solution reduced
as the proteolysis time extended.
4- Decompositionally, the proteolysate of RCn contained the highest
water soluble nitrogen (WSN) and non protein nitrogen (NPN)
levels. The chymosin proteolysate had the highest WSN level,
while that of trypsin possessed the highest NPN level.
5- Physically, the proteolysate of CnCo exhibited the highest
foaming ability followed in order by that of TMP, ACn and RCn,
which possessed foam stability as good as those of CnCo and
TMP. The output of chymosin was the best towards the foaming
ability and stability, those were lowered as the time of proteolysis
or foam holding expended. TMP proteolysate had the highest
emulsion capacity and stability followed by CnCo. Chymosin
output yielded the best emulsion capacity and stability, those were
also harmed as the time of proteolysis or emulsion holding
expended.
Part II: Impact of the supplementation with partially chymosinproteolyzed buffalo’s total milk proteinate on the properties
of cow’s set yoghurt
In this part, four treatments including the control were designed,
where cow’s full cream milk powder (FCMP) was reconstituted at the
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SUMMARY AND CONCLUSION
Manar S. S. Abdallah (2023), M.Sc., Fac. of Agric., Ain Shams Univ.
temperature of 45°C for 15 min whether at the level of 13% FCMP (the
control) with tap water or at the level of 12% FCMP with solution
containing 1% TMP in the native form (i.e. non enzymatic proteolyzed) or
solution of TMP proteolyzed by chymosin for 4 or 8 h. The yoghurt milks
were heat treated at 85°C for 5 min. followed by temperature adjustment to
42°C at which yoghurt milks were inoculated with 2% of fresh yoghurt
starter culture. Three replicates were done for every treatment.
The obtained results of the 2nd part could be summarized as follow:
1- Compositionally, no significant differences in both of moisture as
well as fat contents among fresh yoghurt treatments but the
supplementation with 1% TMP, whether in the native or in the
proteolyzed form, was associated with significant increase in the
protein content of yoghurt. Both of WSN/TN% and NPN/TN % of
fresh yoghurt were significantly increased as it was supplemented
with TMP whether, in the native or rather in the proteolyzed form.
The ash content of yoghurt appeared a significant reduction as a
result of TMP adding regardless its proteolysis period.
2- Microbiologically, the Log count of lactic acid bacteria (LAB) did
not appear any significant differences between the fresh yoghurt
treatments. All Log counts of LAB reached to the highest value
after seven days and then reduced again at the end of cold storage
period (14 days). Neither yeasts & molds nor total coliform
exhibited any considerable count.
3- Fermentatively, the acid development in yoghurt was encouraged
as the added TMP proleolyzed, while the native TMP delayed the
acid developed in yoghurt versus the control. On the contrary, the
pH behaved opposite trending with some variations. During cold
storage period (CSP)of yoghurt the acidity % increased and pH
value decreased.
4- Rheologically, both of hardness, gumminess and chewiness values
of yoghurt increased, while the adhesiveness decreased as it was
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SUMMARY AND CONCLUSION
Manar S. S. Abdallah (2023), M.Sc., Fac. of Agric., Ain Shams Univ.
supplemented with TMP whether, in the native or rather in the
proteolyzed form. The springiness of yoghurt raised as the
proteolysis time prolonged. The cohesiveness values of all TMP
yoghurts, especially in the native form were lower than that of the
control. Although the CSP of yoghurt did not influence the values
of cohesiveness and chewiness, the values of hardness and
gumminess increased, while those of adhesiveness and springiness
decreased.
5- Organoleptically, the 4h proteolyzed TMP-yoghurt gained the
highest total sensory score followed by that of native or 8h
proteolyzed TMP. Whilst, the control came in the last order.
Nevertheless, the judging score of all yoghurt treatments lowered
as the CSP prolonged.
Finally, it could be concluded that, although the TMP derivative
is a protein compound, its proteolysis with chymosin, which κ-casein is
its preferred substrate, resulting in the liberation of peptide, para κ-casein
that helped more in strengthening the weak curd, from which cow’s
yoghurt is suffered and homogenizing its consistency, provided that the
period of proteolysis does not exceed 4 h by 1% enzyme.