Thermal Stability Study On Yak Milk And Colostral Liquid Whey Proteins

Whey is a soluble fraction protein from milk/colostrum or by-product liquid from cheese with vital important components for functionality,physiological and nutritional value in human diet.However,denaturation and aggregation during heat processing is the major limiting factor on protein functionality performance in food systems and its bioavailability.During this research,both yak and Holstein Friesian cows’ milk/colostrum whey proteins composition were studied followed by heat stability of liquid whey at different temperatures and various p H levels.Furthermore,evaluation of heat stability improvement of protein components in liquid whey was studied.First,the whey proteins were extracted from yak or cows’ colostrum and milk,detected the concentration of TWP,Ig G,LF,α-Lac,β-Lg and BSA by using ELISA method.The results showed that TWP,Ig G and LF concentration in yak or cows’ colostrum were significantly higher(P < 0.05)than in milk.The Ig G concentration did not differ significantly between yak and cows’ colostrum as well as in yak or cows’ milk.However,100% of yaks composed high quality colostrum versus 73.33% of Holstein Friesian cows with reference to ≥ 50 g L-1 Ig G concentration.LF,α-Lac and BSA concentrations in yak colostrum were significantly lower compared to cow’s colostrum,while no statistical significant difference from yak or cow’s milk.β-Lg is one of the allergens in milk,β-Lg concentration was lower in yak’s colostrum and milk compared to cow.Therefore,yaks’ milk and colostrum considered to be good source of nutritional ingredients for functional foods.Secondly,the study focused on heat stability evaluation on liquid whey proteins at different temperatures(60,63,72,and 90 o C for 15 sec to 30 min)and various p H levels(3.5,4.6 and 5.5).Evaluation of functional characteristics(turbidity and free-SH)indicated relatively variations on heat treated liquid whey at various p H levels.ELISA technique and UV Spectrophotometer analyses observed a significant reduction(P < 0.05)of whey protein concentrations at high temperature(> 63 o C)and p H especially around its p I,or at p H 5.5,which were either partial or complete denatured individual whey proteins.The results showed that as the temperature and p H increased,loss of turbidity was increased after centrifugation as well as free –SH increased in liquid whey as the indication of protein denaturation.However,liquid whey proteins were stable at low temperatures(≤ 63 o C)and low acid conditions.Third,heat stability improvement study using various protectants(Ca Cl2,SDS and glycerol)at medium acidic conditions(p H 3.5-5.5)above 63 o C in liquid whey from yak milk and colostrum indicated that,addition of protectants improved heat stability of the liquid whey proteins with less precipitates and turbidity changes at p H 3.5.With the increase of heating temperature and p H,heat denaturation effect increased on yak milk and colostral liquid whey proteins(Ig G,LF,α-Lac,β-Lg and BSA)by reducing its concentrations.In general,glycerol was more effective on improving heat stability of liquid whey followed by SDS and Ca Cl2,respectively.In conclusion,the yak colostral liquid whey showed that,yak animal has significant high quality colostrum compared to cows,as well as β-Lg concentration was lower in yak’s colostrum and milk compared to cow.The temperature increase above 63 o C and p H increase near to p I has a significant effect on yak milk and colostrum quality.A combined effect technique improved heat stability of liquid whey at temperatures above 63 o C at medium acidic condition in the presence of low concentration of protectants.