The Research Of Heat-induced Stability And Digestibility Of Caprine Micellar Caseins

Micellar casein concentrates(MCC)and milk protein concentrates(MPC)are micellar caseins ingredients produced by microfiltration and ultrafiltration,respectively.Due to the characteristics of high-protein,high-calcium,low-lactose and low-fat content.It has good application prospects in the development of concentrated liquid products.In the membrane separation production of MCC and MPC,the ionic environment of the casein micelles is changed,resulting in a decrease in the heat stability.Preliminary studies on the heat stability of casein micelles mostly focused on bovine MCC and MPC systems,as well as milk systems,and there is still a lack of research on the heat stability of caprine micellar caseins.In this study,caprine milk and bovine milk MCC were produced by microfiltration separation,and caprine milk and bovine milk MPC were produced by ultrafiltration separation.According to the stress factors in the production and application of MCC and MPC,the reconstitution system was set with different heat treatment conditions(temperature,p H,ionic strength,calcium content),using RP-HPLC,DLS,SAXS,TEM and other means to compare the heat stability and heat-induced destabilization mechanism of caprine milk and bovine milk MCC,as well as caprine milk and bovine milk MPC.The effect of stabilization regulation on the digestibility of caprine and bovine MCC was further studied.Firstly,the heat stability and heat-induced destabilization mechanism of caprine and bovine MCC dispersions were comparatively studied.The results showed that temperature,p H value,ionic strength and calcium content had different effects on the heat stability of caprine and bovine MCC.Compared with bovine MCC,caprine MCC has lower heat stability,mainly due to its higher calcium ion activity,higher degree of κ-casein dissociation,and larger casein micelle size,which made the caprine casein micelles more prone to heat aggregation,and the resulting settleable proteins had a lower ratio of κ-casein.The caprine and bovine casein micelles started to aggregate after heating when the p H was lowered to 6.9and 6.7,respectively.The internal structure of casein micelles was not affected by the heat treatment in this study.Raising p H,as well as adding citrates and an appropriate amount of sodium chloride can improve the heat stability of MCC.Secondly,the heat stability and heat-induced destabilization mechanism of caprine and bovine MPC dispersions were comparatively studied.The results showed that the effects of temperature,p H value,ionic strength and calcium content on the heat stability of caprine milk and bovine MPC were also different.The heat stability of caprine MPC is also lower compared to bovine milk MPC,also mainly due to its higher calcium ion activity,higher degree of κ-casein dissociation and larger casein micelle size.Compared with bovine MPC,the binding rate of denatured whey protein and casein micelles in caprine MPC system is lower,which makes it easier to aggregate after heating.Unlike the MCC system,the presence of whey protein can promote the dissociation of κ-casein when the p H of the MPC system is increased to 7.1 and above.Finally,the effects of stabilization regulation(addition of citrates)on the digestibility of caprine and bovine MCC were compared.Adult and elderly in vitro digestion models were used.The results showed that the addition of citrate could reduce the size and density of the flocculated particles formed by casein micelles in the stomach,thereby improving the digestibility of MCC.Compared with bovine MCC,caprine MCC has better digestibility,and the flocculated particles formed in the stomach have smaller particle size,looser structure,faster casein degradation,higher proteolytic degree,and smaller relative molecular weight of the peptides were produced.MCC has lower digestibility in elderly models compared to adult models of digestion.In conclusion,compared with bovine,caprine micellar casein ingredients have lower heat stability,mainly due to their higher calcium ion activity and higher degree dissociation ofκ-casein.Elevating p H,as well as addition of citrate and appropriate amounts of sodium chloride can improve the heat stability of micellar casein ingredients.In addition,the addition of citrates improves the digestibility of casein micelles.This study contributes to the understanding of the heat-induced destabilization mechanism of caprine micellar casein ingredients and the establishment of stabilization strategies,which can promote its application in protein concentrates and other products.