Study On Membrane-based Separation And Preparation Of Goat Milk Protein

Goat milk is easy to digest,low sensitization and other advantages,in recent years,Goat milk-based infant formula milk powder market share gradually increased.The ratio of whey protein to casein in sheep milk was about 30:70.The ratio of human whey protein to casein was about 60:40.Therefore,the separation and preparation of sheep whey protein ingredients containingβ-casein for the development of infant formula milk powder can better simulate the composition of human milk protein.The traditional whey protein ingredients are derived from whey,a by-product of cheese processing.The process involves multiple heat treatments,which can easily lead to the inactivation of active protein components,and the ingredients do not containβ-casein.In this study,fresh goat milk was used as raw material.After centrifugation degreasing,1.4μm pore diameter ceramic membrane was used for large-aperture microfiltration and sterilization treatment.Then,natural whey protein ingredients containingβ-casein were prepared by low-temperature small-aperture microfiltration separation process,aiming to retain the active ingredients in whey protein and improve the content ofβ-casein in ingredients.The main research contents and results are as follows:(1)Firstly,the effects of temperature,equilibrium time,pH,NaCl addition concentration,sodium citrate addition concentration on the dissociation ofβ-casein from micelles were studied.The results showed that the selectivity ofβ-casein dissociation in micellar state was better at 4℃.When the equilibrium time was 120 min,the dissociation rates ofβ-casein,κ-casein andα-casein were 42.79%,33.03%and 13.63%,respectively.The proportions of these three kinds of free casein in the whey phase were 60.25%,30.47%and9.28%,respectively.(2)Secondly,the effects of pH,membrane pore size,concentration ratio and filtration stage on the co-separation of whey protein andβ-casein were studied.The results showed that the optimal co-separation effect ofβ-casein and whey protein was obtained under the condition of 4℃ for 120 min,pH of 6.7,ceramic membrane with 100 nm pore diameter,concentration multiple of 3 times,and number of filtration stages of 5.The proportions ofβ-casein and whey protein in the ingredients were 31.58%and 68.42%,respectively.The contents of active IgG,LF and LPO were 0.72 g/g,0.98 g/g and 5.28 U/mg,respectively,which were higher than those of traditional membrane filtration whey protein powder and WPC50 whey protein powder,and the degree of protein glycosylation in low-temperature membrane filtration whey protein powder was also lower.(3)Finally,using proteomics technology,the low temperature membrane filtration(4℃),traditional membrane filtration(40℃-45℃)and WPC50 sheep whey protein powder were compared and studied.The results showed that the number of proteins detected in cryogenic membrane filtration,traditional membrane filtration and commercial WPC50 whey protein powder were as follows:246,276 and 256,of which 181 proteins were obtained from cryogenic membrane filtration,conventional membrane filtration and commercial WPC50whey protein powder,3 proteins were obtained from cryogenic membrane filtration and commercial WPC50 whey protein powder,and 53 proteins were obtained from cryogenic membrane filtration and traditional membrane filtration.Compared with the whey protein powder obtained by low temperature membrane filtration,there were 6 significantly up-regulated proteins and 40 significantly down-regulated proteins in the traditional membrane filtration.The differential proteins were consistent with the increase ofβ-casein and high retention of active proteins in the whey protein obtained by low temperature membrane filtration.The differences of differential protein regulation among the three kinds of whey protein powders mainly focused on cell composition and molecular function.Compared with traditional membrane filtered whey protein powder at low temperature,the differential proteins were mainly concentrated in human disease pathway.Compared with WPC50 whey protein powder at low temperature,the differential proteins were mainly concentrated in human disease pathway,tissue system pathway and metabolic process.