Analysis Of Whey And Milk Fat Globule Membrane Proteomes And Digestion Properties In Goat/Cow Milk By Proteomics Technologies

Milk is rich in nutrients and biological functions,which is essential for the healthy growth of newborn mammals,and milk is also an important source of protein in adult diets.Goat and cow milk are the main sources of milk consumption in the Chinese dairy industry.At present,the output of cow milk is significantly higher than that of goat milk,which accounts for the majority of the dairy foods.With further understanding of the nutritional values and biological functions of goat milk,goat milk and its products are favored by more and more consumers.However,the information of proteins in goat and cow milk,especially some low-abundance proteins,is limited.Although whey and milk fat globule membrane(MFGM)proteins only account for a small part of the total milk protein,they have rich biological functions.In present study,qualitative and quantitative proteomics techniques were used to characterize whey and MFGM proteins in goat and cow milk,goat colostrum and mature milk,and gene ontology(GO)annotation,Kyoto Encyclopedia of Genes and Genomes(KEGG)pathway,clustering heat map and other bioinformatics analysis tools were used to analyze the composition and functions of whey and MFGM proteins in goat and cow milk,goat colostrum and mature milk.The digestion properties of goat colostrum and mature milk during gastrointestinal digestion were investigated using in vitro digestion model of infants.The main results are as follows:1.The composition and functional properties of goat milk and bovine milk whey and MFGM proteins were analyzed by qualitative proteomics techniques.A total of 417 whey proteins were identified in goat milk and cow milk,25 of which were common to both,258 proteins were specifically expressed in goat milk,and 134 were specific expression proteins in cow milk.A total of 776 proteins were identified in goat milk and cow milk MFGM.Among them,427 proteins were unique to goat milk.183 proteins were unique to cow milk,and 166 proteins were detected in both.Bioinformatics analysis showed that goat milk and cow milk whey,MFGM proteins have significant differences in protein composition,GO function annotation,KEGG pathway.2.Quantitative characterizations of goat milk and cow milk whey and MFGM proteins using iTRAQ labeled proteomics techniques.One hundred and sixty-five whey proteins with quantitative information were identified in goat milk and cow milk,of which 114 were differentially expressed whey proteins of the two milks(fold change > 1.50 or < 0.67,p < 0.05).Bioinformatics analysis showed that these differentially expressed whey proteins mainly fall into the biological process of response to stress and pathway of complement and coagulation cascades.There were 281 MFGM proteins in goat milk and cow milk with quantitative information,of which 127 were differentially expressed MFGM proteins of two milks(fold change > 1.50 or < 0.67,p < 0.05).Bioinformatics analysis showed that these differentially expressed MFGM proteins contain many proteins related to post-translational modification.The main biological process involved was cholesterol biosynthetic process.The main enriched KEGG pathway was systemic lupus erythematosus and protein processing in endoplasmic reticulum.3.The composition and functional properties of goat colostrum and mature milk whey and MFGM proteins were analyzed using qualitative proteomics techniques.A total of 643 whey proteins were identified in goat colostrum and mature milk,195 of which existed in both milks,119 proteins were only detected in colostrum,and 329 proteins were only found in mature milk.Regarding the MFGM proteins,a total of 734 MFGM proteins were identified in goat colostrum and mature milk,of which 149 proteins were unique to goat colostrum and 191 were unique to mature milk,with a common of 394 proteins.Bioinformatics analysis showed that goat colostrum and mature milk whey,MFGM proteins have significant differences in protein number,composition and biological functions.4.Whey and MFGM proteins of goat colostrum and mature milk were analyzed using quantitative proteomics techniques based on iTRAQ labeling.One hundred and sixty-five whey proteins with quantitative information were identified in goat colostrum and mature,of which 69 proteins were differentially expressed whey proteins between colostrum and mature milk(fold change > 1.50 or < 0.67,p < 0.05).These differentially expressed whey proteins were primarily involved in the biological process of defense response,the cellular component of extracellular space,the molecular function of enzyme regulator activity,and the KEGG pathway of complement and coagulation cascades.There were 322 MFGM proteins with quantitative information in the two milks,of which 68 were differentially expressed proteins between colostrum and mature milk(fold change > 1.50 or < 0.67,p < 0.05).These differentially expressed MFGM proteins were primarily involved in the biological process of single-organism process,the cellular component of membrane-bounded organelle,and the molecular function of carbohydrate derivative binding.5.Infant gastrointestinal digestion was simulated to analyze digestion properties of goat colostrum and mature milk.Zeta-potential values of the digested colostrum were lower than those of mature milk through the whole digestion.Absolute zeta-potential of colostrum duodenal digestion samples showed a decrease from 16.63 ± 2.08 mV to 11.80 ± 2.03 mV while that of mature milk decreased sharply and then increased(p < 0.05).Colostrum had a larger particle size than mature milk and both milks showed decreased particle size with increasing digestion time but an increase for the last 30 min.Colostrum showed more high molecular weight(MW)proteins which cannot be hydrolyzed completely compared with mature milk.The casein-derived peptides identified in digested peptides(< 10 kDa)of colostrum and mature milk accounted for 76.67% and 59.53%,respectively.?-Casein was the most abundant in colostrum while that in mature milk was ?s1-casein.Results indicated that differences in digestion properties between goat colostrum and mature milk were mainly shown in duodenal digestion phase.In summary,qualitatively and quantitatively proteomic characterizations of whey and MFGM proteins in goat and cow milk,goat colostrum and mature milk were analyzed.The digestion properties of goat colostrum and mature milk were also analyzed.The results provide comprehensive information about whey and MFGM proteins of goat and cow milk,which could lay a foundation for further investigation of the specific functions of these proteins,and also provide useful information for the applications of goat and cow milk in the Chinese dairy industry.