Comparative Study On Bovine And Goat Milk Fat And Flavor Substances Of Milk Powder In Accelerated Oxidation

Bovine and goat milk and its related products contain various nutrients,including lipids which are not only important nutrients,but also play a crucial role in determining the sensory and flavor quality of dairy products.However,few researches focusing on the effect of production processes on milk fat globules and the relationship between fat and flavour.Here,we analyze the effect of processing on milk fat globules during the production of whole milk powder,and identify the composition of bovine and goat milk fat globule membranes(MFGM)using proteomic and lipidomic techniques,then investigate the changes in volatiles and fatty acid composition during storage of whole bovine and goat milk powder.In order to provide targets for the identification of raw milk and a theoretical foundation for the evaluation of milk powder quality.The main research elements and results are as follows.(1)The characteristics of milk fat globules and the factors influencing them.The effects of heat treatment and processing on the particle size and stability of the milk fat globule(MFG)emulsion system were investigated using laser particle size analyzer and zeta potential analyzer,followed by electrophoretic analysis and emulsification determination of MFGM protein.The results indicate that goat MFG particle size(range:0.955-13.183 μm,modal particle size:3.311μm)is smaller than that of bovine MFG(range:0.955-15.136 μm,modal particle size:3.802μm).As the heating intensity increased,the MFG particle size increased gradually and the emulsion system became unstable.Meanwhile,the MFGM protein electrophoresis profile revealed a deepening color of caseins andβ-Lg bands,at the same time MFGM protein emulsification is reduced.The MFG particle sizes of the milk samples at the four key units of whole milk powder processing(pasteurization,homogenization,concentration,and spray-drying)were 1.096-8.710 μm,1.096-7.586 μm,0.955-30.200 μm,and 0.724-79.433 μm,with a modal particle size of 1.905 μm,respectively.The results showed that milk processing reduced the particle size of the milk fat globules and increased the lipids dispersion in the milk system.The electrophoretic profile of the concentrated and spray-dried samples revealed primarily casein and β-Lg,indicating that both were bound to fat globules,which could boost the stability of the recovered milk.(2)Proteomics and lipidomic analysis of bovine and goat milk fat globule membranes.1414 and 2060 proteins were identified in the prepared bovine and goat MFGM samples by unlabeled proteomics techniques,respectively.In both bovine and goat MFGM,eight proteins,including xanthine oxidoreductase,butyrin subfamily member A1,and epidermal growth factor,etc,were expressed at high quantities.There were 169 proteins significantly different between the bovine and goat MFGM(p<0.05).Vascular non-inflammatory protein-2,fibrinogen alpha chain,peptidoglycan recognition protein,polymeric immunoglobulin receptor,cysteine sulfite decarboxylase,and cyclic guanosine-dependent protein kinase play a crucial part in the taxonomic identification of bovine and goat MFGM.Using non-targeted lipidomics approaches,3004 and 2857 lipids were identified in bovine and goat MFGM,respectively.Phospholipids,glycolipids,sterols,and sphingolipids accounted for 75.94%,8.29%,3.82%,and 3.76%,respectively of the total lipid other than glycerides in bovine’s milk,while compared to 66.98%,12.42%,4.27%,and 3.57%of goat’s milk respectively.There were 1496 lipids significantly different on bovine and goat MFGM(p<0.05),with glycerol ester molecules such as TG(17:0/10:0/22:6),TG(16:0e/8:0/18:1),TG(8:0/10:4/14:2),TG(14:0/14:0/22:6),DG(15:0/16:0)and MFGM lipids CL(87:12),PE(41:2e),SM(t39:7),CL(66:1),MePC(29:2e),PE(16:0/16:1),PI(18:1/20:3)can also be used as markers for distiguishing goat milk from bovine milk(3)The volatiles changement of whole bovine and goat milk powder in the accelerated oxidation.The volatile substances were determined using headspace solid-phase microextraction-gas chromatography-mass spectrometry.We found 42/47,34/37,and 26/27 volatile substances in whole bovine/goat milk powder,recovered bovine/goat milk,and fresh bo vine/goat milk,respectively.Acids(e.g.,propionic acid,butyric acid,caproic acid,caprylic acid,etc.)are the most important flavoring substances in fresh milk and milk powder,with a content range of 53.99-87.36%.These substances are more abundant in goat’s milk and milk powders than that in bovine milk,which are the main source of odor in goat’s milk.The analysis of whole bovine and goat milk powder with accelerated oxidation at 45℃ revealed that the relative content of acid volatiles decreased as storage time increased,while the relative content of carbonyl substances increased because of fat oxidation.Among them,10 substances changed significantly,with butyric acid decrease while 2-nonanone and 1-chloropentane increase in bovine milk powder and nonanal,octanoic acid,propionic acid,and butylhydroxytoluene decrease while benzaldehyde,2-heptanone,and allyl n-propyl ester increase in goat milk powder.(4)Fatty acid composition during accelerated oxidation of whole bovine and goat milk powder.The total fatty acid content of bovine and goat milk was determined to be(70.53±2.32)g/100g fat and(62.97±3.99)g/100g fat,respectively,using gas chromatography,with no significant changmemt observed by increasing heat treatment intensity.The total fatty acid content of whole bovine and goat milk powder were respectively(69.01±2.42)g/100g fat and(63.81±2.84)g/100g fat,and decreased to(66.33±1.94)g/100g fat and(56.99±1.92)g/100g fat,respectively,in milk powder after 42 days of storage at 45℃.The acids palmitic,myristic,linoleic,and decanoic can be utilized to distinguish bovine from goat milk.During storage,the content of lauric,decanoic,linoleic,caprylic,oleic,stearic,palmitic,myristic,and caproic acids in bovine and goat milk powder decreases significantly.The free fatty acid(FFA)content of goat milk was(0.64±0.17)g/100g fat,higher than that of bovine milk(0.46±0.12)g/100g fat,and the FFA content of goat milk increased to(0.8 0±0.06)g/100g fat after heat treatment at 100℃.The FFA content of whole bovine and goat milk powder were respectively(3.39±1.03)g/100g fat and(2.22±0.32)g/100g fat,and increased to(5.34±0.61)g/100g fat and(4.20±0.45)g/100g fat in milk powder after 42 days of storage at 45℃.The short-chain free fatty acids(caproic acid,caprylic acid,decanoic acid)have a significant impact on the flavor of milk and are the main substances leading to the odor of goat’s milkThis study compares the fat globule morphology,MFGM protein and lipid composition and fatty acid composition of bovine and goat milk,and explores the changes in flavor substances and fatty acids during storage of milk powders,in order to provide a theoretical basis for guiding the production of milk powders and the authentic testing of bovine and goat milk.