Study On Peptide Mapping Of Dairy Products Based On MALDI-TOF

Peptides in milk have attracted attention due to their extra bioactivities such as antibacterial activity,anti-oxidation,and so on.However,research on milk endogenous peptides is rare because most studies present focus on the process of selecting and isolating bioactive fragments from protein hydrolysates in vivo or in vitro.This study aimed at endogenous peptides of dairy products and established the best method for extraction method as well as the detection method by Matrix-assisted laser desorption ionization time-of-flight mass spectrometry(MALDI-TOF MS)respectively.Using multivariate statistical analysis methods,the peptides distribution between different milk with various brands,processings and origins were analyzed.Besides,the effects of some lactic acid bacteria on peptides profile in raw milk during fermentation were studied.First,the differences in peptide distribution between various milk samples were analyzed.It showed that the peptides contained in milk belonging to several brands are slightly different among the similar products,while the pasteurized milk and ultra-high temperature instant sterilized milk were distinguished obviously due to the diversity in the process.11 differential peptides were determined after analysis,providing a new idea for milk product identification,quality control,and nutrition evaluation.Then the distribution of peptides in milk,goat milk,horse milk and camel milk was compared.The peptide distribution of milk and goat milk was pretty similar to each other while the camel milk's was the narrowest,concentrated within 2 kDa.These four products were completely separated and aggregated respectively,indicating that the biological differences play a decisive role in the distribution of peptides,which provides a new direction for solving the problem of adulteration in milk source.The yoghurt was fermented by Streptococcus thermophilus,Lactobacillus bulgaricus,Lactobacillus acidophilus and Bifidobacterium,and the whole fermentation process was observed.It was found that although the metabolic processes of each bacteria were not same,the effect on the distribution of peptide in milk tends to be consistent.In the first three hours of fermentation,the content of low molecular peptides accumulated rapidly.As the progress continued,the range of advantage peptides shifted backward to around 2 kDa,the profile of peptides changed frequently and many new peptides appeared in the range of 2-3 kDa.Interestingly,the results fermented by other four commercial compound powders were in accordance with the conclusion of single-strain fermentation above.