Metabolomics Study Of Different Base Materials Fermented By Lactobacillus Delbrueckii Subsp.bulgaricus ND02

The Lactobacillus delbrueckii subsp.bulgaricus ND02(L.bulgaricus ND02)was isolated from traditional fermented yak milk in Qinghai,China.It has excellent fermentation characteristics and has the potential to improve the nutritional value of fermented dairy products.In order to deeply understand the ecological processes and functions of Lactobacillus bulgaricus in different fermentation systems,this study selected L.bulgaricus ND02 to ferment three base materials of milk,brown milk and whey.The metabolite changes of three fermented products,fermented milk,fermented brown milk and fermented whey before and after fermentation were studied by using LC-MS method,and the differential metabolites were screened using univariate statistical analysis combined with multivariate statistical analysis.Draw the following conclusions:1)The metabolome of milk has undergone significant changes after fermentation by L.bulgaricus ND02.A total of 23 different metabolites were identified in this study,including amino acids,peptides,fatty acids,organic acids,nucleotides and vitamins.The relative content of Pro-Trp,L-valine,L-isoleucine,benzoic acid and vitamin A in L.bulgaricus ND02 fermented milk was significantly higher than that of milk,and the relative content of vitamin A was 349.22 times that of milk.Therefore,this study speculate that L.bulgaricus ND02 may produce vitamin A during the fermentation process.2)After Maillard browning,milk has undergone significant changes in its metabolites.A total of 20 different flavor compounds,including amino acids,peptides,organic acids,nucleosides,aldehydes ketones,dithiophenes,pyrazines,pyranolines,amide compounds,and et al.After brown milk was fermented with L.bulgaricus ND02,its metabolome also changed significantly,mainly focusing on changes in 21 metabolites such as amino acids,peptides,aldehydes,ketone ester compounds,nucleosides and vitamins.The changes of these metabolites together determine the unique color,flavor and nutritional value of brown fermented milk.In addition,after Maillard browning,the amount of lysine in brown milk is greatly reduced,but as the fermentation of L.bulgaricus ND02 progresses,the protein in the milk is degraded,and the lysine level in brown fermented milk is significantly increased,which effectively it solves the problem that the Maillard reaction of milk is prone to occur in the processing process,which leads to the destruction of a large amount of lysine and the reduction of the nutritional value of dairy products.3)After the whey is fermented with L.bulgaricus ND02,its metabolite has changed significantly,mainly including isoleucine,Ala-Leu-Pro-Met,methyl-D-galactopyranoside,oleic acid,succinic acid,xanthine and cytosine adenylate.Changes in 37 metabolites involve multiple complex metabolic pathways such as amino acid metabolism,sugar metabolism,and fat acid metabolism.The relative content of 23 metabolites in L.bulgaricus ND02 fermented whey,including cysteine,Tyr-Trp,cytosine nucleotides and phenyllactic acid,increased significantly.This study revealed the metabolic characteristics of L.bulgaricus ND02 in milk,brown milk,and whey from the metabolic level,and systematically analyzed the changes in the metabolites of three fermented products,fermented milk,brown fermented milk,and fermented whey before and after fermentation.The results show that during the fermentation process,L.bulgaricus ND02 can use its own metabolic system to generate specific amino acids,flavor substances,active peptides and vitamins for different base materials,giving fermented dairy products special physiological effects and nutritional value.This research has certain guiding significance for the future development and improvement of Lactobacillus bulgaricus fermented dairy products.