Process Optimization And Metabolomics Analysis Of Oolong Tea Beverage Fermented By Probiotics

Oolong tea is popular among consumers because of the quality advantages of both black tea and green tea.In recent years,microbial fermented beverages have shown a vast market space due to their unique flavor and nutritional value,and their industry is booming.We try to develop a microbial fermented oolong tea beverage with potential health benefits by introducing probiotics and their active metabolites based on enriching the flavor of tea beverages,etc.In addition,the quality of fermented foods is mainly based on the flavor substances and efficacy components produced and accumulated during microbial fermentation,so monitoring specific metabolites during fermentation using metabolomics is essential to elucidate the nutritional,flavor,functional and safety properties of the products and their formation mechanisms.The results of this study include:(1)The optimal fermentation process for the mixed bacteria fermented oolong tea beverages was: 4.6 times the amount of sucrose added to the tea leaves;1 to 100 tea-water ratio;aerobic fermentation at 30 °C for 3 days followed by anaerobic fermentation at 35 °C for 4 days.The product quality of the thus prepared fermented oolong tea beverages all conformed to the GB/T 21733-2008 tea beverage standard,and the quality changes during storage were all within the acceptable range.(2)The results of β-diversity analysis showed that both aerobic and anaerobic fermentation stages changed the chemical profiles of oolong tea beverages,with the aerobic fermentation stage changing the chemical profiles more significantly.The differential compounds affecting the change of chemical profile in the fermentation process were mainly sugar compounds,catechins,amino acids and alkaloids.(3)The results of α-diversity analysis showed that the characteristic metabolite abundance of oolong tea beverages increased significantly after fermentation.The number of metabolites showed a trend of significantly increasing and then slightly decreasing during the fermentation process,and the metabolite species of tea beverages at the end of fermentation were significantly higher than their negative controls.(4)The main substances affecting the flavor and efficacy of tea broth were free amino acids,caffeine,tea polyphenols,catechins,sugars,alcohols,etc.The content of sugars and free amino acids decreased significantly during the fermentation process,the content of glycosylamine compounds increased,the content of tea polyphenols and caffeine showed an overall increasing trend and was significantly higher than that of the negative control group,and the flavonols increased significantly during the fermentation process.(5)Oolong tea beverages produced 36 metabolites after fermentation,mostly amides and amino acids and their derivatives,12 of which were produced by microbial metabolism.In this study,the optimal fermentation process of mixed bacteria fermented oolong tea beverage was finally determined,and a total of 70 discriminative characteristics of chemical profile changes affecting the fermentation process were screened,mainly sugar compounds,catechins,amino acids and alkaloids,and 36 metabolites were produced before and after fermentation,among which 12 compounds were produced by microbial metabolism.