Optimization of fermentation process, antioxidant activity and flavor quality of fermented longan-Gynostemma pentaphyllum beverage

To explore the antioxidant activity and flavor quality of fermented longan-Gynostemma pentaphyllum beverage, Lactobacillus casei was selected to ferment longan-G. pentaphyllum composite extract, and the fermentation process conditions of fermented longan-G. pentaphyllum beverage were optimized by single factor tests and orthogonal tests combined with sensory evaluation. Its aroma and taste were analyzed by electronic nose and electronic tongue. The results showed that the optimal fermentation process conditions of fermented longan-G. pentaphyllum beverage were obtained as follows: volume ratio of G. pentaphyllum to longan extract of 2:6, starter inoculum 1.4%, fermentation time 5 d and temperature 39 ℃. Under these optimal conditions, the sensory score, total flavonoids, total polyphenols, total acids contents, and 1,1-diphenyl-2-pyridineyl hydrazine (DPPH) free radical scavenging rate of fermented longan-G. pentaphyllum beverage were 89.30 points, 12.20 μg/ml, 2.78 μg/ml, 4.37 mg/ml, and 79.16%, respectively. The color parameters of L^* value, a^* value, and b^* value were 2.33, 35.44, and 29.93, respectively. The radar chart results of the electronic nose and electronic tongue detection response values shown that the fermentation process endowed the fermented beverage of longan-G. pentaphyllum with longan aroma, unique fermentation aroma, and harmonious sourness, enriching the flavor layers of the fermented beverage. In summary, fermentation with L. casei could improve the flavor quality of fermented longan-G. pentaphyllum beverage.