Abstract:To study the effects of kefir granules on the fermentation effect and functional activity of compound fruit and vegetable juice and the changes of antioxidant activity in gastrointestinal digestion.The response surface method was used to optimize the processing conditions of the complex fruit and vegetable juice fermented by kefir grains.The in vitro gastrointestinal digestion model was used to evaluate the changes of polyphenol content，flavonoid content，DPPH scavenging rate and ABTS + scavenging rate at different digestion stages before and after the fermentation of fruit and vegetable juice.Results showed that the kefir grains fermentation compound fruit juice the best process conditions for the fermentation time of 41.7 h，32 ℃ fermentation temperature，quantity of 7.3 %，compared with the 0.837 % fruit and vegetable juice fermentation acidity，number of living bacterium was 8.3 ×108 （CFU/mL）；In the simulated gastrointestinal digestive system，compared with the unfermented samples，the content of polyphenol flavonoids in the fermented fruit and vegetable juice was significantly increased after digestion，and the increase was most obvious in the simulated gastric digestion，while the content of flavonoids was slightly decreased in intestinal digestion.At the end of digestion，DPPH radical scavenging ability and ABTS + scavenging rate were significantly improved，respectively by 12.8%and 14.7%（P ＜ 0.05）compared with the unfermented group，and by 13.3%and 8.5%compared with the undigested group（P ＜ 0.05）.