Abstract:[Objective]This study aims to investigate the variation rules of polyphenolic substances and antioxidant activity of jujube juice fermented by lactic acid bacteria after in vitro simulated gastrointestinal digestion.[Method]The mass fractions of total phenols, free phenols, and bound phenols, as well as the composition of polyphenolic substances and antioxidant activity in the jujube juice fermented by lactic acid bacteria (original jujube juice) at different fermentation stages and in vitro simulated gastrointestinal digestive fluids were determined and compared.[Result]With prolonged fermentation time, the mass fractions of total phenolics in the original jujube juice and the gastric digestive fluid increased and then declined, while that in the intestinal digestive fluid exhibited fluctuating trends. At 48 h of fermentation, all samples reached their peak values: 156.83, 152.50, and 100.71 mg/100 g, respectively. With prolonged fermentation time, the mass fractions of free phenols in the original jujube juice and the gastric digestive fluid showed an increasing trend, while that in intestinal digestive fluid exhibited fluctuating changes. The mass fraction of free phenols in the gastric digestive fluid was higher than those in the original juice and intestinal digestive fluid after 16 h of fermentation, reaching a maximum value of 110.78 mg/100 g after 64 h of fermentation, indicating that the gastric environment significantly promoted the release of free phenols. In addition, bound phenols in the original juice and intestinal digestive fluid accumulated significantly in the early stage of fermentation. Fermentation improved the scavenging rates of free phenols against DPPH and ABTS+ free radicals, and gastric and intestinal digestion enhanced the scavenging effects of free phenols against DPPH and ABTS+ free radicals, respectively. With prolonged fermentation time, the DPPH and ABTS+ free radical scavenging rates of bound phenolics in the original jujube juice exhibited fluctuating trends, while those of the gastric digestive fluid showed an increasing trend in DPPH free radical scavenging activity. In contrast, the ABTS+ free radical scavenging capacity of bound phenolics in the intestinal digestive fluid followed an initial increase followed by a decline. Compared with the free phenol components in the unfermented jujube juice, the free phenol components rutin, hydrocinnamic acid, benzoic acid, and salicylic acid in the original jujube juice showed mass concentration increases of 21.51%, 54.41%, 25.68%, and 28.62%, respectively. Compared with the free phenol components in the original jujube juice, vanillic acid, gallic acid, syringic acid, protocatechuic aldehyde, and luteoloside among the free phenol components in the gastric digestive fluid showed increased mass concentrations, indicating that fermentation and gastric digestion facilitated the release of free phenols. Compared with the bound phenol components in the unfermented jujube juice, rutin, trans-ferulic acid, and 4-hydroxybenzoic acid showed decreased mass concentrations in the original jujube juice. Compared with the bound phenol components in the original jujube juice, rutin, trans-ferulic acid, protocatechuic acid, and protocatechuic aldehyde showed decreased mass concentrations in the gastric digestive fluid. Compared with the bound phenol components in the gastric digestive fluid, the intestinal digestive fluid showed increases of 20.67%, 54.03%, and 29.76% in the mass concentrations of trans-ferulic acid, gallic acid, and protocatechuic acid, respectively.[Conclusion]Lactic acid bacteria fermentation improves the polyphenol composition and antioxidant activity of jujube juice after gastrointestinal digestion, which provides a scientific basis for the development of functional fermented jujube products.
