Glutinous rice fermented with Fu brick tea: effects on phenolic content, antioxidant activities and DNA damage protection

Abstract

Rice‐based fermented foods are centuried with great number of varieties in East Asia. Recently, fermented glutinous rice has also been paid with great attention outside the Asia because of its unique flavor and health‐promoting value. The fermented juice products, such as rice wine, are not only beverages but also irreplaceable ingredients in traditional Chinese medicine, while the fermented rice grains are manufactured into staple foods. Fu brick tea, rich in polyphenols, polysaccharides and other bioactive compounds, is welcomed in west Asia, due to its participation in antioxidation and facilitative effects on the metabolism of carbohydrate and fat. In this study, we developed a novel fermented glutinous rice product with the supplementation of Fu brick tea (FGR‐FBT), with improved health benefits and increased phenolic content. We found that fermentation with Fu brick tea could enrich phenolic compounds, increase the total phenolic content, and enhance the antioxidant activities of glutinous rice. Free radical‐scavenging activities (covering DPPH radical, ABTS radical and hydroxyl radical), reducing power (covering ferric‐reducing antioxidant power and ferric ion reducing power), and chelating activities for metal ions were utilized for antioxidation analysis. The lower IC50 values of 10.75 ± 0.24/30.67 ± 0.29 μg/mL exhibited by FGR‐FBT hydroalcoholic/water extracts and 224.55 ± 3.63/257.71 ± 4.82 μg/mL of FGR respective extracts determined by ABTS radical confirmed stronger antioxidative capabilities displayed by FGR‐FBT. Besides, this novel fermented glutinous rice supplemented with Fu brick tea exhibited a stronger DNA protective ability against oxidation damage. Under the protection of 100–400 μg/mL of FGR‐FBT hydroalcoholic extracts, DNA scission was inhibited according to the reserved 49% to 67% of supercoiled DNA, while only 21% in the control group. Besides, antioxidative compounds including catechins and phenolic acids were extracted by hydroalcoholic solvents and qualitative analyzed using HPLC‐Triple‐TOF‐MS/MS system. Moreover, the biotransformation and bioavailability of phenolic compounds were elevated by solid‐state fermentation with Fu brick tea based on in vitro digestion system and CaCo‐2 transwell evaluation. Together, this novel fermented product as a phenolic‐rich functional food or a nutraceutical additive would improve the bioactivity of traditional foods. These findings could introduce great further interests in the utilization of Fu brick tea to develop novel products.