## 4 Discussion
plantarum_ produced many alcohols as precursors for esters [54], and, after fermentation, farnesol, nonyl alcohol, and benzyldehyde further released the plant aroma of the beverage, contributing to the flavor of the beverage. Furthermore, heterocyclic compounds such as 5-hydroxymethyl-2-furaldehyde were detected before and after fermentation, probably due to the heating of sugars and the production of some new substances [55]. Hexanal with a unique herbal flavor is the most reducing volatile compound and can reduce the strong plant odor of the beverage [56]. The primary antioxidants in red jujube fruits and bamboo shoots are mainly phenolic substances and flavonoid compounds. After fermentation, the R-B mixed juice showed no significant change in total flavonoid content, but an increase in total phenolic content, prob ably due to a low metabolic capacity of _L. plantarum_ TUST-232 for flavonoid compounds in the R-B mixed juice [57]. The removal of the shells from bamboo shoots before fermentation to reduce their effect on the taste of the beverage resulted in a lower total phenolic content in the R-B mixed beverage. [PERSON] et al. [58] reported that fermentation of rye bran by LAB could increase the total phenolic content by 90%, in contrast to an increase of only 15-30% for the fermentation of peeled bran, indicating that the total phenolic content in bran and some food shells may account for a certain proportion. After fermentation, the total phenolic content showed an increase of 11.09% in the beverage, which was related to the conversion and depolymerization of related compounds by enzymes, suggesting that _L. plantarum_ TUST-232 can produce related enzymes in the beverage during fermentation to increase the total phenolic content by decomposing hydroxyl or hydroxyl groups in the phenol ring and producing phenolic acids [9; 27; 59]. In addition, the fermentation time of _L. plantarum_ TUST-232 also played an important role in total phenolic content, and the fermentation conditions provided sufficient time for _L. plantarum_ TUST-232 to increase the total phenolic content in the R-B mixed juice. [PERSON] et al. [60] evaluated the effect of the multi-strain starter culture (two LAB strains and a yeast strain) on the antioxidant and rheological properties of sourdoughs and derived bread. They found that the total phenolic content in the sourdough inoculated with LAB and yeast increased with the extension of fermentation time, resulting in significantly higher total phenolic content than that of the control group. Since the Folin-C method can measure all the phenolic substances, including aromatic amino acids, the increase in free phenolic can also be attributed to the increased protein hydrolysis during fermentation [58]. After fermentation, all four antioxidant indices (Table 3) showed significant improvement, probably due to the high ability of _L. plantarum_ TUST232 to reduce iron ions, scavenge hydroxyl radicals, and inhibit superoxide anions, as well as its strong capability to hydrolyze polyphenols in the R-B mixed juice. [PERSON] et al. [61] used eight LAB strains to ferment _Portulaca oleraca_ L. juice separately, and they found that all LAB strains could significantly improve several antioxidant indices of the juice. The improvement in antioxidant indices caused by LAB may also be related to various metabolites with antioxidant activity, such as glutathione, butyrate, and folic acid [62]. Therefore, the enhanced antioxidant capacity may be closely related to the unique biological activity and metabolic characteristics of _L. plantarum_ TUST-232. Most of the dietary fibers in the R-B mixed juice were insoluble or slowly fermented fibers, resulting in no significant change in the content of dietary fibers after fermentation [63; 64]. Contemporary research has shown that most noncommunicable diseases are caused by an unhealthy diet and lifestyle, and new dietary habits are likely to cause intestinal microbial disorders.