## 3 Results and Discussion
### Effect of Lactic-Acetic Acid Co-Fermentation on Phenolics of Bicultured Jujube Pures
bacteria (AAB) produce acetic acid that can penetrate cell membranes and cause alterations in normal fundamental physiological functions [15]. Significantly, the natural prevalence of conjugates of \(p\)-coumaric acid in the unfermented sample surpassed that of their fermented forms. Post-fermentation, the reduction in \(p\)-coumaric acid concentrations could be attributed to the inefficient hydrolysis of corresponding \(p\)-coumarate esters and \(p\)-coumarylated anthocyanins inherent in jujube samples [39]. These phenolic acids might have been encapsulated in the undigested dietary fiber content, reducing their extractability [40] and subsequent quantification. Additionally, the subsequent evolution of caffe acid in JLAcAp and JLhAp could be explained by the intricate enzymatic cascade facilitating the conversion of \(p\)-coumaric acid into caffe acid, orchestrated by the catalytic prowess of \(p\)-coumarate 3-hydroxylase [41]. Moreover, the dynamic enzymatic reciprocity includes the transformation of chlorogenic acid into caffe acid mediated by cinnamoyl esterase, explaining the observed increase in caffe acid and simultaneous decrease in chlorogenic acid following the lactic-acetic co-fermentation process [17]. The metabolic activities of LAB, encompassing the intricate transformation of sugars, organic acids, and amino acids, profoundly influence the phenolic profile. Substantially, the amino acid phenylalanine undergoes a complex enzymatic transformation into \(p\)-coumaric acid through the orchestrated action of phenylalanine ammonia-lyase and cinnamate 4-hydroxylase. These intricate biochemical reactions appeared to be operative in the context of _Streptococcus thermophilus_ fermentation [19]. As shown in Table 3, the fermentation process resulted in a significant (\(p<0.05\)) reduction in the concentrations of chlorogenic acid. The intricate metabolic landscape of LAB is further elucidated by their capacity to metabolize phenolic acids through strain-specific decarboxylase or reductase activities [18]. In this context, chlorogenic acids are envisaged to undergo decarboxylation mediated by phenolic acid decarboxylase, yielding alternative compounds such as 4-vinyl guaiacol and guaiacol. Although [PERSON] et al. [18] reported a decrease in caffe acid and syringe acid, their report contrasts our findings, as caffe acid concentrations were enhanced in bicultured pures: JLAcAp and JLhAp, whereas syringe acid, undetected in the control sample, evolved after fermentation. The evolution of phenolic compounds, namely gallic acid, protocatechuic acid, and syringe acid, that were undetected in the control sample, forecasts the efficiency of lactic-acetic acid bacteria's intricate microbial synergy in enhancing these bioactives in the fermented product. Morin concentration was enhanced by 151% of the initial value in bicultured puree containing _Lacticaseibacillus casei_, Lc 122, and _Acetobacter pasteurianus_ Ap-As.1.41, whereas quercetin increased by 121%. These two flavonoid molecules were noticeably absent in the bicultures JLhAp and JLpAp, highlighting the unique ability of _Lc. casei_ Lc 122 to exclusively contribute to the expression of morin and quercetin in lactic-acetic co-fermentation. Consequently, this predisposed pure JLcAp to be the richest in total flavonoids, followed by JLhAp. Regarding anthocyanins, high concentrations were observed, with the predominant classes being peonidin-3, 5-diglucoside, and peonidin-3-O-glucoside. The bicultured puree JLcAp recorded the highest peonidin-3,5-diglucoside content at 34.13 mg/100 g, whereas peonidin-3-O-glucoside measured 15.12 mg/100 g. Although cyanidin-3-O-rutinoside was observed to be the lowest among the anthocyanins in the bicultured pures, JLcAp exhibited the highest characteristic content compared to other fermented pures and the control sample.