## 3 Results and Discussion
### Free Amino Acids and Organic Acids Analysis  
The concentrations of free amino acids (FAAs) and organic acids in the fermented functional rose beverages were also analyzed (Figure 1). FAAs play a significant role in the aroma and flavor of food and serve as precursors for many volatile compounds [40]. FAAs can be broadly categorized based on their taste profiles: sweet (Gly, Ser, Ala, Pro, Thr, Cys, Met), bitter (Arg, His, Ile, Leu, Phe, Lys, Tyr, Trp, Val), and umami (Asp, Glu, Asn) [41]. The relative proportions of these taste categories within the total FAAs were as follows: UFR (23.17% sweet, 17.43% bitter, 59.40% umami), LFR (45.74% sweet, 31.84% bitter, 22.41% umami), SFR (26.10% sweet, 21.31% bitter, 52.59% umami), and LSFR (43.71% sweet, 31.25% bitter, 25.03% umami). These results indicate that fermentation by _L. plantarum_ significantly contributed to the conversion of umami amino acids into sweet and bitter amino acids, and the metabolic impact of L. plantarum on the amino acid distribution in the functional rose beverage was considerably greater than that of S. cerevisiae. Furthermore, following fermentation by lactic acid bacteria (LFR and LSFR), the total aromatic amino acid content increased, particularly tryptophan (Trp) and phenylalanine (Phe), which showed substantial increases of 28.73-fold and 20.31-fold, respectively, in LFR, and 5.09-fold and 3.86-fold in LSFR. Previous studies suggest that the degradation of Trp by microorganisms can promote the formation of aromatic compounds [42], while the increase in phenylalanine is conducive to the formation of volatile compounds such as benzyl alcohol, phenylethanol, and benzene derivatives [43], thereby enriching the flavor profile of rose beverages. Additionally, in the LFR and LSFR groups, the content of essential amino acids (Val, Leu, Arg, Trp) significantly increased by 9 to 28 times, substantially enhancing the nutritional value of these fermented beverages [44]. The taste activity values (TAVs) of FAAs were calculated to assess their contribution to the flavor of rose beverages (Figure 1B). However, none of the free amino acids exhibited a TAV greater than 1, suggesting they did not have a significant direct impact on the overall taste perception in this study. As depicted in Figure 1C, notable differences were observed in the types and concentrations of organic acids across the four sample groups. Lactic acid, acetic acid, and citric acid were undetectable in the UFR sample, while lactic acid was absent in the SFR sample. Following fermentation, the total organic acid content increased, with the highest concentrations observed in LFR (8.23 g/L), followed by LSFR (6.29 g/L), and then SFR (2.18 g/L). Similar trends have been reported in tea infusions fermented with L. plantarum and Saccharomyces boulardii [45]. Malic acid, tartaric acid, and succinic acid were identified as the primary organic acids in the unfermented rose beverage, consistent with the findings of [PERSON] et al. [46]. Lactic acid is a characteristic metabolic product of lactic acid bacteria fermentation [47]. Significant increases in lactic acid content were observed in the LFR and LSFR groups (\(p<0.01\)) (Figure 1B). At the end of fermentation, lactic acid accounted for 0%, 57.74%, 52.35%, and 0% of the total organic acids in UFR, LFR, LSFR, and SFR, respectively, indicating its major role in determining the acidity differences among the fermented beverages. Notably, the lactic acid content in LSFR was significantly lower than in LFR. Previous research suggests that certain yeasts can utilize lactic acid as a carbon source, which may explain the reduced lactic acid concentration observed in the co-fermented sample (LSFR) [48]. Acetic acid, a short-chain fatty acid, is recognized for its importance in regulating intestinal health and its potential impact on inflammatory bowel diseases (IBD) [49].