Changes in nutrient composition, antioxidant capacity, phenolics, and volatile organic compounds in black mulberry vinegar across different fermentation stages

Black mulberry has a high nutritional value but is prone to spoilage. This study aimed to explore processing methods that preserve the nutrients and active components of it. To this end, black mulberry was fermented into black mulberry vinegar, and its nutrient, phenolics, and volatile organic compound content was monitored at different stages of fermentation using multivariate statistical analysis combined with High Performance Liquid Chromatography (HPLC) and Gas Chromatography Mass Spectrometry (GC-MS). The results revealed that fermentation significantly altered the content of organic acids and phenolics in black mulberry, leading to a 20fold increase in lactic acid (35599.71 f 4.52 mg/L), 7-fold increase in acetic acid (22551.76 f 1.02 mg/L), 3.8fold increase in chlorogenic acid (17.13 f 0.98 mg/L), and 1.5-fold increase in cinnamic acid (209.14 f 10.86 mg/L). Therefore, fermentation contributed to improvements in taste and enhanced the content of active substances. The 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radical (& sdot;OH) free radical scavenging activities of black mulberry vinegar were significantly higher than those of mulberry juice, indicating that fermentation could improve its antioxidant activity. Among the 61 volatile organic compounds identified, 14 showed odor activity values greater than 1, including isopentyl alcohol, linalool, and 1-octen-3-ol. Black mulberry vinegar not only retained linalool and phenylethanol, which are two characteristic flavor compounds of black mulberry, but also contained two new characteristic flavor compounds, acetoin and ethyl caprate. These compounds endowed the black mulberry vinegar with a pleasing floral and fruity aroma. The results of this study provide potential applications for diversified processing of black mulberry in Xinjiang.