Fermentation Profiling of Blackened Jujube Vinegar Elucidates Flavor Dynamics and Bioactive Enrichment

Previous studies have established that the blackening process significantly enhances both the flavor profile and the content of bioactive compounds in jujubes. Fruit vinegars, which are rich in antioxidants and organic acids, are recognized for their role in supporting digestion and enhancing metabolism. To fully leverage these augmented benefits, the present study developed and comparatively analyzed red jujube vinegar (RJV) and blackened jujube vinegar (BJV). Our results show that BJV attained a significantly higher total acidity (3.73 g/100 mL) compared to RJV (3.33 g/100 mL) and demonstrated a continuous accumulation of polyphenols and flavonoids. A model is proposed in which polyphenols in BJV undergo structural transformation, synergizing with acids generated by Acetobacter to form a distinctive "phenol-acid" antioxidant system. Volatile compound analysis revealed that the smoother, sweet-and-sour flavor profile of BJV is attributable not only to the synergy between organic acids and esters but also to a unique ensemble of characteristic volatiles identified exclusively in BJV. This ensemble includes a series of acids (e.g., 4-methylpentanoic acid), alcohols (e.g., isoamyl alcohol), and esters, with ethyl acetate notably contributing intense banana and pear-like fruity notes. These findings provide a scientific basis for developing high-value, health-promoting vinegar products from blackened jujubes.