Flavor production driven by microbial community dynamics and their interactions during two-stage fermentation of Ziziphus jujuba vinegar

Ziziphus jujuba pulp could be utilized for Ziziphus jujuba vinegar (ZJV) production to reduce waste. However, how to specifically regulate microorganisms during ZJV fermentation to improve its flavor remains an industrial problem. This study evaluated the contribution of ZJV's two-stage fermentation (alcohol fermentation (AF) and acetic acid fermentation (AAF)) to flavor metabolites and microbial community assembly. The ZJV production can represent a sustainable strategy in the management of Ziziphus jujuba pulp wastes. Temperature, alcohol and acid were driving forces of microbiota succession. AF is an important stage for the formation of alcohols, esters, non-volatile acids, and various amino acids. Bacteria and fungi mainly generated esters and alcohols in AF, respectively. Microorganisms capable of protease production and strong stress resistance were conducive to amino acid production (e.g., Virgibacillus and Saccharomyces in AF, Bacillus and Xeromyces in AAF). Solid-state AAF was the key step of acetic acid production and flavor metabolite accumulation. Komagataeibacter with higher acid-tolerant than Acetobacter dominated late AAF and showed a positive correlation with acetic acid. Dominant bacteria promoted the accumulation of various volatile flavor substances (esters, acids, aldehydes, and ketones), while low-abundance fungi facilitated the accumulation of functional metabolites (GABA, acetoin, tetramethylpyrazine). These results guided the targeted control of ZJV fermentation to improve its flavor quality and provided valuable insights for ZJV manufacturers.