Analyzing the contribution of functional microorganism to volatile flavor compounds in Semillon wine and predicting their metabolic roles during natural fermentation.

Indigenous microorganism plays a pivotal role in natural wine fermenting and its distinctive qualities shaping. However, the contributions of functional microbial taxa to wine flavor formation remain underexplored. This study focuses on the natural fermentation systems of Semillon grapes from Wuwei and Zhangye Gansu sub-regions within the Hexi Corridor of China. We characterized the dynamics of microbial community succession during fermentation using a combination of metagenomic sequence and culture-dependent analysis. Concurrently, volatile compounds were quantified using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry. The mechanistic of functional microorganisms in wine flavor formation were unveiled by constructing KEGG metabolic network. The results revealed distinct microbial succession patterns between the two regions. In Zhangye, Hanseniaspora dominated the early fermentation stage, succeeded by Saccharomyces, Fructobacillus, and Brachyspira in middle and late stages. Conversely, in Wuwei, Pichia prevailed initially, with Brachyspira becoming stably enriched. Volatile esters and higher alcohols were identified as the major flavor components, contributing aroma notes of flowers, fresh greens, and stone fruits to the Semillon wine. Correlation analysis indicated positive associations between most key volatile aroma compounds and Saccharomyces, Brachyspira, Hanseniaspora, and Acetobacter. Metagenomic functional prediction highlighted carbohydrate and amino acid metabolic as the predominant pathways, with key processes involving glycolysis, fatty acid biosynthesis, and esterification. Core microbial taxa (Saccharomyces, Hanseniaspora, Starmerella, etc.) regulated flavor compound synthesis through a synergistic metabolic network. This study elucidates the succession of functional microorganisms and the development of flavor profiles during the natural fermentation of Semillon in the Hexi Corridor providing a reference for the development and application of functional microorganisms.