Unravelling flavor formation in Chinese steamed bread made with fermented glutinous rice wine dough: insights from microbial succession, metabolomics, and volatile profiling.

Abstract

To unravel the flavor formation mechanism of Chinese steamed bread (CSB) with traditionally fermented glutinous rice wine (GRW) dough procedure, an integrated multi-omics strategy was employed to characterize the microbial succession and metabolic dynamics during the three-stage fermentation procedure. First, high-throughput sequencing analysis across the stage A (GRW fermentation), stage B (mash and liquid fermentation, MLF), and stage C (GRW-dough fermentation) showed a fungal shift from Rhizopus to Saccharomyces (51.73% to 99.81%) and a bacterial shift to lactic acid bacteria (Weissella and Lactiplantibacillus, 86.31%). Subsequently, untargeted metabolomics focused on the key stage B (MLF) identified 2808 metabolites primarily classified as amino acids and carbohydrates in the MLF. Among them, proline and lactate accumulated as key differential metabolites while sucrose declined significantly. Further metabolic pathway analysis highlighted β-alanine metabolism (Impact = 0.500, p < 0.01), alanine, aspartate and glutamate metabolism (Impact = 0.259, p < 0.01), and starch and sucrose metabolism (Impact = 0.283, p < 0.05) as core pathways supporting flavor precursor synthesis. The metabolites in the MLF shaped the volatile profile of the final product. Specifically, MLF fermented for 8-12 h (B8 ∼ B12) significantly promoted ester formation, including ethyl octanoate and ethyl heptanoate in the GRW-CSB. The MLF (B16) enhanced ketone accumulation with 2,3-butanedione exhibiting a high odor activity value (OAV) of 15.1. Additionally, (E)-2-nonenal and 2-pentylfuran were identified as key aroma-active compounds showing high OAVs of 118.6 at B12 and 9.4 at B16, respectively.