Rhodobacter sphaeroides reshapes lipid oxidation-driven aroma formation in fermented sausages under mild acidification

This study investigated the effects of Rhodobacter sphaeroides (Rh), Lactiplantibacillus plantarum YR07 (YR07), and their mixed inoculation on the fermentation characteristics, lipid oxidation, volatile aroma formation, and non-volatile metabolite composition of fermented sausages. Physicochemical properties and microbial counts were monitored on days 0, 3, 6, 9, and 12, whereas TBARS, volatile compounds, and non-targeted metabolomics were analyzed on day 12. The YR07 group exhibited the fastest acidification rate, while the mixed inoculation resulted in a more moderate acidification process, higher L* and a * values and a lower b* value at day 12, and volatile and non-volatile metabolite profiles distinct from those of the two single-strain treatments, indicating a non-additive effect. KEGG mapping and direct comparisons between groups revealed that Rh-associated differences were primarily concentrated in precursors derived from unsaturated lipids. In contrast, YR07-associated differences were more closely related to metabolite sets associated with amino acid and central carbon metabolism. In summary, the co-inoculation treatment was characterized by a metabolic pattern in which mild acidification was accompanied by a distinct distribution of flavor-related precursors derived from lipid and amino acid sources. This study provides a basis for using R. sphaeroides as an auxiliary fermentation strain in the design of composite fermentation starters and the regulation of fermented sausage aromas.