Metatranscriptomics reveals the effect of fermentation by Pediococcus acidilactici and Rhizopus oryzae on the quality of mutton sausages and the mechanism of odor metabolism.

4-alkyl-branched chain fatty acids (vBCFAs) are key flavor-impact compounds in mutton and its derived products. Pediococcus acidilactici and Rhizopus oryzae were applied to ferment mutton sausages, and GC-MS/SIM and metatranscriptomics were employed to investigate the effects of different fermentation strategies on the quality of mutton sausages and the metabolism of 4-methyloctanoic acid (4-MOA) and 4-ethyloctanoic acid (4-EOA). The results demonstrated that inoculation with the mixed starter cultures exhibited lower pH, thiobarbituric acid, and peroxide values. Moreover, mixed starter cultures were more effective in reducing 4-MOA and 4-EOA compared to single starter culture and control. Metatranscriptomics revealed Streptococcus as the primary active genus in the mixed starter cultures. Additionally, we constructed the fermentation metabolic network of mutton sausages, demonstrating that mixed starter cultures effectively reduced 4-MOA and 4-EOA while enhancing sausages quality. The study provided a theoretical basis for improving the quality of mutton sausages.