Screening and characterization of acetoin-producing lactic acid bacteria and their effect on the flavor quality of soy sauce

Acetoin (ACT) is an important flavor compound found in traditional fermented foods, and a precursor of compounds such as pyrazine, which is a direct source of soy sauce aroma in fermented soybean products. In this study, four acetoinproducing lactic acid bacteria (LAB) were screened from traditional high-salt fermented foods in Hunan Province, China, by the creatine colorimetric method, Gram staining, and catalase test. QT038 and JC094 exhibited the highest acetoin contents of 81.3 mg/L and 76.8 mg/L. JC094, QT019, and LJ064 were determined to be Lactiplantibacillus plantarum , and QT038 was determined to be Lactiplantibacillus paraplantarum . The growth characteristics, temperature tolerance, salt tolerance, and antioxidant capacity of the 4 strains were studied. The strains QT038 and JC094 showed strong tolerance and antioxidant characteristics. Volatile analysis of fermented soy sauce simulation experiment with selected strains revealed JC094 fermented samples contained significantly more flavor compounds, both in variety (38) and total content (3.57 mg/L), compared to other strains. Notably, QT038 and JC094 improved the acetoin levels (0.161 mg/L). The results demonstrated that QT038 and JC094 have the ability to produce higher levels of acetoin to enhance flavor quality and can be further mixed or co-fermented with yeasts in soy sauce fermentation.