Screening of mixed lactic acid bacteria starter and exploring the sources of flavor substances in co-fermentation of Flammulina velutipes with different vegetables

From the paper

Abstract

To augment the flavor components of Flammulina velutipes pickles (FVP) and enhance its acceptability, F. velutipes were co-fermented with various raw materials (cabbages, cowpeas, radishes, millet peppers, gingers, Sichuan peppercorns) using lactic acid bacteria (LAB). This article investigated the fermentation characteristics of LAB on FVP, and both single LAB strains and composite LAB strains suitable for the fermentation of FVP were screened. The organic acids, flavor nucleotides, and free amino acids in the FVP were quantified using high-performance liquid chromatography (HPLC) with external standards. Additionally, the flavor compounds of the FVP were analyzed and identified using headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), an electronic tongue, and an electronic nose. The results indicated that the LAB suitable for fermenting FVP were Lactobacillus plantarum, Lactobacillus casei, and Lactobacillus rhamnosus, with an optimal combination ratio of 2:1:3. Lactic acid, acetic acid, citric acid, and pyruvic acid among organic acids exert a positive influence on the overall flavor profile of FVP. The relatively high contents of arginine and alanine among free amino acids may contribute positively to the taste of FVP. The electronic tongue analysis reveals that the primary flavor differences among the four groups of FVP are attributed to acidity and bitterness, which show a strong positive correlation with sensory evaluation scores. The electronic nose analysis identifies the main differential compounds among the four groups of FVP as terpenes, sulfur compounds, and alcohols, aldehydes, and ketones, which are associated with the addition of spices. A total of 67 flavor compounds were detected in FVP, with key compounds influencing the overall flavor profile including (E,E)-2,4-nonadienal, (E)-2-octenal, 1-octen-3-ol, linalool, eucalyptol, α-pinene, and hexanal. These primary flavor substances were derived from spices such as chili and ginger. Therefore, the co-fermentation of various vegetables, gingers and millet peppers with F. velutipes can significantly enhance the flavor components of FVP and improve its acceptability, with the ameliorative effect of spices being particularly pronounced. This study provides a theoretical reference for the industrial production of FVP.