Effects of Enhanced Fermentation of Saccharomyces cerevisiae and Lactobacillus plantarum on Volatile Flavor of Coffee

Yeast and lactic acid bacteria play an important role in improving the flavor of coffee. In order to evaluate the effect of enhanced fermentation of Saccharomyces cerevisiae (S.c), Lactobacillus plantarum (L.p) and mixed bacteria (S.c+L.p) on coffee aroma, the peeled coffee beans were fermented at 28 ℃ for 72 h with non-inoculated samples as control group (CK). The physical and chemical characteristics, sensory evaluation, headspace solid-phase microextraction/gas chromatography-massspectrometry (HS-SPME/GC-MS) and odor activity value (OAV) were used to evaluate the samples of CK group, S.c group, L.p group and S.c+L.p group. The results showed difference volatile components for roasted coffee beans among different fermentation groups. A total of 111 volatile components were identified, including 68, 66, 79 and 76 volatile components in CK group, L.p group, S.c group and L.p+S.c group with contents of 476.45, 965.58, 723.15 and 552.74 μg/kg, respectively. Among them, pyrazine compound content was the highest in L.p group at 400.19 μg/kg, which mainly gave coffee nut aroma and roasted aroma. OAV analysis showed that there were 16 kinds of substances with OAV value not less than 1 in L.p group samples, of which 2-ethyl-3-methylpyrazine, 3-methylbutyraldehyde, dimethyl trisulfide, linalool, 2,6-dimethylpyrazine and 3-ethyl-2-dimethylpyrazine had higher OAV values, and these compounds contributed greatly to the aroma system of coffee. Sensory evaluation analysis showed that the microbial enhanced fermentation group could give coffee special flavor characteristics, in which S.c group was prominent in fruity aroma, L.p group was more prominent in nutty aroma and roast aroma, while S.c+L.p group was more prominent in flower aroma and baking aroma, and various aromas were more balanced. In conclusion, L. plantarum is more suitable as the aroma-producing starter of fermented coffee, and the enhanced fermentation of S. cerevisiae and L. plantarum is of great significance for the flavor improvement of coffee.