Abstract
The unique geographical environment of karst regions provides pickles with a favorable flavor and taste; however, the contribution of the microbial community to pickle fermentation has not been fully explored. In this study, high-throughput sequencing and untargeted metabolomics were used to characterize 60 naturally fermented pickle samples from 12 different karst regions. The bacterial communities and metabolites of naturally fermented pickles changed significantly between different karst regions. Lactobacillus delbrueckii, L. homohiochii, and L. fermentum were the dominant bacterial species in pickle samples, with relative abundances of 29.66, 8.05, and 7.12%, respectively. There exist significant variations in the core biomarkers of traditional pickles across diverse regions characterized by rocky desertification and varying temperatures. Both L. homohiochii and L. buchneri stimulated complicated interspecies interactions in the bacterial community. Lactobacillus species exhibit excellent inhibitory effects against harmful bacterial populations under E-low- and E-high-temperature conditions. In total, 1976 metabolites were identified in pickles, including many previously undiscovered metabolites (e.g., Citrulline, GABA, tyrosol, and L-hydroxyroline) attributable to the dominances of L. homohiochii, L. brevis, L. buchneri, and L. plantarum. Lower levels of biogenic amines were found in pickles from the low-temperature regions. Furthermore, L. delbrueckii and L. fermentum were significantly negatively (p < 0.05) correlated with spermine and tyramine, and Weissella cibaria was negatively (p < 0.05) correlated with histamine. These data indicated that a low-temperature environment may be beneficial to the fermentation of pickles. This work provides new insights into the flavor of pickles resulting from the geological distribution of bacterial flora in karst regions.