Integrative liquid chromatography-tandem mass spectrometry metabolomics and high-throughput sequencing technology reveal physicochemical characteristics and bacterial diversity of traditionally pickled mustard tuber from different regions of China

This work aimed to investigate and compare the physicochemical properties and bacterial diversity of traditionally pickled mustard tuber from different regions in China. The pickles were obtained from Ningbo (NB), Nei Monggol (NMG), and Harbin (HEB). The pH was monitored by a pH meter. The titratable acidity and salinity were determined via titrimetric analysis. The nitrite content was measured using N-(1-naphthyl)-ethylenediamine dihydrochloride spectrophotometric method. The organic acids were detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The bacterial diversity was conducted through Illumina high-throughput sequencing platform. There were significant differences in the physicochemical properties of pickled mustard tuber from various locations, with the NB pickles having the highest pH, salinity, and nitrite content and the lowest titratable acidity. Importantly, pickles with higher titratable acidity levels had relatively lower nitrite and salinity contents. A total of 63 organic acids were detected, with lactic acid and succinic acid being the most prevalent. Moreover, the organic acid compositions of the NMG and HEB samples were more similar than those of the NB pickles. Additionally, bioinformatic analysis revealed that Firmicutes and Proteobacteria appeared as the predominant bacterial phyla in all samples. Among these, Lactobacillus was the major genera. The most abundant bacteria were found in the HEB pickles. Further correlation analysis showed that there was a strong correlation between bacterial community and 11 internal physicochemical parameters. This study could contribute to a better understanding of the physicochemical characteristics and bacterial diversity of pickled mustard tuber from different locations.