Differences in the bacterial profiles and physicochemical between natural and inoculated fermentation of vegetables from Shanxi Province

Zhidi Chen,Xiuzhi Gao,Jianyi Kang,Yao Zhang,Xinxin Yi,Xiaona Pang,Hongmei Li-Byarlay

doi:10.1186/s13213-020-01605-5

Zhidi Chen, Xiuzhi Gao + Show 5 more

Open Access

https://doi.org/10.1186/s13213-020-01605-5

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Abstract

PurposeFermented vegetables can be divided into two types, natural fermented and artificially inoculated fermented. By detecting and identifying the changes of bacterial diversity using physical and chemical indicators during natural and inoculation fermentation, we analyzed and determined the dominant bacteria in the fermentation process and revealed the relationship between bacteria and volatile substances.MethodsWe used the Illumina Miseq to sequence the bacteria in fermented vegetable samples at different fermentation periods, and calculated the total number of mesophilic microorganisms and lactic acid bacteria. We used the pH and nitrite to monitor the acidification process. GC-MS was used to determine volatile flavor compounds. Finally, we analyzed the correlation between volatile flavor compounds and bacteria.ResultsTotal mesophilic microorganisms and the number of lactic acid bacteria in the inoculated fermentation were higher than the natural fermentation. The bacterial diversity Shannon and Simpson indexes of the natural fermentation, higher than those of inoculated fermentation in 0~7 days, were between 55~71% and 36~45%, respectively. On the 7th day, the proportion of Lactobacillus in the natural fermentation and inoculated fermentation were 53.4% and 90.2%, respectively, which were significantly different. Lactobacillus was the dominant genus in the fermented vegetables and an important genus to promote the formation of volatile flavors. Lactobacillus was negatively correlated with two volatile substances (4-[2,2,6-trimethyl-7-oxabicyclo [4.1.0] hept-1-yl]-3-Buten-2-one (K4) and a-Phellandrene (X1)) and played a leading role in the fermentation process.ConclusionsResults demonstrated that the total number of mesophilic microorganisms and lactic acid bacteria in inoculated fermentation were more than those in natural fermentation. Inoculated fermentation can shorten the fermentation cycle and reduce the content of nitrite. Lactic acid bacteria were the dominant bacteria in fermented vegetables.

Highlights

Fermentation has been applied in food processing for millennia
Evolution of inoculum Change of bacterial viable counts in the samples of natural fermentation (NF) and inoculated fermentation (IF) throughout the 7 days of storage at 25 °C was shown in the Fig. 1
The total mesophilic microorganisms in NF and IF were 8.02 lg colony-forming unit (CFU)/g and 8.53 lg CFU/g, respectively, and the number of lactic acid bacteria (LAB) was 8.01 lg CFU/g and 8.45 lg CFU/g, respectively. It can be seen from the above results that the overall change trend of the total mesophilic microorganisms and the number of LAB in the two fermentation modes was similar

Summary

Introduction

Fermentation has been applied in food processing for millennia. Fermented foods constitute an integral part of the human diet all over the world (Tamang et al 2016). Similar to other fermented foods such as fermented soy, yogurt, and cheese, fermented vegetables have a unique aroma, taste, and great nutritional value, which are entirely dependent upon the fermentation conditions (Mcfeeters 2004). Many clinical and animal studies have demonstrated that fermented vegetables significantly reduce the risks of obesity (Kim et al 2011; Kwak et al 2012), diabetes (Zhang et al 2018), oxidation (Kim et al 2017a), hypercholesterolemia (Jung et al 2014a), cancer (Yeh and Yen 2005), and help to stimulate the immune system (Caggianiello et al 2016). Fermented vegetables have been considered as one of the most nutritional and health-beneficial foods in the world (Kim et al 2012)

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