Citrulline Accumulation Mechanism of Pediococcus acidilactici and Weissella confusa in Soy Sauce and the Effects of Phenolic Compound on Citrulline Accumulation.

Kai Zhou,Zhen-Lin Xu,Chaoqun Shen,Bingyong Li,Yuan-Ming Sun,Jianyuan Yang,Xiao Zhang

doi:10.3389/fmicb.2021.757542

Kai Zhou, Zhen-Lin Xu + Show 5 more

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https://doi.org/10.3389/fmicb.2021.757542

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Abstract

Citrulline is one of the major precursors of ethyl carbamate in soy sauce, and the accumulation of citrulline is attributed to the metabolism of arginine by bacteria with the arginine deiminase (ADI) pathway. However, key strains and factors affecting citrulline accumulation are not yet clear. In this study, two key strains of Pediococcus acidilactici and Weissella confusa were isolated from soy sauce moromi, and the regularity of citrulline formation was studied. Results showed that the conversion rates from arginine to citrulline (A/C rate) and the citrulline accumulation ability of W. confusa and P. acidilactici significantly increased in the presence of different concentrations of NaCl, indicating that salt stress was the main factor for citrulline accumulation. The inconsistent expression of arc genes by salt stress was the reason for citrulline accumulation for P. acidilactici, but for W. confusa, it may be due to the influence of arginine/citrulline on the transportation system: the intracellular citrulline could neither transport to extracellular space nor convert into ornithine. Environmental factors greatly influenced citrulline accumulation of the two key bacteria; A/C rate and citrulline formation in both strains decreased at low temperature (15°C) under high salt stress, but opposite effects were observed for the two key strains under anaerobic light condition. Moreover, quercetin and gallic acid significantly decreased the A/C rate and citrulline accumulation ability of the two key strains. The optimal quercetin and gallic acid as suggested by simulation experiment were 100 and 10 mg/l, respectively, and the lowest A/C rate of 28.4% and citrulline level of 1326.7 mg/l were achieved in the simulation system. This study explored the main factors for citrulline formation by the two key strains and proposed a targeted way to control citrulline in soy sauce.

Highlights

Soy sauce, a traditional fermented condiment, is widely used for food preparation in Asian countries
Two strains, which were identified as P. acidilactici and W. confusa, exhibited an outstanding citrulline accumulation capability (Table 1)
The A/C rates P. acidilactici and W. confusa reached up to 40.9% and 30.2%, respectively, and citrulline was accumulated over 900 mg/l

Summary

Introduction

A traditional fermented condiment, is widely used for food preparation in Asian countries. Citrulline and ethanol are considered to be the major EC precursors in soy sauce (Matsudo et al, 1993; Zhou K. et al, 2017; Zhou et al, 2019). Arginine deiminase (encoded by arcA) and ornithine transcarbamylase (OTC, encoded by arcB) participate in the citrulline formation, and citrulline can be metabolized by OTC into carbamoyl-P and utilized by carbamate kinase (CK, encoded by arcC) to produce CO2, ammonia, and ATP. Approximately 1 mg/ml citrulline will accumulate in the lactic acid fermentation stage, and it will react with ethanol via ethanolysis reaction to produce EC during heating process (Matsudo et al, 1993; Zhang et al, 2015; Zhou et al, 2019). Apart from citrulline, high levels of arginine are conducive to EC formation, but ornithine has the opposite effect during pasteurization (Zhou et al, 2021)

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