The arginine deiminase pathway of koji bacteria is involved in ethyl carbamate precursor production in soy sauce

Abstract

Ethyl carbamate (EC) is a group 2A carcinogen generated from a few precursors in many fermented foods and alcoholic beverages. Citrulline, urea, carbamoyl phosphate, and ethanol are common precursors detected in fermented foods. In this study, citrulline was proved to be the main EC precursor in soy sauce, which was found to be accumulated in moromi mash period and correlated with the utilization of arginine by koji bacteria. Six koji isolates belonging to three genera were identified to be able to accumulate citrulline via the arginine deiminase (ADI) pathway. Among these strains, only Pediococcus acidilactici retained high activities in synthesis and accumulation of citrulline in the presence of high concentration of sodium chloride. These results suggested that P. acidilactici is responsible for the accumulation of citrulline, one of the EC precursors, in the process of soy sauce fermentation.

Characterization of a Bacillus amyloliquefaciens strain for reduction of citrulline accumulation during soy sauce fermentation

“…Isolation and screening of salt-tolerant bacteria with high arginine consumption capacity Isolation and screening of salt-tolerant bacteria with high arginine consumption capacity used a medium color change cultivation method as described (Zhang et al 2014). Arginine utilization capacity was evaluated by measuring the diameter of the purple circles surrounding target colonies.…”

“…Positive isolates were stored at -80°C. These isolates were cultivated using the koji bacteria cultivation method as described (Zhang et al 2014). Each strain was harvested by centrifugation at 4°C, 10,0009g for 5 min and inoculated into 50 ml modified arginine consumption broth [18 % (w/v) NaCl, no Bromcresol Purple], (Zhang et al 2014) and cultured without mixing at 30°C for 48 h.…”

“…Concentrations of ethyl carbamate, ethanol and urea (Zhang et al 2014) as well as total acids and nitrogen in amino acid (Cui et al 2014) were quantified as described. Free amino acids were quantified by HPLC as described (Zhang et al 2014); volatile compounds were analyzed using a headspace solid phase microextraction (HS-SPME) method (Zhao et al 2011).…”

“…NH 2 COOC 2 H 5 + H 2 N CH 2 ð Þ 3 CH NH 2 ð ÞCOOH Citrulline is produced predominantly through the arginine deiminase (ADI) pathway by Pediococcus Electronic supplementary material The online version of this article (doi:10.1007/s10529-016-2147-7) contains supplementary material, which is available to authorized users. acidilactici in days 1-21 during soy sauce fermentation, the lactic acid fermentation stage (Matsudo et al 1993;Zhang et al 2014). The ADI pathway comprises three reaction steps (Sürken et al 2008).…”

“…However, citrulline can become the main end-product instead of ornithine at the optimum pH for bacteria growth (i.e. pH 5.5 for Lactobacillus fermentum IMDO 130101) or in the presence of 18 % NaCl (Vrancken et al 2009;Zhang et al 2014). Thus, isolation and characterization of a strain with the ability to convert all arginine to ornithine through the ADI pathway is crucial for the reduction of citrulline accumulation during soy sauce fermentation.…”