Effects of different co-cultures on the amino acid availability, biogenic amine concentrations and protein metabolism of fermented sufu and their relationships

Abstract

This study aimed to assess the influence of the availability of free amino acids (FAA) and the metabolism of proteins on BA formation in four different co-cultures ((i) uninoculated BA-producing strains as control, (ii) inoculated with B. subtilis, (iii) inoculated with B. tropicus, and (iv) co-inoculated with B. subtilis and B. tropicus at the ratio of 1:1. And all batches were inoculated with a starter) during fermentation for 56 days. Results indicated that batch C, batch BS, batch BT and batch BS + BT samples contained histamine levels of 139.86, 140.33, 219.66 and 256.94 mg/kg in the end, respectively, and high histamine concentrations were mainly produced by B. tropicus strains. Individual evaluation presented a minor correlation between a precursor amino acid and its corresponding BA, but our results revealed that a high concentration of amino acids could upregulate the expression of decarboxylase. Pearson correlation analysis indicate that protein metabolism actually promoted the formation of BA. Compared with that of the control samples, the reduction of the total BA was 29.53% by salt treatment and 26.48% by alcohol treatment inoculated with B. subtilis. Thus, considering the safety of sufu, Bacillus spp. should be controlled for the reduction of BA contents.