Histamine contents and histamine-forming bacteria in sufu products in Taiwan

Twelve white and ten brown sufu products sold in the supermarkets in southern Taiwan were purchased and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, and aerobic plate count (APC) in all samples ranged from 4.6 to 6.6, 6.2% to 12.0%, and 3.0 to 7.9 log CFU/g, respectively. None of these samples contained total coliform and Escherichia coli. Although the average content for each of the nine biogenic amines in all samples was less than 5 mg/100 g, only one brown sufu sample had histamine content (15.8 mg/100 g) greater than the 5.0 mg/100 g allowable limit suggested by the US Food and Drug Administration. Two histamine-producing bacterial strains capable of producing 1.33 mg/100 ml and 1.34 mg/100 ml of histamine in trypticase soy broth (TSB) supplemented with 1.0% l-histidine (TSBH) were identified as Bacillus subtilis by 16S rDNA sequencing with PCR amplification.