Histamine and other biogenic amines and histamine-forming bacteria in miso products

Twenty-seven miso products sold in supermarkets and 13 products sold in retail markets were purchased from southern Taiwan, 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 5.1 to 5.8, 6.1% to 13.8%, and 2.1 to 9.1 log CFU/g, respectively. Only one of the supermarket miso products contained 100 MPN/g total coliform. None of these samples contained Escherichia coli. Although the average content for each of the nine biogenic amines in all samples was less than 5 mg/100 g, two supermarket samples (22.1 and 11.9 mg/100 g) and one retail market sample had histamine content (10.2 mg/100 g) greater than the 5.0 mg/100 g allowable limit suggested by the US Food and Drug Administration. Eight histamine-producing bacterial strains, capable of producing 10.4–39.4 ppm of histamine in trypticase soy broth (TSB) supplemented with 1.0% l-histidine (TSBH), were identified as Staphylococcus pasteuri (one strain), Bacillus sp. (one strain), B. amyloliquefaciens (two strains), B. subtilis (two strains) and B. megaterium (two strains), by 16S rDNA sequencing with PCR amplification.