Chemical characterisation and histamine-forming bacteria in salted mullet roe products

Sixteen salted mullet roe products sold in the retail markets in Taiwan were purchased and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, water content, total volatile basic nitrogen (TVBN) and aerobic plate count (APC) in all samples ranged from 5.4 to 5.8, 5.1% to 7.2%, 15.4% to 27.3%, 32.0 to 69.6 mg/100 g and <1.0 to 7.1 log CFU/g, respectively. None of these samples contained total coliform and Escherichia coli. The average content of each of the nine biogenic amines in all samples was less than 4 mg/100 g, and only one mullet roe sample had the histamine content (8.18 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 10.7 ppm and 9.6 ppm of histamine in trypticase soy broth (TSB) supplemented with 1.0% l-histidine (TSBH) were identified as Staphylococcus carnosus by 16S rDNA sequencing with PCR amplification, and they were isolated from the sample with higher histamine content (8.18 mg/100 g).