Inhibitory effects of high-hydrostatic-pressure treatments on histamine production in mackerel (Scomber japonicus) muscle inoculated with Morganella morganii and Photobacterium phosphoreum

Histamine or scombroid fish poisoning is caused by ingestion of histamine in spoiled fish, which arises because of the activity of bacterial histidine decarboxylase (HDC), resulting in allergy-like symptoms. To investigate the inhibitory effects of HHP on the activity of HDC, crude HDC extracts were prepared from Morganella morganii and Photobacterium phosphoreum, and subjected to HHP (100-400 MPa) or were left untreated (controls). Pressure levels of up to 200 MPa did not significantly affect the activity of crude HDC in M. morganii (<5%); however, HHP treatments of 300 and 400 MPa showed inhibitory activity at 19.4% and 23.2%, respectively. HHP treatments of 100, 200, 300, and 400 MPa considerably inhibited the crude HDC activities of P. phosphoreum at 46.1, 57.0, 63.3, and 84.5%, respectively. HHP treatment was then applied to mackerel muscle inoculated with M. morganii and P. phosphoreum in situ. We observed that HHP significantly delayed the overall microbial growth in mackerel muscle, regardless of the inoculated species. Moreover, histamine production in mackerel muscle inoculated with M. morganii was strongly inhibited by both 200 and 300 MPa (but not 100 MPa). Furthermore, in the sample inoculated with P. phosphoreum, all of the HHP treatment conditions at 100-400 MPa strongly inhibited histamine production. Taken together, the findings of this study might be helpful to enhance the safety of mackerel consumption.