Application of the Bigelow (z-value) model and histamine detection to determine the time and temperature required to eliminate Morganella morganii from seafood

Abstract

In New Zealand, the product most frequently implicated in cases of scombroid or histamine poisoning is the hot-smoked fish, kahawai (Arripis trutta). A properly controlled heating step in the production of hot-smoked seafood could eliminate bacteria able to convert the amino acid histidine to histamine. In this study, we determined the core temperatures and times required during hot smoking of kahawai to eliminate histamine-forming bacteria and to ensure a final product that will not produce histamine if subsequent temperature abuse occurs. Morganella morganii strains previously isolated from portions of hot-smoked kahawai with elevated histamine levels were inoculated onto product to be tested. A variation of the Bigelow or z-value model was used to generate a thermal death time graph, where the production of histamine, in a heat-treated and subsequently temperature-abused sample, was scored as a positive value (growth) and the absence of histamine was scored as a negative value (no growth). From a line fitted to the data, calculated times for the elimination of histamine-forming bacteria at test temperatures of 58, 59, 60, 61, and 62°C were estimated to be 15.27, 8.81, 4.79, 2.68, and 1.46 min; respectively, giving a z value of 3.85°C. This approach to thermal death determination, based on the presence or absence of a bacterial metabolite, proved to be an efficient way to determine the thermal regime required to eliminate bacteria capable of converting histidine to histamine on kahawai.