Histamine development and bacterial diversity in microbially-challenged tonggol (Thunnus tonggol) under temperature abuse during canning manufacture.

Abstract

Histamine formation and bacteriological changes caused by temperature abuse commonly occurring in the manufacturing process of standard canned tuna was assessed in microbiologically challenged tonggol (Thunnus tonggol). The in situ challenge was performed by water-soaking at 26-28°C for 7h to ensure the multiplication and active phase of fish microflora. Right after pre-cooking to back-bone temperature (BBT) of 50-52°C, histamine dropped to 5.17 ± 2.71ppm, and slowly reached 6.84 ± 1.69ppm at 16h abuse. On the contrary, histamine was reduced to 2.87 ± 1.23ppm and eventually reached 5.01 ± 1.32ppm at 24h abuse in the pre-cooked fish previously frozen. The numbers of total aerobic bacteria, Enterobactericeae, psychrotroph, histamine forming bacteria (HFB) and diversity of fish microflora were revealed by cultural and nested PCR-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) techniques. Interestingly, frozen storage effectively halted histamine formation in raw fish throughout 16h abuse despite the presence of HFB. These included the prolific strains of Morganella morganii, Proteus penneri, Proteus mirabilin, Citrobacter spp. The nested PCR-DGGE profile confirmed the presence of M. morganii and Citrobacter spp. in raw fish. These prolific strains were hardly observed in the precooked fish previously frozen. Frozen storage did not only promote even histamine distribution throughout fish muscle but also enhanced histamine loss during thawing and pre-cooking. Therefore, pre-cooking and frozen storage were proven to be the effective combined hurdles not only to reduce but also prolong histamine formation of the challenged toggol throughout 24h of temperature abuse during canning process.