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 7 h 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 ± 2.71 ppm, and slowly reached 6.84 ± 1.69 ppm at 16 h abuse. On the contrary, histamine was reduced to 2.87 ± 1.23 ppm and eventually reached 5.01 ± 1.32 ppm at 24 h 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 16 h 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 24 h of temperature abuse during canning process.

Keywords: Freezing; Histamine; Histamine-forming Bacteria; PCR-DGGE; Precooking; Thunnus tonggol.

Fig. 1

Sampling schemes for histamine and bacteriological analyses ([1] to [8] and [A] to [J], were sampling points for fresh and frozen fish, respectively). Air and water temperatures (at which fish were exposed) were monitored and recorded throughout the process

Fig. 2

Numbers representing fish sections taken for histamine analysis

Fig. 3

Histamine distribution of ten microbial challenged raw tonggol in various sections; (1) (5) upper anterior, (2) (6) lower anterior, (3) (7) upper mid section and (4) (8) lower mid section (a) and 1.5 h delay at butchering area, at which fish exposed to temperatures of 27.6 – 28.6 °C (b)

Fig. 4

Changes of histamine levels in various sides of the microbial-elevated, fresh (left panel: c, e, and g) and previously frozen (right panel: d, f, and h) tonggol exposed to temperature abuse during processing for 16 h. Histamine changes of the positive controls, in which fresh (a) and previously frozen (b) fish were left at 25–28 °C for 16 h without pre-cooking

Fig. 5

Changes of total viable count, psychrophile, Enterobacteriaceae and presumptive histamine-forming bacteria (HFB) counts in fresh (a) and frozen (b) tonggol exposed to temperature abuse in processing area before and after precooking. Histamine changes of the positive controls, in which fresh and frozen fish were left at 25–28 °C for 16 and 24 h, respectively without pre-cooking intervention. Bacteriological enumeration at each sampling period was analyzed from 3 fish with triplicate analysis of each parameter

Fig. 6

PCR-DGGE profiles and strain identification (below table) of bacterial diversity in fish muscles of fresh ([1] to [8]) and frozen ([A] to [J]) tonggol exposed to temperature abuse in processing area for 16 h and 24 h, respectively

Fig. 6

PCR-DGGE profiles and strain identification (below table) of bacterial diversity in fish muscles of fresh ([1] to [8]) and frozen ([A] to [J]) tonggol exposed to temperature abuse in processing area for 16 h and 24 h, respectively