Hsien-Feng Kung

Histamine-Related Hygienic Qualities and Bacteria Found in Popular Commercial Scombroid Fish Fillets in Taiwan

To determine the histamine-related hygienic qualities and bacteria of scombroid fish fillets sold in traditional retail markets, 61 samples were collected from northern and southern Taiwan. It was found that the content of volatile base nitrogen in most samples was below 25 mg/100 g, which is the regulatory level in Taiwan. The ratio of unacceptable samples/total samples for aerobic plate count and Escherichia coli was 100% and 15% in northern samples and 100% and 20% in southern samples, respectively, compared with the requirements of hygienic standards. The average content of various biogenic amines in all samples were lower than 3 mg/100 g, except for histamine average content (4.6 mg/100 g) in southern samples. Among southern samples, four samples contained 12.8 to 28.8 mg/100 g histamine, which is more than 5 mg/100 g that is the allowable limit suggested by the U.S. Food and Drug Administration. Furthermore, 14 bacterial strains were isolated from sailfish fillets on a selective medium for histamine-forming bacteria. These presumptive histamine-forming strains, such as Proteus, Enterobacter, Klebsiella, Rahnella, and Acinetobacter, have been identified and found to produce 20 to 2,000 ppm histamine after incubating at 37 degrees C for 24 h.

Histamine production by Enterobacter aerogenes in sailfish and milkfish at various storage temperatures.

Enterobacter aerogenes was studied for its growth and ability to promote the formation of total volatile base nitrogen (TVBN) and histamine in sailfish (Istiophorus platypterus) and milkfish (Chanos chanos) stored at various temperatures from -20 to 37 degrees C. The optimal temperature for bacterial growth in both fish species was 25 degrees C, whereas the optimal temperature for histamine formation was 37 degrees C. The two fish species inoculated with E. aerogenes, when not properly stored at low temperatures such as 15 degrees C for 36 h, formed histamine at above the U.S. Food and Drug Administration hazardous guideline level of 50 mg/100 g. Milkfish was a better substrate than sailfish for histamine formation by bacterial histidine decarboxylation at elevated temperatures (> 15 degrees C). Although higher contents of TVBN were detected in the spiked sailfish than milkfish during the same storage time at temperatures above 15 degrees C, the use of the 30-mg/100 g level of TVBN as a determination index for fish quality and decomposition was not a good criterion for assessing potential histamine hazard for both fish species. Bacterial growth was controlled by cold storage of the fish at 4 degrees C or below, but histamine formation was stopped only by frozen storage. Once the frozen fish samples were thawed and stored at 25 degrees C, histamine started to accumulate rapidly and reached levels greater than the hazardous action level in 36 h.

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 69.6mg/100g and <1.0 to 7.1logCFU/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 4mg/100g, and only one mullet roe sample had the histamine content (8.18mg/100g) greater than the 5.0mg/100g allowable limit suggested by the US Food and Drug Administration. Two histamine-producing bacterial strains capable of producing 10.7ppm and 9.6ppm 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 (8.18mg/100g).

Effect of salt concentrations and drying methods on the quality and formation of histamine in dried milkfish (Chanos chanos)

The effects of salt concentrations (0-15.0%) and drying methods on the quality of dried milkfish were studied. The results showed that the levels of aerobic plate counts, total coliform, water activity, moisture contents, total volatile basic nitrogen (TVBN) and thiobarbituric acid (TBA) of the dried milkfish samples prepared with the same drying method decreased with increased salt concentrations. The samples prepared with the cold-air drying method had better quality in term of lower TVBN and TBA values than those of samples prepared with other drying methods. The histamine contents in all samples, except two, prepared with various salt concentrations by different drying methods were less than 1.9 mg/100 g. Two unsalted samples prepared with hot-air drying at 35 °C and sun drying methods were found to contain histamine at levels of 249.7 and 67.4 mg/100 g, respectively, which were higher than the potential hazard level of 50 mg/100 g.

The effect of vacuum packaging on histamine changes of milkfish sticks at various storage temperatures

The effects of polyethylene packaging (PEP) (in air) and vacuum packaging (VP) on the histamine related quality of milkfish sticks stored at different temperatures (-20°C, 4°C, 15°C, and 25°C) were studied. The results showed that the aerobic plate count (APC), pH, total volatile basic nitrogen (TVBN), and histamine contents increased as storage time increased when the PEP and VP samples were stored at 25°C. At below 15°C, the APC, TVBN, pH, and histamine levels in PEP and VP samples were retarded, but the VP samples had considerably lower levels of APC, TVBN, and histamine than PEP samples. Once the frozen fish samples stored at -20°C for 2 months were thawed and stored at 25°C, VP retarded the increase of histamine in milkfish sticks as compared to PEP. In summary, this result suggested the milkfish sticks packed with VP and stored below 4°C could prevent deterioration of product quality and extend shelf-life.

Degradation of Histamine by Lactobacillus plantarum Isolated from Miso Products

Histamine is a toxic chemical and is the causative agent of food poisoning. This foodborne toxin may be degraded by the oxidative deamination activity of certain microorganisms. In this study, we isolated four histamine-degrading Lactobacillus plantarum bacteria from miso products. Among them, L. plantarum D-103 exhibited 100% degradation of histamine in de Man Rogosa Sharpe (MRS) broth containing 50 ppm of histamine after 24 h of incubation at 30°C. The optimal growth, histamine oxidase, and histamine-degrading activity of L. plantarum D-103 were observed in histamine MRS broth at pH 7.0, 3% NaCl, and 30°C. It also exhibited tolerance to broad ranges of pH (4 to 10) and salt concentrations (0 to 12%) in histamine MRS broth. Therefore, the histamine-degrading L. plantarum D-103 might be used as an additive culture to prevent histamine accumulation in miso products during fermentation.