[Inhibitory effect of essential oils, food additives, peracetic acid and detergents on bacterial histidine decarboxylase].

The aim of this study is to examine whether various essential oils, food additives, peracetic acid and detergents inhibit bacterial histidine decarboxylase. Crude extract of Morganella morganii NBRC3848 was prepared and incubated with various agents. Histidine decarboxylase activity was significantly inhibited (p<0.05) by 26 of 45 compounds tested. Among the 26 agents, sodium hypochlorite completely decomposed both histidine and histamine, while peracetic acid caused slight decomposition. Histidine and histamine were stable in the presence of the other 24 agents. These results indicated that 25 of the agents examined were inhibitors of histidine decarboxylase.

[Antibacterial activity of essential oil vapor for histamine-producing bacteria].

In this study, we evaluated the antibacterial activity of essential oil vapors against histamine-producing bacteria Morganella morganii NBRC3848 and Raultella planticola NBRC3317. We measured the minimum inhibitory dose (MID) of 14 essential oils towards these two strains. Allyl isothiocyanate (AIT) and salicylaldehyde (SA) vapors showed higher antibacterial activity than the other 12 essential oil vapors. Both AIT and SA vapors suppressed growth of total aerobic bacteria and histamine-producing bacteria in bigeye tuna and mackerel meat during storage at 12°C. These vapors also inhibited histamine accumulation in bigeye tuna meat and mackerel meat. Thus, application of AIT and SA vapors is effective for preventing increase of histamine-producing bacteria and histamine formation in fish meat.

[Control of halophilic histamine-producing bacteria by using natural antimicrobials and other agents].

We have investigated the control of halophilic histamine-producing bacteria, Photobacterium phosphoerum and Photobacterium damselae by using vapor of essential oils and other agents. Three of fourteen essential oils showed high antibacterial activity against histamine-producing bacteria. Among food additives and detergents, ten of twenty-one food additives and seven of nine detergents also showed antibacterial activity. Low concentrations of sodium chloride suppressed the growth of both species. We examined the resistance of these bacteria to dryness on food contact surfaces. After 0.5 hours, no viable cells were detected. So, the bacteria were sensitive to dry conditions. These results should contribute to development of the techniques to prevent histamine food poisoning.

[Antibacterial effect of food additives and detergents against histamine-producing bacteria on food contact material surfaces].

We investigated the antibacterial activity of food additives and detergents against histamine-producing bacteria on food contact material surfaces. Based on minimum inhibitory concentration (MIC) testing with Morganella morganii NBRC3848, Raoultella planticola NBRC3317 and Enterobacter aerogenes NCTC10006, we screened nine food additives and four detergents with relatively high inhibitory potency. We prepared food contact material surfaces contaminated with histamine-producing bacteria, and dipped them into fourteen agents (100 µg/mL). Sodium hypochlorite, benzalkonium chloride, benzethonium chloride, n-hexadecyltrimethylammonium chloride and 1-n-hexadecylpyridinium chloride showed antibacterial activity against histamine-producing bacteria. We prepared low concentrations of the five agents (10 and 50 µg/mL) and tested them in the same way. Sodium hypochlorite showed high antibacterial activity at 10 µg/mL, and the other four showed activity at 50 µg/mL. So, washing the material surface with these reagents might be effective to prevent histamine food poisoning owing to bacterial contamination of food contact surfaces.

[Antimicrobial efficacy of benzyl isothiocyanate].

The potential value of benzyl isothiocyanate (BIT) vapor for food preservation was investigated in comparison with allyl isothiocyanate (AIT) vapor. Measurements of minimum inhibitory concentration (MIC) against various bacteria and fungi indicated that BIT vapor shows higher antibacterial activity towards Gram-positive bacteria, including lactic acid bacteria, than AIT vapor. BIT has a similar inhibitory effect to AIT against Gram-negative bacteria, yeast and fungi, except that it was less effective against Pseudomonas fluorescens JCM 5963. Both BIT and AIT have a strong inhibitory activity against yeast and fungi. AIT vapor suppressed growth of total aerobic bacteria in bigeye tuna meat and pork mince during storage at 10 degrees C and 30 degrees C, while BIT vapor had no effect. Also, AIT vapor strongly inhibited mycelial development of Aspergillus sojae JCM 2251 and Penicillium expansum IAM 13777 inoculated on rice cakes, while BIT vapor only slightly suppressed their growth. BIT has antimicrobial activities, but further studies are needed to establish its suitability for use in food preservation.