Halotolerant and halophilic histamine-forming bacteria isolated during the ripening of salted anchovies (Engraulis encrasicholus)

This study was performed to investigate halotolerant and halophilic histamine-producing bacteria isolated during the ripening of salted anchovies. Of the isolates obtained during the ripening of anchovies, 1.37% showed histamine-forming activity, most of them (70%) belonging to the Staphylococcus genus. S. epidermidis showed a powerful histamine-forming activity, producing more than 1,000 microg/ml in the presence of 3% and 10% NaCl. Another powerful histamine-producing bacterium isolated during the ripening of salted anchovies was S. capitis. It was able to produce about 400 microg/ml of histamine in 10% NaCl under experimental conditions. Most of these species might be expected to be found as a result of contamination of fish during capture and subsequent unhygienic handling. However, no increase in histamine content was found in any batches through the ripening process. Histamine content always was acceptable in accordance with the maximum allowable levels of histamine fixed by the Spanish and European Union regulations.

Incidence of histamine-forming bacteria and histamine content in scombroid fish species from retail markets in the Barcelona area

Incidence and diversity of histidine decarboxylating bacteria were determined in samples of tunafish, bonito and mackerel purchased at different retail markets. Histamine-forming bacteria occurred in a low proportion and always accounted for less than 0.1% of the total bacterial load in the fish samples studied. Similarly, histamine content in fish samples also was low ( < 25 ppm) and all of them met current histamine standards established by the European Union. Histamine was found in 83.3% of the tested tunafish samples with an average of 8.9 ppm. In contrast, none of mackerel samples and only 2 out of 12 of bonito showed detectable amounts of histamine. Morganella morganii and Klebsiella oxytoca were the most active histamine formers under experimental conditions, and produced on average 2765 and 1415 ppm of histamine, respectively, after incubation at 37 degrees C for 18 h. Some new histamine formers, such as Plesiomonas shigelloides, Enterobacter intermedium, Serratia marcescens, Serratia plymuthica and Serratia fonticola, have been identified. Especially Plesiomonas shigelloides would have an important role within histidine decarboxylating bacteria because it was the sole histamine former isolated that has frequently been associated with the marine aquatic environment. However, only 8-340 ppm of histamine was formed by these strains in laboratory trials.

Determination of histamine in fish using an enzymic method

The present paper describes a quick and simple enzymic method for evaluating histamine content in fish. After preparing a perchloric acid extract, it was neutralized to pH 6.8 with KOH. The action of a diamine oxidase on the histamine caused the formation of hydrogen peroxide. The addition of a second enzyme, a peroxidase, in the presence of hydrogen peroxide and a chromogen (leuco crystal violet) in reduced form (colourless) facilitated its oxidation into crystal violet (coloured). Following a two-hour incubation period, absorbance was measured at 596 nm. The correlation between histamine level and absorbance was acceptable in the concentration range from 3 to 30 mg/kg of histamine (r = 0.9946; p < 0.001). The accuracy of the method, expressed by CV, varied between 2.6% and 4.9%, and the recovery between 95.7% and 100.1%, depending on the concentration of analyte in the sample. The diamine oxidase used was very selective in relation to the histamine. Only the presence of tyramine, when histamine concentration was low (< 10 mg/kg), tended to interfere to a slight degree in the technique. Using a regression analysis, no statistically significant differences were found between the results obtained from the analysis of 18 tuna fish samples by HPLC and the enzymic method (r = 0.9867; p < 0.001).

Protein hydrolysis and proteinase activity during the ripening of salted anchovy (Engraulis encrasicholus l.). A microassay method for determining the protein hydrolysis

The protein hydrolysis and proteinase activity during the ripening of salted anchovy were studied. A rapid, simple, and inexpensive microassay method for determining the protein hydrolysis by trinitrobenzenesulfonic acid (TNBS) has been developed. A linear relationship was observed between proteolysis determination by the TNBS method and ripening time in the fish muscle and in the brine (r = 0.99). A linear relationship was also observed between the ratio nonprotein nitrogen and total nitrogen (NPN/TN) and ripening time (r = 0.98). Proteolysis by the TNBS method and NPN/TN determination could be considered as objective methods to follow and assess the ripening process of an anchovy. A value of proteolysis by the TNBS method of 240 mM leucine in the fish muscle and/or 200 mM leucine in the brine would indicate the ripening point. The crude enzyme prepared of fish muscle and brine showed that alkaline proteinases dominate.

Evaluation of three decarboxylating agar media to detect histamine and tyramine-producing bacteria in ripened sausages

Histidine- and tyrosine-decarboxylase activity of 175 strains of bacteria isolated from eight retail samples of Spanish ripened sausages was tested in three decarboxylating agars (Niven medium, Joosten and Northolt medium and modified decarboxylating agar of Maijala) and confirmed by an enzymic method (histamine) and thin-layer chromatography (tyramine). Enterobacteria and pseudomonads showed the highest percentage of positive responses to histamine and tyramine in the three decarboxylating agars, but only enterobacteria were subsequently confirmed as histamine-producing. Confirmed tyramine-producing strains were all identified as enterococci or lactic acid bacteria. The medium described by Joosten and Northolt was more sensitive and faster at detecting tyramine-producing microorganisms. However, all three media failed to detect one histamine-positive strain of lactic acid bacteria used as a control.

New approach for the removal of mature biofilms formed by wild strains of Listeria monocytogenes isolated from food contact surfaces in an Iberian pig processing plant

One of the main objectives of the food industry is to guarantee food safety by providing innocuous food products. Therefore, this sector must consider all the possible biotic or abiotic contamination routes from the entry of raw materials to the release of the final product. Currently, one important problem in this regard is the presence of biofilms on food contact surfaces which can transmit pathogens such as L. monocytogenes. In industrial conditions biofilms are found in a mature state, so it is essential that when carrying out removal effectiveness studies in vitro the tests are realized with models that produce these structures in a similarly mature state. The main objective of this study was to evaluate the effectiveness of an alternative treatment (i.e. enzymatic detergent that include natural antimicrobial agents) and a conventional treatment (i.e. chlorinated alkaline) for the elimination of mature L. monocytogenes biofilms. The results showed a cell detachment from the formed mature biofilms with an effectivity of between 74.75%-97.73% and 53.94%-94.02% for the enzymatic treatment and the chlorinated alkaline detergent, respectively. On a qualitative level, it was observed that the dispersion in the structure was much higher for the enzymatic treatment than for the chlorinated alkaline, which continued to show obvious structure integrity. All this leads to the conclusion that treatments with an enzymatic detergent have a significantly greater impact on the removal of mature L. monocytogenes biofilms, although a further disinfection process would be needed, enhancing even more the treatment effectivity. This may imply that the industrial approach to addressing this problem should be modified to include new perspectives that are more effective than traditional ones.