Chemical characterisation, biogenic amines contents, and identification of fish species in cod and escolar steaks, and salted escolar roe products

Forty-one cod steaks, fifteen escolar steaks, and fifteen salted escolar roe products sold in Taiwan market were purchased and tested to determine the biogenic amine, histamine-forming bacteria, and identification of fish species. The levels of pH value, salt content, Aw, TVBN and APC in all samples ranged from 5.3 to 7.0, 0.7 to 5.6%, 0.80 to 0.99, 0.8 to 59.9 mg/100 g and 2.5 to 7.3 log CFU/g, respectively. None of these samples contained coliform bacteria and Escherichia coli. The average content of histamine in all samples was less than 5 mg/100 g US Food and Drug Administration guideline value. Nine histamine-forming bacterial strains isolated from cod, escolar, and salted escolar roe samples produced 2.0-62.3 ppm of histamine in trypticase soy broth (TSB) supplemented with 1.0% l-histidine (TSBH). Assay of DNA direct sequence and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) revealed that mislabeling rate of 41 cod steaks was 31.6% (13/41). Among them, 7 samples (17%) and 6 samples (14.6%) were identified as Ruvettus pretiosus (oilfish) and Reinhardtius hippoglossoides (Greenland halibut), respectively. In addition, most of escolar steaks and salted escolar roe products were identified as Lepidocybium flavobrunneum (escolar), while other samples were identified as R. pretiosus.     

A survey of histamine content in seafood sold in markets of nine countries

Histamine content was investigated in some fresh scombroid fish including tuna (Thunnus spp), mackerel (Scomber Japonicus) etc, and non-scombroid fish including mahi–mahi (Coryphaena hippurus), sardine (Sardina pilchardus), herring (Clupea harengus) etc, and fish products (sauce, dried fish) which came from Fiji, Germany, the Netherlands, Norway, Thailand, Cambodia, the Philippines, Japan and China. Histamine was detected in 35 of the 159 fish samples tested for a detection rate of about 21%. Fish samples exceeding 50 ppm histamine occurred in about 9% of the samples with 5 samples exceeding 500 ppm of which 2 were above 1000 ppm. Fish sold in markets in some countries may cause a histamine risk to consumers while other countries may have the necessary controls in place.     

Histamine level and histamine-forming bacteria in dried fish products sold in Penghu Island of Taiwan

Forty-six dried fish products sold in retail markets in Penghu Islands, Taiwan were purchased and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, water content, water activity (Aw), total volatile basic nitrogen (TVBN), aerobic plate count (APC), Escherichia coli and total coliform (TC) in all samples ranged from 5.60 to 7.57, 1.8% to 27.1%, 19.32% to 61.90%, 0.63 to 0.92, 10.41 to 168.56 mg/100 g, 3.18 to 9.28 log CFU/g, <3 to 210 MPN/g and <3 to >1100 MPN/g, respectively. There had 30.4% of the tested dried fish products to contain histamine level more than 5 mg/100 g of FDA guideline for scombroid fish and/or product. Among them, all of the nine samples of Selariodes leptolepis had the highest histamine content of 6.31–47.90 mg/100 g. Thirteen histamine-producing bacterial strains isolated from tested samples produced 8.7–531.2 ppm of histamine in trypticase soy broth supplemented with 1.0% l-histidine (TSBH). Among these histamine-producing bacteria, Enterobacter aerogenes (one strain) isolated from S. leptolepis sample was proven to be a prolific histamine-former.     

Modelling the recovery of Listeria monocytogenes in high pressure processed simulated cured meat

Current EC regulations require that ready-to-eat products should not exceed the limit of 100 CFU/g for Listeria monocytogenes throughout their shelf-life. On that basis a quantitative analysis for high hydrostatic pressure to produce safe (regarding L. monocytogenes levels) cured meat products with low salt concentration has been developed. An extended Doehlert design for a range of pressures (450–800 MPa), sodium chloride (0–34.9 g/L) and sodium nitrite (mg/L) concentrations, as well as the resulting a_w (0.955–0.987) levels, was generated. Based on the logistic regression analysis, it appears that the recovery of L. monocytogenes is influenced by the applied pressure, the storage time and the synergistic effect of pressure and a_w on inhibiting microbial recovery. This means that the sodium chloride and sodium nitrite concentrations tested indirectly affected the recovery of Listeria and consequently the shelf-life of the product by regulating the a_w levels. The lower the water activity, the less the inactivation and recovery induced by pressure immediately and during storage, respectively.     

Effect of starter cultures on microbial ecosystem and biogenic amines in fermented sausage

The microbial ecology of fermented sausages inoculated with different starter cultures (Pediococcus pentosaceus + Staphylococcus xylosus, batch A; Lactobacillus farciminis + Staphylococcus saprophyticus, batch B) was studied by culture-dependent and independent methods. The concentration of biogenic amines, pH and a_w (water activity) were followed. The starter B can inhibit indigenous bacteria effectively judged by traditional microbiological method and PCR-DGGE fingerprint. There was no statistical difference in pH between batches A and B at 2 days when substantial amounts of BAs were produced, while the amounts of histamine, putrescine, cadaverine and tyramine in batch B was lower than in batch A significantly (P < 0.001). As a result, the starter cultures which can complete, grow well and inhibit amine-positive bacteria play an important role in reducing the production of BAs during ripening of fermented sausage.     

Bacteriological quality and histamine-forming bacteria associated with fish meats and environments in HACCP and non-HACCP fish processing factories

Twenty fish meats and 21 environmental surface samples obtained from a Hazard Analysis Critical Control Points (HACCP) fish processing factory and two non-HACCP fish processing factories in Pingtung, southern Taiwan were tested to determine the hygienic quality and histamine-forming bacteria. The levels of aerobic plate count (APC), total volatile basic nitrogen and total coliform in fish samples obtained from the HACCP factory were significantly lower than those of fish samples obtained from the two non-HACCP factories. The average content of the eight biogenic amines in HACCP fish samples was less than 1.0 mg/100 g, while that in non-HACCP fish samples was less than 1.5 mg/100 g. In environmental surface samples, the average levels of ATP bioluminescence and APC (swabbing method) of HACCP processing factory were significantly (P < 0.05) lower than those of non-HACCP processing factories. Fifteen histamine-forming bacterial strains isolated from fish meats and environmental samples producing 2.3–561.5 ppm of histamine in trypticase soy broth supplemented with 1.0% l-histidine (TSBH), belonged to Enterobacteriaceae (thirteen strains) and Staphylococcus spp. (two strains).     

Histamine content and histamine-forming bacteria in mahi-mahi (Coryphaena hippurus) fillets and dried products

Forty-two mahi-mahi fillets and 17 dried products sold in retail markets in Taiwan were tested for histamine and histamine-forming bacteria. The levels of pH, salt content, water content, Aw, TVBN, APC, TC and Escherichia coli in mahi-mahi fillet samples ranged from 5.6 to 6.5, 0.05 to 2.44%, 70.9 to 82.8%, 0.95 to 0.99, 5.9 to 23.5 mg/100 g, 3.1 to 7.0 log CFU/g, <3 to 1650 MPN/g and <3 to 45 MPN/g, respectively. The levels of pH, salt content, water content, Aw, TVBN, APC, TC and E. coli in dried mahi-mahi samples ranged from 5.7 to 6.4, 0.63 to 20.13%, 7.1 to 42.9%, 0.51 to 0.85, 21.4 to 133.9 mg/100 g, 3.6 to 8.7 log CFU/g, <3 to 5900 MPN/g and <3 to 2500 MPN/g, respectively. The average content of various biogenic amines in fillets samples was less than 0.3 mg/100 g. Four of the 17 dried samples (23.4%) had histamine levels greater than the FDA guideline of 5 mg/100 g for scombroid fish and/or product with one of them containing 68.15 mg/100 g of histamine, which is greater than the 50 mg/100 g hazard action level. Eight histamine-producing bacterial isolates, capable of producing 12.6 ppm–562 ppm of histamine in trypticase soy broth supplemented with 1.0% l-histidine (TSBH), were identified as Raoultella ornithinolytica (three isolates), Pantoea agglomerans (two isolates), Proteus vulgaris (two isolates) and Enterobacter amnigenus (one isolate), by 16S rDNA sequencing with PCR amplification.     

Effect of water activity and temperature on the growth of Aspergillus flavus,the expression of aflatoxin biosynthetic genes and aflatoxin production in shelled peanuts

The contamination of peanuts with Aspergillus flavus and subsequent aflatoxins is considered to be one of the most serious safety problems in the world. Water activity (a_w) and temperature are limiting factors for fungal growth and aflatoxins production during storage. To optimize the practical storage parameter, the effect of a_w (0.85–0.99) and temperature (15–42 °C) on fungal growth, aflatoxin production and the expression of aflatoxin biosynthetic and regulatory genes in shelled peanuts was investigated. A. flavus grew at a lower rate when temperature ≤20 °C or a_w ≤ 0.85. For the growth of A. flavus in shelled peanuts, the optimum conditions were a_w was 0.98, and the optimum temperature was 37 °C. The maximum amount of AFB₁ in peanuts was obtained at 28 °C and a_w 0.96. Real-time analysis showed that 16 of 25 genes had highest expression levels at 28 °C under a_w 0.92, while 9 genes had highest expression levels at 37 °C under a_w 0.92. Compared with 37 °C, all aflatoxin biosynthetic pathway genes were down-regulated at 42 °C. All the pathway genes and laeA were up-expressed at a_w of 0.96 under 28 °C, compared to a_w 0.99. Furthermore, there was a good positive correlation between the ratio of aflS/aflR and AFB₁ production. The expression of laeA was also positively correlated with AFB₁ production while the expression of brlA was correlated with the A. flavus growth. The results of this study suggest that AFB₁ production in peanut kernels can occur over a wider range of a_w × temperatures levels compared to formula media and peanut media. Previous studies have showed that AFB₁ could not be produced on formula media at 37 °C without the expression of most aflatoxin structural genes. But, in the un-autoclaved shelled peanuts, high concentration of AFB₁ was produced at 37 °C with up-regulation of some aflatoxin biosynthetic genes. From a food safety point of view, the results can be used to optimize certain food technological processes and develop prevention strategies to control such carcinogenic natural metabolites in grains (such as peanuts, maize and rice) and derived products.     

A simple and rapid method for histamine analysis in fish and fishery products by TLC determination

A simple and rapid thin-layer chromatography (TLC)-densitometry method for histamine analysis in fish and fishery products was established. Histamine was extracted from seafood with 80% ethanol. The sample extracts and standard solutions of histamine were applied to cellulose TLC plate and developed by ascending chromatography with ammonia–ethanol 1:3 (v/v) as mobile phase. Histamine was visualized with pauly’s reagent, the intensity of the colored spots was digitized and calculated by image processing method software, Lane & Spot Analyzer (ATTO, Tokyo, Japan). Successful separation of histamine from other (imidazole compounds) pauly’s reagent-positive components in 80% ethanol fish extracts was achieved. The linearity of the histamine estimation using this method was good within the range from 30 ng to 1000 ng of histamine (r² = 0.9997). Histamine can be satisfactorily detected and completely separated from histidine, 4-methyl-imidazole and other pauly’s reagent-positive compounds. This method does not need expensive instrument, any tedious pretreatment to eliminate potential interference other imidazole compounds such as histidine or carnosine. It is also less reagents compared with HPLC method. Moreover, it is a simple, rapid, sensitive, reproducible. Therefore this method is suitable for monitor of histamine in multiple fish and fishery products simultaneously that contain as little as 20 ppm histamine (2.0 mg/100 g).     

Growth potential of Listeria monocytogenes in traditional Austrian cooked-cured meat products

European Union legislation limits for Listeria monocytogenes in ready-to-eat foods are based on whether or not foods favour the multiplication of this bacterium. The latter is defined by criteria for water activity (a_w), pH and shelf-life. We studied a peculiar group of traditional Austrian meats implicated in foodborne listeriosis made from cured cooked comminuted meat with gelatin/aspic (Presswurst), blood (Blutwurst) or fat as a binder (Leberpaté, Streichwurst, Zwiebelstreichwurst). Average pH values were 5.74 ± 0.45; 6.62 ± 0.31; 6.18 ± 0.36; 6.19 ± 0.15; 6.28 ± 0.04 for Presswurst (n = 15), Blutwurst (n = 15), Leberpaté (n = 10), Streichwurst (n = 18) and Zwiebelstreichwurst (n = 3), respectively. Corresponding a_w values were: 0.968 ± 0.004; 0.965 ± 0.004; 0.961 ± 0.005; 0.963 ± 0.003 and 0.957 ± 0.005. There were no statistically significant differences of pH among spreadable meat products. Presswurst had significantly lower pH values, but a significantly higher level of lactic acid bacteria. With the exception of one low pH Presswurst sample, all foods under study would favour the growth of L. monocytogenes. In a 9 days challenge test, Blutwurst showed a strong potential for supporting L. monocytogenes growth (2.4–4.6 log). In contrast, Presswurst was not able to support growth in all temperatures tested. A pH vs. a_w chart was designed delineating the growth/no-growth border (defined as 0.43 log increase over 216 h) at 2, 4 and 8 °C. For a given sample (i.e. a pH/a_w data pair), it could be easily assessed if the product would likely be “safe” for 9 days at temperatures of <2 °C, 2–4 °C etc. by simply plotting the data point in the chart. Agreement of predicted bacterial growth and multiplication in food samples was studied in one Presswurst and three Blutwurst products. In our conservative approach, additional anti-listerial effects of lactic acid bacteria and food additives were not considered, but could be integrated, if desired. The usefulness of such a pH vs. a_w chart for small businesses, the competent authority and for didactic purposes is discussed.     

Biogenic amines,histamine and label of dressed fried fish meat products in Taiwan

One hundred and four dressed fried fish meat products, including 44 packaged and 60 unpackaged, were purchased from supermarkets and retail outlets, respectively in Taiwan between September 2002 and March 2003. The levels of histamine and biogenic amines and labeling condition were determined. It was found that 9%, 11%, 2%, and 18% of the packaged products did not meet the labeling requirement of ingredient, expiry date, address and telephone information, and nutrition information, respectively. Although no sample exceeded histamine level of 500 ppm, all packaged products and 24 out of 60 unpackaged ones showed detectable amounts of histamine. Fourteen samples of packaged products and two samples of unpackaged ones had histamine above 50 ppm, with level ranged from 53 to 87 ppm and from 75 to 108 ppm, respectively. The biogenic amines content of packaged product was higher than unpackaged one with average level of 725 ± 252 ppm and 595 ± 181 ppm, respectively. The dressed fried fish meat products with histamine level above 50 ppm sold in Taiwan should be considered.     

Survival of Salmonella spp. in low water activity chicken base paste and powder formulated at different salt levels

Dry flavor ingredients such as black pepper and hydrolyzed vegetable protein (HVP) have been frequently recalled from the supply chain due to contamination with Salmonella. These spices are commonly used in preparation of savory meat flavor bases. This study evaluated the effect of various salt levels on the survival of Salmonella spp. in chicken bases formulated with pepper and HVP, in either paste or powder form. The salt content (% w/w), a_w and pH for regular-salt, 45% reduced-salt and 90% reduced-salt paste formulations were 33.0, 0.686, 5.75; 18.2, 0.691, 5.85; and 3.5, 0.751, 5.96, respectively, and powder formulations were 34.0, 0.254, 6.15; 18.5, 0.290, 6.28; and 3.1, 0.301, 6.50, respectively. To mimic natural contamination, a dry sand inoculation technique was used to prepare the samples. A five serovar cocktail of Salmonella was used and the final inoculation level in the samples was 7.5 ± 0.2 log CFU/g. Inoculated paste samples were stored at 21 °C for up to 12 weeks, and up to 42 weeks for powder formulations. Salmonella counts did not increase in either treatment during storage. The effect of salt levels on Salmonella survival was insignificant. There was a 5.2 ± 0.4 log reduction in paste formulations by 3 week. However, low Salmonella counts (<1.0 log CFU/g) were detected in samples from 6 to 12 weeks. In powder formulations, minimal log reductions of 1.3 ± 0.1 were observed over 42 weeks. When preparing a food product that does not undergo a kill step, it is necessary to ensure the absence of Salmonella in the ingredients, as well as practicing strict adherence to good manufacturing practices including proper environmental monitoring and sanitation in food processing. Furthermore, adequate consumer cooking instructions are important to ensure proper Salmonella lethality during preparation of reconstituted dry products.     

Listeria monocytogenes in ready-to-eat vacuum and modified atmosphere packaged meat and fish products of Estonian origin at retail level

The prevalence, counts and genetic diversity of Listeria monocytogenes in ready-to-eat (RTE) vacuum and modified atmosphere packaged meat and fish products was studied in Estonia. Within two consecutive years 370 RTE food samples were collected at retail level from which 11% were found to be positive for L. monocytogenes. Contamination was higher among RTE fish products (17%) than in RTE meat products (6%). Generally, the counts of L. monocytogenes in positive products remained under ten colony forming units (CFU) per gram of product. Only 1.6% of the RTE meat and fish products contained L. monocytogenes in range of 10–100 CFU/g and 0.3% more than 100 CFU/g at the end of shelf-life. The food category containing highest L. monocytogenes prevalence was RTE lightly salted fish products with the prevalence of 32%. Only one (0.3%) RTE food sample exceeded the 100 CFU/g food safety criterion set out in the EU Regulation 2073/2005. Pulsed-field gel electrophoresis (PFGE) characterization of the isolates showed an overall similarity higher than 70%, and nine clusters based on 100% similarity were revealed. PFGE genotyping revealed that the few predominant pulsotypes were associated with particular food plants.     

Growth of Listeria monocytogenes in salmon roe – A kinetic analysis

The objective of this study was to investigate the growth kinetics of Listeria monocytogenes in unsalted and salted (3%) salmon roe. Growth curves, developed using inoculated samples incubated at constant temperatures between 5 and 30 °C, were analyzed by curve-fitting to the Huang and Baranyi models using the USDA IPMP 2013. The experimental results showed that L. monocytogenes in salted samples exhibited approximately 40% longer lag times than the cells in unsalted samples under the same temperature condition, while the rates of bacterial growth were not affected by the addition of salt. The Ratkowsky square-root (RSR) model, Huang square-root (HSR) model, and an Arrhenius-type model were all shown suitable for evaluating the effect of temperature on specific growth rates. The estimated nominal minimum growth temperature in the RSR model was −0.5 °C, whereas the minimum growth temperature in HSR model was 2.57 °C. The HSR models may be more suitable for describing the temperature effect in salted salmon roe. The lag times of L. monocytogenes were found to change log-linearly with the specific growth rates. The mean h₀ in the Baranyi model was 0.742 in unsalted samples and 1.193 in salted samples, and did not appear to change with temperature in a systematic manner. In summary, kinetic models were developed for examining the effect of temperature on growth of L. monocytogenes in unsalted and salted salmon roe samples. The results may be used by the food industry and regulatory agencies to estimate the growth of L. monocytogenes in salmon roe, and to conduct risk assessments of this microorganism.     

Inactivation of Anisakis pegreffii larvae in anchovies (Engraulis encrasicolus) by salting and quality assessment of finished product

There is an increasing reporting of Anisakiasis in humans at the world level and this disease has become a concern for the public health and for the fish and derived product trade. Humans acquire the infection by the ingestion of live larvae present in raw or almost raw (e.g., marinate, salted) fish products if the processing is insufficient to devitalize the worms. The aim of this study was to asses a dry salting process in killing Anisakis pegreffii larvae in naturally infected European anchovies (Engraulis encrasicolus) and to evaluate the quality assessment. The results show that a dry salting process with a salt concentration of 21% in all parts of the anchovy fillets devitalize A. pegreffii larvae in a 15 day period. The finished product showed a good panel acceptance and anchovies reached a good quality grade.     

Occurrence and antibiotic resistance profiles of Listeria monocytogenes isolated from seafood products and market and processing environments in Iran

This study was designed to determine the occurrence of Listeria monocytogenes in popular seafood products and their market and processing environments. The frequency of L. monocytogenes contamination was found to be 4.83% in raw and 14.5% in RTE seafood products. In raw products, the prevalence of L. monocytogenes was significantly higher (P < 0.05) in freshwater fish (11.4%) than in seawater fish (1.80%) and shrimp (1.69%). Cold-smoked fish had the highest frequency of L. monocytogenes contamination among the RTE products. The microbial load of L. monocytogenes in seafood products was in the range of <0.3 to 1100 MPN/g; and did not exceed 100 MPN/g in most of the examined samples. The incidence of L. monocytogenes in environmental and personnel samples was 17.1% and 16.2% in markets, and 21.3% and 18.2% in processing plants, respectively. It was found that contamination of processed fish fillets and shrimp flesh with L. monocytogenes mainly originated from the processing environments, rather than the raw materials. In addition, the implemented cleaning procedures were insufficient to eliminate L. monocytogenes from the market and processing environments. Serological examinations revealed that serotype 1/2a (45.7%) was the predominant serotype of L. monocytogenes followed by 4b (40.3%), 1/2c (5.39%), 1/2b (4.68%), and 4c (3.96%). Regarding seasonal variability, 1/2a was the dominant serotype during warm seasons, whereas 4b was the most prevalent serotype during cold seasons. The isolates of L. monocytogenes were highly resistant to penicillin, ampicillin, tetracycline, and vancomycin. The results indicate that prevalence of L. monocytogenes serotypes 1/2a and 4b, which are associated with foodborne outbreaks of human listeriosis; and their resistance to commonly used antibiotics for treatment of human listeriosis could be a public health concern.     

Aspergillus flavus growth response to cinnamon extract and sodium benzoate mixtures

The effects of selected combinations of cinnamon extract (CE, 0, 50, 100, 200, 400 or 800 ppm) and sodium benzoate (NaB, 0, 12.5, 25, 50, 100, 200, 400 or 800 ppm) on the growth response of Aspergillus flavus inoculated on potato-dextrose agar (PDA) adjusted to 0.98 a_w and pH 3.5 or 4.5 were evaluated for 30 days. Minimal inhibitory concentrations (MIC) were determined, transformed into fractional inhibitory concentrations (FIC) and a FIC_index was computed. Cinnamon extract MIC was 200 ppm and not affected by pH, whereas for NaB a pH reduction from 4.5 to 3.5 reduced the MIC from 800 to 400 ppm. At pH 3.5 additive mixtures included 200 ppm of NaB, whereas at pH 4.5 these mixtures exhibited a synergic effect (FIC_index = 0.75). Mixtures of CE and NaB are promising antifungal agents.     

Inhibition of biogenic amine formation in a salted and fermented anchovy by Staphylococcus xylosus as a protective culture

This study was carried out to reduce biogenic amine contents in Myeolchi-jeot, a salted and fermented anchovy (Engraulis japonicus). The effects of potential starter cultures on the degradation of histamine and tyramine were determined by HPLC analysis. Out of seven potential starter cultures tested, Staphylococcus xylosus No. 0538 possessed not only the greatest capability to degrade histamine, but a detectable ability to degrade tyramine as well. In a phosphate buffer containing 0.5 mM histamine and 0.5 mM tyramine, 38.0% of the histamine and 4.4% of the tyramine were degraded by resting cells of the S. xylosus No. 0538 within 24 h. The other cultures tested had less or no effect in degrading histamine and tyramine. The S. xylosus No. 0538 was also found to produce bacteriocin-like inhibitory substance(s) and have the highest antimicrobial activity against Bacillus licheniformis strains defined as amine producers. Finally, the S. xylosus No. 0538 was used as starter culture and applied to the ripening of Myeolchi-jeot, and then overall production of biogenic amines was reduced by 16.0%, compared to control. Consequently, the findings of this study are expected to enhance the safety of not only Myeolchi-jeot but other salted and/or fermented anchovy products.     

Impact of three sterol-biosynthesis inhibitors on growth of Fusarium langsethiae and on T-2 and HT-2 toxin production in oat grain under different ecological conditions

The health-beneficial properties of oats have led to an increase in the consumption of oats and oat-based food products in recent years. Fusarium langsethiae grows on small grain cereals, especially oats and can result in contamination with type A trichothecenes (T-2 toxin (T-2) and HT-2 toxin (HT-2)) in crops pre- and post-harvest. The aim of this work was to assess the efficacy of three fungicides (fenpropimorph, prochloraz and tebuconazole) on temporal growth of two F. langsethiae strains and the accumulation of T-2 and HT-2 in oat grains, under different water activities (a_w; 0.95 and 0.98) and temperatures (15 and 25 °C). All the antifungal agents reduced growth rates when compared to controls, and this increased with increasing fungicide dose. The ranges of ED₅₀ values (mg/kg) were 65–270 for fenpropimorph, 0.25–4.2 for prochloraz, and 0.3–14 for tebuconazole. The ED₉₀ values (mg/kg) ranged from 170 to > 800, 0.5 to > 10 and 0.5 to > 15 for these three fungicides respectively. The ED₅₀ values were not statistically significantly affected by the factors a_w, temperature or strain. However, there were significant differences among the fungicides. Fenpropimorph proved less efficient that the two azoles, which do not differ significantly. In general, levels of HT-2 were higher than T-2 in all cultures regardless of environmental conditions. Overall, HT-2 concentration was always higher at 25 than 15 °C and increased from day 14 to day 21. Levels of both toxins generally decreased with increasing fungicide dose regardless of fungicide type, strain and incubation time. No toxins were detected in cultures at 0.95 a_w in the presence of any of the three fungicides. Also under wetter conditions at 0.98 a_w neither mycotoxin was found in cultures treated with prochloraz at doses >1 mg/kg (15 °C) or >3 mg/kg (25 °C) or tebuconazole at doses >6 mg/kg (15 or 25 °C). ANOVA showed that in treatments with each fungicide the factors dose, time and temperature significantly affected toxin production while there was no difference between the strains.     

Degradation of histamine by the halotolerant Staphylococcus carnosus FS19 isolate obtained from fish sauce

Histamine is found in many fermented food products and may have detrimental effects on the health of its consumers. Histamine and other amines are degraded by the oxidative deamination activity of certain microorganisms. In this study, the growth characteristics and histamine-degrading activity of a Staphylococcus carnosus FS19 isolate derived from fish sauce were investigated. This bacterium exhibits optimal growth at 35 °C, pH 8 and 9% sodium chloride when cultivated in tryptic soy broth. The histamine-degrading activity of the S. carnosus FS19 isolate was optimised at 40 °C and pH 6 in 9% buffered sodium chloride. When added to fish sauce samples, this bacterium exhibits remarkable histamine-degrading activity. The histamine concentration was reduced by approximately 15.1% and 13.8% in the fish sauce samples that contained 18% and 21% salt, respectively. However, no histamine degradation was observed in samples with a salt content greater than 21%. In addition, a slight degradation of other amines, including putrescine and cadaverine, was also observed in some of the samples. In contrast, tyramine degradation did not occur in any of the samples. Therefore, S. carnosus FS19 is a culture that could potentially reduce the histamine content of fermented fish products.