Histamine Production by Morganella morganii in Mackerel, Albacore, Mahi-mahi, and Salmon at Various Storage Temperatures

Morganella morganii was studied for its growth and histamine formation in mackerel, albacore, mahi‐mahi, and salmon stored at various temperatures from ‐30 °C to 37 °C. The optimal temperature for histamine formation was 25 °C. Mackerel, albacore, and mahi‐mahi were shown as good substrates for histidine decarboxylation by M. morganii at elevated temperatures (> 15 °C). M. morganii inoculated in all fish species including salmon formed histamine above the FDA guideline. Their growth was controlled by cold storage of the fish at 4 °C or below, but histamine formation was controlled only by frozen storage. Although histamine was not detected in any frozen samples, it accumulated rapidly in the previously frozen fish stored at 25 °C.     

A rapid method for detection of histamine-producing bacteria

A method for detecting histamine-producing bacteria is described. The method is based on automated conductance measurements in a histidine-containing medium (HDB) incubated at 25°C, with a large and distinct increase in the conductance being indicative of the presence of histamine-producing bacteria. An initial low pH (5.5) is optimal for measuring the histidine decarboxylating activity of Morganella morganii, but clear results are obtained at higher pH values (6.0–7.0) as well. It is shown that the histidine decarboxylating activity of M. morganii is unaffected by the presence of non-histamine producing bacteria. Using this new method in the examination of mackerel spoiled at high temperatures, the results obtained indicated the presence of large amounts of histamine-producing organisms. These were subsequently isolated and identified as belonging to the family Enterobacteriaceae.     

Bacterial Growth and Histamine Production on Vacuum Packaged Tuna

Vacuum and nonvacuum packaged samples of tuna or tuna spiked with Klebsiella oxytoca T₂, Morganella morganii JM or Hafnia alvei T₈ were stored at 2°C and 10°C and examined for bacterial growth and histamine production on day 3, 6, 10 and 15. Unlike those stored at 2°C, tuna samples stored at 100°C showed significant bacterial growth over time and had high levels of histamine (>200 mg/100g tuna on day 15). Vacuum packaging did not show any beneficial effect in controlling bacterial growth and histamine production on tuna samples at these two temperatures. Low temperature storage was more effective than vacuum packaging in controlling histamine production by the bacteria tested.     

Bacterial Histamine Production as a Function of Temperature and Time of Incubation

Optimal temperature, lower temperature limit, extent, and rate of histamine production in a tuna fish infusion broth (TFIB) varied for the strains of Proteus morganii, Klebsiella pneumoniae, Hafnia alvei, Citrobacter freundii, and Escherichia coli studied. P. morganii and K. pneumoniae produced large quantities of histamine in a relatively short incubation period (<24 hr) at 15°C, 30°C, and 37°C; production was fastest at 37°C. H. alvei, C. freundii, and E. coli produced toxicologically significant levels of histamine (>2500 nmoles/ml) only at 30°C and 37°C on prolonged incubation (≥48 hr). At 72 hr of incubation, optimal temperature for histamine production was 37°C for E. coli and C freundii; 30°C for P. morganii strain 110SC2, K. pneumoniae, and H. alvei; and 15°C for P. morganii strain JM. The lower temperature limits for production of toxicologically significant levels of histamine in TFIB were 7°C for K. pneumoniae; 15°C for both P. morganii strains; and 30°C for H. alvei, C. freundii, and E. coli.     

A Viscoelastic Model for Honeys Using the Time–Temperature Superposition Principle (TTSP)

The viscoelastic parameters storage modulus (G′) and loss modulus (G″) were measured at different temperatures (5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, and 40 °C) using oscillatory thermal analysis in order to obtain a viscoelastic model for honey. The model (a 4th grade polynomial equation) ascertains the applicability of the time–temperature superposition principle (TTSP) to the dynamic viscoelastic properties. This model, with a regression coefficient higher than 0.99, is suitable for all honeys irrespective their botanical origin (monofloral, polyfloral, or honeydew). The activation energy (relaxation“ΔH _a” and retardation “ΔH _b”), and the relaxation modulus fit the model proposed. The relaxation modulus has a 4th grade polynomial equation evolution at all temperatures. The moisture content influences all the rheological parameters.     

Histamine accumulation and histamine-forming bacteria in Indian anchovy (Stolephorus indicus)

Accumulation of histamine, trimethylamine (TMA), and total volatile base nitrogen (TVB-N), as well as microbial population incidence in Indian anchovy (Stolephorus indicus) during storage in ice and at 15 and 35 °C were investigated. Histamine was as low as 1.9 mg/100 g in 15 days at ice storage, but it increased to 19.0 mg/100 g after 32 h at 15 °C. Histamine rapidly increased to 25.4 mg/100 g when stored at 35 °C for 8 h. TVB-N and TMA began to sharply increase after 11 days in ice storage, but abruptly increased after 16 and 8 h of storage at 15 and 35 °C, respectively. A high number of Enterobacteriaceae (10¹⁰–10¹¹ cfu/g) was detected and shown to be the dominant group of microbial flora during spoilage of Indian anchovy at both 15 and 35 °C. A total of 153 bacterial strains were selected from the prescreening step using various selective media. Only 75.8% of these selected isolates showed a positive reaction in Niven's differential medium, and 27.6% of the positive isolates were true histamine formers when confirmed by the enzymatic method. Prolific histamine formers were identified as Morganella morganii, Proteus vulgaris, and Enterobacter aerogenes, and produced high histamine content of 104.1–203.0 mg/100 ml. Optimum growth and histamine production of selected strains of these three species was at 35 °C in histamine evaluation broth (HEB) containing 0.5% NaCl, pH 5. E. aerogenes produced the highest histamine of 500 mg/100 ml at the optimum condition. All studied strains did not produce histamine at ⩾10% NaCl.     

Histamine, Cadaverine and Putrescine Forming Bacteria from Ripened Spanish Semipreserved Anchovies

Histidine decarboxylase activity and production of putrescine and cadaverine were assessed in 200 bacterial isolates from ripened semipreserved Spanish anchovies. Highest levels of histidine decarboxylase activity were observed in Morganella morganii, with 2336.74 ± 356.32 ppm of histamine, produced in laboratory media, after 24 hr incubation at 37°C. Microorganisms producing histamine also produced detectable putrescine and cadaverine. The Niven medium was used to evaluate the 200 isolates for histidine decarboxylase activity, after incubation 24 hr at 37°C. An enzymic technique was used to distinguish false positives and to quantify bacterial histamine levels. The number of microorganisms was the most important factor in the accumulation of histamine.     

The effect of temperature upon the longevity,fecundity and circannual development of Anthrenus sarnicus Mroczkowski (Coleoptera: Dermestidae)

Eggs of Anthrenus sarnicus Mroczkowski, laid at 25°C and placed at temperatures ranging from 15 to 32.5°C when 0–1 day old, hatched over the range 20–30°C, incubation taking about 11 days at 30°C and about 25 days at 20°C. Reduction in relative humidity to as low as 25% at 25°C did not affect the duration of the egg period but egg fertility was slightly reduced. When eggs were laid in the conditions at which they were to hatch the range was lower (15–25°C) than when they were laid at 25°C.When bred on a mixture of fishmeal, yeast and cholesterol in the dark at 65% r.h. development took approx 1 yr at both 20 and 25°C. At 15°C, some larvae also took just over 1 yr to develop and others took approx 2 yr. There was a little evidence to suggest the possibility of some larvae taking approx 3 yr.Adults laid eggs at temperatures from 15 to 30°C, but some pairings at all temperatures were infertile. The mean pre-oviposition period at 15°C was 30 days reducing to about 14 days at higher temperatures. The mean oviposition period fell from 21 days at 15°C to 5 days at 30°C and during this period 30–40 eggs were laid at 15–25°C but fewer than 20 at 30°C. There was a post-oviposition period of about 10 days. Total longevity of males averaged 53 days at 15°C and 18 at 30°C. Adult life for laying females averaged 66 days at 15° reducing to 30 days at 30°C; non-laying females lived a little longer.     

Increased Aflatoxin Production by Aspergillus parasiticus Under Conditions of Cycling Temperatures

The effects of cycling temperatures (5°C for 12 hr and 25°C for 12 hr) on aflatoxin production by Aspergillus parasiticus NRRL 2999 in yeast extract sucrose (YES) medium were studied. Cycling temperatures, after preincubation at 25°C for various times, resulted in more aflatoxin B₁, G₁, and total aflatoxin production than did constant incubation at either 25°C, which is generally considered to be the optimum for aflatoxin production, or 15°C, which is the same total thermal input as the 5-25°C temperature cycling. With increased preincubation time at 25°C, toxin production increased and the lag phase of growth was shortened or not evident. Cultures that were preincubated at 25°C for 1, 2, and 3 days prior to onset of temperature cycling showed the greatest increase in maximum aflatoxin production over the 25°C and 15°C constant temperatures. Cultures that were not preincubated at 25°C but subjected to constantly fluctuating temperatures produced maximum amounts of aflatoxin equivalent to cultures incubated at a constant 25°C. The maximum aflatoxin production at all temperatures studied occurred during the late log phase of growth and at pH minimums. Aflatoxins were found in higher concentrations in the broth than the mycelia under temperature cycling conditions, at 15°C, and at 25°C during the first 21 days of incubation, whereas greater amounts of toxin were retained in mycelium at 25°C in the later incubation period (28-42 days).     

Inactivation ofEscherichia coliinoculated in liquid whole egg by high hydrostatic pressure

The resistance ofEscherichia coliin liquid whole egg was studied at several pressures (300, 350, 400 and 450MPa), temperatures (50, 20, 2 and –15°C) and times (5, 5+5, 10, 5+5+5, 15min). The highest reduction was obtained at 50°C (about 7log₈units). At 20 and –15°CE. coliwas more resistant to pressure than at 50 and 2°C. The intermittent treatments were more effective than continuous treatments at lower pressures (350MPa). The destruction increases upon increasing the pressure and the time treatment. Survivor curves were studied at 400MPa for two temperatures (20 and 2°C) and different times (0–60min), obtaining a decimal reduction time of 14.1min at 20°C and 9.5min at 2°X.     

Effect of Sodium Erythorbate on Residual Nitrite, pH and Bacterial Growth in Liver Sausage Formulated with Different Levels of Mechanically Separated Pork

Some microbiological, chemical, and physical characteristics of liver sausage formulated with 0, 25, 50, and 75% mechanically separated pork (MSP), 156 ppm sodium nitrite and 0 or 550 ppm sodium erythorbate were studied during refrigerated storage (5°C, 6 days) and subsequent elevated-temperature holding (20–24°C, 48 hr). Growth of inoculated Clostridium sporogenes was inhibited by 156 ppm nitrite in all sausages even after 48 hr at 20–24°C, regardless of MSP level. Growth of aerobic mesophiles and facultative anaerobes at 20–24°C was also inhibited in sausage formulated with 156 ppm nitrite and 550 ppm erythorbate. Erythorbate addition and increased MSP levels resulted in higher Hunter a color values. Residual nitrite, pH values, and total iron content of liver sausage increased with increasing MSP content.     

Quantifying phosphine penetration through the bark of pine (Pinus radiata D.Don) logs

Phosphine (PH₃) is used as an in-transit phytosanitary treatment (10-d fumigation period) for pine (Pinus radiata D.Don) logs exported from New Zealand to China. The ability of PH₃ to penetrate through the bark of the logs is not well known. We designed equipment to accurately quantify PH₃ penetration into the bark of wooden blocks (100 × 100 × 50 mm; n = 12) cut from the upper and lower trunk of recently harvested pine trees fumigated at 15 or 25 °C. Fumigations simulated commercial conditions consisting of two phases; phase I with 2.0 g m⁻³ of PH₃ for the first 5 days (1–120 h) and 1.5 g m⁻³ of PH₃ in phase II for the next 5 days (121–240 h). During the 10-d schedule, we achieved the required commercial CT (concentration × time) of ≥48,000 ppm h at both temperatures. Bark thickness (i.e., trunk location) did not significantly affect fumigant penetration. Phosphine penetration through the bark of the wooden blocks was greatest after each application, then the penetrated concentrations diminished over time. Greater penetration occurred at 15 °C than at 25 °C. Further studies are required to better understand the dynamics of PH₃ penetration particularly at lower temperatures and through insect-infested blocks.     

Effect of vanillin concentration,pH and incubation temperature onAspergillus flavus,Aspergillus niger,Aspergillus ochraceusandAspergillus parasiticusgrowth

The effects of incubation temperature (10–30°C), pH (3.0–4.0) and vanillin concentration (350–1200ppm) on the growth ofAspergillus flavus, Aspergillus niger, Aspergillus ochraceusandAspergillus parasiticuswere evaluated using potato–dextrose agar adjusted to water activity (a_w) 0.98. The radial growth rates after a lag period followed zero-order kinetics with constants that varied from 0 (no growth) to 0.63mmh⁻¹. The lag period depended on vanillin concentration, pH and incubation temperature. The germination time and the radial growth rates were significantly affected by the three studied variables (P<0.001). The inhibitory conditions (no growth after 30 days) depend on the type of mold. A niger, the most resistant species, was inhibited at 15°C, pH 3.0 and 1000ppm. ForA. ochraceus, the most sensitive, the inhibitory conditions in presence of 500ppm vanillin were pH 3.0 and temperature ≤25°C or pH 4.0 with temperature ≤15°C.     

Synergistic Effect of Orange Essential Oil or (+)-limonene with Heat Treatments to Inactivate Escherichia coli O157:H7 in Orange Juice at Lower Intensities while Maintaining Hedonic Acceptability

This study investigates the effects of different concentrations (50–200 ppm) of (+)-limonene or orange essential oil (EO) when designing thermal treatments to pasteurize orange juice (OJ) at different temperatures (54–60 °C). The addition of 200 ppm of (+)-limonene or orange EO to commercial OJ reduced the heating time to inactivate 5 log₁₀ cycles of the target pathogen Escherichia coli O157:H7 by 3.8 or 2.5 times, respectively. Results demonstrated that EOs and heat acted synergistically. Interestingly, the synergistic effect was constant in the studied range of temperatures. OJ added with 100 ppm of (+)-limonene or 200 ppm of orange EO maintained the sensory acceptance after a heat treatment able to inactivate 5 log₁₀ cycles of E. coli O157:H7. This study opens up the possibility of designing scientific-based combined processes for OJ pasteurization founded on the controlled incorporation of orange EO or (+)-limonene.     

Induction of a lag phase by chiller temperatures in Escherichia coli growing in broth or on pork

When log phase cultures of Escherichia coli in brain–heart infusion (BHI) were cooled from 12°C to temperatures below 7°C (the minimum required for growth), the optical densities of cultures increased at declining rates for up to 6 days during incubation at temperatures between 6 and 3°C inclusive, but did not increase at temperatures ≤2°C. However, the numbers of E. coli recovered from cultures on selective or non-selective agars were similar at all times of incubation up to 8 days at temperatures below the minimum for growth. From optical density measurements it appeared that when log phase cultures were cooled to 2°C, then returned to 15°C, a lag developed with time at 2°C to reach a maximum of about 1 h after about 4 h. When cultures were returned to 12°C after times at 2°C between 0·5 and 8 days, the time during which optical densities did not increase was constant at about 2 h, but the initial rate of optical density increase declined with time at 2°C. On pork fat tissue the lag time, determined by increases in the numbers of E. coli cfu on tissues inoculated with cells returned from incubation at 2°C for 16 h to a growth permitting temperature between 7 and 30°C, was longer than the lag time determined from optical density measurements of broth cultures subjected to the same temperature regime. Lag times for E. coli adapted to and growing on normal pH pork lean tissue were longer than for E. coli on fat tissue, while unadapted E. coli did not initiate growth on lean tissue, after incubation at 2°C, at 12°C or lower temperatures. The observations indicate that lag phase development in log phase E. coli subjected to chiller temperatures is complex, and that prediction of lag resolution in log phase cells exposed to temperatures that fluctuate around the minimum for growth will require modeling of lag induction as well as lag resolution.     

Identification and decarboxylase activities of bacteria isolated from decomposed mahimahi (Coryphaena hippurus) after incubation at 0 and 32°C

Identification and amine-forming ability of bacterial isolates from decomposed mahimahi (Coryphaena hippurus) were studied in order to identify spoilage microflora and determine the potential for a chemical index of spoilage based on the metabolites produced. Mesophilic bacteria isolated from a fish incubated at 32°C for 24 h were essentially all Gram-negative rods; 89% of these were Vibrio alginolyticus. Strong histamine-forming (> 100 mg/100 ml) mesophiles consisted of eight cultures of Morganella morganii and one of Proteus mirabilis. Weak histamine-forming (< 10 mg/100 ml) mesophiles were all V. alginolyticus, and these comprised 15% of the isolates assigned to that species. Decarboxylation of ornithine and lysine occurred in 38 and 92%, respectively, of the mesophilic isolates. Psychrotrophic isolates obtained from a fish incubated 14 days at 0°C were predominantly Gram-negative genera. Of these, 9% were histamine-forming cultures of Alteromonas putrefaciens, a weak histamine former that produced < 1 mg/100 ml at 5 and 20°C. Decarboxylation of ornithine and lysine occurred in 13 and 15%, respectively, of the psychrotrophic isolates.     

The effect of pH,sodium chloride,sodium nitrite and storage temperature on the growth of Clostridium perfringens and faecal streptococci in laboratory media

The effects of salt concentration (1–12% w/v) in combination with unheated sodium nitrite (0–400 μg/ml) on growth of mixed strains of Clostridium perfringens and of faecal streptococci at three pH values (5.6, 6.2, 6.8) and storage temperatures ranging from 10°C to 35°C is reported. At pH 6.2, following storage at 15°C, 1% salt and 50 μg/ml nitrite inhibited growth of C. perfringens. At 20°C and pH 6.2, 200 μg/ml nitrite plus 3% salt, or 50 μg/ml plus 4% salt were required to inhibit growth. Growth of C. perfringens was prevented by levels of curing salts used commercially providing the pH was 6.2 or below. At pH 6.8 or above at least 4% salt and 50 μg/ml nitrite was required to prevent growth at 20°C. The faecal streptococci grew in medium containing 6% salt and 400 μg/ml nitrite irrespective of pH or storage temperature. In 8% salt growth was prevented by storing at or below 17.5°C or, if pH was 6.2 or lower, by adding 200 μg/ml nitrite irrespective of storage temperature. Growth of faecal streptococci was not controlled by concentrations of curing salts which would be acceptable in meat products.     

Inhibitory effect of spices on in vitro histamine production and histidine decarboxylase activity ofMorganella morganii and on the biogenic amine formation in mackerel stored at 30°C

The inhibitory effects of clove, cinnamon, cardamom, turmeric and pepper on the histamine production and histidine decarboxylase activity ofMorganella morganii (a potent histamine-producing bacteria in fish) was examined at 30°C using HPLC. Cinnamon and clove exhibited a significant (P<0.01) inhibitory effect, whereas turmeric and cardamom had a moderate effect. These spices were applied to whole mackerel at a level of 3% and their inhibitory effect on biogenic amine formation at 30°C was also examined. As in the in vitro study, clove and cinnamon showed a significant (P< 0.05) inhibitory effect on histamine, putrescine and tyramine formation but not on that of cadaverine. Cardamom and turmeric exhibited a moderate effect and pepper was ineffective. Therefore, clove and cinnamon are more helpful than cardamom and turmeric in the minimization of the formation of toxic histamine in mackerel.     

Destruction of Salmonella enteritidis inoculated in liquid whole egg by high hydrostatic pressure: comparative study in selective and non-selective media

The destruction of Salmonella enteritidis inoculated in liquid whole egg at approximately 10⁷−10⁸cfu ml^−lwas studied under combinations of pressure (350 and 450 MPa), temperature (50, 20, 2 and −15°C) and time (5, 10, 15 min and cycles of 5+5 and 5+5+5 min). One non-selective medium (tryptone soy agar) and two selective media (brilliant green agar and salmonella-shigella) were used to evaluate viability of S. enteritidis after pressurization. The inactivation rate increased with pressure and exposure time, being minimal at 350 MPa and −15°C for 5 min (over 1 log₁₀of reduction) and reaching total inactivation (8 log₁₀of reduction) in several treatments at 50°C. Treatments in cycles showed greater effectiveness than continuous treatments of the same total time. The effect of pressure was enhanced by elevated temperatures. The higher counts were obtained in the non-selective medium, indicating the presence of injured cells after pressure treatment. D -values obtained for two temperatures (2 and 20°C) and different times (0–60 min) under controlled pressure (400 MPa) showed that microbial inactivation followed a first-order kinetics with a decimal reduction time evaluated in tryptone soy agar medium of 9·5 min at 2°C and 8·8 min at 20°C.     

Development of twoListeria monocytogenesgrowth models in a meat broth and their application to beef meat

Growth variation ofListeriastrains was taken into account by building two growth models with strains previously characterized, respectively, by their slow (L. monocytogenes CLIP 19532) and fast (L. monocytogenes 14) growth in different conditions of pH, a_wand temperature. Strains of intermediate growth were studied in a meat broth and strains used for the models were grown on the surface of beef meat. Ten growth repetitions at 14°C– a_w0.98–pH 6.2 showed that generation times were similar [ratio value (R=standard deviation/average): 3.2%] but that range of lag times was wide (R=27.4%). In broth, calculated lag and generation times were not significantly different between strains from 30 to 14°C, but variations became larger as temperatures came close to 4°C. Model values corresponded well to experimental generation times and to a lesser extent to lag times. On meat at 4°C and 14°C both strains had experimental lag times three-fold longer than predicted lag times. Experimental generation times were shorter than predicted values at 14°C and longer at 4°C: differences between growth in broth and on meat could be due to the characteristics of the meat, the experimental conditions of growth, the mode of inoculation and the way of adjustment of a_w. Growth variations were found between available predictive models.