Growth and histamine production by Morganella morganii under various temperature conditions

The generation times (G) for Morganella morganii were determined using absorbance measurements (at 0–10°C) or conductance measurements (at 15–25°C). Growth was rapid at 15–25°C (G = 2.6 at 15°C and G = 1.08 h at 25°C) but at the lower temperatures growth was greatly reduced. Growth and histamine production by M. morganii in histidine-containing broth (HDB) and in mackerel (packed in air-permeable plastic bags) was studied. It was found that large amounts of histamine are formed at low temperatures (0–5°C), where no growth takes place, following storage at higher temperatures (10–25°C). Measurements of conductance can be used to separate between samples with no or only insignificant content of histamine (< 50 ppm) which had detection times (DT) above 10 h and those with elevated content of histamine (> 50 ppm) which had shorter DT.     

Modelling the effect of temperature, carbon dioxide, water activity and pH on growth and histamine formation by Morganella psychrotolerans

A mathematical model was developed to predict growth and histamine formation by Morganella psychrotolerans depending on temperature (0-20 degrees C), atmosphere (0-100% CO2), NaCl (0.0-6.0%) and pH (5.4-6.5). Data from experiments with both sterile tuna meat and Luria Bertani broth was used to develop the mathematical growth and histamine formation model. The expanded Logistic model with a growth dampening parameter (m) of 0.7 was used as primary growth model. A primary model for histamine formation during storage was obtained by combining the expanded Logistic growth model with a yield factor (YHis/CFU). 120 maximum specific growth rate (micromax)-values were generated for M. psychrotolerans and used to model the combined effect of the studied environmental parameters. A simple cardinal parameter type secondary model was used to model the effect of the four parameters on micro(max). The maximum population density (log Nmax) was correlated with log (YHis/CFU) and a simple constrained polynomial (quadratic) secondary model was developed for the effect of the environmental conditions on these model parameters. The developed model describes the effect of initial cell concentrations, storage conditions and product characteristics on histamine formation. This is a significant progress compared to previously available models for the effect of storage temperature only.     

Growth and histamine formation of Morganella morganii in determining the safety and quality of inoculated and uninoculated bluefish (Pomatomus saltatrix).

The objective of this study was to determine the effect of normal microflora and Morganella morganii on histamine formation and olfactory acceptability in raw bluefish under controlled storage conditions. Fillets inoculated with and without M. morganii were stored at 5, 10, and 15 degrees C for 7 days. Microbial isolates from surface swabs were identified and screened for histidine decarboxylase activity. Olfactory acceptance was performed by an informal sensory panel. Histamine levels were quantified using high-performance liquid chromatography and fluorescence detection. While olfactory acceptance decreased, histamine concentration and bacterial counts increased. Storage temperature had a significant effect on histamine levels, bacterial counts, and olfactory acceptance of the bluefish. Inoculation with M. morganii had a positive significant effect on histamine formation for bluefish held at 10 and 15 degrees C (P < 0.0001). The results of the study will serve in supporting U.S. Food and Drug Administration (FDA) regulations regarding guidance and hazard levels of histamine in fresh bluefish.     

Detection of Morganella morganii,a prolific histamine former,by the polymerase chain reaction assay with 16S rDNA-targeted primers

A polymerase chain reaction (PCR) assay for the rapid and sensitive detection of the most prolific histamine former, Morganella morganii, was developed. 16S rDNA targeted PCR primers were designed, and the primer specificity and sensitivity of the PCR assay were evaluated. The 16S rDNA sequence (1,503 bp) for M. morganii showed 95% identity to those for enteric bacteria, i.e., Enterobacter spp., Klebsiella spp., Citrobacter spp., Hafnia alvei, Proteus spp., and Providencia spp. The unique primers for M. morganii were designed on the basis of the variable regions in the 16S rDNA sequence. The primers showed positive reactions with all M. morganii strains tested. However, PCR amplification was not detected when the primers were tested with other enteric or marine bacteria. When the sensitivity of the assay was evaluated, M. morganii was detected at levels ranging from 10(6) to 10(8) CFU/ml in albacore homogenate after the PCR amplification. The sensitivity of the assay was greatly improved with the enrichment of samples, and 9 CFU of M. morganii per ml of albacore homogenate was detected after 6 h of enrichment at 37 degrees C.     

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.     

Application of the Bigelow (z-value) model and histamine detection to determine the time and temperature required to eliminate Morganella morganii from seafood

In New Zealand, the product most frequently implicated in cases of scombroid or histamine poisoning is the hot-smoked fish, kahawai (Arripis trutta). A properly controlled heating step in the production of hot-smoked seafood could eliminate bacteria able to convert the amino acid histidine to histamine. In this study, we determined the core temperatures and times required during hot smoking of kahawai to eliminate histamine-forming bacteria and to ensure a final product that will not produce histamine if subsequent temperature abuse occurs. Morganella morganii strains previously isolated from portions of hot-smoked kahawai with elevated histamine levels were inoculated onto product to be tested. A variation of the Bigelow or z-value model was used to generate a thermal death time graph, where the production of histamine, in a heat-treated and subsequently temperature-abused sample, was scored as a positive value (growth) and the absence of histamine was scored as a negative value (no growth). From a line fitted to the data, calculated times for the elimination of histamine-forming bacteria at test temperatures of 58, 59, 60, 61, and 62 degrees C were estimated to be 15.27, 8.81, 4.79, 2.68, and 1.46 min, respectively, giving a z value of 3.85 degrees C. This approach to thermal death determination, based on the presence or absence of a bacterial metabolite, proved to be an efficient way to determine the thermal regime required to eliminate bacteria capable of converting histidine to histamine on kahawai.     

Molecular Detection of a Histamine Former, Morganella morganii, in Albacore, Mackerel, Sardine, and a Processing Plant

ABSTRACT: Testing for Morganella morganii , a prolific histamine former, was carried out in fish and processing plant to determine its origin and contamination source using PCR assay coupled with Southern hybridization. M. morganii was mostly found in mackerel and sardines but rarely in albacore. It was most frequently present in the gill followed by the skin but rarely in the intestine and cavity. No M. morganii was found in the processing plant but was detected on the surfaces of conveyer belts and plastic totes during processing. The compiled results indicated that histamine-forming bacteria are endogenous to fish and pointed out the importance of sanitation in the processing plant to prevent cross-contamination.     

The impacts of water and ethanolic extracts of propolis on vacuum packaged sardine fillets inoculated with Morganella psychrotolerans during chilly storage

The impacts of water and ethanolic extracts of propolis at a dose of 0.4 or 0.8% on vacuum packaged sardine fillets inoculated with Morganella psychrotolerans DSM 17886 during storage at 3 ± 1°C for 15 days were investigated. All fish groups were inoculated with M. psychrotolerans (10⁸ cfu/ml) at a rate of 1%. Sensory, colorimetric, chemical analysis (total volatile basic nitrogen, thiobarbituric acid, peroxide values, and free fatty acids), pH value, and microbiological analysis (viable mesophilic and psychrophilic bacteria, coliform, and lactic acid bacteria count) were carried out. An enhance in L* values was found in the group treated with 0.8% ethanolic extracts of propolis on the seventh day of the storage. Application of propolis extract on fish fillets significantly inhibited bacterial growth during storage and extended shelf life of sardine for 4 and 6 days by the use of water extract and for 8 days by the use of ethanolic extract at doses of 0.4 and 0.8%, respectively. The result of the study revealed that application of propolis extracts, mainly ethanolic propolis extracts on sardine fillets resulted in lower lipid oxidation and bacterial growth, therefore, could be natural food additive for preservation of fish fillets.     

湿米粉中菌相分析与微生物生长预测模型的建立

采用选择性培养基对湿米粉的初始菌相进行分析,研究5℃、10℃、15℃、25℃温度贮藏下的湿米粉中的优势腐败菌生长变化规律.运用SAS 9.1统计学软件拟合优势菌在不同温度下的生长动力学模型.利用平方根模型描述温度与优势菌最大生长速率和延滞期的关系,得到优势菌生长的二级模型.结果表明,乳酸菌、肠杆菌、葡萄球菌、酵母菌、霉菌是引起米粉腐败的主要微生物.初步分离得到乳酸菌、肠杆菌、霉菌各2株,酵母、葡萄球菌各1株.其中乳酸菌是湿米粉初始菌相中优势腐败菌,其数量与细菌总数相当,增长速度最快.Gompertz模型能较好的拟合优势菌在不同温度下的生长,判定系数均在0.9以上.温度与微生物最大生长速率和延滞期之间存在良好的线性关系.     

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.     

鲭鱼品质评价及品质变化与组胺含量研究进展

海水鱼类的新鲜度体现了鱼肉的可食用价值,海水鱼中的青皮红肉鱼类含有较高的组氨酸,会因保存不当导致体内组胺含量升高,对消费者健康产生危害。组胺是一种食源性化学危害,易导致过敏人群产生中毒现象。组胺中毒又称为鲭鱼中毒,是组胺引起毛细血管扩张和支气管收缩所致,研究表明鲭科鱼类的组氨酸含量高,组氨酸会在产组胺微生物的组氨酸脱羧酶的作用下产生组胺,判定组胺中毒的最有效的方法是检测鲭鱼体内的组胺含量,低水平的组胺并不会对人体产生危害,组胺摄入量过多会对人体产生危害,组胺已成为评价鲭鱼品质的标准之一。本文主要对鲭鱼品质的感官评定和理化评定(组胺、K值、挥发性盐基氮等)方式进行综述,并对组胺产生的影响因素如微生物、温度、鱼的种类等进行综述,为鲭鱼品质鉴定和组胺含量的控制提供依据。     

Short communication: Development and evaluation of predictive models of body weight for crossbred Holstein-Zebu dairy heifers

Equations to predict body weight (BW) of crossbred Holstein-Zebu dairy heifers were developed and compared with current models (Heinrichs et al. for Holsteins, United States; Reis et al. for crossbred Holstein-Zebu, Brazil). The data set was constructed from 150 measurements of BW (320 ± 107 kg) and biometric measurements such as heart girth (HG, 161 ± 19.5 cm), withers height (WH, 126 ± 11.0 cm), and hip height (HH, 132 ± 11.3 cm) of heifers from 5 commercial dairy producers in the southern Amazon region in Brazil. The data were evaluated using mixed nonlinear models with herd as a random effect. Three nonlinear equations were fitted: BW (kg) = 0.00058·HG (cm)^2.6135; BW (kg) = 0.000618·HG (cm)^2.7362; and BW (kg) = 0.000196·HH ^2.8793. An independent database was constructed to evaluate the models from 38 treatment means of 4 feeding trials: BW 258 ± 54.3 kg, HG 142.5 ± 11.8 cm, WH 113.2 ± 6.0 cm, and HH 118.7 ± 9.1 cm (mean ± SD). The evaluations were based on the relationship between observed and predicted values of BW by linear regression, root mean square prediction error (RMSPE), and concordance correlation coefficient analysis. Only the proposed model using HG accurately predicted observed BW, with bias (observed – predicted) of 4.83 kg and RMSPE of 5.41% of observed BW (87.7% of random error). The models using WH and HH failed to accurately predict observed BW, with a bias of −3.06 and 72.02 kg, and RMSPE of 9.40% of observed BW (75.2% of random error and 23.1% of systematic error) and 30.81% of observed BW (81.2% of mean bias). Additionally, the models of Heinrichs and Reis used for comparison did not predict BW accurately, with a bias of 19.32 and 29.37 kg and RMSPE of 9.08% of observed BW (68.4% of mean bias and 31.4% of random error) and 12.58% of observed BW (81.9% of mean bias). The largest concordance correlation coefficient of the proposed HG-nonlinear model (0.930), compared with the models of Heinrichs and Reis of 0.845 and 0.708, confirmed the greater accuracy and precision of the new equation to predict BW in crossbred Holstein-Zebu dairy heifers.     

A predictive model to determine the effects of pH, milkfat, and temperature on thermal inactivation of Listeria monocytogenes.

Listeria monocytogenes is a foodborne pathogen of significance because of its comparatively high heat resistance, zero tolerance in ready-to-eat foods, and growth at refrigeration temperatures. A 3 x 3 x 3 factorial study was done to determine the effects of milkfat (0%, 2.5%, 5.0%), pH (5.0, 6.0, 7.0), and processing temperature (55 degrees C, 60 degrees C, 65 degrees C) on the thermal resistance of L. monocytogenes in a formulated and homogenized milk system. Data were fit to a modified Gompertz equation where parameter estimates characterized three regions of a survival curve: the shoulder, maximum slope, and tail. Statistical analysis was done for each of the 27 individual treatment sets to visualize individual effects on parameter estimates and to evaluate how well the Gompertz equation represented the data. A regression model for the Gompertz equation was generated to predict the logarithmic surviving fraction of L. monocytogenes based on all 27 treatments and their single and interactive effects. The shoulder region of the survival curve was affected by pH; however, the maximum slope was affected by temperature, milkfat, and the interaction of temperature x milkfat. Validation of the model suggests that the predictions are best suited for processing above 62 degrees C. Trends over time for a 4-log reduction in cells (4D values) were evaluated using results from the 27 individual treatment sets, the regression model for the Gompertz equation, and a linear equation. At lower temperatures, 4D values by the three methods varied by twofold. At higher temperatures, all methods gave similar 4D values, suggesting that death became more linear. Based on this study all three factors affect heat resistance for specific regions of a survival curve, and a predictive model was developed that can be used as a preliminary estimate for L. monocytogenes inactivation.     

Mathematic predictive models for calculating copper, iron and zinc dialysability in infant formulas

Differences in the dialysability of a mineral element from infant formulas of the same type were detected in a previous study. As these may be due to the effects that different levels of the components of the formulas could have on dialysability, we attempted to establish mathematical models to predict the dialysability of Cu, Fe and Zn from infant formulas according to their ascorbic, citric, or selected amino acid contents. A simple linear regression was applied between the ascorbic acid, citric acid and amino acid contents and the Cu, Fe and Zn dialysability of 18 powdered infant formulas of different types. Significant correlations (P<0.05) were obtained between the dialysability of Fe and ascorbic acid, citric acid, cysteine (Cys), glycine (Gly) and lysine (Lys) contents; between Cu and Cys, arginine (Arg) and tyrosine (Tyr) contents; and between Zn and Cys, Gly, Lys and Arg contents. A multiple regression was applied in those cases in which a significant correlation (P<0.05) was obtained. A joint effect of ascorbic and either citric acid or Cys on Fe dialysability was observed. The effect of Arg on Zn dialysability and the joint effect of Tyr and Cys on Cu dialysability must also be mentioned.     

Growth characteristics and development of a predictive model for Bacillus cereus in fresh wet noodles with added ethanol and thiamine

Response surface methodology was used to determine growth characteristics and to develop a predictive model to describe specific growth rates of Bacillus cereus in wet noodles containing a combination of ethanol (0 to 2% [vol/wt]) and vitamin B(1) (0 to 2 g/liter). B. cereus F4810/72, which produces an emetic toxin, was used in this study. The noodles containing B. cereus were incubated at 10°C. The growth curves were fitted to the modified Gompertz equation using nonlinear regression, and the growth rate values from the curves were used to establish the predictive model using a response surface methodology quadratic polynomial equation as a function of concentrations of ethanol and vitamin B(1). The model was shown to fit the data very well (r(2) = 0.9505 to 0.9991) and could be used to accurately predict growth rates. The quadratic polynomial model was validated, and the predicted growth rate values were in good agreement with the experimental values. The polynomial model was found to be an appropriate secondary model for growth rate (GR) and lag time (LT) based on the correlation of determination (r(2) = 0.9899 for GR, 0.9782 for LT), bias factor (B(f) = 1.006 for GR, 0.992 for LT), and accuracy factor (A(f) = 1.024 for GR, 1.011 for LT). Thus, this model holds great promise for use in predicting the growth of B. cereus in fresh wet noodles using only the bacterial concentration, an important contribution to the manufacturing of safe products.     

Growth of Clostridium perfringens from spore inocula in cooked cured beef: development of a predictive model

The objective of this study was to develop a model to predict the growth of C. perfringens from spores at temperatures applicable to the cooling of cooked cured meat products. C. perfringens growth from spores was not observed at a temperature of 12 °C for up to 3 weeks. The two parameters: germination, outgrowth, and lag (GOL) time and exponential growth rate, EGR, were determined using a function derived from mechanistic and stochastic considerations and the observed relative growths at specified times. A general model to predict the amount of relative growth for arbitrary temperature was determined by fitting the exponential growth rates to a square root Ratkowsky function, and assuming a constant ratio of GOL and generation times. The predicted relative growth is sensitive to the value of this ratio. A closed form equation was developed that can be used to estimate the relative growth for a general cooling scenario and determine a standard error of the estimate. The equation depends upon microbiological assumptions of the effect of history of the GOL times for gradual changes in temperature. Applying multivariate statistical procedures, a confidence interval was computed on the prediction of the amount of growth for a given temperature. The model predicts, for example, a relative growth of 3.17 with an upper 95% confidence limit of 8.50 when cooling the product from 51 to 11 °C in 8 h, assuming a log linear decline in temperature with time.