Stimulating effect of sorbitol and xylitol on germination and growth of some xerophilic fungi

Sorbitol and xylitol are polyols often used in foods as naturally occurring sugar substitutes. They provide sweet taste and reduced calories in products of intermediate moisture. This type of food is susceptible to spoilage by xerophilic molds which affect shelf life of foods and produce significant losses. The aim of the present work was to study the effect of glycerol, sorbitol and xylitol on the germination and growth of four xerophilic fungi at different temperatures and water activity levels. Penicillium chrysogenum, Wallemia sebi, Eurotium chevalieri and Eurotium repens were cultivated on malt extract agar with the addition of the respective polyols and a_w adjusted to 0.85, 0.88, 0.90 and 0.93. Incubation was made at 25, 30 and 35 °C. Results of the present study demonstrated that sorbitol and xylitol affect the growth kinetics of the four fungal species. The observed tendency was that these solutes shortened the germination times and increased the growth rates. The effect of each solute depended on the fungal species and the a_w/temperature combinations. At lower a_w the influence was more evident on the germination times while the effect on growth rates was more pronounced at higher a_w levels.     

蜡样芽胞杆菌生长/非生长界面模型的建立和评价

蜡样芽胞杆菌是软烤虾仁产品的主要变质菌,它是一种条件致病菌,通过产生腹泻毒素和呕吐毒素导致食物中毒。该研究旨在建立一种概率模型来预测出蜡样芽胞杆菌的生长/非生长情况或者生长概率。用lo-gistic回归模型建立不同温度、水分活度和pH环境因子作用下蜡样芽胞杆菌的生长/非生长界面模型。实验结果表明蜡样芽胞杆菌在脑心浸液肉汤培养基中生长的最低温度为9.99℃,最低水分活度为0.931,最小pH值为4.5。在此基础上建立的蜡样芽胞杆菌生长/非生长界面模型的χ2=49.73,P<0.000 1。用logistic回归模型建立的生长/非生长模型拟合效果达到极显著水平。模型的预测值同时很好地量化了环境因子对蜡样芽胞杆菌的协同作用,为软烤虾仁产品中蜡样芽胞杆菌的生长/非生长界面模型的建立提供了参考。     

Combined effects of temperature, water activity, and pH on Alicyclobacillus acidoterrestris spores

A response surface model was developed to describe the effects of temperature (35 to 55 degrees C), pH (3.5 to 5.5), and water activity (a(w), 0.960 to 0.992) on germination of Alicyclobacillus acidoterrestris spores. Germination and growth or viability loss depended, to varying extents, on the interactions among the independent variables and the complexity of the medium. In particular, maximum growth was achieved at temperatures between 35 and 42 degrees C and at pH values from 3.5 to 4.5. The model was validated against data not used in its development. Bias factors of 0.999 and 0.817 for 2- and 7-day models, respectively, were obtained, indicating that the models were "fail safe." Results indicated that the model provided reliable predictions of growth of A. acidoterrestris spores.     

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.     

Influence of pH,water activity and temperature on the inactivation of Escherichia coli and Saccharomyces cerevisiae by pulsed electric fields

The aim of this study was to examine the influence of pH, water activity (a_w) and temperature on the killing effect of pulsed electric fields (PEF). Escherichia coli and Saccharomyces cerevisiae suspended in a model media were subjected to 20 pulses with 4 μs duration in a continuous PEF system, during which the effects of pH (4.0–7.0), a_w (1.00–0.94) and inlet temperature (10°C and 30°C) could easily be studied. Electrical field strengths were set to 25 kV/cm for S. cerevisiae and 30 kV/cm for E. coli and the highest outlet temperature was monitored to 44°C. A synergy of low pH values, high temperatures and PEF processing was observed. A drop in pH value from 7.0 to 4.0 resulted in the reduction of E. coli by four additional log units, whereas for S. cerevisiae, the pH effect was less pronounced. Lowering a_w seems to protect both E. coli and S. cerevisiae from PEF processing.     

Development and validation of a combined temperature, water activity, pH model for bacterial growth rate of Lactobacillus curvatus

A model was established to predict growth rate as a function of temperature, pH and water activity. The model is based on two, earlier developed models, one for growth rate as a function of temperature and water activity and the other for growth rate as a function of temperature and pH. Based on the assumption that combinatory effects between pH and water activity do not exist, the two models were multiplied to produce one overall model. The overall model was then fitted to data sets measured earlier, and the parameters of the model were determined. A new data set with values for controlling variables outside the range of the earlier developed model was then used to validate the overall model statistically. The model was well able to extrapolate outside the measured data range. Finally, the model was updated with all measured data. No significant changes in the parameters were found. The approach followed underpins the gamma concept, since in the gamma concept it is assumed that the effects of controlling variables can be multiplied, and cardinal parameters are not a function of other variables (temperature, pH, and water activity).     

Modeling the boundaries of growth of Salmonella Typhimurium in broth as a function of temperature, water activity, and pH

The growth limits of a mixture of five strains of Salmonella Typhimurium in tryptic soy broth were examined at different environmental conditions. The response of the pathogen was monitored in a total of 350 combination treatments of temperature (10 to 35 degrees C), pH (3.76 to 6.44), and water activity (aw, 0.913 to 0.990) for 62 days. No growth/growth (turbidity) data were modeled by logistic polynomial regression. The concordance index of the logistic model was 99.8%, indicating a good fit to the observed data. The minimum pH and aw values that permitted growth were 3.94 and 0.942, respectively, and occurred in the temperature range of 25 to 35 degrees C. At temperatures below this range, the minimum pH and aw allowing growth increased as the temperature decreased. The results showed an abrupt change in the probability of growth close to the boundary with minor changes of the environmental factors. The probabilities predicted by the model were compared with published data on the actual response of Salmonella Typhimurium or other salmonellae serotypes in 50 cases of food products, including salad dressing, mayonnaise, meat, cheese, vegetables, and fruits. The model predicted successfully the response of the pathogen in 90% of the tested cases. The results of the study indicated that the developed model predicts satisfactorily the growth/no growth interface of Salmonella Typhimurium in foods and can provide useful quantitative data for the development of safer food products and processes.     

Influence of pH on the growth of some toxigenic species of Aspergillus, Penicillium and Fusarium

The effect of pH on the growth rates of 61 isolates belonging to 13 important toxigenic fungi are reported here: four species each of Aspergillus and Fusarium, and five of Penicillium, over the pH range 2 to 11 at 25, 30 and 37 degrees C. Nearly all species studied were able to grow over the entire range examined on a laboratory agar medium. However, in general, Aspergillus species were more tolerant of alkaline pH while Penicillium species appeared to be more tolerant of acidic pH.     

温度,pH,Aw,糖醇对奶油蛋糕褐变的影响

研究了温度、pH、Aw、木糖醇对奶油蛋糕褐变的影响.通过设置栅栏,来观察各个因子对褐变的影响.结果表明:低温、低pH能够抑制奶油蛋糕的褐变,适当降低Aw值能够显著延缓褐变,30%木糖醇替代能够有效地延缓褐变,同时不影响蛋糕的组织结构.     

Occurrence of xerophilic fungi in bakery gingerbread production

The production process of a coconut type of gingerbread was examined for possible sources of contamination with xerophilic fungi. In the production flow chart, critical control points were found at which some effective steps could be made to eliminate undesirable fungal contamination, affected by water activity and temperature, and to prevent mould spoilage of the products. The following xerophilic fungi were detected, isolated and identified: Eurotium amstelodami, E. chevalieri, E. herbariorum, E. rubrum and Wallemia sebi. The resistance of these fungi against elevated temperature and preserving agents was investigated. It was found that Eurotium species were more resistant than W. sebi. Preservation against xerophilic fungi was more effective with the use of propionic acid than with potassium sorbate.     

Effect of water activity and temperature on competing abilities of common postharvest citrus fungi

The effect of temperature (4-30 degrees C) and water activity (a(w), 0.995-0.90) on the 'in vitro' interactions between Penicillium digitatum, Penicillium italicum and Geotrichum candidum were evaluated. The effect of temperature on growth of green and blue mould decays and their interactions on wounded oranges was also studied. The major competing abilities were observed at optimal conditions of temperature and a(w) for growth (25 degrees C and 0.995 a(w)), and no differences between growth rates when the fungi were growing alone or paired were observed in the other studied conditions. P. italicum and G. candidum were able to reduce the growth rate of P. digitatum when it was growing paired 'in vitro', suggesting that inhibitory metabolites were produced. In the 'in vivo' assays, growth rates of green mould were higher than those of blue mould at any temperature studied. However, at 4 degrees C, P. italicum began its rot development 1 week before P. digitatum. When these two pathogens were inoculated into the same wound at 25 degrees C, blue mould was practically inhibited. The difference between the results obtained in 'in vitro' and 'in vivo' assays suggests that other factors could interact with fungi, favoring the development of one pathogen to the detriment of the others.     

Influence of pH and temperature on growth of Bacillus cereus in vegetable substrates

Bacillus cereus is a food-borne pathogen which most often contaminates foods of plant origin. Spores of psychrotrophic strains have the ability to germinate and grow at refrigeration temperatures in different vegetable substrates, such as carrot broth, zucchini broth, and cooked carrot purée. In some circumstances, factors such as pH, heat treatment, and storage temperature play a fundamental role in controlling the growth of these psychrotrophic strains and in extending the shelf life of refrigerated, minimally processed vegetable-based products in relation to pathogenic spore-forming bacteria. The combination of mild acidification (pH 5.0) and refrigeration (相似文献   

Influence of water activity and temperature on growth and mycotoxin production by Alternaria alternata on irradiated soya beans

The aim of this study was to determine the effects of water activity (a_w) (0.99-0.90), temperature (15, 25 and 30 °C) and their interactions on growth and alternariol (AOH) and alternariol monomethyl ether (AME) production by Alternaria alternata on irradiated soya beans. Maximum growth rates were obtained at 0.980 a_w and 25 °C. Minimum a_w level for growth was dependent on temperature. Both strains were able to grow at the lowest a_w assayed (0.90). Maximum amount of AOH was produced at 0.98 a_w but at different temperatures, 15 and 25 °C, for the strains RC 21 and RC 39 respectively. Maximum AME production was obtained at 0.98 a_w and 30 °C for both strains. The concentration range of both toxins varied considerably depending on a_w and temperature interactions. The two metabolites were produced over the temperature range 15 to 30 °C and a_w range 0.99 to 0.96. The limiting a_w for detectable mycotoxin production is slightly greater than that for growth. Two-dimensional profiles of a_w × temperature were developed from these data to identify areas where conditions indicate a significant risk from AOH and AME accumulation on soya bean. Knowledge of AOH and AME production under marginal or sub-optimal temperature and a_w conditions for growth can be important since improper storage conditions accompanied by elevated temperature and moisture content in the grain can favour further mycotoxin production and lead to reduction in grain quality. This could present a hazard if the grain is used for human consumption or animal feedstuff.     

Effect of temperature and pH on immunoreactivity and milk clotting activity of some rennet enzymes

Summary The effect of temperature (30° –40 °C) and pH (6.0–6.8) on the milk clotting activity and immunoreactivity of proteinase fromMucor miehei (Fromase 100 and Fromase 46 TL) and chicken pepsin was investigated. Under these conditions, similar to those used in cheese-making, the immunoreactivity of fungal proteinase is less suppressed than the milk clotting activity by about 15%–25%. In contrast, the immunoreactivity of chicken pepsin is completely maintained even when the milk clotting activity is decreased by up to 25% of its original. The results obtained show that the immunochemical method cannot replace the assay of catalytic activity, where denatured enzyme molecules may be present in the analysed sample. In such cases a different approach must be chosen.

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Einfluß von Temperatur und pH auf die Immunreaktivität und Milchgerinnung einiger Lab-Enzyme

Zusammenfassung Gegenstand der Untersuchung war der Einfluß von Temperatur (30° –40 °C) und pH-Wert (6,0–6,8) auf die Milchgerinnung und die Immunreaktivität der Proteinase vonMucor miehei (Fromase 100 und Fromase 46 TL) und des Hühnerpepsins. Unter diesen Bedingungen, die denen der Käseherstellung entsprechen, sinkt die Immunreaktivität der mikrobiellen Proteinase um etwa 15%–25% weniger als ihre Milchgerinnungsaktivität. Das Hühnerpepsin verhält sich grundsätzlich anders: seine Immunreaktivität bleibt voll erhalten, während seine Milchgerinnungsaktivität bis auf 25% sinkt. Daraus ergibt sich, daß die immunchemischen Methoden nicht die Bestimmung der katalytischen Aktivitäten ersetzen können, wenn die Möglichkeit besteht, daß die analysierten Proben auch denaturierte Enzyme enthalten können. In solchen Fällen muß man andere Verfahren wählen.

     

Effects of heat-processing regime, pH, water activity and their interactions on the behaviour of Listeria monocytogenes in ground pork. Modelling the boundary of the growth/no-growth areas as a function of pH, water activity and temperature

The influence of four heat‐processing regimes and a storage phase on the behaviour of Listeria monocytogenes in ground pork was studied. The effects of pH and water activity (a_w) were also tested. During the heat process phase, a_w, the heat‐processing regime and its interactions with pH or a_w, had a significant effect on the behaviour of L. monocytogenes. During the storage phase, all parameters tested and their interactions had significant effects. Nevertheless, the area in which the growth of L. monocytogenes was observed at the end of the experiment was not influenced by the heat‐processing regime tested. On the contrary, pH, a_w and their interactions had significant effects on Listeria behaviour. The boundary of the growth area delimited by environmental conditions where growth was higher than 1.0 Log CFU g^?1 from those where growth was lower than this limit was correctly predicted by Augustin's model.     

Performance evaluation of a model describing the effects of temperature,water activity,pH and lactic acid concentration on the growth of Escherichia coli

A square root-type model for Escherichia coli growth in response to temperature, water activity, pH and lactic acid was developed by Ross et al. [Int. J. Food Microbiol. (2002).]. Predicted generation times from the model were compared to the literature data using bias and accuracy factors, graphical comparisons and plots of residuals for data obtained from both liquid growth media and foods. The model predicted well for 1025 growth rate estimates reported in the literature after poor quality or unrepresentative data (n=215) was excluded, with a bias factor of 0.92, and an accuracy factor of 1.29. In a detailed comparison to two other predictive modes for E. coli growth, Pathogen Modeling Program (PMP) and Food MicroModel (FMM), the new model generally performed better. The new model consistently gave better predictions than the other models at generation times 相似文献   

Influence of temperature on growth rate and lag phase of fungi isolated from Argentine corn

The influence of temperature on the growth of nine strains of fungi belonging to the genera Eurotium, Aspergillus, Penicillium and Fusarium has been investigated for the temperature range 15–35° C. The lag phase and the growth rate were evaluated by using a laboratory medium. The maximum growth rate for E. repens, A. wentii and P. chrysogenum was observed at about 25° C, for P. citrinum near 30° C and for F. semitectum and F. moniliforme between 20 and 25° C. The growth rate of A. niger, A flavus and A. parasiticus increased with increasing temperatures in the range studied. For all strains studied it appeared that the higher the growth rate the lower the lag phase was.