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1.
A survey of aw and pH in commercial samples of processed cheese produced in Argentina, indicated the aw varied between 0.950–0.978 and pH ranged from 5.2–6.1 Staphylococcus aureus growth studies in model systems (laboratory media with added NaCl) with aw and pH adjusted to resemble that of commercial samples of processed cheese showed that S. aureus grows very well at a temperature of 30°C, but complete growth inhibition occurs at refrigerator temperature. The results obtained with model systems were confirmed by S. aureus growth experiments in inoculated cheese. 相似文献
2.
Combined Effect of Water Activity, pH and Sub-optimal Temperature on Growth and Enterotoxin Production of Staphylococcus aureus 总被引:2,自引:0,他引:2
Staphylococcus aureus growth and enterotoxin production in relation to a, (0.99–0.87), pH (4.0–7.0) and temperature (8–30°C) was determined in Brain-heart-infusion broth with respectively NaCl and sucrose as humectants. Growth of S. aureus was not observed at aw 0.85, at pH 4.3 or at 8°C. At 12°C no growth occurred at a, 0.90 or at a, 0.93 in combination with pH < 5.5. At aw 0.96 no growth occurred at pH ≤ 4.9. Production of staphylococcal enterotoxin type A (SEA) occurred under nearly all conditions allowing growth. Production of SEB appears to be determined by aw; at aw 0.96 SEB was produced at all temperatures allowing growth, while at a, 0.93 SEB was hardly produced. Production of SEC and SEF was affected both by aw and temperaure. Production of these toxins was rarely observed at a, 0.93. No SEC and SEF were produced at 12°C. Extrapolation of these findings to food is discussed. 相似文献
3.
The combined effect of pH, water activity (aw) and certain additives (sodium nitrite and nitrate, polyphosphates, wine and pepper) on growth and survival of two strains of S. aureus in model salami systems at 25°C was investigated. These additives are usually used in Argentinean salami formulation. The combinations of aw 0·925-pH 5·00, or aw 0·915 - pH 5·50 or aw 0·900 - pH 6·00, together with the addition of the additives, resulted in synergistic growth inhibition of both strains. Sodium nitrite and nitrate played an important role in the inhibition, while pepper, polyphosphates and wine had no effect in controlling the growth of these organisms. 相似文献
4.
Hamdi Barbaros Ozer Güven Uraz Ebru Beyzi-Yilmaz & Ahmet Ferit Atasoy 《International Journal of Food Science & Technology》2004,39(7):727-735
The survival of Staphylococcus aureus (St. aureus), Bacillus cereus, Yersinia enterocolitica, Eschericia coli O157:H7, Shigella flexneri (Sh. flexneri) and Salmonella enteritidis (Sa. enteritidis) in urfa cheese (a traditional white‐brined Turkish cheese) which was stored in brine concentrations varying from 12.5 to 17.5% (wt/v) was tested. Two sets of cheeses were made, namely scalded and unscalded cheeses (scalding was done by heating at 95 °C for 3 min). The variations in the counts of pathogenic colonies were monitored throughout a 90‐day storage period at <10 °C. Results indicated that scalding caused statistically significant reductions in the colony counts of Y. enterocolitica, E. coli O157:H7, Sh. flexneri and Sa. enteritidis during the early periods of storage. In contrast, St. aureus and B. cereus were not generally affected by scalding and brine concentrations, although B. cereus in 17.5% (wt/v) brine was affected. In the unscalded cheeses, 12.5 and 15.0% (wt/v) brine concentrations seemed to be insufficient to eradicate the pathogenic organisms examined. 相似文献
5.
The kinetics of Staphylococcus aureus (strains A, B, D) growth in bread crumb were determined as a function of water activity (Aw) from 0.836 to 0.909 at pH 5.2 to 5.5 and at 35°c. Adding glycerol to the dough or equilibrating the bread over saturated salt solutions adjusted the Aw of the bread. Growth kinetics data, plotted as enumerated colony counts versus incubation time, were fitted using the logistic function to determine maximum growth rates. Similar maximum growth rates resulted, irrespective of the method used to adjust Aw. Extrapolation of growth rate‐Aw results predicts the Aw corresponding to a zero growth rate. 相似文献
6.
Mirna L. Surez-Quiroz Oscar Gonzlez-Rios Michel Barel Bernard Guyot Sabine Schorr-Galindo Joseph P. Guiraud 《Food microbiology》2004,21(6):629-634
Post-harvest processing (traditional or ecological wet method, and dry method) and coffee pH did not play a significant role in Aspergillus ochraceus growth and OTA production. However, Aw did play a key role: the optimum for growth and toxigenesis was 0.95; below 0.80, coffee was protected. Temperature affected the rate of toxin production, when Aw was compatible: toxigenesis occurred from 10°C with an optimum at 35°C. The critical stage in the process was drying, where conditions propitious to A. ochraceus (Aw of 0.99–0.80) could be found for 2 days or more. Caffeine and chlorogenic acids had an inhibiting effect on OTA production. 相似文献
7.
Nam Keun Lee In-Cheol Yeo Joung Whan Park Byung-Sun Kang Young Tae Hahm 《Journal of Bioscience and Bioengineering》2010,110(3):298-303
In this study, an effective substance was isolated from Bacillus subtilis SC-8, which was obtained from traditionally fermented soybean paste, cheonggukjang. The substance was purified by HPLC, and its properties were analyzed. It had an adequate antagonistic effect on Bacilluscereus, and its spectrum of activity was narrow. When tested on several gram-negative and gram-positive foodborne pathogenic bacteria such as Salmonella enterica, Salmonella enteritidis, Staphylococcus aureus, and Listeria monocytogenes, no antagonistic effect was observed. Applying the derivative from B. subtilis SC-8 within the same genus did not inhibit the growth of major soybean-fermenting bacteria such as Bacillus subtilis, Bacillus licheniformis, and Bacillus amyloquefaciens. The range of pH stability of the purified antagonistic substance was wide (from 4.0 to >10.0), and the substance was thermally stable up to 60 °C. In the various enzyme treatments, the antagonistic activity of the purified substance was reduced with proteinase K, protease, and lipase; its activity was partially destroyed with esterase. Spores of B. cereus did not grow at all in the presence of 5 μg/mL of the purified antagonistic substance. The isolated antagonistic substance was thought to be an antibiotic-like lipopeptidal compound and was tentatively named BSAP-254 because it absorbed to UV radiation at 254 nm. 相似文献
8.
Ethanol in low concentrations (5–10% weight) affected aerobic growth (at 37°C) of two strains of Stuphylococcus aureus. Growth inhibition in laboratory media was observed with ethanol about 6–7% weight water activities (aw) of ~0.97. This suggested that the ethanol antibacterial effect was not only from its aw lowering ability. Electron microscopy observations showed intense morphological modifications in cells in broth with 5% to 6.5% ethanol, and clearly indicated that cell wall changes of S. aureus was partly responsible for the antibacterial action of ethanol. 相似文献
9.
The ability of eleven imitation (or substitute) cheeses to support the growth and toxin production of Staphylococcus aureus at 26°C was evaluated. All established enterotoxin serotypes were tested by inoculating suspensions of the requisite strains into 100-g samples of cheese (about 30 staphylococci/g). Water activity (aw) of the cheese samples ranged from 0.942–0.973; pH values ranged from 5.33–6.14. Seven cheeses supported extensive growth of S. aureus; one or more serotypes of enterotoxin were produced in six cheeses. Enterotoxin in the cheese was detected in 4 days at 3 × 106 staphylococci/g. However, the ability of some cheeses to support growth and toxin production of S. aureus could not be correlated with pH, aw, or product formulation. 相似文献
10.
ABSTRACT
Influence of water activity (Aw), pH and heat treatment on the chemical changes such as Maillard browning, oxidation and lipolysis in canned paneer has been studied by response surface methodology. Browning in canned paneer in terms of hydroxymethylfurfural content increased during storage; however, it was pH dependent. At pH above 5.0, the rate of browning decreased as Aw increased from 0.90 to 0.98. At pH below 5.0, the rate increased with increased Aw from 0.90 to 0.98. Maximum browning rates were observed at pH 5.2–5.6, low Aw values (0.90–0.92) and high heat treatment levels (up to F value 0.8). At all pH levels, increased Aw increased the oxidation rate, more so at low pH levels. Up to an F value of 0.3, heat treatment seemed to have aided the oxidation rate, but higher F values retarded the oxidation rate, more so at low Aw. Lipolysis occurred during storage, but pH had little effect on the rate of lipolysis. High Aw supported high lipolysis rates.PRACTICAL APPLICATIONS
Raw paneer (Indian cottage cheese), popular with people in Indian subcontinent and with Indian diasporas scattered in several countries, has a shelf life of less than a day at ambient temperatures. Several attempts are being made by workers to improve the shelf life of paneer by canning process so that its market within the country and abroad improves. However, canning at usual canning time–temperatures is leading to intense chemical changes in paneer, which is not being accepted by consumers. Authors have tried to obviate such unacceptable chemical changes by reducing the intensity of canning process by adjusting so called “hurdles” of the product by hurdle technology. The present paper is a part of that attempt describing the chemical changes in paneer subjected to low heat intensity canning process with altered “hurdles.” Because the chemical changes occurring in a food product are a function of various parameters called “hurdles” like pH, water activity, heat treatment, etc., the present work attempted to identify the combination of the “hurdles” at which chemical changes are the slowest, which may find better acceptance with consumers. 相似文献11.
Véronique Zuliani Isabelle Lebert Pascal Garry Jean-Luc Vendeuvre Jean-Christophe Augustin & André Lebert 《International Journal of Food Science & Technology》2006,41(10):1197-1206
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 (aw) were also tested. During the heat process phase, aw, the heat‐processing regime and its interactions with pH or aw, 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, aw 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. 相似文献
12.
Studies on sliced vacuum-packed Bologna-type sausage showed that some pathogenic bacteria may develop quickly at refrigeration temperatures. Yersinia enterocolitica grew rapidly even at 5°C, reaching 106 g?1 within 2 weeks. Other bacteria did not grow at 5°C, Staphylococcus aureus and Bacillus cereus grew at 8°C and Salmonella typhimurium and Salmonella enteritidis but not Clostridium perfringens grew at 12°C. Therefore even at temperatures which may be found in commercial refrigerators, growth of pathogenic bacteria is possible to levels which have been shown to represent a hazard to health. Gas permeability of the packgging film had relatively little effect. 相似文献
13.
David Aldred Victoria Cairns-Fuller Naresh Magan 《Journal of Stored Products Research》2008,44(4):341-346
This study determined the efficacy of three essential oils (bay, clove and cinnamon oil) and the antioxidant resveratrol (0–500 μg g−1) on the control of growth and ochratoxin A (OTA) production by Penicillium verrucosum and Aspergillus westerdijkiae (=A. ochraceus) under different water activity (aw, 0.90, 0.95, 0.995), and temperature (15, 25 °C) conditions on irradiated wheat grain. The most effective treatment (resveratrol) was then tested on natural grain. The ED50 values for growth inhibition by the oils were 200–300 μg g−1 at the aw and the temperatures tested. For resveratrol, this varied from <50 μg g−1 at 0.90–0.95 aw to >350 at 0.995aw at both temperatures. The ED50 values for the control of OTA were slightly lower than for control of growth, with approx. 200 μg g−1 required for the oils and 50–100 μg g−1 of the antioxidant, at 0.90/0.95aw and both temperatures. In wet grain (0.995aw), higher concentrations were required. For growth there were statistically significant effects of single-, two- and three-way interactions between treatments except for concentration×temperature and concentration×temperature×essential oil/antioxidant treatment. For OTA control, statistically significant treatments were aw, temperature×aw, concentration×temperature, treatment×concentration, and three-way interaction of concentration×aw×treatment for P. verrucosum and A. westerdijkiae. Subsequent studies were done with the best treatment (resveratrol, 200 μg g−1) on natural wheat grain with either P. verrucosum or A. westerdijkiae at 0.85–0.995aw and 15/25 °C over 28 days storage. This showed that the populations of the mycotoxigenic species and OTA contamination could be reduced by >60% by this treatment at the end of the storage period. 相似文献
14.
Ubonrat Siripatrawan Waranya Vitchayakitti Romanee Sanguandeekul 《International Journal of Food Science & Technology》2013,48(1):22-27
The potential of using propolis collected from Thailand as a natural antioxidant and antimicrobial agent for food applications was investigated. The propolis extract was prepared by using different ethanol aqueous solutions, including 30%, 40%, 50% and 70%. Total phenolic content (TPC), phenolic compound and antioxidant activity of the propolis were determined using Folin–Ciocalteau method, high performance liquid chromatography (HPLC) and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging activity, respectively. The antimicrobial ability was tested against Staphylococcus aureus (TISTR 118), Salmonella enteritidis (DMST 17368), Escherichia coli (TISTR 780) and Pseudomonas aeruginosa (ATCC 27853) using disc diffusion technique. The major phenolic compounds found in Thai propolis were rutin, quercetin and naringin. The TPC and DPPH radical scavenging activity increased with increasing ethanol concentration in the solvent. Propolis extract showed antimicrobial activity, in terms of inhibitory zone for S. aureus and limited growth underneath paper discs, against all tested bacteria. 相似文献
15.
U. Messelh?usser M. Fricker M. Ehling-Schulz H. Ziegler D. Elmer-Englhard W. Kleih U. Busch 《Journal für Verbraucherschutz und Lebensmittelsicherheit》2007,184(3):190-193
Bacillus cereus is a Gram-positive, facultative anaerobic, spore-performing bacterium. Some B. cereus strains have the ability to produce two different types of toxins: (a) diarrhoeic toxin: the disease is similar to a C. perfringens toxin-infection; it is caused by a heat-labile protein, (b) emetic toxin: the disease is similar to Staphylococcus-aureus intoxikation; it is caused by a heat-stable protein.
Statements about the frequency of B. cereusfood-poisonings are difficult because a reporting system for this disease is missing in Germany and there exists no valid
methodology to diagnose this disease with conventional microbiological or biochemical methods. Nevertheless B. cereus, beside S. aureus, seems to be the most important bacterium to cause food-associated intoxications. 相似文献
16.
Daekeun Hwang Jin Hwa Park Yohan Yoon Sang-Do Ha Min Suk Rhee Minseon Koo Hyun Jung Kim 《Journal of Food Safety》2023,43(1):e13025
In this study, we developed a mathematical model to describe the fate of Bacillus cereus in Saengsik, a powdered ready-to-eat food with reduced moisture content, and to estimate the probability of B. cereus infection from Saengsik consumption, using quantitative microbial risk assessment (QMRA). The isothermal kinetic behavior of B. cereus was analyzed as a function of temperature (5–40°C). Bacterial cell counts were fitted to the Weibull model using GinaFit, and the obtained delta values (required time for the first decimal reduction) for each temperature were 128.3–17,124.1 hr and concave (ρ < 1) were observed under all experimental conditions. The obtained delta values were analyzed using the Davey model as a function of temperature, and the performance of the developed model of survival of B. cereus was appropriate based on the validation parameters (Bf, Af, and RMSE) within the acceptable range. QMRA model was developed using data on the prevalence and concentration of B. cereus along with time and temperature along the retail-to-consumer steps. Using a baseline model with the currently available data, the probability of B. cereus infection was zero. These results provide useful information for the risk assessment and management of microbial risk in foods, especially those with very low-moisture content. 相似文献
17.
《Food research international (Ottawa, Ont.)》2000,33(3-4):273-280
The effect of different concentrations (0–1.2% v/v) of mint (Mentha piperita) essential oil on the growth/survival of Salmonella enteritidis and Staphylococcus aureus was studied in nutrient broth, using the viable count method and conductance measurements. In particular the addition of mint essential oil reduced the total viable counts of St. aureus about 6–7 logs while this of S. enteritidis only ca. 3 logs. The detection time measurements showed also that the inhibitory effect of mint essential oil was affected by the incubation temperature as well as by the concentration of essential oil added in the growth medium. At low concentration of essential oil (<0.1%), the addition of glucose in the growth medium prevented the formation of staphylococcal enterotoxin B, while the reduction of viable cells was only 2 logs. This glucose effect was not evident in Salmonella enteritidis samples. The percentage of glucose utilization in the growth medium of both pathogens, was reduced drastically with the addition of essential oil and as a consequence the assimilation or formation of different compounds, such as lactate, formate and acetate in the growth medium was also affected. 相似文献
18.
Frédéric Carlin Christine Albagnac Ammar Rida Marie-Hélène Guinebretière Olivier Couvert Christophe Nguyen-the 《Food microbiology》2013
The growth rates of strains covering the seven major phylogenetic groups of Bacillus cereus sensu lato (as defined by Guinebretiere et al., 2008) at a range of temperature (7 °C–55 °C), pH (4.6–7.5) and aw (0.929–0.996, with 0.5%–10% NaCl as humectant) were determined. Growth rates were fitted by non-linear regression to determine the cardinal parameters Tmin, Topt, Tmax, pHmin, pHopt, awmin and μopt. We showed that cardinal parameters reflected the differences in the temperature adaptation observed between B. cereus phylogenetic groups I to VII. The ability of growing at low pH (up to 4.3) or low aw (from aw 0.929 and up to 10% NaCl) varied among strains. The strains of groups III and VII, the most tolerant to heat, were also the most adapted to high NaCl (all strains growing at 8% NaCl) and the ones of groups I and VI the least adapted (no growth at 7% NaCl). All strains of groups II and VII were able to grow at pH 4.6, and only a few strains of group VI. Phenotypic differences between the two psychrotrophic groups II and VI were revealed by contrasted acid and salt tolerance. The cardinal values determined in this work were validated by comparing with cardinal parameters of a panel of strains published elsewhere and with predictions of growth in a range of foods. 相似文献
19.
The influence of growth conditions, treatment medium characteristics and PEF process parameters on the lethal effect on Yersinia enterocolitica of pulsed electric fields (PEF) treatments in batch has been investigated. Growth phase, temperature of growth, pH, conductivity of the treatment medium, pulse width and frequency of pulses did not influence the sensitivity of Y. enterocolitica to PEF. However, an Aw decrease from >0.99 to 0.93 of the treatment medium increased the PEF resistance of Y. enterocolitica with 3.5 log10 cycles after a treatment of 22 kV/cm, 800 μs and 880 kJ/kg. Inactivation of Y. enterocolitica increased with the field strength, treatment time and total specific energy up to a maximum of 6 log10 cycles after 28 kV/cm, 2000 μs and 3559 kJ/kg. A nonlinear relationship was found among the survival fraction and the treatment time or the specific energy that was accurately described by a mathematical model based on the Weibull distribution. The inactivation of Y. enterocolitica by PEF was characterized by maximum field strength thresholds. Above these thresholds, specific energy necessary to obtain a given level of inactivation scarcely decreased by increasing the electric field strength, and inactivation of Y. enterocolitica only depended on the specific energy applied. 相似文献
20.
Initially, the effect of water activity (aw) on heat resistance of Bacillus cereus spores (decimal reduction time) was investigated. A linear relationship was found between log D and 1-aw. The combined effects of temperature (85-105°C), pH (4.5-6.5) and water activity (0.80-1) were then studied. A four parameter model was fitted to the data. This model appeared to be parsimonious with each parameter having a biological significance. Interactions between factors were observed but they accounted for <2.4% of the total variation and they were not taken into account by the model. 相似文献