壳聚糖抗菌膜中山梨酸钾迁移的数学模型及实验分析

运用Fick第二定律对壳聚糖抗菌膜中山梨酸钾的迁移过程进行预测,建立其数学模型。结果表明,当山梨酸钾初始浓度相同,壳聚糖浓度升高时,扩散系数D减小;当壳聚糖浓度不变时,山梨酸钾浓度升高扩散系数D变大。通过幂律模型Mt/M∞=k×tn可确定实验中的山梨酸钾在壳聚糖抗菌膜中迁移机制的类型为菲克扩散。     

Use of logistic regression with dummy variables for modeling the growth-no growth limits of Saccharomyces cerevisiae IGAL01 as a function of sodium chloride, acid type, and potassium sorbate concentration according to growth media

A global logistic model was used to study the effects of both quantitative variables (NaCl, acid, and potassium sorbate concentrations) and dummy variables (laboratory medium or brine, and citric, lactic, or acetic acids) on growth of Saccharomyces cerevisiae IGAL01. The deduced equations, with the significant coefficients selected by a backward stepwise procedure, allowed estimations of the simultaneous comparison of behaviors of levels of the qualitative variables as a function of the quantitative variables and the development of the growth-no growth limits according to laboratory medium or brine and the different types of acidifying agents. The S. cerevisiae growth region in yeast malt glucose peptone broth was always wider than that in brine, in which this yeast was inhibited by 0.03% potassium sorbate and 6% NaCl, when the acid concentration (regardless of type) was 0.2 to 0.3%. These results demonstrate the applicability of such model designs to include qualitative variables in investigations related to the development of growth-no growth limits.     

Modeling the aerobic growth and decline of Staphylococcus aureus as affected by pH and potassium sorbate concentration.

The effects of pH (5.0, 5.2, 5.4, 5.6, and 5,8) and concentration of potassium sorbate (10.0 and 16.6 mM) at two water activity values (0.90 and 0.92) on the aerobic growth and decline of Staphylococcus aureus ATCC 6538P, 196-E, and FDA-C243 were studied using brain-heart infusion broth. The inoculum was approximately 4 to 5 log CFU/ml, and the incubation temperature was 30 degrees C. Samples were periodically enumerated on tryptic soy agar. The Gompertz model was used to obtain microbial growth parameters, specific growth rate was obtained as a derived parameter, and the inhibition index was calculated. A linear model was fitted in cases of bacteriostatic or bactericidal action of the treatment. The ATCC 6538P strain showed the highest resistance in the range of tested conditions. Microbial behavior was modeled considering the main controlling factors, and a response surface methodology was used to determine the effects of undissociated acid concentration and pH. These results can be used to establish treatment conditions for microorganism growth or inhibition.     

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.     

Mathematical modeling of Saccharomyces cerevisiae inactivation under high-pressure carbon dioxide

High-pressure carbon dioxide inactivation curves of Saccharomyces cerevisiae at different temperatures were analysed using the modified Gompertz model. Comparable lambda and mu values were obtained under pressure treatment as function of temperature. The phase of disappearance (lambda) and the inactivation rate (mu) of S. cerevisiae were inversely related. Higher mu values were obtained at 50 degrees C than at 40, 30 and 20 degrees C under 10.0 MPa CO2 pressure. Increased pressure and temperature had significant effects on the survival of S. cerevisiae. Arrhenius, linear and square-root models were used to analyse the temperature dependence of the inactivation rate constant. For the Arrhenius model the activation energy (E(mu)) was 56.49 kJ/mol at 10.0 MPa, and 55.70, 53.83 and 52.20 kJ/mol at 7.5, 5.0, and 2.5 MPa, respectively. Results of this study enable the prediction of yeast inactivation exposed to different CO2 pressures and temperatures.     

Combined effects of potassium sorbate,hot water and thiabendazole against green mould of citrus fruit and residue levels

Postharvest treatments of potassium sorbate only controlled recently established infections of Penicillium digitatum on Femminello siracusano lemons but did not confer any persistent protection. The loss of efficacy of potassium sorbate to control green mould decay was related to its irregular deposition on the fruit surface, as revealed by environmental scanning electron microscopy of oranges, and to the brief persistence of potassium sorbate residues. When treatment was done at 53 °C, the co-application of potassium sorbate with thiabendazole reduced thiabendazole residues in Moro and Sanguinello oranges, compared to thiabendazole treatment alone. However, treatment efficacy against two isolates of P. digitatum (thiabendazole-sensitive and thiabendazole-resistant) notably improved, indicating that potassium sorbate and hot water potentiated thiabendazole activity. Potassium sorbate residues remarkably decreased during fruit storage and were not affected by the co-application of thiabendazole.     

Vanadate inhibition of mitochondrial respiration and H+ ATPase activity in Saccharomyces cerevisiae

The effects of vanadate on mitochondrial respiration and H+ ATPase activity in Saccharomyces cerevisiae were studied. A 50% inhibition of oxygen uptake in isolated mitochondria was produced by 4.4 mM-V2O5. Activity of H+ ATPase in whole mitochondria was inhibited by 50% by 5.5 microM-V2O5, in submitochondrial particles by 55 microM-V2O5; and in the chloroform-released H+ ATPase by 0.5 mM-V2O5. Vanadate was also found to relieve growth inhibition caused by the mitochondrial H+ ATPase inhibitors NN'-decyclohexylcarbodiimide and oligomycin. These results imply that vanadate could affect mitochondrial respiration by interacting with the H+ ATPase in S. cerevisiae.     

高浓度柠檬酸对酿酒酵母生长的抑制效应

在果酒酿造过程中,酿酒酵母会面临果实中有机酸尤其柠檬酸的胁迫。 该研究系统地考察了酿酒酵母（Saccharomyces cere- visiae）EC1118和2323在酵母膏蛋白胨葡萄糖液体培养基中的生长情况,在3种不同柠檬酸浓度和pH值培养条件下,分析两种酿酒酵 母的生长曲线,揭示柠檬酸对酿酒酵母生长抑制的机制。 结果表明,高浓度柠檬酸（0.10～0.40 mol/L）会抑制酿酒酵母生长;pH值≤2.80 时,酿酒酵母的生长均受到抑制。高浓度柠檬酸的抑制效应是氢离子和柠檬酸根的叠加影响,而且柠檬酸根的影响占主导。该研究结 果将为进一步解除有机酸对酿酒酵母抑制效应以及果酒研制提供一定参考。     

Individual effects of sodium, potassium, calcium, and magnesium chloride salts on Lactobacillus pentosus and Saccharomyces cerevisiae growth

A quantitative investigation on the individual effects of sodium (NaCl), potassium (KCl), calcium (CaCl2), and magnesium (MgCl2) chloride salts against Lactobacillus pentosus and Saccharomyces cerevisiae, two representative microorganisms of table olives and other fermented vegetables, was carried out. In order to assess their potential activities, both the kinetic growth parameters and dose-response profiles in synthetic media (deMan Rogosa Sharpe broth medium and yeast-malt-peptone-glucose broth medium, respectively) were obtained and analyzed. Microbial growth was monitored via optical density measurements as a function of contact time in the presence of progressive chloride salt concentrations. Relative maximum specific growth rate and lag-phase period were modeled as a function of the chloride salt concentrations. Moreover, for each salt and microorganism tested, the noninhibitory concentrations and the MICs were estimated and compared. All chloride salts exerted a significant antimicrobial effect on the growth cycle; particularly, CaCl2 showed a similar effect to NaCl, while KCl and MgCl2 were progressively less inhibitory. Microbial susceptibility and resistance were found to be nonlinearly dose related.     

Mathematical modeling of Saccharomyces cerevisiae inactivation under high‐pressure carbon dioxide

High‐pressure carbon dioxide inactivation curves of Saccharomyces cerevisiae at different temperatures were analysed using the modified Gompertz model. Comparable λ and μ values were obtained under pressure treatment as function of temperature. The phase of disappearance (λ) and the inactivation rate (μ) of S. cerevisiae were inversely related. Higher μ values were obtained at 50°C than at 40, 30, and 20°C under 10.0 MPa CO₂ pressure. Increased pressure and temperature had significant effects on the survival of S. cerevisiae. Arrhenius, linear and square‐root models were used to analyse the temperature dependence of the inactivation rate constant. For the Arrhenius model the activation energy (E_μ) was 56.49 kJ/mol at 10.0 MPa, and 55.70, 53.83, and 52.20 kJ/mol at 7.5, 5.0, and 2.5 MPa, respectively. Results of this study enable the prediction of yeast inactivation exposed to different CO₂ pressures and temperatures.     

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   

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.     

Combined effect of water activity and pH on the inhibition of Escherichia coli by nisin

The Doehlert design and surface response methodology were used to study the influence of pH and water activity (aw) on Escherichia coli inhibition by nisin. Combining stress factors at levels where they are not inhibitory by themselves, a reduction of E. coli survival fraction can be achieved with lower nisin doses than in a single nisin treatment. For all the pH values assayed, a synergistic effect of aw and nisin concentration was detected, and the isoresponse lines showed the existence of an area of maximum inhibition. Factors that reduced viable cell counts by 4 to 5 log cycles were 1,000 to 1,400 IU of nisin per ml at pH 5.5 to 6.5 and a water activity of 0.97 and 0.98. The addition of different ionic and nonionic solutes to control aw suggested that the effect of aw in the inhibitory action of nisin on E. coli cells was not solute-specific. The use of the Doehlert experimental design was effective to determine the optimal combination of stress factors, as well as to point out the most important variables that affected E. coli inhibition.     

Galactose inhibition of the constitutive transport of hexoses in Saccharomyces cerevisiae

The relationship between the pathways of glucose and galactose utilization in Saccharomyces cerevisiae has been studied. Galactose (which is transported and phosphorylated by inducible systems) is a strong inhibitor of the utilization of glucose, fructose and mannose (which have the same constitutive transport and phosphorylation systems). Conversely, all these three hexoses inhibit the utilization of galactose, though with poor efficiency. These cross-inhibitions only occur in yeast adapted to galactose or in galactose-constitutive mutants. The efficiency of galactose as inhibitor is even greater than the efficiencies of each of the other three hexoses to inhibit the utilization of each other. Phosphorylation is not involved in the inhibition and the transport of sugars is the affected step. The cross-inhibitions between galactose and either glucose, fructose or mannose do not implicate utilization of one hexose at the expense of the other, as it occurs in the mutual interactions between the latter three sugars. It seems that, by growing the yeast in galactose, a protein component is synthesized, or alternatively modified, that once bound to either galactose or any one of the other three hexoses (glucose, fructose or mannose), cross-interacts respectively with the constitutive or the inducible transport systems, impairing their function.     

Evaluation of the effects of sodium chloride,potassium sorbate,nisin and lysozyme on the probability of growth of Clostridium sporogenes

The aim of this study was to evaluate the combined effect of salt (sodium chloride, 0–8% w/v), sorbate (potassium sorbate, 0–4.5% w/v), nisin (0–500 ppm) and lysozyme (0–500 ppm) on the survival of Clostridium sporogenes as a non‐toxigenic surrogate of Clostridium botulinum in terms of the probability of growth by using a central composite rotatable design. The results indicated that salt and sorbate were the most effective factors in preventing the growth of Cl. sporogenes in high‐moisture (>95%) and low‐acid conditions. The probability of growth of Cl. sporogenes in broth was reduced by combinations of salt and sorbate. Nisin and lysozyme had insignificant effects on the probability of growth of Cl. sporogenes (P > 0.05). Lysozyme individually and in combination with nisin had no inhibitory effect on Cl. sporogenes. Overall, the addition of sorbate and lysozyme may allow the salt concentration to be reduced while preventing growth.     

Effect of ultrasound on the survival of Saccharomyces cerevisiae: influence of temperature,pH and amplitude

The resistance of Saccharomyces cerevisiae cells to the action of ultrasound (20 kHz, wave amplitude in the range 71–110 μm) was analyzed at 35, 45 and 55°C in Sabouraud broth at pH 3.0 and 5.6. The inactivation rate where a first-order kinetic was observed exhibited D values between 0.5 and 31 min. The resistance of the yeast decreased as ultrasonic wave amplitude increased, with the z values for this effect ranging between 128 and 323 μm. In the pH range investigated, the reduction of pH did not affect ultrasound yeast sensitivity except for experiments performed at 71.4 μm wave amplitude and 45°C. At moderate temperatures, decimal reduction time values were reduced by the simultaneous effect of ultrasound but at 55°C, no advantages were observed by adding sonication. Structural studies performed in cells sonicated at 45°C and 95.2 μm of wave amplitude indicated the treatment provoked puncturing of cell walls with leakage of content as well as damage at subcellular level. However, when ultrasound was applied at 55°C, no structural differences were appreciated between sonicated cells and only heat-treated cells.     

山梨酸钾、异抗坏血酸钠及包装方式对鲜切梨的影响

目的在于寻找一种操作简单、费用低廉且有效的保鲜贮藏方法。通过正交实验,观察鲜切梨表面微生物的生长和表面颜色的变化情况,筛选出最佳的处理方案为:0.1%山梨酸钾、2.0%异抗坏血酸钠处理,保鲜盒包装,5℃贮藏。然后测定此条件下鲜切雪花梨的生理生化变化,结果表明,鲜切梨内层各项指标要优于外层。0.1%山梨酸钾、2.0%异抗坏血酸钠处理,保鲜盒包装可以有效抑制PPO和POD活性,提高CAT活性,抑制膜脂过氧化程度的加重,改善鲜切梨的感官及内在品质。