Kinetics of the thermal degradation of patulin in the presence of ascorbic acid.

Degradation of the mycotoxin patulin between 25 and 85 °C without and with added ascorbic acid was studied, and the effectiveness of linear and nonlinear models for predicting reaction rates was compared. In agreement with previous reports, ascorbic acid significantly increased (P ≤ 0.05) the rate of patulin degradation at all temperatures studied. The data for patulin degradation in the absence of ascorbic acid were adequately modeled using a zero-order linear kinetic model. However, the predictive abilities of zero and higher-order linear models were not adequate to describe the more complex reactions that likely occurred when ascorbic acid was added. In contrast, the nonlinear Weibull model adequately described the patulin-ascorbic acid reaction throughout the temperature range studied. Zero-order rate constants and Weibull scale values for each of the respective reactions followed the Arrhenius law. Activation energies of 58.7 ± 3.9 and 29.6 ± 1.9 kJ mol⁻¹ for the reaction without and with ascorbic acid, respectively, confirmed decreased patulin stability in the presence of ascorbic acid and suggested that the mechanisms for the 2 degradation reactions were different.

Modified agar diffusion bioassay for better quantification of Nisaplin(®).

AIMS: To investigate the effect of different well sizes and pre-diffusion times at 4 °C, on the sensitivity, accuracy and precision of nisin quantification by agar diffusion bioassay. METHODS AND RESULTS: Nisin solution (0.625-125 µg ml(-1) ) was filled in wells (3.5 mm or 7 mm diameter) made on agar plates inoculated with Micrococcus luteus, followed by pre-diffusion (0, 24, 48 or 72 h), incubation and measurement of inhibition zone. Regression analysis indicated that wells with 3.5 mm diameter had smaller standard deviation and higher predictive accuracy, compared to wells with 7 mm diameter. Based on Tukey's test, pre-diffusion resulted in significantly different inhibition zones at different nisin concentrations. Pre-diffusion also improved sensitivity of the assay. Different regression models were considered to explore the relationship between inhibition zone and nisin concentration for different pre-diffusion times. A spline model was determined to be the best-fit model, and 48 h was the best pre-diffusion time. CONCLUSIONS: Wells with 3.5 mm diameter demonstrated higher accuracy for nisin quantification compared to wells with 7 mm diameter. 48 h was the best pre-diffusion time for nisin concentration in the range 0.625-125 µg ml(-1) . SIGNIFICANCE AND IMPACT OF THE STUDY: The findings from this study will be helpful in quantifying nisin and compounds with antimicrobial properties accurately over a wide range of concentrations using agar diffusion bioassay.

Effect of sucrose on physical properties of spray-dried whole milk powder.

Spray-dried whole milk powders were prepared from whole condensed milk with various sucrose concentrations (0%, 2.5%, 5%, 7.5%, and 10% w/w), and their glass transition temperature and some physical properties of importance in chocolate manufacture were evaluated. In milk powder samples, the glass transition temperature and free-fat content decreased in a nonlinear manner with sucrose addition. Moreover, increasing sucrose concentration reduced the formation of dents on the particle surface. Addition of sucrose in whole condensed milk increased linearly the apparent particle density and in a nonlinear manner the particle size of spray-dried milk powders. The particle size volume distribution of milk powders with the highest sucrose concentration differed from the log-normal distribution of the other samples due to the formation of large agglomerates. Neither vacuole volume, nor the amorphous state of milk powders was affected by sucrose addition.

Response surface modeling for the inactivation of Escherichia coli O157:H7 on green peppers (Capsicum annuum L.) by chlorine dioxide gas treatments.

The effects of chlorine dioxide (ClO2) gas concentration (0.1 to 0.5 mg/liter), relative humidity (RH) (55 to 95%), treatment time (7 to 135 min), and temperature (5 to 25 degrees C) on inactivation of Escherichia coli O157:H7 on green peppers were studied using response surface methods. A four-factor, central, composite, rotatable design was used. The microbial log reduction was measured as a response. A direct membrane-surface-plating method with tryptic soy agar and sorbitol MacConkey agar was used to resuscitate and enumerate ClO2-treated E. coli O157:H7 cells. The statistical analysis and the predictive model developed in this study suggest that ClO2 gas concentration, treatment time, RH, and temperature all significantly (P < 0.01) increased the inactivation of E. coli O157:H7. ClO2 gas concentration was the most important factor, whereas temperature was the least significant. The interaction between ClO2 gas concentration and RH indicated a synergistic effect. The predictive model was validated, and it could be used to determine effective ClO2 gas treatments to achieve a 5-log reduction of E. coli O157:H7 on green peppers.

Heat inactivation of Escherichia coli O157:H7 in apple cider containing malic acid, sodium benzoate, and potassium sorbate.

The effect of pH modification and preservative addition in apple cider on the heat resistance of Escherichia coli O157:H7 was investigated. E. coli O157:H7 and various amounts of potassium sorbate (0 to 0.2%), sodium benzoate (0 to 0.2%), and malic acid (0 to 1%) were added to apple cider. Thermal inactivation experiments were performed at 47, 50, and 53 degrees C, and D- and z-values were calculated. In apple cider without additives, the D-value at 50 degrees C (D50) was about 65 min, but addition of preservatives and malic acid significantly (P < 0.01) decreased D-values. D50-values decreased to 13.9 min in cider with 0.5% malic acid, 13.2 min with 0.1% sorbate, and 7.0 min with 0.1% benzoate added. Addition of both sorbate and malic acid had similar effects as either one alone, thus additive effects were not present. However, addition of both 0.2% benzoate and 1% malic acid did show additive effects, lowering D50 to 0.3 min. Addition of all three components (0.2% sorbate, 0.2% benzoate, and 1% malic acid) resulted in a D50 = 18 s. The z-value of cider without additives was about 6 degrees C, whereas z-values of cider containing malic acid, benzoate, and/or sorbate ranged from about 6 degrees C to 26 degrees C. This increase may result in a longer 5-log reduction time at higher temperatures (i.e., 70 degrees C) in cider with benzoate as compared to cider without additives.

Biological control of Botrytis cinerea growth on apples stored under modified atmospheres.

The combined effect of modified-atmosphere packaging and the application of a bacterial antagonist (Erwinia sp.) on Botrytis cinerea growth on apples (cv. 'Golden Delicious') was investigated. Inoculated apples were stored in polyethylene bags at 5 degrees C. The initial gas composition in each bag was set according to a central composite experimental design involving five levels of O2 (1 to 15%) and CO2 (0 to 15%). Control samples under ambient conditions were also included. Without the antagonist, measurements of mold colony diameter over time showed that O2 had no effect on the growth of B. cinerea, while increased CO2 levels delayed its growth by about 4 days. Application of the antagonist resulted in a significant interaction between O2 and CO2. At low O2 levels, CO2 had no effect on mold growth, but at high O2, CO2 enhanced mold growth. O2 and the antagonist worked synergistically to reduce mold growth by about 6 days at low levels of CO2. However, at high CO2 levels, O2 had no effect. The strongest antagonistic effect was observed under ambient conditions. Overall, results showed that high CO2 atmospheres can slow the growth of B. cinerea and that Erwinia sp. was an effective antagonist against B. cinerea growth on apples, particularly under ambient conditions.

Migration and sorption phenomena in packaged foods.

Rapidly developing analytical capabilities and continuously evolving stringent regulations have made food/package interactions a subject of intense research. This article focuses on: (1) the migration of package components such as oligomers and monomers, processing aids, additives, and residual reactants in to packaged foods, and (2) sorption of food components such as flavors, lipids, and moisture into packages. Principles of diffusion and thermodynamics are utilized to describe the mathematics of migration and sorption. Mathematical models are developed from first principles, and their applicability is illustrated using numerical simulations and published data. Simulations indicate that available models are system (polymer-penetrant) specific. Furthermore, some models best describe the early stages of migration/sorption, whereas others should be used for the late stages of these phenomena. Migration- and/or sorption-related problems with respect to glass, metal, paper-based and polymeric packaging materials are discussed, and their importance is illustrated using published examples. The effects of migrating and absorbed components on food safety, quality, and the environment are presented for various foods and packaging materials. The impact of currently popular packaging techniques such as microwavable, ovenable, and retortable packaging on migration and sorption are discussed with examples. Analytical techniques for investigating migration and sorption phenomena in food packaging are critically reviewed, with special emphasis on the use and characteristics of food-simulating liquids (FSLs). Finally, domestic and international regulations concerning migration in packaged foods, and their impact on food packaging is briefly presented.