Influence of water activity and acidity on Bacillus cereus spore inactivation during combined high pressure-thermal treatment

Inactivation of Bacillus cereus spores by ohmic heating: Efficiency and changes of spore biological properties

Bacillus cereus spores pose a significant concern during food processing due to their high resistance to environmental stress. Ohmic heating (OH) is an emerging and alternative heating technology with potential for inactivating such spores. This study evaluated the inactivation effects and the biological property changes of Bacillus cereus spores during OH treatments. OH effectively inactivated spores in milk, orange juice, broth, rice soup, and buffer solution in less time than oil bath heating (OB). A decrease in NaCl content improved spore inactivation at the same temperature. Spores were more sensitive to acid at 80-85 °C with OH treatment. Furthermore, OH at 10 V/cm and 50 Hz could reduce the spore resistance and inhibit an increase in spore hydrophobicity and spore aggregation. Both heating methods resulted in significant dipicolinic acid (DPA) leakage and damage to the cortex and inner membranes of the spores. However, OH at 10 V/cm and 50 Hz had the lowest DPA leakage and inflicted the least damage to the inner membrane. The damage to the spore's inner membrane was considered the primary reason for inactivation by OB and OH treatments. Still, OH at 10 V/cm and 50 Hz might also block the germination or outgrowth of treated spores or cause damage to the spore core.

Joint effect of heat, pH and grape extract on Bacillus cereus spores survival in a rice solution

Rice due to its high carbohydrate content, is an ideal medium for Bacillus cereus growth, a spore-producing microorganism. The objective of this study was to determine the antimicrobial activity of a grape extract in combination with heat treatments and different pH against B. cereus spores in a rice solution. The survivor data obtained were fitted to the Weibull survival function, and the values of parameters a and b (scale and shape indexes, respectively) were determined. Results showed that the grape extract affected the survival of B. cereus spores at 90 °C and 95 °C, reaching greater logarithmic reductions in acidic pH values. This behaviour was reflected in a parameter of the Weibull survival function which decreased as the temperature increased and at acidic pH values. In addition, a secondary model was developed by relating the logarithm of a to the independent variables (temperature and pH). A global model relating B. cereus inactivation with temperature and pH was developed, and validated by calculating the accuracy factor. The results demonstrate the usefulness of grape extract as a by-product, which can be used as an additional control measure for rice, especially when combined with mild heat treatments and acidic pH values.

High-pressure pulses for Aspergillus niger spore inactivation in a model pharmaceutical lipid emulsion

High hydrostatic pressure (HHP) is a non-thermal process widely used in the food industry to reduce microbial populations. However, rarely its effect has been assessed in products with high oil content. This study evaluated the efficacy of HHP (200, 250, and 300 MPa) at different temperatures (25, 35, and 45 °C) by cycles (1, 2, or 3) of 10 min in the inactivation of Aspergillus niger spores in a lipid emulsion. After treatments at 300 MPa for 1 cycle at 35 or 45 °C, no surviving spores were recovered. All treatments were modeled by the linear and Weibull models. The presence of shoulders and tails in the treatments at 300 MPa at 35 or 45 °C resulted in sigmoidal curves which cannot be described by the linear model, hence the Weibull + Tail, Shoulder + Log-lin + Tail, and double Weibull models were evaluated to elucidate the inactivation kinetics. The tailing formation could be related to the presence of resistance subpopulations. The double Weibull model showed better goodness of fit (RMSE <0.2) to describe the inactivation kinetics of the treatments with the higher spore reductions. HHP at 200-300 MPa and 25 °C did not reduce the Aspergillus niger spores. The combined HHP and mild temperatures (35-45 °C) favored fungal spore inactivation. Spore inactivation in lipid emulsions by HHP did not follow a linear inactivation. HHP at mild temperatures is an alternative to the thermal process in lipid emulsions.

High-pressure pasteurization of low-acid chilled ready-to-eat food

The working population growth have created greater consumer demand for ready-to-eat (RTE) foods. Pasteurization is one of the most common preservation methods for commercial production of low-acid RTE cold-chain products. Proper selection of a pasteurization method plays an important role not only in ensuring microbial safety but also in maintaining food quality during storage. Better retention of flavor, color, appearance, and nutritional value of RTE products is one of the reasons for the food industry to adopt novel technologies such as high-pressure processing (HPP) as a substitute or complementary technology for thermal pasteurization. HPP has been used industrially for the pasteurization of high-acid RTE products. Yet, this method is not commonly used for pasteurization of low-acid RTE food products, due primarily to the need of additional heating to thermally inactivate spores, coupled with relatively long treatment times resulting in high processing costs. Practical Application: Food companies would like to adopt novel technologies such as HPP instead of using conventional thermal processes, yet there is a lack of information on spoilage and the shelf-life of pasteurized low-acid RTE foods (by different novel pasteurization methods including HPP) in cold storage. This article provides an overview of the microbial concerns and related regulatory guidelines for the pasteurization of low-acid RTE foods and summarizes the effects of HPP in terms of microbiology (both pathogens and spoilage microorganisms), quality, and shelf-life on low-acid RTE foods. This review also includes the most recent research articles regarding a comparison between HPP pasteurization and thermal pasteurization treatments and the limitations of HPP for low-acid chilled RTE foods.