Efficacy of Pressure-Assisted Thermal Processing, in Combination with Organic Acids, against Bacillus amyloliquefaciens Spores Suspended in Deionized Water and Carrot Puree

ABSTRACT:  Effect of organic acids (acetic, citric, and lactic; 100 mM, pH 5) on spore inactivation by pressure-assisted thermal processing (PATP; 700 MPa and 105 °C), high pressure processing (HPP; 700 MPa, 35 °C), and thermal processing (TP; 105 °C, 0.1 MPa) was investigated.  Bacillus amyloliquefaciens  spores were inoculated into sterile organic acid solutions to obtain a final concentration of approximately 1.3 × 10⁸ CFU/mL.  B. amyloliquefaciens  spores were inactivated to undetectable levels with or without organic acids after 3 min PATP holding time. At a shorter PATP treatment time (approximately 2 min), the inactivation was greater when spores were suspended in citric and acetic acids than in lactic acid or deionized water. Presence of organic acids during PATP resulted in 33% to 80% germination in the population of spores that survived the treatment. In contrast to PATP, neither HPP nor TP, for up to 5 min holding time with or without addition of organic acids, was sporicidal. In a separate set of experiments, carrot puree was tested, as a low-acid food matrix, to study spore recovery during extended storage following PATP. Results showed that organic acids were effective in inhibiting spore recovery in treated carrot puree during extended storage (up to 28 d) at 32 °C. In conclusion, addition of some organic acids provided significant lethality enhancement ( P  < 0.05) during PATP treatments and suppressed spore recovery in the treated carrot puree.     

Effect of combined microwave‐hot air drying and superheated steam drying on physical and chemical properties of rice

Jasmine rice (Oryza sativa L.) was subjected to two drying operations: combined microwave‐hot air drying (MHA) at initial power intensity of 3, 4 and 6 W g^?1 and superheated steam drying (SHS) at 300 °C and 400 °C. During drying, kinetic rate constants of SHS were significantly higher than those of MHA. Both drying operations could decrease enthalpy of starch gelatinisation from 9.28 J g^?1 to 1.64–6.17 J g^?1, increase gelatinisation extent to 33.51–82.33%, decrease crystallinity from 28.87% to 18.15–21.33%, improve scavenging ability of 1,1‐diphenyl‐2‐picrylhydrazyl, increase ferric reducing antioxidant power and increase hardness of cooked rice from 5.66 N to 5.83–6.55 N, depending on microwave power and drying medium temperature. However, taste profiles and liking scores were comparable to the regular brown rice. Therefore, MHA and SHS operations could be potentially used for reducing drying process and promoting antioxidant activity.     

High-throughput detection of spore contamination in food packages and food powders using tiered approach of ATP bioluminescence and real-time PCR

A rapid and quantitative method for detection of Bacillus spores in food/non-alcoholic beverage packages and food powders has been developed using filtration-based ATP bioluminescence and real-time PCR, targeting the sporulation gene (spo0A). In combination with heat activation, the presence and amount of viable bacterial spores (i.e., Bacillus amyloliquefaciens, Bacillus licheniformis, and Bacillus thuringiensis) was determined within 20 min through ATP signal amplifications. The detection limits of heat activation-ATP bioluminescence assay for B. amyloliquefaciens and B. licheniformis spores on food packages were 1.4 × 10² and 1.0 × 10³ CFU/cm², respectively. In contaminated food powders, B. thuringiensis spores could be detected by the ATP assay within the range of 7.9 × 10⁰ to 3.2 × 10⁴ CFU/mg powder while the PCR detection limit was 614 CFU/mg. Linear relationships between luminescent signal (RLU/mg) and plate count (CFU/mg) were found. The same sample after heat activation-ATP assay could be directly used for real-time PCR as a streamlined detection to confirm the identity of Bacillus spores in food packages and food powders even though some bacterial DNA loss was observed. This tiered approach, filtration-based one-tube ATP luminescence method as a rapid, viable screening and using real-time PCR as confirmation, could serve as a high-throughput tool for the detection of Bacillus spores in the food and beverage industry.     

Estimation of Accumulated Lethality Under Pressure-Assisted Thermal Processing

A study was conducted to develop an integrated process lethality model for pressure-assisted thermal processing (PATP) taking into consideration the lethal contribution of both pressure and heat on spore inactivation. Assuming that the momentary inactivation rate was dependent on the survival ratio and momentary pressure–thermal history, a differential equation was formulated and numerically solved using the Runge–Kutta method. Published data on combined pressure–heat inactivation of Bacillus amyloliquefaciens spores were used to obtain model kinetic parameters that considered both pressure and thermal effects. The model was experimentally validated under several process scenarios using a pilot-scale high-pressure food processor. Using first-order kinetics in the model resulted in the overestimation of log reduction compared to the experimental values. When the n ^th-order kinetics was used, the computed accumulated lethality and the log reduction values were found to be in reasonable agreement with the experimental data. Within the experimental conditions studied, spatial variation in process temperature resulted up to 3.5 log variation in survivors between the top and bottom of the carrier basket. The predicted log reduction of B. amyloliquefaciens spores in deionized water and carrot purée had satisfactory accuracy (1.07–1.12) and regression coefficients (0.83–0.92). The model was also able to predict log reductions obtained during a double-pulse treatment conducted using a pilot-scale high-pressure processor. The developed model can be a useful tool to examine the effect of combined pressure–thermal treatment on bacterial spore lethality and assess PATP microbial safety.