Thermal inactivation of Bacillus cereus spores during cooking of rice to ensure later safety of boudin

Inactivation mechanism of phenyllactic acid against Bacillus cereus spores and its application in milk beverage

Phenyllactic acid (PLA) as a natural phenolic acid exhibits antibacterial activity against non-spore-forming bacteria, while the inhibitory effect against bacterial spore remained unknown. Herein, this study investigated the inactivation effect of PLA against Bacillus cereus spores. The results revealed that the minimum inhibitory concentration of PLA was 1.25 mg/mL. PLA inhibited the outgrowth of germinated spores into vegetative cells rather than germination of spores. PLA disrupted the spore coat, and damaged the permeability and integrity of inner membrane. Moreover, PLA disturbed the establishment of membrane potential due to the inhibition of oxidative metabolism. SEM observations further visualized the morphological changes and structural disruption caused by PLA. Besides, PLA caused the degradation of DNA of germinated spores. Finally, PLA was applied in milk beverage, and showed promising inhibitory effect against B. cereus spores. This finding could provide scientific basis for the application of PLA against spore-forming bacteria in food industry.

Quantitative risk assessment of Bacillus cereus in wet rice noodles from raw material to marketing phase

From 2018, several foodborne diseases caused by the consumption of wet rice noodles contaminated with microorganisms have attracted the attention of consumers and surveillance departments. We explored the crucial risk factors for the contamination of Bacillus cereus during the various steps of the wet rice noodles production chain (from raw material to marketing phase). A total of 273 samples were collected in each corresponding production phase. The contamination level was quantitatively detected in the samples, and the corresponding temperature and time were recorded and analyzed using @Risk software. The quantitative detection results of raw material were determined as the initial contamination level in the model to predict the final contamination level and assess the key risk factors for B. cereus contamination in wet rice noodles. The model predicted that the final contamination level of B. cereus was in the range of -3.55 to 4.34 log CFU/g in 95% wet rice noodles at the marketing phase. The highest predicted contamination level was 6.28 log CFU/g, and the risk of exceeding the threshold was 0.80%. The model was verified to be valid for R² > 0.96, and the predicted results could be used for reference. Moreover, the sensitivity analysis revealed that in addition to raw material, the key control factors were buffering temperature in the packaging delivery phase, transporting temperature and time from factory to marketing phase; their correlation coefficients (r) were 0.18, 0.16, and 0.15, respectively. Therefore, manufacturers need to adjust the current predelivery buffering and transporting mode. It is recommended to reduce the predelivery buffering temperature, and refrigerated trucks are preferred to control the proliferation of B. cereus in transported food, thus reducing the occurrence of foodborne diseases and improving the safety of food.

Inactivation of Salmonella enterica Serovar Typhimurium and Staphylococcus aureus in Rice by Radio Frequency Heating

ABSTRACT

The objectives of this study were to determine the effect of the milling degree (MD) of rice (Oryza sativa L.) on the heating rate, pathogen inactivation (Salmonella Typhimurium and Staphylococcus aureus), and color change resulting from radio frequency (RF) heating. Rice samples inoculated with pathogens were placed in a polypropylene jar and subjected to RF heating for 0 to 75 s. The heating rate of rice with a 2% MD was the highest during RF heating, followed by those with a 0, 8, and 10% MD; the reduction of pathogens showed the same trend. The reductions of pathogen levels in rice with MDs of 0 and 2% were significantly higher than those observed for rice with MDs of 8 and 10% under the same treatment conditions. For example, log reductions of Salmonella Typhimurium in rice by 55-s RF heating were 3.64, 5.19, 2.18, and 1.80 for MDs of 0, 2, 8, and 10%, respectively. At the same treatment conditions, log reductions of S. aureus were 2.77, 5.08, 1.15, and 0.90 for MDs of 0, 2, 8, and 10%, respectively. The color of rice measured according to L*, a*, and b* was not significantly altered after RF heating, regardless of the MD. Therefore, the MD of rice should be considered before RF heating is applied to inactivate foodborne pathogens.

HIGHLIGHTS

Effect of temperature and soluble solid on Bacillus subtilis and Bacillus licheniformis spore inactivation and quality degradation of pineapple juice

Bacillus subtilis and Bacillus licheniformis spores can survive processing temperatures used in the thermal processes of high-acid foods. Therefore, this study investigated the thermal inactivation of B. subtilis and B. licheniformis spores in pineapple juice at different temperatures (85-100°C) and soluble solids (SS, 11-30°Brix). The quality of juices and microbial loads after the thermal treatments during storage at 4 °C for 35 days was then checked. A linear decrease in D-value was observed with increasing temperature of treatment. Furthermore, the D-values determined in pineapple juice were: D_90°C=13.2 ± 0.5 mins, D_95°C = 6.8 ± 0.9 mins and D_100°C = 2.1 ± 1.7 mins for B. subtilis spores, and D_85°C = 16.6 ± 0.4 mins, D_90°C = 7.6 ± 0.5 mins and D_95°C = 3.6 ± 1.5 min, for B. licheniformis. Generally, the susceptibility of the bacteria to soluble solid change was affected by the interaction between temperature, SS and strain. In addition, pasteurization processes of ≥95°C for ≥33.8 mins was needed to ensure a recommended 5-log reduction of B. subtilis spores and limit vitamin C degradation of pineapple juice within three-week of storage at 4 °C.

Ohmic heating processing of milk for probiotic fermented milk production: Survival kinetics of Listeria monocytogenes as contaminant post-fermentation, bioactive compounds retention and sensory acceptance

The survival kinetics of Listeria monocytogenes (9 log CFU/mL) as a post-fermentation contaminant in probiotic fermented milk (Lactobacillus acidophilus La-5, 8-9 log CFU/mL) processed with milk subjected to ohmic heating (0, 4, 6, and 8 V/cm; CONV, OH₄, OH₆, OH₈, 90-95 °C/5 min) was investigated using Weibull predictive model. Additionally, the presence of bioactive compounds (antioxidant activity, inhibition of the enzymes α-glucosidase, α-amylase, and angiotensin-converting) and sensory analysis (consumer test) of probiotic fermented milks were evaluated. Overall, OH provided a decrease in the viability of Listeria monocytogenes, suitable Lactobacillus acidophilus counts, and satisfactory results in the gastrointestinal tract survival. The Weibull model presented an excellent fit to the data of all conditions. Furthermore, lower δ values (217-298 against 665 h, CONV), and increased R² values (0.99 against 0.98, CONV) were obtained for the OH-treated samples, emphasizing the best performance of OH data. In addition, OH improved the generation of bioactive compounds as well as the sensory acceptance. Indeed, considering functional and safety purposes, OH presented as an interesting technology to be used in milk for manufacturing probiotic fermented milk.