A quantitative microbiological exposure assessment model for Bacillus cereus in pasteurized rice cakes using computational fluid dynamics and Monte Carlo simulation

Biofilm Formation and Control of Foodborne Pathogenic Bacteria

Biofilms are microbial aggregation membranes that are formed when microorganisms attach to the surfaces of living or nonliving things. Importantly, biofilm properties provide microorganisms with protection against environmental pressures and enhance their resistance to antimicrobial agents, contributing to microbial persistence and toxicity. Thus, bacterial biofilm formation is part of the bacterial survival mechanism. However, if foodborne pathogens form biofilms, the risk of foodborne disease infections can be greatly exacerbated, which can cause major public health risks and lead to adverse economic consequences. Therefore, research on biofilms and their removal strategies are very important in the food industry. Food waste due to spoilage within the food industry remains a global challenge to environmental sustainability and the security of food supplies. This review describes bacterial biofilm formation, elaborates on the problem associated with biofilms in the food industry, enumerates several kinds of common foodborne pathogens in biofilms, summarizes the current strategies used to eliminate or control harmful bacterial biofilm formation, introduces the current and emerging control strategies, and emphasizes future development prospects with respect to bacterial biofilms.

Effects of packaging parameters on the microbial decontamination of Korean steamed rice cakes using in-package atmospheric cold plasma treatment

The effects of packaging materials, package shape, and secondary packaging on the inactivation of indigenous mesophilic aerobic bacteria in Korean steamed rice cakes using in-package atmospheric dielectric barrier discharge cold plasma (ADCP) treatment were investigated. Inactivation of indigenous mesophilic aerobic bacteria by ADCP treatment (21 kV, 3 min) was significantly increased by 0.6 and 0.8 log CFU/g (p < 0.05) from 0.7 ± 0.1 and 0.5 ± 0.1 CFU/g, respectively, when polypropylene (PP) and low-density polyethylene (LDPE) were laminated with nylon, respectively. Secondary packaging lowered the inactivation level by 0.7-0.8 log CFU/g from 1.1 to 1.3 log CFU/g. In-package ADCP treatment did not alter the water vapor permeability, oxygen transmission rate, and tensile properties of PP, LDPE, nylon/PP, and nylon/LDPE. Thus, the results demonstrated that lamination of PP or LDPE with nylon and treatment before secondary packaging may be effective strategies for microbial inactivation by in-package ADCP treatment.

Thermal and non-thermal treatment effects on Staphylococcus aureus biofilms formed at different temperatures and maturation periods

The objective of this study was to investigate the effect of temperature and maturation period on the resistance of Staphylococcus aureus biofilms to thermal and non-thermal treatments. First, biofilm development was compared at three different temperatures (15, 25, and 37°C) for 5 days. The cell population at 15 and 25°C remained relatively consistent approximately at 6.3 log CFU/cm², whereas 37°C resulted in the highest cell population on day 1 (7.6 log CFU/cm²) followed by a continual decline. Then, biofilm resistance to steam and sodium hypochlorite (NaOCl) treatments was evaluated. Obtained results highlighted that biofilms had different resistance to both treatments depending on development conditions. Specifically, steam treatment of 10 s eliminated 4.1 log CFU/cm² of the biofilm formed at 25°C for 5 days. The same treatment inactivated over 5 log population of biofilms developed in other temperature and maturation period conditions. Treatment with NaOCl reduced approximately 1 log CFU/cm² of biofilm cells developed at 25°C for 5 days. However, inactivation was found to be over 2 log CFU/cm² under other development conditions. An extracellular polymeric substances (EPS) quantification using 96-well plates and stainless steel coupons was conducted. In the 96-well plate experiment, it was found that the highest amount of polysaccharide was secreted at 25°C (p < 0.05), while total biomass and protein contents were greatest at 37°C (p < 0.05). No significant difference in EPS content was observed for stainless steel, but the results displayed a similar trend to the 96-well plate. In particular, biofilms developed at 25°C tended to secret the highest amount of polysaccharide, which aligned with the current literature. This finding indicated that polysaccharide was the main contribution to the enhanced resistance of S. aureus biofilms. Overall, it was shown that biofilms formed at 25°C for 5 days exhibited the greatest resistance to thermal and nonthermal treatments due to the elevated exopolysaccharide secretion. This study demonstrates that temperature and maturation period significantly affect the resistance of S. aureus biofilms to thermal and non-thermal treatments.

Effects of Low-Temperature Drying with Intermittent Gaseous Chlorine Dioxide Treatment on Texture and Shelf-Life of Rice Cakes

We investigated the effect of chlorine dioxide (ClO2) under low temperature drying to suppress rice cake stickiness during the cutting process by initiating the onset of retrogradation until the stickiness is minimized for shelf-life extension. The intermittent ClO2 application at low-temperature drying was conducted at 10 °C for different drying periods (0, 6, 12, 18, and 24 h). Texture analysis showed significant differences with increasing values of hardness (901.39 ± 53.87 to 12,653 ± 1689.35 g) and reduced values of modified adhesiveness (3614.37 ±578.23 to 534.81 ± 89.37 g). The evaluation of rice cake stickiness during the cutting process revealed an optimum drying period of 18 h with no significant difference (p ≤ 0.05) compared to the 24 h drying process. Microbial contamination during the drying process increased, with microbial load from 6.39 ± 0.37 to 7.94 ± 0.29 CFU/g. Intermittent ClO2 application at 22 ppm successfully reduced the microbial load by 63% during drying process. The inhibitory property of ClO2 was further analyzed on a sample with high initial microbial load (3.01 ± 0.14 CFU/g) using primary and modified secondary growth models fitted to all experimental storage temperatures (5–25 °C) with R2 values > 0.99. The model demonstrated a strong inhibition by ClO2 with microbial growth not exceeding the accepted population threshold (106 CFU/g) for toxin production. The shelf-life of rice cake was increased by 86 h and 432 h at room temperature (25 °C) and 5 °C respectively. Microbial inactivation via ClO2 treatment is a novel method for improved food storage without additional thermal sterilization or the use of an additional processing unit.