Developing a sterilization processing and a grading system to produce a uniform quality of sterilized whole corn (Zea mays L. var. ceratina)

Using Numerical Analysis to Develop a Retort Process to Enhance Antioxidant Activity and Physicochemical Properties of White Radish (Raphanus sativus L.) in Different-Sized Packages

Thermal processing of white radish using retort sterilization at different temperatures was investigated according to the dimension of the package. Four different samples with the same weight and volume were placed in packages with different dimensions. The degree of sterilization (i.e., F0-value) at the cold point targeted at 6 min was determined based on experimental data and heat transfer simulation. The sterilization time was considerably increased with a decrease in surface area to unit volume ratio (φ) at each temperature. The sterilization time for the sample with the highest φ (155.56) was approximately five times faster than the sample with the lowest φ (72.22) at all heating temperatures. Numerical simulation conducted with a proper heat transfer coefficient (h) showed mostly good agreement with the experimental data (RMSE < 2 °C). Changes in color and total phenolic content were higher for samples heated at higher temperatures. Hardness values of white radish samples measured for center and edge parts separately were more uniform for samples with a high φ. Results in this study suggest that optimizing heating conditions of root vegetables must consider their package dimensions to satisfy quality attributes after sterilization. Numerical simulation can be utilized as a useful tool to design the sterilization process.

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.

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

The objective of this study was to develop quantitative microbial exposure assessment models for Bacillus cereus in packaged rice cakes (PRC). Probability distribution for growth of B. cereus in PRC was estimated and effects of thermal processing and acidification on extending the shelf-life of PRC were quantitatively assessed. Heat penetration curves at cold point of pasteurized PRC were successfully predicted using heat transfer simulation model and nonlinear regression model (root mean squared errors (RMSE) < 1.64 °C). The final contamination level in PRC of slab-shape package (>-0.85 log CFU/g at 95% percentile) was lower than that in oval-shape package (>3.41 log CFU/g at 95% percentile). This is due to the shorter come-up time at the cold point in the slab-shape in comparison with the oval package. Acidification significantly inhibited the growth of B. cereus and decreased the thermal resistance of B. cereus, which resulted in a decrease of the median values (1.82 log CFU/g for both B2C and B2B products). Results of quantitative microbial exposure assessment for Bacillus cereus in PRC showed that a combination of acidification and low temperature pasteurization could improve the safety of PRC (<-2.43 log CFU/g at 95% percentile).