The effect of cold storage and cooking on the viability of Clostridioides difficile spores in consumer foods

The increased detection of clinical cases of Clostridioides difficile coupled with the persistence of clostridial spores at various stages along the food chain suggest that this pathogen may be foodborne. This study examined C. difficile (ribotypes 078 and 126) spore viability in chicken breast, beef steak, spinach leaves and cottage cheese during refrigerated (4 °C) and frozen (-20 °C) storage with and without a subsequent sous vide mild cooking (60 °C, 1 h). Spore inactivation at 80 °C in phosphate buffer solution, beef and chicken were also investigated to provide D_80°C values and determine if PBS was a suitable model system for real food matrices. There was no decrease in spore concentration after chilled or frozen storage and/or sous vide cooking at 60 °C. Non-log-linear thermal inactivation was observed for both C. difficile ribotypes at 80 °C in phosphate buffer solution (PBS), beef and chicken. The predicted PBS D_80°C values of 5.72±[2.90, 8.55] min and 7.50±[6.61, 8.39] min for RT078 and RT126, respectively, were in agreement with the food matrices D_80°C values of 5.65 min (95% CI range from 4.29 to 8.89 min) for RT078 and 7.35 min (95% CI range from 6.81 to 7.01 min) for RT126. It was concluded that C. difficile spores survive chilled and frozen storage and mild cooking at 60 °C but may be inactivated at 80 °C. Moreover thermal inactivation in PBS was representative of that observed in real food matrices (beef and chicken).

Inactivation of Escherichia coli by ozone treatment of apple juice at different pH levels

This research investigated the efficacy of gaseous ozone on the inactivation of Escherichia coli ATCC 25922 and NCTC 12900 strains in apple juice of a range of pH levels, using an ozone bubble column. The pH levels investigated were 3.0, 3.5, 4.0, 4.5 and 5.0. Apple juice inoculated with E. coli strains (10(6)CFU/mL) was treated with ozone gas at a flow rate of 0.12L/min and ozone concentration of 0.048 mg/min/mL for up to 18 min. Results show that inactivation kinetics of E. coli by ozone were affected by pH of the juice. The ozone treatment duration required for achieving a 5-log reduction was faster (4 min) at the lowest pH than at the highest pH (18 min) studied. The relationship between time required to achieve 5log reduction (t(5d)) and pH for both strains was described mathematically by two exponential equations. Ozone treatment appears to be an effective process for reducing bacteria in apple juice and the required applied treatment for producing a safe apple juice is dependant on its acidity level.

Anthocyanins and color degradation in ozonated grape juice

Grape juice samples were ozonated with processing variables of ozone concentration (1.6-7.8% w/w) and treatment time (0-10 min). Effects of processing variables on grape juice color values (L, a and b) and anthocyanins were determined. The changes in lightness (L) values and total color difference (TCD) values were fitted well to zero-order kinetics whereas, a and b followed first-order kinetics. Three major anthocyanins were observed in the grape juice namely cyanidin-3-O-glucoside (Cy3Gl, 133.9 mg/L), delphinidin-3-O-glucoside (Dy3Gl, 21.4) and malvidin-3-O-glucoside (My3Gl, 3.2mg/L). Significant reductions in anthocyanin content were observed during ozonation. During ozonation Cy3Gl was found to be stable compared to Dy3Gl and My3Gl. Changes in Cy3Gl were fitted well to the fraction conversion model. The results presented in this study indicate that both color and anthocyanin content are significantly affected during ozone processing. Thus, the effects of ozonation on the grape juice should be considered by processors prior to its adoption as a preservation technique.