Comparison of spore inactivation with novel agitating retort, static retort and combined high pressure-temperature treatments

- Spore inactivation by novel heat and high pressure treatments was investigated.
- Agitating process enhanced homogenous heat load distribution over the product.
- Agitating mode required lower process times than static mode for killing spores.
- Combined high pressure-temperature treatments showed synergistic effects.
- Utilizing novel mechanisms in food processing enabled milder treatments.

Optimization of food preservation technologies is necessary for improved product quality and nutrition as well as energy and environmental sustainability. In the current study, inactivation of Bacillus subtilis spores in a model soup (pH 6.1) with agitating retort, static retort and combined high pressure-temperature treatments was investigated. With isothermal experiments, D95° C and z values for B. subtilis spores in the soup were obtained as 4.67 min and 8.65 °C. Log-linear model performed well for describing isothermal spore inactivation kinetics with satisfactory R2adj values (0.94-0.97). Agitating retort treatments caused a dramatic reduction in processing times, as 17 min processing in agitating mode was required for 7-log inactivation of B. subtilis spores, compared to 53 min in static mode at 110 °C. For agitating process, observed and predicted lethality values were similar. This implied a homogenous heat load distribution within the soup with the help of high frequency agitation. Combined HPP and mild temperature treatments were highly synergistic for elimination of B. subtilis spores in the same model soup used in heat treatments. HPP treatments combining 650 MPa and 55-65 °C for 10 min resulted in up to 4.5 log kill effect on spores. The findings from the current study can be utilized in selection of test conditions for similar products in future safety studies. Results clearly showed that using novel mechanisms in food processing provide an opportunity for milder processing which can lead to better food quality and sustainability.