Thermal destruction kinetics of Bacillus licheniformis spores in carrot juice extract as influenced by pH, type of acidifying agent and heating method

• This study has relevance to process establishment in acidified thermal processing.
• Acidified thermal processing allows the use of boiling water temperature processing.
• The process reduces energy consumption relative to the conventional processing.
• The process reduces quality degradation due to the use of lower temperature and shorter time.
• Kinetic data on indicator microorganism useful for process verification.

The combined effects of different heating methods (conventional (CH) vs. Ohmic (OH)), types of acidifying agent (citric vs malic acid) and pH levels (pH 4.5, 5.5 and 6.2) were investigated to study their influence on destruction kinetics of spores of Bacillus licheniformis. The ultimate aim to generate relevant kinetic data on an indicator microbial spore is useful for assessing the efficacy of thermal processes for acid or acidified low acid foods. Kinetic parameters were evaluated according to the first-order kinetic model. Temperature and pH showed a highly significant (p < 0.01) effect on the spore destruction kinetics. Ohmic heating showed marginally better rate of bacterial destruction than conventional heating. The overall range of D and z values were 1.1–11.2 min and 12.6–17 °C, respectively, depending up on the pH and temperature levels, method of heating as well as the type of acidulate used. The shortest D97°C = 1.1 min was obtained at pH of 4.5 when citric acid was used as an acidifying agent in OH. No significant difference (p > 0.05) was observed with respect to D and z values between the two types of acidifying agents.