- Article
The deliberate inactivation of probiotic cultures requires conditions that guarantee the absence of viable cells; however, inactivation kinetics are seldom characterized in the food matrices used at production scale. This work determined the thermal and high-pressure inactivation of Lacticaseibacillus rhamnosus CECT 278 (LR) and Lactobacillus acidophilus DSM 24936 (LA) grown in reconstituted skimmed milk (8% w/v). Cultures were heat-treated at 70, 75 and 80 °C and survival data were fitted to the Weibull model, or subjected to high-pressure processing (HPP) at 400 and 500 MPa for 10–20 min with an initial temperature of 13–16 °C. Non-pre-treated milk harboured a heat-resistant microbial population, potentially comprising spore-forming bacteria, that survived 90 min at 90 °C and interfered with the assessment of the inactivation of both strains; autoclaving the milk at 121 °C for 5 min reduced this background population below the detection limit. LA was more heat-resistant than LR at 70 °C (δ = 8.12 vs. 3.01 min), although its resistance decreased far more sharply with temperature (δ = 3.23 min at 75 °C vs. 2.63 min for LR). HPP at 400 MPa reduced LA below the detection limit (10 CFU/mL) within 20 min, whereas LR required 500 MPa to reach the same endpoint. Decontamination of the fermentation medium is therefore a prerequisite for obtaining reliable inactivation data in dairy matrices. Both technologies were applied to the same cultures and matrix, and the applicable processing window was found to be limited by the stability of the fermented matrix rather than by the resistance of the strains. The functional properties of the inactivated cells were not assessed in this work.
12 November 2026
