Hyperbaric inactivation at 150–250 MPa of Alicyclobacillus acidoterrestris spores at room temperature and effect of innovative technologies pre-treatments

This study evaluated hyperbaric inactivation (HI) at 150, 200 and 250 MPa, up to 24 h (at ambient temperatures,18–23 °C) to inactivate Alicyclobacillus acidoterrestris (ACB) spores in apple juice. The effects of pre-treatments on spores by thermal pasteurization (90 °C, 30 s), high pressure processing (600 MPa, 3 min, HPP), pulsed electric field (30 kV, 80 μs, 1400 Hz, PEF), and ultrasound (67 W, 20 kHz, 5 min, US) prior to HI was evaluated. The results were fitted to non-linear inactivation kinetic models, including Biphasic, Log-logistic, and Weibull. Without a previous pre-treatment, ACB spores were reduced ≈4.56 log units by HI after 24 h, regardless of the pressure level (initial load around 6 log CFU/mL). The pre-treatments did not affect ACB spores during HI (≈4–5 log units' inactivation after 24 h under pressure), except for PEF that resulted in a lower inactivation (≈3.5 log units after 24 h under pressure). Phase contrast microscopy revealed that the spores were unable to form a vegetative cell during HI. HI at 5 °C resulted in a lower inactivation level, with 3.86, 2.54 and 1.77 log units of inactivation, respectively, at 150, 200 and 250 MPa after 96 h.

Industrial relevance

The results of this work point to the possibility of using HI, before or after conventional thermal pasteurization and other nonthermal technologies (HPP, PEF, and US) to process apple juice, to inactivate ACB spores at room temperature and also under refrigeration. This methodology should be further studied in the context of ACB spores' high thermal stability and its industrial relevance.