Improving the efficiency of ultra-high pressure homogenization treatments to inactivate spores of Alicyclobacillus spp. in orange juice controlling the inlet temperature

- We evaluate inlet temperature on UHPH inactivation of Alicyclobacillus spores.
- Increasing inlet temperature of orange juice increases UHPH inactivation of spores.
- Lethal effect of UHPH treatments is mainly due to the thermal effect caused.
- Inlet temperatures above 70 °C are required to inactivate at least 105 spores/ml.

Samples of orange juice inoculated with strain CECT 7094 of Alicyclobacillus acidoterrestris or strain CECT 5324 of Alicyclobacillus hesperidum were pre-heated to five different temperatures (20, 50, 60, 70 and 80 °C) before applying a 300 MPa Ultra High Pressure Homogenization (UHPH) treatment. Treated and control samples were kept during 30 days at 22 °C, 30 °C and 43 °C to evaluate the ability of the surviving spores to germinate and grow. UHPH treatments hardly affected the spore counts at the lowest inlet temperature (20 °C), but significant reductions were observed when inlet temperature raised to 60 °C, achieving lethality values above 5 Log CFU/ml when juice samples were pre-heated at 70 for A. hesperidum and 80 °C for A. acidoterrestris. During the later storage of the juice samples Alicyclobacillus counts increased significantly during the first 15 days in samples pre-heated at 20 °C and 50 °C when they were stored at both 30 °C and 43 °C, achieving similar counts than control samples, but not at 22 °C. Nevertheless, in samples pre-heated at 70 and 80 °C spore counts remained below the detection limit indicating that these treatments were the most efficient inactivating Alicyclobacillus spp. spores.