Inactivation study of Bacillus subtilis, Geobacillus stearothermophilus, Alicyclobacillus acidoterrestris and Aspergillus niger spores under Ultra-High Pressure Homogenization, UV-C light and their combination

Abstract

Lethality rates of Bacillus subtilis, Geobacillus stearothermophilus, Alicyclobacillus acidoterrestris, and Aspergillus niger spores were studied into phosphate-buffer saline (PBS) and PBS supplemented with caramel (PBSC) after Ultra-High Pressure Homogenization (UHPH) and UV-C treatments applied separately and combined. UHPH procedures were carried out at different pressures (100, 200 and 300 MPa) and inlet temperatures (20, 50 and 70 °C), while UV-C treatments consisted in a combination of doses (from 0.9 to 21.5 J/mL) and eventually temperatures (20 and 50 °C) or cycles. UHPH treatments were efficient at inactivating A. niger conidiospores in PBS but much less efficient in the inactivation of bacterial spores. Efficacy of UHPH against bacterial spores was increased pre-heating the samples at 70 °C. UV-C was more efficient against bacterial spores in PBS, but much less in PBSC. When UV-C treatments were applied through several cycles their efficacy against B. subtilis spores increased. Combination of UHPH at 200 MPa and UV-C moderately increased the lethal effect on B. subtilis spores than when these treatments were applied separately. Nevertheless, the combination of both technologies has a complementary effect allowing acting on a wide range of microorganisms, increasing the possibilities to obtain a safer and durable product.