Inactivation of Alicyclobacillu acidoterrestris in apple juice under ultraviolet irradiation treatments

Heat processing is the most commonly used treatment for microbial inactivation. However, temperature may have adverse effects on sensory and nutritional attributes of foods. Non-thermal technologies have received increasing attention for preservation of beverages, due to their potential for inactivating spoilage and pathogenic microorganisms. In addition, they can help minimizing quality losses, namely flavour, colour and nutritional value. Ultraviolet-C radiation (UV-C) is widely used as an alternative strategy to control microorganism in food products. Alicyclobacillus acidoterrestris is a thermo-acidophilic, non-pathogenic and spore-forming bacterium, able to grow at low pH (3.0–3.5) and high temperatures (50–70 °C). It has been considered a new type of spoilage bacterium, with important potential spoilage concern for hot-fill fruit and fruit juices. The main objective of this work was to study the influence of UV-C radiation treatments with seven different intensities (0.32, 0.86, 2.59, 5.59, 8.45, 11.50 and 13.44 W/m2) on A. acidoterrestris inactivation in apple juices. Commercial juices were artificially inoculated with bacterium, with initial loads around 107 CFU/mL. They were then exposed to UV-C radiation and the treatment impact on microbial loads was assessed throughout exposure times. Results showed that the log-survival of A. acidoterrestris decreased linearly with treatment time, for all intensities tested. A decimal reduction time at a given UV-C intensity was estimated by fitting a first order kinetic model to experimental data. When the most severe intensity was used (i.e., 13.44 W/m2), the number of spores decreased drastically (around 5-log reduction, which attains US Food and Drug Administration requirements) after 8 min of treatment. For the remaining UV-C intensities, this inactivation was achieved for higher exposure times. Overall it can be concluded that UV-C radiation is a promising treatment with a drastic impact on the loads of A. acidoterrestris in apple juices, especially when high intensities are used.