Short Wave Ultraviolet Light (UV-C) Effectiveness in the Inactivation of Bacterial Spores Inoculated in Turbid Suspensions and in Cloudy Apple Juice

Abstract

Liquid foods might present interferences in their optical properties that can reduce the effectiveness of short-wave ultraviolet radiation (UV-C) treatments used for sterilization purposes. The effect of turbidity as UV-C interference factor against the inactivation of bacterial spores was analysed by using phosphate-buffered saline solutions (PBS) of different turbidity values (2000, 2500, and 3000 NTU) which were adjusted with the addition of apple fibre. These suspensions were inoculated with spores of Bacillus subtilis and Alicyclobacillus acidoterrestris. While higher UV-C doses increased the inactivation rates of spores, these were reduced when turbidity values increased; a dose of 28.7 J/mL allowed inactivation rates of B. subtilis spores of 3.96 Log in a 2000-NTU suspension compared with 2.81 Log achieved in the 3000-NTU one. Spores of B. subtilis were more UV-C-resistant than A. acidoterrestris. Cloudy apple juice inoculated with A. acidoterrestris spores was processed by UV-C at different doses in a single pass and with recirculation of the matrix through the reactor. Inactivation increased significantly with recirculation, surpassing 5 Log after 125 J/mL compared with 0.13 Log inactivation after a single-pass treatment at the same UV-C dose. UV-C treatments with recirculation affected the optical properties (absorption coefficient at 254 nm and turbidity) of juice and increased browning as UV-C doses became higher.