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.
Highlights
In recent years short-wave ultraviolet light (UV-C) has been tested as an alternative to thermal treatments in food industry, for the microbiological decontamination of surfaces, and for the reduction of the microbial load in liquid foods [1]
Many of the currently sold UV-C machines for the pasteurisation of these products assure to meet the FDA requirements for the elimination of E. coli, but among the microorganisms that are potentially present in these foods, bacterial spores are the ones which oppose the highest resistance to thermal treatments commonly used for pasteurisation processes and to pressure-based technologies such as high-hydrostatic pressure and ultra-high-pressure homogenisation [2,3,4]
Fruit matrices themselves can oppose different types and levels of interference depending on their singular properties and it is important to understand at what degree those interferences can affect the efficiency of UV-C treatments
Summary
In recent years short-wave ultraviolet light (UV-C) has been tested as an alternative to thermal treatments in food industry, for the microbiological decontamination of surfaces, and for the reduction of the microbial load in liquid foods [1]. Many of the currently sold UV-C machines for the pasteurisation of these products assure to meet the FDA requirements for the elimination of E. coli, but among the microorganisms that are potentially present in these foods, bacterial spores are the ones which oppose the highest resistance to thermal treatments commonly used for pasteurisation processes and to pressure-based technologies such as high-hydrostatic pressure and ultra-high-pressure homogenisation [2,3,4]. That has been described in apple juice batches contaminated with spores of Alicyclobacillus acidoterrestris [6] This bacterium might not produce any visible signs of deterioration, like gas or higher turbidity before reaching an excessive cell concentration, but it is harmless to humans and represents no health hazard it spoils the product with the production of odd flavours and odours because of the synthesis of guaiacol making it not suitable for consumption. It is considered a target microorganism for novel technologies for fruit juice processing [7,8]
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