Analysis of the effectiveness of ultra-high pressure homogenisation, short-wave ultraviolet radiation and their combination on the hygenization of apple juice and their effect on the quality and nutritional aspects

This doctoral thesis explores non-thermal technologies for the hygienization of apple juice, specifically focusing on ultra-high pressure homogenization (UHPH) and short-wave ultraviolet (UV-C) radiation. The research evaluates the effectiveness of these methods individually and in combination, targeting microbial inactivation while preserving the quality and nutritional properties of the juice.

The study applied UHPH at pressures of 100, 200, and 300 MPa and UV-C radiation at doses ranging from 1.8 to 200 J/mL. These treatments were tested on clear and cloudy apple juice matrices, both with and without added ascorbic acid or chia seed extract. Variables such as turbidity and absorption coefficient (α254) were adjusted to mimic real-world interferences that hinder UV-C penetration. Bacterial (e.g., Bacillus subtilis, Alicyclobacillus acidoterrestris, Geobacillus stearothermophilus) and fungal spores (e.g., Aspergillus niger, Talaromyces macrosporus, Neosartorya spinosa) were inoculated to validate microbial inactivation.

UHPH was found to effectively reduce microbial load, achieving up to 4-5 log reductions in endemic microbiota and A. niger spores at pressures of 200-300 MPa. Bacterial spores required higher pressures (300 MPa) and inlet temperatures (above 70°C) for effective inactivation. The treatments also changed some properties of the juice, including Brix, color, turbidity, and particle size. Enzymes like polyphenol oxidase were completely inactivated at 300 MPa, and pectin methylesterase activity was reduced by over 70%.

UV-C radiation worked best in low-turbidity juice with minimal α254 values. Higher doses and multiple passes increased effectiveness, but results varied depending on the microorganism. A. niger spores showed the highest resistance. Nutritional effects were minimal, though extended UV exposure could affect sensitive compounds.

The combination of UHPH and UV-C showed an additive effect in reducing microorganisms for most cases. For fungal spores like T. macrosporus and N. spinosa, there was a synergistic effect, significantly improving the results. Sensory testing revealed that the treated juices maintained their quality, though slight changes in flavor and odor were noted. Antioxidant properties were preserved or enhanced, especially with the addition of chia seed extract.

This study concludes that UHPH and UV-C, used separately or together, are effective alternatives to traditional heat treatments for apple juice. They ensure safety while preserving the juice's taste, appearance, and nutritional value. Combined, these technologies offer exciting possibilities for producing high-quality, minimally processed beverages.