Kinetics model of microbial degradation by UV radiation and shelf life of coconut water

The aim of this present study was to investigate the effect of UV radiation on microbial inactivation kinetic, quality and shelf life of coconut water. Zero-order and first-order kinetic models were used to investigate microbial degradation (Escherichia coli O157:H7, Staphylococcus aureus, Salmonella Enteritidis, and Lactobacillus plantarum) by UV radiation (0.0, 0.2, 0.4, 0.8, 1.6, 3.2, 4.8, 8.0 and 12.0 J/mL). UV dose of 1.6, 3.2 and 4.8 J/mL was applied to investigate the effect of UV radiation on physical properties (pH, °Brix, color and turbidity), chemical properties (total phenolic compound or TP and polyphenol oxidase or PPO activity) of coconut water and to investigate the shelf life of coconut water by determination of pink discoloration, total plate count (TPC), and yeast and mold count (YMC) during cold storage at 4 °C for 18 days compared to pasteurized sample (95 °C 100 s). Results showed that microbial inactivation of all bacteria tested in this study followed first-order kinetic model according to higher coefficient of determination (0.9115-0.9656). E. coli O157:H7 was found to be the most sensitive bacteria to UV radiation with regard to highest population reduction in coconut water. In addition, no significant changes were detected in the investigation of L*, b*, pH, °Brix, titratable acidity, and turbidity of coconut water treated with UV radiation (p > 0.05). However, UV treatment showed significant effect on a*, TP and PPO activity (p ≤ 0.05). TPC of all samples increased while YMC decreased during storage at 4 °C. According to microbial investigation during storage at 4 °C, it was found that shelf life of fresh coconut water (control) was 4 days and increased to 6, 10 and 16 days for samples treated with UV dose of 1.6, 3.2 and 4.8 J/mL, respectively. These results of this study support the application of UV radiation in coconut water to preserve quality and prolong shelf life in conjunction with safety aspects as an alternative method to thermal processing.