Purpose: To assess the ability of UV irradiation to inactivate microorganisms in coconut water, a highly opaque liquid food. UV inactivation kinetics of two surrogate viruses (MS2, T1UV) and three pathogenic bacteria (E. coli ATCC 25922, Salmonella Typhimurium, Listeria monocytogenes) in peptone and coconut water were investigated.
Methods: Optical properties of the samples were measured using a spectrophotometer. UV-C irradiation was applied to stirred samples, using a collimated beam operating at 253.7 nm wavelength. A series of known UV doses (0 – 40 mJ·cm-2) were delivered to the samples. A balanced design with three replicates for each treatment was exposed to selected UV treatments. The samples were then double plated and cultured to determine the microbial inactivation.
Results: UV-C irradiation effectively inactivated MS2 and T1UV in the test fluids, confirming accurate dose delivery. Inactivation levels of all organisms were proportional to UV dose. At the highest dose of 40 mJ·cm-2, three pathogenic organisms were inactivated by more than 5 log (P<0.05). Results show that UV-C irradiation effectively inactivated viruses and pathogenic microbes in coconut water.
Significance: Fluid optics were the key controlling parameters for effective microbial inactivation. UV dose must be calculated not only from the incident UV intensity but must also consider the attenuation in the samples. This study shows that high levels of inactivation of pathogens can be achieved in coconut water, and suggests significant potential for UV treatment of other liquid foods.