Comparative resistances of selected spoilage and pathogenic bacteria in ultraviolet-C-treated, turbulent-flowing young coconut liquid endosperm

- Inactivation rates varied between spoilage bacteria.
- Inactivation rates of pathogens were not significantly different.
- Klebsiella sp. was most resistant to UV-C, while Kluyvera sp. was least resistant.

This study determined and compared the inactivation rates of selected spoilage and pathogenic bacteria in turbulent flowing, UV-C treated liquid endosperm (pH 5.80, 6.10 °Brix) obtained from young (6-9 months) coconut drupes. Inoculation of test organisms significantly altered the UV-C absorbance and transmittance of the liquid endosperm from 0.90 to 1.08 and 12.74%-8.39%, respectively. Inactivation rates were expressed in terms of decimal reduction times (D values), defined as the exposure time necessary to reduce the test organism by 90% or 1-log cycle. Furthermore, the DUV-C values, or the UV-C dose necessary to reduce the organism by 90% were also determined. Results showed that while the D and DUV-C values significantly varied among the spoilage organisms (D = 2.93-5.60 s; DUV-C = 7.63-14.56 mJ/cm2), no significant differences were detected in the inactivation rates of the tested pathogens (D = 3.19-3.76 s; DUV-C = 8.28-9.78 mJ/cm2). The inactivation parameters obtained in this work were close to those previously established in non-turbulent, small volume coconut liquid endosperm, suggesting that for this commodity, stirring may not be necessary to optimize microbial inactivation if UV-C shall be applied to small volumes or thin films. The results established in this work may serve as baseline information in the continuous optimization of UV-C process for coconut liquid endosperm and other similar products, for the maintenance and control of food quality and safety.