Inactivation of Clostridium sporogenes Spores in Buffer and Coconut Water Using UV-C Irradiation

Introduction: Clostridium sporogenes is an anaerobic non-pathogenic spore forming bacteria. It is widely used as a surrogate for Clostridium Botulinum to validate sterilization processes for low-acid foods. Application of thermal processing methods can alter the nutritional content and organoleptic properties of the foods. Ultraviolet (UV) light technology is comparatively more cost-effective, efficient, and sustainable than thermal pasteurization. It acts directly on the nucleic acids of the target microbe and impedes the microbe’s replication.

Purpose: This study was designed to assess the ability of UV irradiation to inactivate Clostridium sporogenes in coconut water, a highly opaque liquid food. 

Methods: Coconut water was extracted from raw green coconuts. Optical properties of the coconut water were measured using a double-beam spectrophotometer. UV irradiation was applied to stirred samples of coconut water, using a collimated beam system operating at 253.7 nm wavelength. A series of known UV doses (0 - 80 mJ.cm^-2) was delivered to samples of coconut water that had been inoculated with the target microbes. Spores were cultured and counted to determine inactivation.

Results: UV-C irradiation effectively inactivated Clostridium sporogenes spores in buffer and coconut water. At the highest dose of 80 mJ·cm^-2, spores were inactivated by more than 4 log CFU/mL (R²=0.99, p<0.05) in both fluids. The D₁₀ value of Clostridium sporogenes was estimated to be 19.12 mJ·cm^-2. The observed sensitivity of the organisms agreed with literature values Overall, this work demonstrates that UV-C has a potential for inactivation of Clostridium sporogenes spores.

Significance: This study demonstrated that high levels of inactivation spores can be achieved in coconut water (highly opaque fluid), and suggested significant potential for UV-C treatment of a low acid beverages.