Ultraviolet processing of coconut water at multiple wavelengths in continuous flow: Shelf-life and quality effects

Abstract

This study evaluated the effect of germicidal ultraviolet (UV) processing in continuous flow on bacterial inactivation, quality parameters, and shelf life of coconut water (CW). Fresh CW was treated with an excimer lamp (EL) emitting at 222 nm and three UV LED sources emitting at 257, 267, and 286 nm. Physical (pH, acidity, total soluble solid content), quality (color), nutritional (total phenolic content, ascorbic acid) parameters, peroxidase (POD) enzyme activity, and Escherichia coli (E. coli) inactivation were investigated. The impact of UV processing on CW shelf-life was determined by measuring total plate count, and yeast and mold count during cold storage at 4 °C for 15 days and was compared to the thermal process (90 °C, 2 min). A 5-log₁₀ reduction in E. coli was achieved in CW for all light sources tested of which UV LEDs at 267 nm were the most effective. At the corresponding fluence levels (12–40 mJ/cm²), no significant change in physical parameters was observed. The EL was the most effective for POD inactivation, reaching 60% inactivation at 29.2 mJ/cm², while fluence higher than 200 mJ/cm² was required for UV LEDs to achieve the same level of inactivation. Major changes in quality parameters were observed at fluence higher than 100 mJ/cm². A wavelength-fluence diagram was built using the kinetic of E. coli and color change to optimize UV process conditions for CW. According to microbiological analysis during refrigerated storage, a shelf life of 12 days was achieved for UV-treated samples. This study contributes to the further development of nonthermal UV processing of beverages.