Ultraviolet (UV-C) radiation as a practical alternative to decontaminate thyme (Thymus vulgaris L.)

Alternative and cost-effective decontamination methods for dehydrated herbs and spices are subject of interest in industry. In this work, a fluidized bed ultraviolet (UV-C) system was tested for decontamination of dehydrated thyme. The samples were exposed to UV-C radiation at 254 nm at 25.7, 51.4, 102.8, and 205.6 J/cm² delivered at an intensity of 26.7 mW/cm². UV-C at 205.6 J/cm² resulted in 1.8, 1.3, and 0.3 log cfu/g reductions in total aerobic mesophilic bacteria, total yeast/mold, and Bacillus cereus, respectively. Total phenolic content, total antioxidant activity, moisture content, and the sensory attributes were not affected by the UV-C treatments. UV-C caused a small increase in L* and a* values but these changes were not detected in sensory evaluation. In conclusion, UV-C treatment up to 205.6 J/cm² applied in a fluidized bed setting can potentially be used in decontamination of thyme without adverse effects on quality. Practical applications: UV-C radiation is a widely used effective technology to reduce the microbial load on various surfaces, liquids, and air environments. In this study, the potential of a fluidized bed UV system was explored to reduce natural microbial load of thyme. The results indicated that UV-C application may be an effective technology for decreasing the microbial load of thyme without inducing significant changes to the physical, chemical, and sensorial quality, therefore it has a potential as an alternative method for decontamination of thyme and similar herbs and spices industrially.