UV-A Light Dehydration: Kinetics of Microbial Inactivation Against Gram-Positive and Gram-Negative Bacteria

UV-A light exposure (365 nm, 4.6 ± 0.2 mW/cm²) was combined with low relative humidity (RH) air flow at room temperature to dehydrate sweet potatoes and reduce the population of inoculated bacteria. Control samples underwent dehydration with low RH air at room temperature and in the absence of UV-A light to assess the importance of UV-A light in the dehydration and microbial reduction processes. The UV-A light-dehydrated sweet potatoes resulted in the removal of approximately 97.2% ± 2% of the original mass of water, which was significantly higher than the control samples. Infrared spectroscopy analyses confirmed the preservation of the physical and chemical integrity of the UV-A light-dehydrated samples. Despite the absence of pretreatments for enzyme inactivation, the UV-A light-dehydrated sweet potato did not exhibit a decrease in luminosity or darkening of color often associated with dehydration. Additionally, the utilization of UV-A light for the dehydration of sweet potatoes inoculated with ~6 log(CFU/g_{Dry solids}) of Escherichia coli K12 resulted in a 99.9% ± 0.1% or 3.1 ± 0.5 log(CFU/g_{Dry solids}) reduction with only a 92.2% ± 0.1% or 1.3 ± 0.5 log(CFU/g_{Dry solids}) reduction resulting from the control samples dehydrated without UV-A exposure. In the case of samples inoculated with ~6 log(CFU/g_{Dry solids}) of Listeria innocua L2 there was a 99.2% ± 0.5% or 2.2 ± 0.3 log(CFU/g_{Dry solids}) reduction when UV-A light was utilized and only a 60.9% ± 10.3% or 0.4 ± 0.1 log(CFU/g_{Dry solids}) reduction when samples were dehydrated in its absence.