Synergistic effect between high-intensity ultrasound (HIU), UV-A light, and natural antimicrobials on microbial inactivation in milk was studied. Milk with either εpoly(lysine) or Nisin was subjected to HIU (30 s) and then to UV-A light (15 min).Statistically significant treatments were stored at 4 or 25°C for 24 hr. Escherichia coli K12 was reduced by ~2 logarithmic cycles with ε-poly(lysine). During storage, there was decline in microorganisms at 4°C and no detectable load at 25°C. E. coli K12 was reduced by ~1 logarithmic with Nisin, and during storage, the population decreased at 4°C and increased at 25°C. Listeria innocua L2 was not affected by ε-poly(lysine), but it was reduced by ~4 logarithmic cycles with Nisin. During storage, L. innocua decreased after 24 hr at 4°C, and increased at 25°C. The treatments caused slight changes in color and pH. Novelty impact statement:In this study, we confirmed that a short exposure to highintensity ultrasound and UV-A light in combination with natural preservatives can serve as an aid to inactivate gram-positive and gram-negative microorganisms in milk.This combination can result in a reduction of up to 99.99% in the initial microbial population, which can be reduced even further if it is followed by a storage time of 24 hr under refrigeration. These treatments also seem to have marginal effect on the color and pH of milk.

Ultraviolet (UV) light has exhibited antimicrobial effects, with recent studies looking at UV-A light in particular. The objective of this study was to determine the antimicrobial mechanism and microbial inactivation kinetics of UV-A light on processed cheese. Processed cheese was inoculated with Escherichia coli K12 and Listeria innocua to yield a final concentration of ∼5 log[colony-forming units (CFU)/g] and then exposed to UV-A light for 0−60 min to determine the kinetics of microbial inactivation. The experimental data were fitted with the Weibull model of inactivation kinetics. To achieve an ∼6 log(CFU/g) decrease, UV-A light exposure for ∼70 min was required for E. coli K12 and ∼130 min for L. innocua L2. The processed cheese was analyzed using infrared spectroscopy after UV-A exposure for 0 and 60 min and showed no apparent changes in the surface chemistry. A decrease in the moisture content was noted, which caused an increase in the concentration of lipids on the surface. A statistically significant (P < 0.05) effect was observed in the color of the cheese after UV-A light exposure for 60 min. The effect of UV-A light exposure on the oxidative stress and membrane damage of both bacteria was analyzed through fluorometric techniques. A significant (P < 0.05) increase in oxidative stress and membrane damage was observed for both bacteria, which was more pronounced for E. coli K12. Our findings suggest the UV-A light could prove to be a suitable alternative for surface decontamination of dairy products.

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