Synergistic effect of high‐intensity ultrasound, UV‐A light, and natural preservatives on microbial inactivation in milk

Abstract

Synergistic effect between high-intensity ultrasound (HIU), UV-A light, and natural antimicrobials on microbial inactivation in milk was studied. Milk with either ε-poly(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 high-intensity 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.