Effects of combination treatments of nisin and high-intensity ultrasound with high pressure on the microbial inactivation in liquid whole egg

Abstract

The consecutive combinations of nisin with high hydrostatic pressure (nisin-HHP) and ultrasound with high hydrostatic pressure (US-HHP) were explored to achieve enhanced microbial inactivation in liquid whole egg processing. The HHP processing conditions were fixed to either 250 MPa for 886 s or 300 MPa for 200 s at the treatment temperature of 5 °C, which have been determined as the optimum HHP processing conditions considering egg protein coagulation and microbial inactivation kinetics. Between the two types of combinations, the nisin-HHP combination showed more promising results. The addition of nisin prior to pressure treatments significantly increased the lethal effects of HHP against Listeria seeligeri up to 5 log cycles. Because the individual effects of each nisin and HHP on the Listeria were almost negligible, the Listeria reductions are considered to be due to the synergistic action of nisin and HHP. However, the combination of nisin-HHP on E. coli showed exactly the same degree of inactivation by HHP alone, which supports protection mechanism of gram negative bacteria against the action of nisin. The US-HHP combination caused no reductions of Listeria and only a slightly increased inactivation of E. coli under the experimental conditions.