Enhancing the Lethal Effect of High-Intensity Pulsed Electric Field in Milk by Antimicrobial Compounds as Combined Hurdles

Abstract 

High-intensity pulsed electric field (HIPEF) is a nonthermal treatment studied for its wide antimicrobial spectrum on liquid food, including milk and dairy products. Moreover, the antimicrobial effect of HIPEF may be enhanced by combining HIPEF with other treatments as hurdles. Nisin and lysozyme are natural antimicrobial compounds that could be used in combination with HIPEF. Therefore, the purpose of this study was to determine the effect of combining HIPEF with the addition of nisin and lysozyme to milk inoculated with Staphylococcus aureus with regard to different process variables. The individual addition of nisin and lysozyme did not produce any reduction in cell population within the proposed range of concentrations, whereas their combination resulted in a pH-dependent microbial death of Staph. aureus. The addition of nisin and lysozyme to milk combined with HIPEF treatment resulted in a synergistic effect. Applying a 1,200-μs HIPEF treatment time to milk at pH 6.8 containing 1IU/mL of nisin and 300IU/mL of lysozyme resulted in a reduction of more than 6.2 log units of Staph. aureus. Final counts resulting from the addition of nisin and lysozyme and applying HIPEF strongly depended on both the sequence of application and the milk pH. Thus, more research is needed to elucidate the mode of action of synergism as well as the role of different process variables, although the use of HIPEF in combination with antimicrobial compounds such as nisin and lysozyme is shown to be potentially useful in processing milk and dairy products.

Key words: nisin, lysozyme, high-intensity pulsed electric field, milk