Antilisterial effects of lysozyme-nisin combination at temperature and pH ranges optimal for lysozyme activity: Test of key findings to inactivate Listeria in raw milk

Abstract

This study aimed to determine antilisterial potential of lysozyme (LYS)-nisin (NIS) combination at temperatures and pHs optimal for LYS activity. Tests in buffers at pH 4.5 and 6.0 showed that heating at 50 or 60 °C combined with LYS-NIS caused higher Listeria innocua inactivation (- 6.2 to >6.6 log) than heating alone (- 0.05 to 5.5 log), or heating combined with LYS (- 4.34 to 6.0 log) or NIS (3.9 to >6.6). The antimicrobial performance of LYS-NIS in buffer at 50 °C was not pH-dependant (5.8–5.9 logs) while heating at 60 °C with LYS-NIS at pH 6.0 (>6.6 logs) caused higher Listeria reduction than that at pH 4.5 (5.7 logs). Heating at 50 °C for 45 min alone or in combination with LYS-NIS caused 0 and 5.5 logs Listeria reduction in milk, respectively. In contrast, Listeria inactivation in milk at 60 °C occurred mainly by heat (5.5 logs) with limited contribution of LYS and/or NIS. Milk heated at 50 °C maintained 73% of NIS and 63% of LYS activity. Application of LYS-NIS at 50 °C provides an opportunity to improve milk safety with less destruction of milk enzyme and microbial flora necessary to obtain desired ripening periods, and aroma and flavour in traditional cheeses.