Characteristics of pasteurized and sterilized milk using lysozyme as anantibacterial agent

Egg white lysozyme is a protein with a sweet taste and antibacterial activity. It is capable of hydrolyzing the bonds between N-acetylmuramic acid (NAM) and Nacetylglucosamine (NAG) in the peptidoglycan wall of bacterial cells. However, egg white lysozyme has not been used as a biopreservative agent for milk. In this study, the impact of adding egg white lysozyme to pasteurized and sterilized milk on physical, microbiological, and organoleptic properties during refrigerated storage was investigated. A factorial randomized block design was employed and the data was analyzed using analysis of variance (ANOVA) with Tukey's post hoc test. The results showed that the milk used in this study met the minimum requirements of the Indonesian National Standard SNI 01-3141-2011 for fresh milk. The addition of lysozyme (70 µM) to pasteurized or sterilized milk did not affect the water activity (aw) or water content. However, pasteurized milk with lysozyme had significantly lower microbial populations than milk without lysozyme (P<0.05). On the other hand, there was no significant difference in the microbial population of sterilized milk with or without lysozyme. For both pasteurized and sterilized milk, with or without lysozyme, the microbial populations remained similar throughout 8 days of refrigerated storage. Additionally, the addition of lysozyme improved the sweetness of both pasteurized and sterilized milk. In conclusion, this study confirmed that lysozyme can be used to reduce the microbial population, particularly in pasteurized milk, and improve its sweet taste.