Antimicrobial activity of lysozyme-nisin co-encapsulated in liposomes coated with polysaccharides

Abstract

Natural antimicrobials are an innovative alternative for food safety and encapsulation can improve their controlled release and stability. In the present work, lysozyme and its combination with nisin were encapsulated into phosphatidylcholine (PC) liposomes coated with pectin or polygalacturonic acid. The mean particle sizes of liposomes encapsulating lysozyme were 92, 116, and 97 nm for PC, PC-pectin and PC-polygalacutronic acid, respectively. Co-encapsulation of lysozyme and nisin resulted in particle sizes of 86, 77, and 80 nm, respectively. The formulations showed high encapsulation efficiency (77–87%), zeta potential around −30 mV, and spherical structures were observed by transmission electron microscopy. Liposomes encapsulating lysozyme inhibited Listeria monocytogens, but not Salmonella Enteritidis, while liposomes co-encapsulating the mixture nisin/lysozyme inhibited both bacteria. The PC-pectin liposomes were more efficient in inhibiting Listeria spp. when compared to the other liposomes tested. The antimicrobial activity was assessed at 37 °C using milk as model, showing that PC-pectin liposomes reduced the population of L. monocytogenes by 2 log CFU/mL in whole milk and 5 log CFU/mL in skim milk. Under refrigeration temperature, PC-pectin liposomes reduced the population of L. monocytogenes to below detection limit for up to 25 days in skim milk, indicating that liposomes containing polysaccharides can be a promising technology for the controlled release of lysozyme and nisin in foods.