Development of Polyelectrolyte-Coated Liposomes as Nanostructured Systems for Nisin Delivery: Antimicrobial Activity and Long-Term Stability

The use of natural antimicrobial peptides is a viable preservation alternative in the production of safe and good-quality products for consumption. Nanoliposomes containing nisin were prepared by film hydration with phosphatidylcholine (PC) and cholesterol, and coated with the polyelectrolytes (PEs) chitosan, cationic maltodextrin or poly-L-lysine (PLL), and characterized in their physical, thermal, functional and storage stability properties. As results, nisin encapsulation efficiency was around 90% for all formulations. The average diameter varied between 93.2 and 115.8 nm, with an increase in size after incorporation of PE, and the zeta potential ranged from + 11.3 to + 23.9 mV. These physical parameters showed good stability during 60 days of refrigeration (4 degrees C). The thermal characteristics of the liposomes were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). An improvement in the thermal stability of liposomes coated with PEs was observed. Infrared spectroscopy (FTIR) revealed predominantly PC peaks as the bulk component of the nanostructures, but representative peaks of PEs and nisin suggested their presence on the surface of liposomes. Finally, antimicrobial activity was observed against Gram-positive bacteria (L. monocytogenes, S. aureus, and B. cereus) and Gram-negative bacteria (E. coli and S. enterica), in brain heart infusion (BHI), whole, and skimmed milk agar. The formulations containing PEs and nisin maintained the physical properties and antimicrobial activity after 60 days of storage. Therefore, liposomes coated with cationic PEs have the potential to deliver antimicrobial peptides to reduce undesirable bacteria in foods.