Liposome encapsulated nisin Z: optimization, stability and release during milk fermentation

Liposomes prepared from different proliposomes (Pro-lipo(R) H, Pro-lipo(R) S, Pro-lipo(R) C and Pro-lipo(R) DUO) were tested for their capacity to encapsulate nisin Z. Factors affecting the entrapment process (pH and concentration of nisin Z solution and cholesterol concentration in the lipid membranes) were optimized. The use of nisin Z monoclonal antibodies made it possible to quantify, using a competitive enzyme immunoassay, and visualize, using transmission electron microscopy, nisin Z. Nisin Z was entrapped in different liposomes with encapsulation efficiencies (EE) ranging from 9.5% to 47%. The pH of nisin Z aqueous solution and nisin Z concentration had a significant effect on the amount of encapsulated nisin. An increase in cholesterol content in lipid membranes up to (20%, w/w) resulted in a slight reduction in EE. Nisin-loaded vesicles did not severely disturb Cheddar cheese fermentation and showed stability to Cheddar cheese temperature cycle. Long term stability of liposome-encapsulated nisin Z was demonstrated for 27 days at 4 degreesC in different media including milk with different fat levels (3.25%, 2.0% and 1.0%), skim milk, sweet whey and phosphate buffer saline (PBS). Liposome stability determined as the quantity of released nisin Z was highest in milk followed by PBS and whey, respectively. (C) 2003 Elsevier Science Ltd. All rights reserved.