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Thin Film Hydration and Reversed-phase Methods for Liposome Preparation

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Thin film hydration method

A liposome is composed of a multilamellar vesicle (MLV), and uni-lamellar vesicle (ULV). MLV had a high encapsulation efficiency, but also great variation in the vesicles size, size distribution and lamellarity. A major lipid component of phosphatidylcholine (PC), which consists of a mixture of natural phospholipids made of a polar end formed by a choline and a phosphate group linked to the hydrophobic portion linked by ester bonds with the glycerol. Specificity of liposome could enhance by adjusting lipid ratios, adding cholesterol to increase membrane leakage by incorporating membrane proteins to promote bacterial membrane fusion, etc. Liposome delivery system was stabilized and protected from undesired interactions. Encapsulation of bacteriocin into lipid nanovesicles was achieved by the thin film hydration method. By this technique, a preformed lipid film was hydrated with an aqueous buffer containing the bacteriocin, at a phase transition temperature of lipids.

The bacteriocin solution is entrapped into lipid composition and perhaps attributed to electrostatic and hydrophobic interactions between bacteriocin and phospholipids. Most bacteriocin was cationic amphiphilic molecules and therefore, they possibly encapsulated in the inner aqueous phase of liposome and also immobilized into liposome membranes. In this thin-film hydration method emphasis, bacteriocin has been performing the direct application of food protection, such as proteolytic degradation or interaction with food components. On the other hand, nisin-loaded PC nanovesicles caused no significant inhibition of target pathogens in comparison to free nisin, whereas PC:phosphatidylglycerol (PG) liposomes produced a significant inhibition, suggesting PG-containing nanovesicles to release their contents more efficiently. Liposomes prepared from different proliposomes with lower contents of negatively charged phospholipids were less susceptible to the nisin-membrane destabilizing action in comparison with other liposomes.

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Reversed-phase method

Alternatively, in the reversed-phase method an aqueous solution of the bacteriocin dropped into the lipid solution to form water in oil emulsion, which was sonicated yielding a homogeneous opalescent dispersion of reverse micelles. The organic solvent was evaporated, resulting in a highly viscous organogel, which was reverted to nanovesicles after addition of ultrapure water. These two methodologies were compared to encapsulate the nisin in PC nanovesicles, also testing both probe-type and bath type ultrasound. Film hydration using bath-type ultrasound resulted in liposomes of smaller size and with adequate maintenance of antimicrobial activity. This nanovesicle was applied in milk as food model, inhibiting L. monocytogenes growth. Nisin and BLIS P34 were encapsulated in PC liposomes and incorporated into Minas frescal cheese. Liposome encapsulation prolonged the nisin and BLIS-P34 antilisterial activities due to gradually releasing as compared with both free nisin and BLIS-P34. Current study released rates of fluorescently labelled nisin from liposomal nanocarriers. Interestingly, acidic pH and convenient ethanol concentration in food-simulating liquid (FSL) improved the stability and retention capacity of loaded drug. The partition coefficient (i.e., nisin concentration in FSL/nisin concentration in nanoliposomes, at equilibrium) values were from 0.23 to 8.78, strong dependencies on nisin affinity toward encapsulating systems as well as on the surrounding FSL (i.e., phosphate-buffered saline, pH 6.8; acetic acid 0.3%, pH 2.8, or ethanol 10%, pH 7). The interaction between nisin and nanoscale bilayer systems was demonstrated by membrane activity of nisin from adsorption and aggregation to pore formation. Table 3 includes some articles about bacteriocin liposomes methods applied for antilisterial activity.

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