# Microencapsulation of Natural Food Antimicrobials: Methods and Applications
## 2 Encapsulation Methods
### Liposome Encapsulation  
Liposomes are small and spherical bilayer vesicles with a hydrophilic core surrounded by at least one phospholipid bilayer and are produced from dispersed amphiphilic lipids in an aqueous solution encapsulating an aqueous core. Based on the arrangement of bilayers, the size and preparation method, liposomes are divided into different forms: small unilamellar vesicles (SUV) (20-50 nm), large unilamellar vesicles (LUV) (100-300 nm) and multilamellar vesicles (MLV) (2-10 \(\upmu\)m) [67]. Various water or lipid soluble compounds can be encapsulated within liposomes consisting of both aqueous and lipid phases in their structure [68]. Lipid vesicle microencapsulation has been mostly investigated in pharmaceutical applications as targeted drug delivery carriers to keep chemically labile substances from undesirable interactions before release. In recent years, this technology has been used for the encapsulation of food ingredients such as enzymes, proteins, antioxidants, flavors and vitamins [33; 69; 70]). LUV constitutes the most suitable liposomes system for food applications due to their high encapsulation efficiency, favorable stability over time and easy formation techniques [38]. The main advantage of liposome encapsulation is the preservation of the stability of water soluble compounds in high-water-activity applications compared to the other encapsulation methods, such as spray drying, fluidized beds and extrusion [71] (Figure 4). However, application of liposomes for the encapsulation of hydrophobic substances is restricted because of the fast release of the agent incorporated in the lipid bilayer [72]. On the other hand, lipid oxidation, along with hydrolysis, significantly reduces physical and chemical stability of liposomes [73]. Some reports have demonstrated the ability of liposome encapsulation to stabilize entrapped bioactive agents  
Figure 3: Antisolvent precipitation method for production of biopolymer particles (adapted from [PERSON] 2015 [66]).  
against degradation by enzymes, reactive chemical substances, changes in pH, temperature and ion concentration, and to increase therapeutic effectiveness along with decreasing toxic effects of entrapped antimicrobial agents [33; 68]. Three liposome mixtures, including PC (distearoyilphosphatidyl choline), PC/PG (distearoyilphosphatidylglycerol) 8:2 and PC/PG 6:4, were used for the encapsulation of the antimicrobial peptide nisin. Utilization of liposomes for the encapsulation of pH-sensitive nisin was appropriate due to the approximately equal EE of nisin in liposomes with or without anionic phospholipids (PG) at pH 5.5-11.5 at 25 C. The encapsulation of nisin reduced the diameter size of PC/PG liposomes because the interactions between positively charged nisin and negatively charged lipids added to a realignment of phospholipids lead to the formation of more packed and smaller vesicles [33].  
Improved solubility and product stability, bioavailability and decreased toxicity are the main advantages of liposomal antimicrobial delivery systems. Various plant herbs, spices and lysosomes have been encapsulated in liposome and polysaccharide particles (alginate, chitosan or starch) [34]. The type of plant extraction (aqueous, alcoholic and citric acid) and the type of materials used for capsule formation had a significant effect on the EE of plant herbs and spices. The lowest liposomal EE was for most of plant compounds extracted in citric acid. Additionally, the higher EE of plant water extracts was usually obtained for liposomes than for polysaccharide particles. The highest EE of lysozyme (about 90%) was achieved in alginate and starch particles, not liposomes [34].