# Microencapsulation of Natural Food Antimicrobials: Methods and Applications
## 3 Microencapsulation of Natural Food Antimicrobials
### Antimicrobial Peptides  
Generally, antimicrobial peptides (AMP) are composed of 20-50 amino acids possessing a broad spectrum of antimicrobial activity and can be found in a wide variety of life forms, from microorganisms to humans. The net positive charge and the amphipachicity are considered as the main properties of AMPs [100]. The AMP has the ability to kill microbial pathogens through membrane permeabilization and disruption of biological activity of pivotal cytoplasmic substances including proteins, enzymes and RNA and DNA [101]. Antimicrobial peptides from bacteria can be produced ribosomally or nonribosomally. Ribosomally biosynthesized peptides are known as bacteriocins, of which only a few have been used in the food industry because of their high salt sensitivity and proteolysis [102]. Among the studied bacteriocins, such as pediocin, subtilis, lacticin, sakacin, leucocin, enterocin, mutacin and mesenterocin [103], nisin has been the only bacteriocin recognized as GRAS by the FDA since 1980. Nisin is a 3.4 kDa antimicrobial peptide consisting of 34 amin acids with unsaturated amino acids and lanthionin residues. Nisin A differs from nisin Z by a single amino acid substituting histidine at position 27 in nisin A and asparagine in nisin Z. Additionally, other nisin variants have been identified, such as Q, F and U ([PERSON] et al., 2015). It is produced by certain strains of _Lactococcus lactis_ sp. _lactis_ and has antimicrobial activity against a wide range of Gram-positive bacteria, including foodborne pathogens such as _L. monocytogenes_[104]. This metabolite can also inhibit bacterial growth of heat resistant and/or spore-forming microorganisms, particularly those belonging to the _Listeria_, _Bacillus_ and _Clostrodium_ species found in dairy products and canned foods [102; 105]. However, the antimicrobial activity of free nisin added into food products can be reduced over time as a result of establishing complex interactions with food ingredients such as fats and proteins in addition to the possible proteolytic degradation [71]. Additionally, the emergence of bacteriocin-resistant bacteria might occur through direct incorporation of nisin in food systems [106]. Microencapsulation is an appropriate alternative able to overcome limitations of direct bacteriocin application in foods and achieve a sustained release of antimicrobial peptides in delivery systems [35; 69]. The slow release of antimicrobial agents such as be bacteriocins from microcapsules can improve their antimicrobial activity by reducing the contact time of agents with some food components, resulting in partial inactivation. The antimicrobial activity of alginate microcapsules containing nisin formed by vibrating technology was evaluated against _Brochothrix thermosphacta_ 7R1. The residual activity of encapsulated nisin in active microcapsule units per mL (AMU/mL) was measured under various conditions (4 and 20 \({}^{\circ}\)C, pH 2.5, 4.5 and 6.0) over 168 h. The best result was achieved for the active microcapsules under storage conditions of 4 \({}^{\circ}\)C and pH 6.0. The efflux of nisin from microcapsules at higher temperatures and higher pH can lead to the reduction in AMU/mL. The microencapsulation of nisin had a significant effect on total inactivation of 10\({}^{4}\) and 10\({}^{6}\) CFU/mL resting cells of _Brochothrix thermosphacta_ 7R1 [35]. The antimicrobial activity of nisin encapsulated in liposomes was assessed against _L. monocytogenes_ and _E. coli_ O157:H7. The inhibitory effect of PC and PC/PG 6/4 (mol%) liposomes containing 5.0 or 10.0 \(\mathrm{\SIUnitSymbolMicro mL}\) nisin (with or without EDTA) were almost equal to free nisin plus EDTA against _L. monocytogenes_. The highest growth inhibition against _E. coli_ was obtained for liposome-coencapsulated nisin and EDTA. A consistent release of nisin and EDTA within 48 h was obtained for liposomes with PC/PG 6/4 formulation and other liposomes with a low amount of PC or PG releasedactive agents more slowly [69].