Chitosan as Antimicrobial Agent: Applications and Mode of Action

Chitin is the second most abundant natural biopolymer after cellulose. The chemical structure of chitin is similar to that of cellulose with 2-acetamido-2-deoxy-β- d -glucose (NAG) monomers attached via β(14) linkages. Chitosan is the deacetylated (to varying degrees) form of chitin, which, unlike chitin, is soluble in acidic solutions. Application of chitinous products in foods and pharmaceuticals as well as processing aids has received considerable attention in recent years as exotic synthetic compounds are losing their appeal. This review summarizes some of the important developments related to food applications of chitin, chitosan and their derivatives.

Food applications of chitin and chitosans

Perspectives for chitosan based antimicrobial films in food applications

A review of lignocellulose bioconversion using enzymatic hydrolysis and synergistic cooperation between enzymes--factors affecting enzymes, conversion and synergy.

Fungi possess the biochemical and ecological capacity to degrade environmental organic chemicals and to decrease the risk associated with metals, metalloids and radionuclides, either by chemical modification or by influencing chemical bioavailability. Furthermore, the ability of these fungi to form extended mycelial networks, the low specificity of their catabolic enzymes and their independence from using pollutants as a growth substrate make these fungi well suited for bioremediation processes. However, despite dominating the living biomass in soil and being abundant in aqueous systems, fungi have not been exploited for the bioremediation of such environments. In this Review, we describe the metabolic and ecological features that make fungi suited for use in bioremediation and waste treatment processes, and discuss their potential for applications on the basis of these strengths.

Untapped potential: exploiting fungi in bioremediation of hazardous chemicals

Lignin is the most abundant renewable source of aromatic polymer in nature, and its decomposition is indispensable for carbon recycling. It is chemically recalcitrant to breakdown by most organisms because of the complex, heterogeneous structure. The white-rot fungi produce an array of extracellular oxidative enzymes that synergistically and efficiently degrade lignin. The major groups of ligninolytic enzymes include lignin peroxidases, manganese peroxidases, versatile peroxidases, and laccases. The peroxidases are heme-containing enzymes with catalytic cycles that involve the activation by H2O2 and substrate reduction of compound I and compound II intermediates. Lignin peroxidases have the unique ability to catalyze oxidative cleavage of C-C bonds and ether (C-O-C) bonds in non-phenolic aromatic substrates of high redox potential. Manganese peroxidases oxidize Mn(II) to Mn(III), which facilitates the degradation of phenolic compounds or, in turn, oxidizes a second mediator for the breakdown of non-phenolic compounds. Versatile peroxidases are hybrids of lignin peroxidase and manganese peroxidase with a bifunctional characteristic. Laccases are multi-copper-containing proteins that catalyze the oxidation of phenolic substrates with concomitant reduction of molecular oxygen to water. This review covers the chemical nature of lignin substrates and focuses on the biochemical properties, molecular structures, reaction mechanisms, and related structures/functions of these enzymes.

Structure and Action Mechanism of Ligninolytic Enzymes

During the last decade, marked progress has been made in the study of the fine details of the structures of milk proteins such as caseins, beta-lactoglobulin, alpha-lactalbumin, and lactotransferrin. Many of the functional properties of the individual milk proteins, as well as the milk protein products, may be described at the molecular level. This article is an attempt to thoroughly review the three-dimensional structures of major milk proteins, and to correlate them with the functional aspects of these proteins as food ingredients.

Structures and functionalities of milk proteins

Composite films of chitosan-laurate were shown to have low water permeability, while films containing other fatty acids or esters were not effective in this respect. Electron microscopy revealed the microstructure of these films to be very different, in terms of density, pore formation, channeling, surface contour, and packing pattern. The surface energy of the films was estimated, and the dispersion force component (γ s d ) and the polar component (γ s d ) were calculated

Chitosan-lipid films: microstructure and surface energy

Feruloyl esterase forms a part of the enzyme complex that acts collectively and synergistically to completely hydrolyze xylan to its monomers. The enzyme has found potential uses in a wide variety of applications of interest to the agrifood and pharmaceutical industries. This review describes the enzymology of feruloyl esterases involved in xylan degradation. The occurrence of feruloyl esterases in various microorganisms and their physiochemical properties are presented. The nature of the enzyme substrates and products, the role of synergistic interactions with xylanases and other accessory enzymes, as well as the sequence-structure relating to the reaction mechanism are emphasized.

Feruloyl esterase: a key enzyme in biomass degradation.

Cut apple pieces coated with double layers of buffered polysaccharide/lipid showed a 50-70% reduction in the rate of CO 2 evolution and about 90% decrease in C 2 H 4 as compared with uncoated controls at ∼23 o C. This substantial decline in the rates of gas evolution was attributed primarily to the diffusion barrier properties of the lipid layer and secondarily to the inhibitory effect of the ascorbate buffer which contained calcium. Internal CO 2 increased and leveled off at concentrations of ∼120 mL/L after 8 h. The internal concentration of C 2 H 4 decreased after an initial rise and reached a low level comparable to that observed in the untreated samples after 24 h

Dominic W. S. Wong

Papers

Structure and Action Mechanism of Ligninolytic Enzymes

Structures and functionalities of milk proteins

Chitosan-lipid films: microstructure and surface energy

Feruloyl esterase: a key enzyme in biomass degradation.

Gas exchange in cut apples with bilayer coatings