Sei-ichi Aiba

Biodegradability of Plastics

Plastic is a broad name given to different polymers with high molecular weight, which can be degraded by various processes. However, considering their abundance in the environment and their specificity in attacking plastics, biodegradation of plastics by microorganisms and enzymes seems to be the most effective process. When plastics are used as substrates for microorganisms, evaluation of their biodegradability should not only be based on their chemical structure, but also on their physical properties (melting point, glass transition temperature, crystallinity, storage modulus etc.). In this review, microbial and enzymatic biodegradation of plastics and some factors that affect their biodegradability are discussed.

Chitosan and gelatin based edible films: state diagrams, mechanical and permeation properties

Films of chitosan and gelatin were prepared by casting their aqueous solutions (pH≈4.0) at 60°C and evaporating at 22 or 60°C (low- and high-temperature methods, respectively). The physical (thermal, mechanical and gas/water permeation) properties of these composite films, plasticized with water or polyols, were studied. An increase in the total plasticizer content resulted in a considerable decrease of elasticity modulus and tensile strength (up to 50% of the original values when 30% plasticizer was added), whereas the percentage elongation increased (up to 150% compared to the original values). The low-temperature preparation method led to the development of a higher percentage renaturation (crystallinity) of gelatin which resulted in a decrease, by one or two orders of magnitude, of CO2 and O2 permeability in the chitosan/gelatin blends. An increase in the total plasticizer content (water, polyols) of these blends was found to be proportional to an increase in their gas permeability.

Edible films made from gelatin, soluble starch and polyols, Part 3

The thermal and mechanical properties of edible films based on blends of gelatin with soluble starch plasticized with water, glycerol or sugars were investigated. Two different methods, known as ‘the high temperature’ and ‘the low temperature’ methods, consisting of casting aqueous solutions of blends at 60 and 20 °C, respectively, were employed for the preparation of films. With increasing water, glycerol or sorbitol content, a drop of elasticity modulus and tensile strength (up to 50% of the original values for 30% plasticizer) was observed. The tensile strength and percentage elongation increased with high gelatin contents (> 20% ww). The development of a higher percentage renaturation of gelatin (reaching 70% for 5% water content) by the ‘low temperature’ method caused a reduction in gas and water permeabilities. The former decreased by one or two orders of magnitude for O2 and CO2, respectively. The semi-empirical model for calculation of gas permeability and the semi empirical equations for upper and lower limits of tensile moduli of composites were applied with limited success and the obtained values were compared to those experimentally determined.

Edible films made from hydroxypropyl starch and gelatin and plasticized by polyols and water

Two methods, known as the low and the high temperature methods, which consist of casting aqueous solutions of hydroxypropyl starch and gelatin at 20 and 60°C, respectively, were employed for film preparation. The physical (thermal, mechanical and gas/water permeation) properties of these composite films, plasticized with water or polyols, were studied. An increase in the total plasticizer content resulted in a considerable decrease in elasticity modulus and tensile strength (up to 60% of the original values when 25% plasticizer was added), whereas the percentage elongation increased (up to 200% compared to the original values). The low temperature method led to the development of higher percentage renaturation (crystallinity) of gelatin which resulted in a decrease, by one or two magnitude orders, of CO2 and O2 permeability in the hydroxypropyl starch/gelatin blends. An increase in the total plasticizer content (water, polyols) of these blends was found to be proportional to an increase in their gas permeability.

Studies on chitosan: 4. Lysozymic hydrolysis of partially N-acetylated chitosans

The lysozymic digestibility of partially N-acetylated chitosans was studied by measuring the reducing sugars produced and the molecular weights of their hydrolysates. Moderately N-deacetylated chitosans (MDC), obtained by N-deacetylation of chitin under heterogeneous conditions, were about four times more digestible at an early stage than partially N-acetylated chitosans (PAC-H) with similar acetyl content, prepared by N-acetylation of highly N-deacetylated chitosans under homogeneous conditions. The molecular weights of the hydrolysates of MDC decreased rapidly but gradually reached a constant value in contrast to the behaviour of PAC-H. The Km was 0.14 mM for 30% N-acetylated MDC and 0.12 mM for 65% N-acetylated PAC-H although the degree of N-acetylation of the latter was twice as much as the former. These differences were due to the different distribution patterns of N-acetyl groups in two types of the chitosans. MDC with 20-30% acetyl content have the sequences of more than three N-acetyl-D-glucosamine residues but PAC-H with about 30% acetyl content are random-type copolymers of N-acetyl-D-glucosamine and D-glucosamine units. PAC-H with more than 50% acetyl content have the sequences of more than three N-acetyl-D-glucosamine residues.

Preparation of chitooligosaccharides from chitosan by a complex enzyme

Chitosan of 24% degree of acetylation was depolymerized by a mixture of cellulase, alpha amylase, and proteinase to give the title oligosaccharides. The removal of products by membrane separation permitted yield maximization of products having degree of polymerization in the 3-10 range.

Studies on chitosan: 3. Evidence for the presence of random and block copolymer structures in partially N-acetylated chitosans.

The chemical structures of moderately N-deacetylated chitosans (MDC) derived from chitin under heterogeneous reaction conditions and partially N-acetylated chitosans (PAC) derived from highly N-deacetylated chitosans (HDC) under homogeneous reaction conditions were deduced from the data of the stability of their solutions in alkaline media, the swelling behaviour and X-ray diffraction patterns of their films in connection with the degree of N-acetylation of them. The solutions of PAC with more than 51% acetyl content, which were prepared from HDC by N-acetylation, were stable and remained clear and homogeneous by adding 1.2 equivalents of NaOH. On the contrary the solutions of PAC with more than 52% acetyl content, which were prepared from MDC, became turbid by neutralization with less than 1.15 equivalents of NaOH. The films of PAC prepared from HDC were highly swollen in water. The degree of swelling of the chitosan film with 51% acetyl content, prepared from the 6% acetyl content chitosan, was 121% while that of the 53% acetyl content chitosan, prepared from the 30% acetyl content chitosan, was 28%. From these data it was possible to set up a hypothesis that PAC prepared from HDC were considered as random-type copolymers of N-acetyl-glucosamine and glucosamine units whereas MDC were considered as block-type copolymers.

Production of N-acetyl-D-glucosamine from α-chitin by crude enzymes from Aeromonas hydrophila H-2330

The selective and efficient production of N-acetyl-D-glucosamine (GlcNAc) was achieved from flake type of alpha-chitin by using crude enzymes derived from Aeromonas hydrophila H-2330.

Enzymatic production of N-acetyl-D-glucosamine from chitin. Degradation study of N-acetylchitooligosaccharide and the effect of mixing of crude enzymes

N-Acetyl-D-glucosamine (GlcNAc) was produced from chitin by use of crude enzyme preparations. The efficient production of GlcNAc by cellulases derived from Trichoderma viride (T) and Acremonium cellulolyticus (A) was observed by HPLC analysis compared to lipase, hemicellulase, and pectinase. b-Chitin showed higher degradability than a-chitin when using cellulase T. The optimum pH of cellulase T was 4.0 on the hydrolysis of b-chitin. The yield of GlcNAc was enhanced by mixing of cellulase T and A. q 2003 Elsevier Science Ltd. All rights reserved.

Studies on chitosan: 1. Determination of the degree of N-acetylation of chitosan by ultraviolet spectrophotometry and gel permeation chromatography

A new method for determining the degree of N-acetylation of chitosan is proposed, which is based on ultraviolet (u.v.) absorbance at 220 nm of acetamide groups. Using the molar absorption coefficient of the acetamide group of N-acetyl-d-glucosamine and N,N′-diacetyl-d-chitobiose, the degree of N-acetylation of chitosan could be calculated. This principle was applied on high pressure liquid chromatography with an aqueous gel permeation support and a.u.v. detector. It was found that u.v. absorption peak areas in chromatograms were proportional to the concentration of acetamide groups and by this relationship the degree of N-acetylation could be estimated. This method is very useful for the characterization of chitosan because not only the degree of N-acetylation but also molecular weight can be measured at a time. This work indicates that the method is quite useful for tracing the time course of reactions between chitosan and reagents (acetic anhydride and others) because low molecular weight compounds are swept out from the main peak of chitosan in the chromatogram and the separation and purification of a reaction product can be omitted.