Charles J. Knill

Degradation of cellulose under alkaline conditions

Abstract A review of the important area of cellulose degradation under alkaline conditions is presented; it focuses on its relevance to the possible disposal of radioactive wastes in an underground repository in which cement-based waste encapsulation grouts and backfill may be employed. An overview of the alkaline degradation pathways of monosaccharides and substituted monosaccharides is initially presented, before progressing to the reactions involved in the alkaline degradation of cellulose, namely end-wise degradation, termination, alkaline scission, and oxidative alkaline degradation. Physical factors affecting reaction rates and the alkaline degradation of hemicellulose are also discussed. A review of the identity of the commonly detected alkaline degradation products (and their numerous synonyms) is presented, along with discussion of the rates of degradation of cellulose.

Carbohydrate polymers as wound management aids

Wound management aids have, in recent years, seen a transition from being simple natural coverings which give a wound protection from the external environment during the formation of the scab to specialized high technology materials which are produced from both synthetic and natural polymers. Much of the development has resulted from a greater understanding of the processes involved in wound healing coupled with advances in technology to produce biocompatible materials with the necessary physical and chemical characteristics for enhancement of the healing process. Polysaccharides, being naturally occurring biomolecules, were an obvious choice for investigation as potential wound management aids. In recent years it was recognised that not only can polysaccharides be produced with the required physical characteristics for a wound management product but that the actual polysaccharide or polysaccharide derivative may itself actively participate in the process of wound healing. This paper sets out to review the various types of polysaccharides which were used as wound management aids, the physical forms in which they are used and also the biological properties of polysaccharides which enable them to participate actively in the wound healing process.

Production of L(+) lactic acid using Lactobacillus casei from whey

The aim of this work was to study the fermentation of whey for the production of L(+) lactic acid using Lactobacillus casei. The effect of different process parameters such as pH of the medium, temperature, inoculum size, age of inoculum, agitation and incubation time was monitored to enhance the lactose conversion in whey to L(+) lactic acid. Fermentations were performed without any pH control. The optimization of the fermentation conditions resulted in significant decrease in fermentation time, besides increase in lactose conversion to lactic acid. The optimized process conditions resulted in high lactose conversion (95.62%) to L(+) lactic acid production (33.73 g/L) after an incubation period of 36 h.

Effects of organic solvents on the activity of free and immobilised laccase from Rhus vernicifera

Rhus laccase (RL) was covalently immobilised onto chitosan, and the effects of immobilisation on pH optimum, enzyme activity, thermostability, and re-use evaluated, using either N,N-dimethyl-p-phenylenediamine or 2,6-dimethoxyphenol as substrate. Immobilisation greatly enhanced enzyme thermostability, resulted in negligible loss of activity, and showed excellent re-use potential, with >80% relative activity retained after 15 cycles in aqueous solvent. Immobilised Rhus laccase (I-RL) was more catalytically active in both hydrophobic and hydrophilic organic solvents than free RL. With water-immiscible organic solvents, both free RL and I-RL required a minimum water content to achieve activity. With water-miscible organic solvents, in general a water content of ∼20-50% (v/v) was required to achieve activity using free RL, whereas with I-RL less water was generally required to achieve enzyme activity, and therefore considerably higher relative activity was exhibited at lower water contents. Kinetic investigations showed that the rate of substrate disappearance generally followed a pseudo-first-order law, and for evaluated water-immiscible organic solvents rate constants generally increased with decrease of hydrophobicity, however, in water-miscible organic solvents no such relationship was observed. Some discussion of the potential interactions between organic solvent molecules and enzyme active centres was provided to explain obtained results.

NATURAL POLYMERS FOR HEALING WOUNDS

Some carbohydrate polymers have properties making them suitable for application as wound management aids. A variety of neutral (e.g. cellulose, dextran, & (1→3)-β-D-glucans), basic (e.g. chitin & chitosan), acidic (e.g. alginic acid & hyaluronic acid), and sulphated polysaccharides (e.g. heparin, chondroitin, dermatan & keratan sulphates), have been the focus of interest with respect to biomedical/wound care applications. Recent investigations have also examined more unusual complex heteropolysaccharides, isolated from plant and microbial sources, which possess potentially useful biological and/or physicochemical characteristics with respect to wound care applications. A review of the function and requirements of wound management aids, their physical forms, and the structural features of the polysaccharides that are commonly used for their preparation, is presented, along with a brief overview of selected commercially available products (specifically hydrogels).

Effects of lacquer polysaccharides, glycoproteins and isoenzymes on the activity of free and immobilised laccase from Rhus vernicifera.

The purified polysaccharides, glycoproteins, and isoenzymes of Rhus laccase, and crude enzymes, from Chinese lacquer (Rhus vernicifera sap) were used to determine their influence on the enzymic activity of Rhus laccase on several substrates (4-phenylenediamine, isoeugenol and coniferyl alcohol). No product identity changes were observed when these components were added singularly or in combination to the enzymic reactions (only relative product yields varied significantly), however, the polysaccharides (GP1 and GP2) and glycoprotein (stellacyanin, St) exhibited negative effects, and the two isoenzymes (L1 and L2) exhibited positive synergistic effects, on the activity of Rhus laccase. With respect to the activity of the crude enzymes, the negative effects of GP1, GP2 and St were greater than the positive effects of L1 and L2, compared with free Rhus laccase on its own (using 4-phenylenediamine as substrate), the estimated inhibitory effect (of GP1, GP2 and St) being by at least a factor of 50 (even with the positive effect of L1 and L2). This contributes to understanding of lacquer storage stability and drying rates. Immobilisation of crude enzymes using a variety of techniques (using natural and modified polysaccharides, and an inorganic support) where evaluated using isoeugenol as substrate. Agar embedding and zirconium chloride chelation methods resulted in the highest substrate conversion levels. The yields and products of isoeugenol catalysis using Vietnamese crude enzymes/purified Rhus laccase and commercial Denilite laccase were also compared and contrasted with their Chinese lacquer sap equivalents.

Kinetic analysis of ethanol production from glucose fermentation by yeast cells immobilized onto ceramic supports

Porous ceramic supports have been developed and utilized for the immobilization of yeast cells to produce ethanol by the fermentation of glucose. The relationship between the porous structure of the ceramic support and the quantity of yeast cells immobilized and the production of ethanol by the fermentation have been investigated. A comparison of the properties of the ceramic supports with those of a calcium alginate gel indicated that the ceramics are the better of the two types of material and have potential for industrial application.

EFFECT OF METAL IONS ON THE RHEOLOGICAL FLOW PROFILES OF HYALURONATE SOLUTIONS

ABSTRACT The effects of various metal ions on the rheological flow profiles of hyaluronate solutions were investigated, by controlled incubation of metal chloride salt solutions with sodium hyaluronate (NaHA) solution under ambient conditions. Results from application of the Williamson model to the flow profiles of incubated solutions showed a progressive decrease in Williamson zero shear viscosity (η 0 ) with increasing atomic number / atomic mass of the metal ion, which, with the exception of data for Li + , could be related to a power equation ( y = cx b ). Such reductions in viscosity were not a result of hydrolysis (determined by GPC), but may be due to diffusing ions disrupting hydrogen bonding and shielding electrostatic repulsions between carboxylate groups.

NOVEL CHITOSAN-ALGINATE FIBRES FOR ADVANCED WOUND DRESSINGS

ABSTRACT A range of commercial chitosans were sourced and their molecular size profiles and degrees of acetylation (DA) were determined by HPSEC and 1 H-NMR spectroscopy, respectively. Chitosans were subsequently utilised for modification of alginate fibres, and levels of chitosan incorporated into base fibres were estimated by elemental analysis. Elongation (%) and tenacity of resultant chitosan/alginate fibres were determined in order to assess their potential application in wound dressings. A range of chitosan contents (˜ 0-6 % w/w) resulted from a variety of alginate and chitosan starting materials. Fibres produced from sodium alginate (A1, 6%) using hydrochloric acid (0.2M) at a draw ratio of 1.18, and treated with chitosan (C1, 3.2%) were deemed to have the best properties. In general, use of a water washing stage resulted in the production of better chitosan/alginate fibres. Treatment with chitosans generally resulted in a reduction in tenacity (and a reduction in % elongation if a water washing stage was not used), i.e. no increase in fibre strength was observed, implying that the chitosan is more like a coating rather than penetrating/reinforcing the alginate fibre.

Kinetic Analysis of Beer Primary Fermentation Using Yeast Cells Immobilized by Ceramic Support Adsorption and Alginate Gel Entrapment

Yeast cells were immobilized by absorption onto porous ceramic support and evaluated for continuous beer primary fermentation using a bioreactor in comparison to yeast cells immobilized by entrapment in calcium alginate gel. The effects of temperature and flow rate as a function of reaction/fermentation time on fermentation rate were investigated. The fermentation reaction (in terms of loss of total soluble solids in the beer wort as a function of time) was first-order with half-lifes in the range of ∼ 9–11 hours at ∼ 10–12°C at beer wort linear flow rates of ∼ 0.8–1.6 cm/minute for ceramic support, compared with ∼ 16 hours for Ca-alginate gel, the former support matrix being more efficient and demonstrating greater potential for future commercial application.