화학적 방법에 의한 저분자화 알지네이트의 생산기술 및 응용

Abstract

Alginate, a linear polysaccharide derived from brown seaweed, is a collective term for a family of copolymers containing 1,4-linked β-mannuronic acid and α-gluuronic acid resides in varying properties and sequential arrangement. Alginate has been used as food stabilizer, gelling agent, encapsulation material for drug, plant growth stimulator and wound dressing material. However, the nature of al -ginate's high molecular weight limits its application to some fields due to its high viscosi ty and poor solubility in water. Therefore, alginate with low viscosity and high solubility in water is desired for its broad application. Generally, polysaccharide can be degraded by chemical, enzymatic, and irradiation methods. The chemical method and enzymatic treatment are typical conventional methods for manufacturing of alginates in low molecular weights. Enzymatic degradation could give chemical deformation minimized but require further purification process due to the formation of side products with the problems in environment and recovery factor. The irradiation degradation process, however, give no serious side products and is considered simpler, faster and more environmentally friendly than aforementioned conventional one. Therefore, it can be used for mass production. but, the equipment cost may be a weak point for mass production. In this study, hydrogen peroxide(H2O2) was used for producing low molecular weight sodium alginates(LMWSAs) under e-beam irradiation or controlled sonication. Hydrogen peroxide, an excellent oxidizing agent can be easily decomposed to produce active radical and/or ions. It generates free hydroxyl radicals and/or hydroxyl anions which are active to depolymerize the alginate. The free radicals attacks the C-1 hydrogen atoms of mannuronate or guluronate to rearrange their structures followed by breaking glycosidic bonds. A ultrasonic wave is also useful to depolymerize the high molecular weight polysaccharides. The chain breaking reaction can be occured by the pulsation of bubbles by bubble collapse or cavitation effects. Polysaccharides such as cellulose are degraded by the scission of glycosidic bonds and the rate of hydroxyl radical generation can be accelerated by irradiation of e-beam or ultrasound. The sodium alginates were characterized by using solution viscometry, GPC, FT-IR, 13C-NMR and 1H-NMR. Based on FT-IR, 13C-NMR and 1H-NMR taken before and after degradation it was revealed, that the depolymerization was initiated by the breakage of the glycosidic bonds of sodium alginate. Incorporation of hydrogen peroxide and e-beam irradiation are much more effective than any other methods in lowering the molecular weight of sodium alginate. Another target of this work was to investigate the antibacterial properties of sodium alginate depolymerized. The alginate in wound dressings has been used as an important tool of modern wound management. By incorporating silver ions into alginate, antibacterial properties can be expressed. In order to incorporate silver ions onto the alginate, sodium alginate was reacted with aqueous solutions of silver nitrate. The silver ions of silver nitrate were exchanged with sodium ions in sodium alginate, resulting in the formation of alginate powder containing silver ions. Particle size and solubility of silver alginate can be controlled by adjusting the mole ratio of sodium and silver ions. SEM and TEM micrographs showed the silver alginate particles were sphere-shape and the particle was approximately 0.7 ㎛ average in size. LMWSAs and silver alginate exhibit more strong antibacterial properties against the bacteria such as Escherichia coli, Staphylococcus aureus, and Propionibacterium acnes., than pristine sodium alginate. MIC and cell optical density data showed that the antibacterial properties were improved with decreasing the molecular weight of alginate. These results mean that silver ions in LMWSA could give dramatically improved functionality in bactericide.