Physiochemical and antimicrobial characteristics of chitosan prepared with microwave-assisted deacetylation
| Autor: | Zih-Lin Chen, 陳子琳 |
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| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 The deacetylation of chitin with different concentration of sodium hydroxide catalyzed with microwave catalysis system was investigated. Microwave-assisted catalysis system accelerates the rate of deacetylation. Chitosans with different degree of deacetylation (DD; 18%, 20%, 23%, 27%, 31%, 47%, 53%, 60%, 64%, 70%, 75%, 80%, 85% and 87 %) were obtained with 35-50% sodium hydroxide at 100℃ for 5-100 min. Under the conditions of 300 W and 100℃, chitosan of DD 18% can be obtained with 35% NaOH in 35 min, while chitosan of 87% DD can be obtained with 50% NaOH in 100 min. The results indicate that the NaOH concentration and the reaction time are the critical influencing factors for deacetylation. The viscosity of chitosans with DD 90%, 85%, 80% and 75% was determined and used to calculate the average molecular weight. The average molecular weights obtained were 89.1 kDa, 214 kDa, 257 kDa and 371.5 kDa for the above chitosans, respectively. Since the average molecular weight decreases as the DD of chitosan increases, the results imply that the degradation of chitosan backbone occurs as the deacetylation progresses. The determination of DD with colloid titration was inaccurate because of the incomplete dissolution of chitosan with DD above 50% in 5% acetic acid. To determine the DD of chitosan with DD above 50% with colloidal titration, the chitosan was initially dissolved in 85% phosphoric acid and then mixed with 5% acetic acid. The resulting DD markedly increased as compared with the traditional titration. Ninhydrin method was also used to analyze the DD of chitosan. The positive correlation was observed between the DD of chitosan and optical density of the ninhydrin reaction mixure. The inhibition of the growth of Escherichia coli, Bacillus cereus, Enterobacter aerogenes, Citrobacter freundii, Serratia marcescens, and Staphylococcus aureus with chitosans of different DD was also studied. The results show that the inhibitory capability increases as the DD increases. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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