| Summary: | 碩士 === 國立臺灣大學 === 食品科技研究所 === 87 === In this study,α-chitosan is used as raw material. In chitosan molecule, the carboxymethyl group was attached to NH2 and C6 of glucosamine unit by carboxy- methylation, and the products were used for analysis and their chemical-physical properties were compared. The items such as yield, solubility, particle size of distribution, values of L, a, b, and intrinsic viscosity et al, were measured to observe the changes occurring in the process of carboxymethylation. Furthermore, their chelating ability of metal ions and inhibition of bacteria growth were also tested.
In the carboxymethylation,the yield might reach 178~183%, for different degrees of deacetylated chitosan, and as the degree of deacetylation(DD)increased, the yield also increased. The solubility of the products which were carboxymethylated at pH7~11was 0.8g/dL, but those conducted below pH6 were almost insoluble, and the critical point seems to be pH6.8 as the precipitate might occur below this point.
No apparent color change happened after carboxy- methylation, and the L, a, b values showed no changes in the process.
For the distribution of particle size in chitosan, there were 2000~3000nm changes after the process, and chitosan with DD70% showed most significant changes and enlarged to 55000nm. The particle size of distribution became smaller with increased degree of deacetylation.
The intrinsic viscosity of carboxy-methylaed chitosan with DD70, 80, and 90% were 19.57, 15.77 and 14.94dl/g respectively, and that proved positively related to their molecular weights.
As for chelating ability of metal ions, copper was most strong, and followed by zinc and iron; the chelating abilities were affected by pH values for zinc and iron, but not for copper.
The larger the pH value, the better the chelating abilities of zinc and iron ions. On the contrary, the degree of deacetylation influenced the chelating ability less. After processing, zinc and iron ions increased 3,8 and 2 times respectively.
In CM-chitosan, the NH2 group was attached with CM group and lost its function. Therefore they showed no inhibition to the growth of G(+)and G(-) bacteria, even when 1000ppm or up to 2000ppm of CM-chitosan were added. In other words, chitosan lost its ability to inhibit the growth of bacteria after carboxymethylation. As the degree of deacetylation increased, chitosan showed a stronger ability to inhibit the growth of bacteria, and this means the effect of the degree of deacetylation is more distinct than that of concentration.
The chitosan had an astringent taste but it disappeared after carboxymethylation and tasted salty instead.
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