Modified amylose biodegradability by α-amylases

The site-selective syntheses of water-soluble (O-2/O-3)-substituted amylose derivatives containing butyl ester, carboxymethyl, succinyl or quaternary ammonium side groups was carried out. In addition, routine chemical methods which did not employ protection-deprotection steps provided water soluble (O-2/O-3/O-6)-substituted products. The biodegradation of these products as a function of site-of-substitution and degrees of substitution (ds) was studied by the O-amylases from Aspergillus oryzae and Bacillus subtitis. Consistent with the results reported previously for acetyl amylose (Ref.1), the O-2/O-3 substituted butyl amylose derivatives degraded faster and to higher percentages than the corresponding O-2/O-3/O6 substituted derivatives. Also, the overall rates and percentages of degradation for butyl amylose were much lower than acetyl amylose derivatives of comparable degree and site of substitution. Therefore, for the two enzymes studied, the introduction of longer chain length acyl side groups greatly reduced substrate degradability. For the charged derivatives. the rate and percentage of degradation decreased in the order carboxymethyl > succinyl > quaternary ammonium at comparable degree and site of substitution. We concluded that, as the length of the charged side chain substituent increased the rate and extent of biodegradation decreased. Furthermore, in contrast to the results for neutral acetyl and butyl side groups, there was no significant difference in the rate and %-degradation for charged side chain substituent groups when comparing O-2/O-3 and O-2/O-3/O-6-substituted derivatives. Finally, the introduction of anionic or cationic side chain groups resulted in decreased susceptibility to α-amylase catalyzed chain cleavage when compared to similarly substituted acetyl and butyl amylose derivatives.