Enzymatic hydrolysis of α-glucan crystallites

Crystalline starchy substrates (lintners, i.e. parts of granules resistant to mild acid hydrolysis, and amylose spherocrystals) were subjected to enzymatic degradation by α-amylase from Bacillus sp. The crystallinity of these substrates before and after amylolysis was studied by X-ray diffractometry and differential scanning calorimetry. Chain length distribution was investigated by high-performance size-exclusion chromatography and anion-exchange chromatography. Regardless of the initial morphology, particles with A-type crystallinity were more susceptible to amylolysis than those with B-type. The final rate of hydrolysis after 30 h was less than 10% for high-amylose starch lintners, between 20 and 37% for potato and C-type lintners, and greater than 62% for pure A-type lintners. For C-type lintners, the final rate of hydrolysis increased in relation to the proportion of A-type crystallinity as evaluated by X-ray diffraction. A progression towards B-type was observed during amylolysis of both A- and C-type lintners, confirming the greater susceptibility of the A-type structure. However, this dependence on crystalline type cannot account for the behavior of all studied lintners during enzymatic action. The effect of other parameters, such as morphology and crystal defects and the interrelations of the crystals, should also be taken into consideration.