Effect of starch structures on the efficiency of enzyme hydrolysis

Normal, waxy, ae-waxy, Hylon V & VII maize starches were dispersed in 90% dimethyl-sulfoxide (DMSO) solution and hydrolyzed using [alpha]-amylase of Bacillus licheniformis to determine the effect of starch structures on the efficiency of enzyme hydrolysis. Waxy maize starches displayed lower hydrolysis rates compared to non-waxy starches. High performance size-exclusion chromatography (HPSEC) results showed that waxy maize starches displayed larger molecules ranging between degree of polymerization DP 39 and DP 150 to a greater extent than high-amylose starches. Thin layer chromatography (TLC) results showed that Bacillus licheniformis [alpha]-amylase produced malto-hexaose (G6) and malto-heptaose (G7) as the major products. High performance anion-exchange chromatography (HPAEC) results of 90 min enzyme hydrolysates showed that the high-amylose V & VII and ae-waxy maize starches had greater proportion of molecules ranging between DP 22 - DP 40 compared with normal and waxy starches. Glucose yields of the dry-milled corn flour of varying protein and oil contents when subjected to enzyme hydrolysis using [alpha]-amylase, glucoamylase and pullulanase showed that the corn flour with higher oil contents displayed lower glucose yields (r = -0.66, p-value = 0.0002). However, varying protein contents did not effect the enzyme hydrolytic rate (r = 0.06, p-value = 0.75). The onset gelatinization temperatures (To) of starches from dry-milled corn varied from 55.1 to 68.4 0C and the enthalpy changes varied from 9.6 to 13.9 J/g. Starch with lower onset gelatinization temperature displayed higher enzyme hydrolytic rates in dry-milled corn flour (r = -0.63, p-value = 0.02). Starch pasting temperature was negatively correlated to the enzyme hydrolytic rate (r = -0.66, p-value = 0.01)