Enzymatic degradation of hydroxypropyltrimethylammonium wheat starches

The enzymatic degradation of hydroxypropyltrimethylammonium modified starches synthesised by dry process was compared with that of hydroxypropyltrimethylammonium modified starches synthesised in glycerol–water plasticised molten medium. The enzymatic degradation rate of products from both origins decreased as the degree of substitution increased. However, two distinct enzymatic degradation profiles were obtained. Dry process products displayed a regular decrease pattern as DS increased. Molten medium synthesised cationic starches displayed a constant degradation level on a wide DS range with α,β-amylase and amyloglucosidase, whereas isoamylase degradation rapidly reached its degradation limit at DSs 0.05. The various plasticising conditions used to synthesise cationic starch in molten medium show no influence on the enzymatic degradation. By measuring the affinity of α-amylase, β-amylase and isoamylase for native, extruded non-modified and hydroxypropyltrimethylammonium-modified starches. It was evident that the enzymes’ affinity for the substrate diminishes with increasing chemical modification, particularly in the case of α-amylase, suggesting that the location of cationic groups impairs the enzyme’s recognition of the substrate. Structural elements of limit dextrins were analysed by 1H NMR.