Starch granule characterization by kinetic analysis of their stages during enzymic hydrolysis: 1H nuclear magnetic resonance studies

1H nuclear magnetic resonance (NMR) spectroscopy was used to study the kinetics of digestion of starch by two hydrolytic enzymes; specifically we studied the reactions of α-amylase from B. licheniformis (E.C. 3.2.1.1) and glucoamylase from Aspergillus niger (E.C. 3.2.1.3) with starch granules (early stages of digestion) and with oligosaccharides (a later stage). This was done to provide a characterization of starch granules from various sources, with respect to the kinetics of glucose release from them. For the smaller oligosaccharides, α-amylase was inhibited by its reaction product maltose, while glucoamylase was not inhibited by its main product, glucose. The hydrolysis of oligosaccharides up to seven glucose units in length (maltoheptaose) followed Michaelis–Menten kinetics. For starch granules, experimental evidence suggests that the digestion kinetics changes subsequent to the hydrolysis of starch chains, which are accessible to enzymic attack. The rapid-digestion stage, consisting of enzymic attack on accessible starch chains, was precisely described by classical Michaelis–Menten kinetics, without considering product inhibition. During the slow-digestion stage, the rate decreased significantly; this is posited as being due to the inaccessibility of inter-glucose linkages becoming the rate-determining step.