Digestion of starch: In vivo and in vitro kinetic models used to characterise oligosaccharide or glucose release

We give an overview of the kinetics of starch digestion, emphasizing in vitro studies and the various mathematical models used to analyse the data. The emphasis in this review is on ungelatinised starch (wherein granules are still intact and unswollen), applicable to domestic animal feed and to some human food. The mammalian digestive system uses a complex but well ordered series of processes to degrade and absorb nutrients from the diet of an individual. Mechanical action like mastication and churning of food throughout the various subsections of the gastrointestinal tract work together with biochemical components in secretions containing acids, buffers, and hydrolytic enzymes. Many attempts have been made to mimic digestion in vitro in an effort to model its complexities. Characterisation of enzyme-catalysed hydrolysis in vitro using purified enzymes, separately for simplification, has proven difficult, as the starch granule’s complex structure causes enzyme action to follow unconventional kinetics. The susceptibility of starch granules to digestion by glucohydrolases depends on a set of factors that include the granular structure, the method of preparation and the nature of the starch, and those molecules bound to it. Within a starch granule, the branching structure, molecular size and molecular weight distributions, and crystallinity, may all affect its physical properties, thus controlling digestibility. Characteristics such as solubility and the presence of fibre, fat and protein all contribute to the rate of digestion.