Physicochemical Properties of Slowly Digestible Starch (SDS)

Postprandial Glycemic Response

The slow digestion property of Slowly Digestible Starch (SDS) products can be confirmed with a postprandial glycemia test. The microencapsulation of normal cornstarch by zein protein was investigated, and the starch capsules displayed a significant increase in SDS. In a further in vivo study using a mouse model, both the cornstarch material and the encapsulated starch material showed slow digestion profiles, with the prolonged and sustained elevation of blood glucose, confirming that microencapsulation did not alter the inherent slow digestion property of native normal cornstarch.

Dietary carbohydrates are the main source of energy in the human diet and are also the main determinant of postprandial blood glucose levels. In recent decades, the effects of carbohydrate-rich diets on human health have been debated because of their potential untoward effects on glycemic control and plasma lipid concentrations. A high intake of refined carbohydrate foods has been particularly associated with increased plasma glucose and insulin levels in the postprandial period, the elevation of fasting and postprandial plasma triglycerides, and a reduction in high-density lipoprotein (HDL)–cholesterol levels. A large body of evidence indicates that blood glucose concentrations are an important and independent risk factor for cardiovascular diseases, not only in diabetic patients but also in individuals with normal fasting glucose levels. Delayed dietary carbohydrate digestion and absorption may have significant beneficial implications for the prevention and treatment of metabolic disorders. Many factors influence the digestion of carbohydrates in the small intestine, including their viscosity, the physical form of the food, the cooking and processing methods, the type of starch (amylose or amylopectin), the presence of anti-nutrients, and the amounts of fiber, fat, and protein present.

The postprandial glycemic and lipid responses are linked to the risk of chronic diseases. The rate of digestion of dietary carbohydrates in the intestine plays a clinically relevant role in the regulation of postprandial metabolism. After a meal, glucose levels are modulated by the rate of carbohydrate digestion in the small intestine and by the fermentation of undigested carbohydrates in the colon. Moreover, when the carbohydrate reaches the colon, it has a beneficial effect on the composition of the colonic microbiota and on short-chain fatty acid production, which improves the metabolism of glucose and lipids. This explains why a diet based on legumes, vegetables, fruits, and high amounts of Slowly Digestible Starch (SDS) can significantly improve an individual’s cardiovascular risk profile, particularly in type 2 diabetic patients, and can substantially reduce the overall risk of cardiometabolic diseases.

When heated in excess water, starch granules undergo gelatinization in three distinct stages: the granule swelling, the disruption of the ordered (crystalline and molecular) structures, and the solubilization of the starch molecules. Gelatinization causes irreversible changes in the starch properties, including its water uptake, granule swelling, crystal melting, birefringence, solubility, and viscosity. These changes greatly affect the functional properties of starch and its digestion. These changes also involve a sequence of thermal events that results in the phase transition of the starch granules. When starches are heated in limited water, biphasic endotherms are often observed with differential scanning calorimetry (DSC), which is related to the gelatinization and melting of the starch crystallites.

In the Slowly Digestible Starch (SDS) gelatinization studies mentioned above, the thermal parameters of modified and native starches were determined with DSC, and the results showed that the gelatinization parameters of starch differ considerably before and after modification.

Starch Pasting Properties

Pasting involves the swelling of the starch granules, the leaching of carbohydrates, the formation of a three-dimensional network of leached molecules, and the interactions between the granule remnants and the leached material. It is determined by the botanical origin of the starch, its amylose content, the distribution of amylopectin chain lengths, the swelling power, the starch concentration, and the processing conditions, such as the shearing and heating rates.

The determination of starch pasting profiles with a rapid visco analyzer (RVA) was originally proposed by Charles (Chuck) Walker in rain-damaged wheat. RVA starch pasting profiles are currently used extensively in the human food industry, e.g., to determine the different parameters related to the starch pasting properties of cereals and starchy foods.

The typical profile of a starch sample analyzed with RVA indicates the main parameters measured during the analysis. The pasting temperature provides information about the minimum temperature required to cook a given sample. Other parameters, such as the rate of breakdown in viscosity and the hot paste viscosity or trough, depend upon the temperature and degree of mixing. The reassociation of the starch molecules during cooling is commonly referred to as the “setback.” It involves the retrogradation of the starch molecules and has been correlated with the texture of various products. The final viscosity of the starch is the parameter most commonly used to define the pasting properties of a given sample.

In recent years, several authors have evaluated the use of multivariate data analysis techniques to better interpret RVA profiles and have obtained further information about the starch pasting properties of a sample.

The RVA results of Xu and Zhang showed that encapsulated starch was considerably altered. In that study, the microencapsulation of normal cornstarch with zein protein and its slow digestion property were investigated. A significant increase in Slowly Digestible Starch (SDS) was detected in the starch capsules (weight ratio of zein to starch, 1:6) containing plasticizers (glycerol and oleic acid) after high-temperature (70 °C) treatment. The temperature at peak viscosity increased, and the peak viscosity of the microencapsulated starch was substantially reduced, indicating improved thermal resistance after microencapsulation. These data suggest that the starch granules were densely packed in the zein matrix after the high-temperature treatment, which may slow the enzymatic digestion and generate a relatively high amount of SDS.

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