Starch serves as a food reserve in plants and is an important component in the human diet, where the digestion is mediated by α-amylase. Generally, refined starches are quickly and substantially digested by enzymatic hydrolysis and then absorbed by the intestines to serve as the source of energy or be stored in the body. However, some starches resist digestion by α-amylase. Englyst et al. (1992, Eur. J. Clin. Nutr. 46 (suppl 2): S33-S50) classified ingested starches on the basis of their probable digestive rate in vivo. They proposed three classes of dietary starch: 1) rapidly digestible starch (RDS), which is likely to be digested in the human intestines; 2) slowly digestible starch (SDS), which is likely to be slowly yet completely digested in the small intestine; and 3) resistant starch (RS), which is unlikely to be digested in the small intestine.
A need has been recognized for a modified starch to serve as a resistant starch, which provides the consumer with low-calorie carbohydrate product. Such resistant starch would thus be an excellent source of carbohydrate for use in food products, including medical foods and dietary supplements, for both diabetic and prediabetic individuals, or be a choice for healthy individuals in order to reduce the calorie of foods or to slow the rate of starch digestion. Such resistant starch would also be useful for individuals wishing to moderate their glucose response or achieve sustained energy release via consumption of foods.
Literatures demonstrate health-related role for slowly digestible starch, as a result of slow glucose release over an extended period. The benefits include increased satiety for longer periods (which would be useful in weight management), sustained energy release (which is useful in enhancing athletic performance including endurance), and improvements in concentration maintenance and memory.
Such slowly digestible or resistant starch could also be useful as drugs, i.e., as mentioned above, for diabetic or prediabetic individuals to reduce the risk of disease. Moreover, such starch may be useful for the treatment of hyperglycemia, insulin resistance, hyperinsulinemia, dyslipidemia and the like. It may also be useful for the treatment of obesity.
U.S. Pat. No. 6,890,571 discloses a slowly digestible starch product prepared by debranching low amylose starches by isoamylase and allowing the resultant linear short chains to crystallize into a highly crystalline form. U.S. Pat. No. 6,623,943 discloses a process for physically and chemically preparing a resistant starch. The slowly digestible starch of U.S. Pat. No. 6,890,571 and resistant starch of U.S. Pat. No. 6,623,943 are not pectin cross-linked and accordingly, the dietary fiber contents thereof are not as high as that of pectin-modified starch.
The modified starch in U.S. Pat. No. 6,670,470, which is useful in paper coating and sizing, is prepared by oxidizing a starch with hydrogen peroxide, esterifying said oxidized starch and cross-linking the starch. Such chemically-modified starch is not an ideal edible form.
Accordingly, there is a need for modified starches which are slowly digestible or resistant to digestion and are safe to be used in place of or in addition to conventional carbohydrate products in foods or in medical uses.