In vitro Starch Digestibility and Nutritionally Important Starch Fractions in Cereals and Their Mixtures

The variable glycemic response to starchy foods has been the subject of much interest particularly in the dietary management of diabetes [1, 2]. It is now well known that rate and extent of starch digestion is influenced by a variety of intrinsic and extrinsic factors [3-5]. The glycemic index (GI) is an in vivo measurement based on glycemic response to carbohydrate-containing foods, and allows ranking of foods on the basis of the rate of digestion and absorption of carbohydrates that they contain [6]. In vitro methods have also been used to classify foods based on their digestion characteristics similar to the in vivo situation, and to identify slow release carbohydrate foods [7, 8]. Recently, an in vitro technique using controlled enzymatic hydrolysis has been reported to characterize starchy foods in terms that reflect the rate and extent of starch digestion in the human gut. Hence, the method is useful in predicting the glycemic response to dietary starches [9]. In the Indian dietaries, nearly 60-70% of the carbohydrates are derived from cereals such as rice, wheat, ragi (finger millet) and jowar (sorghum). The cereals do not differ in their carbohydrate content [10]. Differences in starch digestibility are reported to relate to the source and nature of starch [11, 12]. Several studies have shown that, for individual foods with different glycemic indices, postprandial plasma glucose and insulin responses are influenced by both the amount of carbohydrate consumed and its source [13-16]. However, few, if any, studies have determined the in vitro starch digestibility in the cereals, that are commonly used in the Indian diets. Hence, the present study was planned to study the effect of source of starch, on in vitro starch digestibility, with an aim to characterize the nutritional properties of starch fractions in selected cereals. In addition, the amylose content was determined in both raw and processed cereals.