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Resistant Starch— A Review
M.G. Sajilata, Rekha S. Singhal, and Pushpa R. Kulkarni

ABSTRACT CT: resistant starch evoked interest bioavailability starch ABSTRACT: The concept of resistant starch (RS) has evoked new interest in the bioavailability of starch and in its use as source dietary fiber, particularly adults. now considered pro proper operties a source of dietary fiber, particularly inadults. RS is now considered to provide functional properties and find applicaformation, formation, var ariety foods. tions in a variety of foods. Types of RS, factors influencing their formation, consequence of such formation, their methods prepar eparation, have briefly review eview. of preparation, their methods of estimation, and health benefits have been briefly discussed in this review.eywords: resistant starch functionality, formation, prepar eparation, determination, digestibility, Keywords: resistant starch (RS), functionality, formation, preparation, determination, digestibility, physiological effects, applications, commercial sources

Introduction
From the early years of emergence of nutritional science, it has been recognized that the ingested nutrients in the diet are notcompletely utilized in the body. An increasing volume of evidence suggests that with very few exceptions, only a proportion of the total ingested nutrients in a diet or food is available, and the term “availability” has come into use for this proportion (Southgate 1989). The nutrients measured by chemical analysis may not always be fully utilizable, mainly due to the indigestible cell walls, abulky or dense structure, a low solubility, the presence of some compounds inhibiting the digestion, as well as components abundantly present in plant foods such as dietary fiber, phytic acid, and tannic acid, which may significantly reduce the absorption and utilization of some nutrients (Rosado and others 1987). During food processing, derivatization of nutrients and formation of cross linkagesoccur, thereby making the food inaccessible for digestion or/and metabolism. Such parts of nutrients are also “unavailable” (Erbersdobler 1989). Starch, which is the major dietary source of carbohydrates, is the most abundant storage polysaccharide in plants, and occurs as granules in the chloroplast of green leaves and the amyloplast of seeds, pulses, and tubers (Ellis and others 1998). Therelatively recent recognition of incomplete digestion and absorption of starch in the small intestine as a normal phenomenon has raised interest in nondigestible starch fractions (Cummings and Englyst 1991; Englyst and others 1992). These are called “resistant starches,” and extensive studies have shown them to have physiological functions similar to those of dietary fiber (Asp 1994; Eerlingen and Delcour1995). The diversity of the modern food industry and the enormous variety of food products it produces require starches that can tolerate a wide range of processing techniques and
MS 20050127 Submitted 2/28/05, Revised 8/2/05, Accepted 10/29/05. The authors are with Food Engineering and Technology Dept., Inst. of Chemical Technology, Matunga, Mumbai – 400 019, India. Email: rekha@udct.org.preparation conditions (Visser and others 1997). These demands are met by modifying native starches with chemical, physical, and enzymatic methods (Betancur and Chel 1997), which may lead to the formation of indigestible residues. The availability of such starches therefore deserves consideration. This review therefore focuses on the availability of the major nutrient, that is, the starch, withspecial reference to RS.

Starch and its classification
Chemically, starches are polysaccharides, composed of a number of monosaccharides or sugar (glucose) molecules linked together with -D-(1-4) and/or -D-(1-6) linkages. The starch consists of 2 main structural components, the amylose, which is essentially a linear polymer in which glucose residues are -D-(1-4) linked typically constituting 15%...