Resistant starch - a review of the physical properties and biological impact of RS3

Resistant starch (RS) encompasses forms of starch, which are not accessible to digestive enzymes. By far, retrograded starch, and particularly retrograded amylose, are the most thermally stable forms. Retrograded amylose is especially useful as a source of thermally stable RS3 for commercial food applications, since it survives most food processes. Retrograded starch has been studied extensively for understanding the behavior of gels and certain staling processes in foods. Characterization of retrograded starch has been done as it interferes with the total dietary fiber (TDF) assay, with an emphasis on the negative impact of retrogradation. Until recently, little is known on the nutritional and commercial value for retrograded starch as an RS3 product. Early studies into the digestibility implied that retrograded amylose was non-nutritive, but more recent studies show that amylases, in fact, slowly attack the structure. Consequently, glucose and other oligosaccharides are released from retrograded starch over a sustained period through the normal digestive process. Modulation of glucose release and uptake in humans can be an important consideration in the use of resistant starch in food products for certain target groups, such as diabetics and athletes. Sources of resistant starch are reviewed, with a focus an the principles behind the production of a food ingredient highly concentrated in retrograded amylose. Applications include a product for modulating the glucose response of diabetics, and effects on an extruded cereal product. (C) 2000 Elsevier Science Ltd. All rights reserved.