"...The two main components of starch are amylose and amylopectin. As a general rule starches that contain more amylose (the linear fraction of starch) produce more RS after retrogradation than those with mainly amylopectin content (the crystalline fraction of starch).
In other words starches rich in amylose are generally more resistant to digestion and also more susceptible to retrogradation.
Retrogradation occurs when starch is heated in water above its gelatinization temperature and then cooled. When cooked beyond certain temperature starch granules gelatinize (melt) thus becoming more readily digestible.
However, these starch gels are unstable and upon cooling re-form crystals that are resistant to hydrolysis by amylases (digestive enzymes). Reheating of starch reduces the RS content while continuous cycles of reheating and cooling have shown to increase RS.
Studies suggest that the energy value of RS is approximately 2 kcal/g (8 kJ/g) as opposed to the energy value for completely digestible starch 4.2 kcal/g (15 kJ/g) (Liversey 1994).
Physiological effects of RS
As already mentioned above RS escape digestion in the upper intestinal tract and once in the large intestine they are subject to fermentation by the microflora with end-products SCFA (short chain fatty acids), hydrogen, carbon dioxide and methane.
As being of most importance to the human health we will now focus our attention mainly on SCFA. SCFA are a product of bacterial fermentation. The main components are butyrate, propionate and acetate with the first one being produced in significantly higher levels in comparison with the other two.
SCFA are the main energy source of the colonocytes (the colon mucosa). They help lower the pH of the intestine, increase colonic blood flow, help reduce the presence of toxic ammonia, and help prevent the development of abnormal colonic cell populations. SCFA are known as a bio-marker for colonic health.
It’s worth mentioning also that RS serve as a physical protection for the probiotics. These are cultures of live microorganisms, which are shown to regulate the flora in the intestinal tract. Therefore, resistant starch is prebiotic, based on its probiotic protecting and stimulating properties..."