Resistant starch is defined as a portion of starch that cannot
be digested by amylases in the small intestine and passes to
the colon to be fermented by microbiota (13). Englyst et al.
(1) proposed a classification system based on starch digestive rate. This system divides starches into rapidly digestible
starches, slowly digestible starches, and resistant starches based
on the results of in vitro digestion. There are currently 5 types
of resistant starch (Table 1). Substantial research has been
conducted on each of the 5 types of resistant starch, and
they are briefly summarized next.
Type I. Starch is synthesized in the endosperm of cereal
grains or seeds, and starch granules are surrounded by protein matrix and cell wall material. These physical structures
hinder the digestibility of starch and reduce the glycemic
response (14). When cooked as whole kernels or coarsely
ground seeds, the thick cell wall of legume seeds and the protein matrix in cereal grains prevent water penetration into the
starch in the matrix. Therefore, the starch does not have adequate moisture to readily gelatinize and swell. Without proper
swelling to expose the starch molecules, the starch is not readily susceptible to enzymatic hydrolysis. The cell wall material
and the protein matrix also provide a physical barrier, preventing enzymes from reaching and hydrolyzing the starch.
Examples of type I resistant starch (RSI)9–containing foods
are breads made with whole or coarsely ground kernels of
grains (15) and pasta made with durum wheat by extrusion
(16). Durum wheat has a high protein content and hard texture and is used for making semolina with coarse particles.
Consequently, the postprandial glycemic response is substantially lower after ingesting semolina pasta compared with
white bread. Residual starch that is not digested in the small
intestine passes into the colon as RSI.