Resistant starch is defined as being not hydrolyzed to D-glucose in the small intestine within 120 min of being consumed but is instead fermented in the colon. According to its structure or its routes of escaping digestion, RS is classified into five types.
- Introduction to Resistant Starch
- Structure and Thermal Properties of Starch Granules
- Factors that affect the digestibility of starch
- Resistant Starch (RS) Preparation
- Resistant Starch (RS) Detection
- The Health Effects of Resistant Starch (RS)
- The Use of Resistant Starch (RS) in Foods
RS1: Physically inaccessible starch
RS1 is physically inaccessible to digestive enzymes because it is trapped within the food matrix in proteins, cell wall materials, and other physical barriers in whole or partly milled grains, tubes, and seeds. A good example of RS1 is the RS in pasta. The compact protein matrix of pasta has been reported to be responsible for its higher RS content than other wheat products. Grinding and protease hydrolysis that can destroy the physical barriers in foods reduce the RS1 content.
RS2: Raw granular starch with a B- or C-type polymorph
RS2 is comprised of native, uncooked granules with B- or C-type polymorphs, such as those found in raw potatoes, unripe banana starches, and high-amylose maize starches, whose granule crystallinity makes them resistant to enzymatic hydrolysis. A disadvantage of RS2 for food applications is that its RS content decreases substantially after thermal processing. A particular type of RS2 called HAM (high-amylose maize starch) is uniquely stable to most cooking operations because of the presence of long-chain double-helical crystallites.
RS3: Retrograded starch
This starch is first gelatinized in hot water and then cooled for retrogradation. During retrogradation, the two polymer chains reassociate to form double helices stabilized by hydrogen bonds, making the structure more resistant to enzymatic hydrolysis. Linear amylose molecules are preferred for the formation of RS3 because they retrograde at a faster rate and form more resistant crystallites than amylopectin.
Food processing, which involves heat and moisture, generally destroys RS1 and RS2 but may form RS3. RS3 is a potential new food ingredient, because it is generally stable to heat treatments and continues to exist after most types of food processing.
RS4: Chemically modified starch
RS4 is a chemically modified starch that includes the modifications of esterification, etherification, or cross-linking. RS4 is further grouped into subcategories based on its solubility in water and the experimental protocols used for analyses. Chemical modifications reduce digestion of starch by the formation of steric hindrances at the sites of enzymatic action. For example, octenyl succinic anhydride modification of starch introduces hydrophobic octenyl succinate (OS) groups into starch molecules, which interfere with binding of starch by amylolytic enzymes. Cross-linking of starch is another effective approach to prepare RS4.
RS5: Amylose-lipid complex and resistant maltodextrin
RS5 has been proposed as two different components. The first component involves amylose-lipid complexes, which is a single helical structure formed between amylose and lipids. The second component is resistant maltodextrin, which is obtained by subjecting native starch to sequential applications of pyroconversion and enzymatic hydrolysis. Resistant maltodextrins are non-sweet and low molecular weight compounds containing the native α-(1→4) and α-(1→6) bonds as well as β-(1→2) and β-(1→3) bonds and levoglucosans and have properties similar to those of dietary fiber. The majority of reports describe RS5 as amylose-lipid complexes.