What is Resistant Starch?
Resistant starch (RS) is defined as the total amount of starch and the products of starch degradation that resist digestion in the small intestinal tract of healthy individuals. It is also referred to as “enzyme-resistant starch.” RS has physiological functions similar to that of dietary fiber.1
Resistant starch passes through the upper digestive tract to the colon, where it is then fermented by bacteria, producing important metabolites, such as short chain fatty acids. These metabolites appear to have important biological effects. They can reduce colon cancer precursors, regulate macronutrient metabolism and alter secretion of hormones. All these contributed, by these metabolites, can lead to improved physical and mental health.2 The average daily intake of resistant starch in America is 6 g,3 which is quite low as the Daily Value is 25-28 grams of dietary fiber.4
Resistant starch can be classified into five categories:
RS I: physically inaccessible because it is entrapped in its storage cell. The cell wall materials and the protein matrix prevent water penetration into starch and they also provide a physical barrier, preventing enzymes from reaching and hydrolyzing the starch. Examples include those foods with whole or partially milled cereal grains such as muesli, breads made with whole or coarsely ground kernels of grains.
RS II: starch like potato starch, high-amylose maize starch, or raw banana starch that display the B- or C- type polymorph, are highly resistant to enzymatic hydrolysis5 and they are classified as RS II starch. However, after cooking, most of the starch, such as that in baked potato and cooked banana, becomes highly digestible as a result of starch gelatinization and loss of B- and C- type crystallites.2 An exception is high-amylose starch produced by genetic engineering and strategic breeding. This non-naturally occurring RS II displays a high gelatinization temperature, above the boiling point of water. After boiling or cooking at a temperature below its gelatinization temperature, this type of starch retains its crystalline structure and remains resistant to enzymatic hydrolysis.2
RS III: retrograded starches produced through gelatinization and retrogradation process during food processing and manufacturing. Amylose molecules have linear structures. They have a great tendency to form double helices, particularly at 4 – 5oC and with adequate moisture content. Retrograded amylose has a high gelatinization temperature, up to 170oC, and cannot be dissociated by cooking.2 After starchy foods are stored, particularly in a refrigerator, amylose molecules and long branch chains of amylopectin form double helices and lose their water-binding capacity. The double helices of starch molecules do not fit into the enzymatic binding site of amylase, thus they cannot be hydrolyzed by this enzyme.
RS IV: chemically modified starch that resists amylase digestion, formed either by cross-linking or adding chemical derivatives. The FDA has regulated the methods to modify starch for food usage.6 Starch with high level of cross-linking loses the ability to swell during cooking and remains in a granular form after cooking, and poorly hydrolyzed by amylases.2 Adding a chemical derivative to starch, changes the structure of the starch and partially restricts the enzymatic hydrolysis of the starch molecule due to steric hindrance, resulting in resistant starch.
RS V: refers to amylose-lipid complex that resists amylase digestion. The amylose-lipid complex formation is an instant reaction and the complex can reform after cooking. RS V is considered thermally stable.2
Bakery products have been fortified with RS II and RS III. Qzturk et al. (2009)7 evaluated rheological and baking properties of breads that were supplemented with three different commercial resistant starches at contents between 0% and 30%. The authors reported that commercial starches with high content of RS did not have a substantial deteriorative effect on the crumb color values, external appearance and symmetry of bread loaves. However, some researchers have said that the replacement of wheat flour by resistant starch affects bread quality due to gluten dilution.8
To decrease the detrimental effect on bakery quality from resistant starch, enzymes like transglutaminase (TG) have been used.9 TG can improve the crosslinking of gluten proteins, increasing the gluten strength and water holding capacity.9 A combination of enzymes (transglutaminase, glucose oxidase and xylanase) were used when wheat flour was partially substituted by resistant starch (12.5 g/100g) and the dough had similar behavior to the regular dough.10 Vital gluten also has been used with cross-linked corn starch to replace 5 – 15% wheat flour to make stronger, more stable dough and bigger loaf volume bread.11
FDA regulates the process to modify starch in the Code of Federal Regulations (Title 21 Part 172.892).6 In these regulations, the chemicals and enzymes used to treat starch are listed and their limitations are included. The USA, Canada, Mexico, Chile, EU, Australia and Japan are some countries that have authorized chemically modified RS in the food industry.
- Eerlingen, R.c, and J.a Delcour. “Formation, Analysis, Structure and Properties of Type III Enzyme Resistant Starch.” Journal of Cereal Science 22.2 (1995): 129-38.
- Birt, D. F., T. Boylston, S. Hendrich, J.-L. Jane, J. Hollis, L. Li, J. Mcclelland, S. Moore, G. J. Phillips, M. Rowling, K. Schalinske, M. P. Scott, and E. M. Whitley. “Resistant Starch: Promise for Improving Human Health.” Advances in Nutrition: An International Review Journal 4.6 (2013): 587-601.
- Murphy, Mary M., Judith Spungen Douglass, and Anne Birkett. “Resistant Starch Intakes in the United States.” Journal of the American Dietetic Association 108.1 (2008): 67-78.
- “Dietary Fiber.” Accessdata. Fda. Gov. Food and Drug Administration, 6 June 2016.. www.accessdata.fda.gov/scripts/InteractiveNutritionFactsLabel/dietary-fiber.html Accessed 6 Oct. 2016.
- Jane, Jay-Lin, Zihau Ao, Susan A. Duvick, Maria Wiklund, Sang-Ho Yoo, Kit-Sum Wong, and Candice Gardner. “Structures of Amylopectin and Starch Granules: How Are They Synthesized?” Journal of Applied Glycoscience 50.2 (2003): 167-72.
- “21CFR172.892.” CFR – Code of Federal Regulations Title 21. 1 Apr. 2016. www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=172.892 Accessed 6 Oct. 2016.
- Ozturk, Serpil, Hamit Koksel, and Perry K. W. Ng. “Farinograph Properties and Bread Quality of Flours Supplemented with Resistant Starch.”International Journal of Food Sciences and Nutrition 60.6 (2009): 449-57.
- Michniewicz, J., G.g. Biliaderis, and W. Bushuk. “Effect of Added Pentosans on Some Properties of Wheat Bread.” Food Chemistry 43.4 (1992): 251-57.
- Sanchez, Diana B. O., Maria C. Puppo, Maria C. Añon, Pablo D. Ribotta, Alberto E. León, and Carmen C. Tadini. “Effect of Maize Resistant Starch and Transglutaminase: A Study of Fundamental and Empirical Rheology Properties of Pan Bread Dough.” Food Bioprocess Technol Food and Bioprocess Technology 7.10 (2014): 2865-876.
- Altuna, Luz, Pablo D. Ribotta, and Carmen C. Tadini. “Effect of a Combination of Enzymes on the Fundamental Rheological Behavior of Bread Dough Enriched with Resistant Starch.” LWT – Food Science and Technology 73 (2016): 267-73.
- Hung, Pham Van, and Naofumi Morita. “Dough Properties and Bread Quality of Flours Supplemented with Cross-linked Cornstarches.” Food Research International 37.5 (2004): 461-67.