Major storage component in oat is starch and it is the most abundant component of the oat grain. Oat grain contains starch about 55–60% in most oat cultivars. Starch occurs as aggregates which size ranges from 20 to 150 μm, composed of several starch granules (size of the individual granules is 2-15 μm across). Starch has two components, amylose and amylopectin (see figure 1), and it is known as a storage polysaccharide. Oat contains also an important part of oat dietary fiber - β-glucan - which is a mixed-linkage polysaccharide.
Oat starch can contain about 25-30% amylases which are a class of hydrolases that can specifically cleave the O-glycosidid bonds in starch. Oat starch has typical gelatinization characteristics. When oat starch is cooled high viscosity is not usually developed. Compared to other cereals, cooled oat starches are clearer, less firm, more elastic, more adhesive, and less susceptible to retrogradation.
Figure 1. Two components of starch: A) amylose, B) amylopectin ¹
¹ Figure from reference Ben Halima N, Ben Saad R, Khemakhem B, Fendri I, Abdelkafi S. (2015)
Departing from other cereals oat starch contains more lipids, which can either be internal lipids that are located inside the granule or present as inclusion complexes with amylose on the surface of the granule. Lipids alter the physicochemical properties of starch, such as gel hardness and retrogradation. Oat starch contains also phosphorus, which presumably relates to phospholipids.
In studies (Van Amelsvoort et al., 1992, Behall et al., 1989, Behall et al., 1988) it has been found that postprandial blood glucose and insulin responses are lower with meals that included amylose. The enzymatic degradation of amylose into glucose in alimentary tract is slower than for amylopectin. Thus amylose increases blood glucose slower than amylopectin.
Aro A, Mutanen M, Uusitupa M. (2012). Ravitsemustiede (Science of nutrition). 4. uudistettu painos (4th revised edition). Helsinki: Kustannus Oy Duodecim.
Banas A, Dexbski H, Banas W, Heneen WK, Dahlqvist A, Bafor M, Gummeson PO, Marttila S, Ekman Å, Carlsson AS, Stymne S. (2007). Lipids in grain tissues of oat (Avena sativa): differences in content, time of deposition, and fatty acid composition. Journal of Experimental Botany 58, 2463-2470.
Bechtel DB, Pomeranz Y. (1981). Ultrastructure and cytochemistry of mature oat (Avena sativa L.) endosperm: The aleurone layer and starchy endosperm. Cereal Chemistry 58, 61-69.
Behall KM, Scholfield DJ, Canary J. (1988). Effect of starch structure on glucose and insulin responses in adults. Am J Clin Nutr 47, 428-432.
Behall KM, Scholfield DJ, Yuhaniak I, Canary J. (1989). Diets containing high amylose vs amylopectin starch: effects on metabolic variables in human subjects. Am J Clin Nutr 49, 337-344.
Ben Halima N, Ben Saad R, Khemakhem B, Fendri I, Abdelkafi S. (2015). Oat (Avena sativa L.): Oil and nutriment compounds valorization for potential use in industrial applications. Journal of Oleo Science 64, 915-932.
Doehlert DC, McMullen MS, Hammond JJ. (2001). Genotypic and Environmental Effects on Grain Yield and Quality of Oat Grown in North Dakota. Crop Sci 41, 1066-1072.
Hoover R, Vasanthan T. (1992). Studies on isolation and characterization of starch from oat (Avena nuda) grains. Carbohydrate polymers 19, 285-297.
Sayar S, White PJ. (2011). Oat starch: Physicochemical properties and function, in: Webster FH, Wood PJ. (Eds.), Oats: Chemistry and Technology. American Association of Cereal Chemists, Inc (AACC), 109-122.
Singh R, De S, Belkheir A. (2013). Avena sativa (oat), a potential neutraceutical and therapeutic agent: an overview. Critical Reviews in Food Science and Nutrition 53, 126-144.
Van Amelsvoort JM, Weststrate JA. (1992). Amylose-amylopectin ratio in a meal affects postprandial variables in male volunteers. Am J Clin Nutr 55, 712-718.