Oat starch

1VTT Biotechnology and Food Research, VTT, Finland 2 Department of Food Technology, Lund University, Lund, Sweden 

Oat is primarily a cool season crop.1 It is grown mainly in Russia, the United States, Canada and Europe. The principal use of oat is as an animal feed. However, the popularity of oat as a part of the human diet has increased because of reports describing the beneficial nutritional properties of oat (3-glucans.2 1 Oat also has other desirable nutritional properties. The protein content of oat is much higher than that of other cereal grains, and oat oil has a favorable ratio of polyunsaturated to saturated lipid. 

Oat starch has properties that have captured industrial interest, but its use has been limited, largely because of difficulties in separation of the grain into starch, fiber and protein fractions.5 

Dry-milling of oat groats yields approximately 35% oat bran and 65% oat flour.6 The starch content of the flour is 67.0-73.5%.7 Separation of oat flour into starch, protein 

Starch Chemistry and Technology, Third Edition ISBN 978-0-12-746275-2 

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Hafer, m. oats, -flocken, /.pi. rolled oats, -malz, n. oat malt, -mehl, n. oatmeal, -schleim, m. oat gruel. -Starke,/, oat starch, -wurz, -wurzel, /. salsify. 

Fe, Ti, Mn, Ni, Co, etc, which can form in plants polishing metals or in plants manufg pyrotechnics) suspensions of finely divided coal, coke or charcoal suspension of finely divided cereals ( such as of flour, rice, oats, starch, ecc) suspension of wood dust suspension of sugar dust suspension of explosive particles (such as of TNT, PA, Tetryl, etc)... 

Oat Starch.—The corpuscles of this variety—Fig. 543—are much smaller, hut more homogeneous, than those of wheat or barley and instead of being circular, they have a polygonal outline, and are devoid of visible riags or hila. Many of the granules remain connected, presenting rounded or oval bodies, with a reticulated... 

C-CP-MAS NMR produces a broad resonance with a chemical shift of 31.2 ppm,129 a characteristic of mid-chain methylene carbons of fatty acids in the V-amylose complex. The results showed that up to 43% of amylose in non-waxy rice starch, 33% in oat starch, and 22% in normal maize and wheat starch granules are complexed with lipids at a single helical conformation, and the remaining amylose is free of lipids and is in a random coil conformation.212 Up to 60% of apparent amylose in waxy barley starch is complexed with lipids.212... 

A commercial fractionation process in which groats are dry-milled and the comminuted groats are soaked in a solution of cellulases and hemicellulases has been developed.9 In addition to the starch the process produces fiber and protein fractions. Unlike wheat starch, oat starch cannot be separated from the grain by selective hydration and centrifugation, because of hydrated bran and protein layers. 

Several different methods have been used for the isolation of oat starch in the laboratory in yields of 42.7-61.0%, depending on the variety.7 10 Lowest yields are obtained from cultivars with high protein content. A much better yield (60-80%) was reported by Sowa and White.8... 

Figure 15.1 (a) Isolation of oat starch using sodium hydroxide at low shear rate. (Adapted from reference 6)... 

Oatrim can be used in cheeses as a fat replacer.12 Other possible applications are in ice cream and frozen desserts, milk shakes, hot chocolate, instant-type breakfast drinks, cereals, salad dressings, soups, sauces and gravies. Oat starch in combination with oat hydrolysate or with xanthan gum has been used for thickening of sweet and sour sauces.18... 

Cationic oat starch was used to improve the dry strength of paper handsheets and found to be comparable to wheat starch in functionality.14 Oat starch might possibly be a replacement for rice starch in pharmaceutical applications.19 Oat flour has been used in adhesive preparations.19... 

Even a very mild acid-catalyzed hydrolysis (0.5 hour with 1M HC1 at 40°C), followed by heating at 95°C, induced considerable changes in the oat starch granule, viz., a breaking down of the granule structure and formation of a continuous phase of amylopectin. 13The tendency for aggregation decreased when oat starch was annealed.15... 

The chemical composition of isolated oat starch is given in Table 15.1. When an oat-flour slurry is centrifuged, the bottom layer is the prime starch. This starch can be purified with repeated washings, and a starch with a protein content of 0.44-0.6% and a lipid content of 0.67-1.11% (dry basis) can be obtained.10,27 The moisture, ash and nitrogen contents are similar to those of wheat, whereas the lipid content is higher than that of wheat, and the amylose content is lower.15... 

Lysophosphatidylcholine makes up about 70% of the lipids present in oat starch.11 For AC Hill oat starch, free fatty acids dominated the neutral lipids (NL), lysophosphatidylcholine (a phospholipid, PL) and digalactosyldiglyceride (a galactolipid, GL).20 The predominant fatty acid was C18 2 in NL and C16 0 in PL and GL. Most of the phosphorus present in oat starch is present in lipids.8 There is a significant... 

White et al.8,30,31 have, in several papers, studied the chemical composition of oat starch amylose and amylopectin (Table 15.2). Gel permeation chromatography (GPC) of the total starch gave rise to two peaks, but some of the material had an unusual iodine affinity and was, therefore, described as an intermediate fraction.8... 

The amylose fraction from three different oat starches was characterized by high-performance size-exclusion chromatography (HP-SEC) and shown to be free of amylopectin.31 The degree of polymerization is given in Table 15.2. By treating amylose with isoamylase, it was found to be branched.31 The major fraction had a DP of 700, whereas a second fraction had a DP of 72. The amylose chain length was reported to decrease with increased amylose and starch-lipid content.30 The intrinsic viscosity of amylose has been reported to be 246-299 mL/g.7... 

The x-ray diffraction pattern of oat starch is the A-type, as expected for a cereal starch.22 33 36 The crystallinity of oat starch was reported to be higher than that of wheat starch when determined at the same moisture content.22 A relative crystallinity in the range of 28.0-36.5% was reported for starch from six different Canadian oat varieties.33 Heat-moisture treatment caused the intensity of d-spacings in the x-ray diffraction pattern to increase.16... 

The high lipid content of oat starch is reflected in the high value of the transition enthalpy (AHCX) measured for the amylose-lipid complex (Table 15.4). This transition is reversible, and on a rerun greater AHCX, as well as Tcx (endotherm peak temperature), was found.26 When the oat starch was defatted, the endotherm assigned to the amylose-lipid complex disappeared from the DSC thermogram.26 Extraction at room temperature with 1-propanol water (3 lv/v) did not influence the thermogram of the starch, but if the starch was refluxed in the same solvent, a decrease in AH and a complete elimination of the endotherm ascribed to the amylose-lipid complex occurred.28 For oat starches with a lipid content of 1.1-1.7%, it was possible to... 

Table 15.3 DSC parameters for gelati nization of oat starch in excess water ...

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