Isolation of Oat Starch from Oat Flour

Cereal Chem. 69(3):233-236 Oat starch was isolated from oat flour by 1) high shear in water after hydroxide (pH 11.0) led to 72-75% isolated starch with 0.3% protein. a presoak, 2) low shear after digestion with protease, and 3) low shear Digestion of oat flour (25% solids) with Aspergillus oryzae protease at at alkaline pH. Oat flour was soaked in water (25% solids) at 20 0 C for pH 7.5 and 37 0 C for 6 hr gave 78% starch with 1.1% protein. Oat starch 6 hr and subjected to high shear using a tissue homogenizer. After 1 isolated with sodium hydroxide showed a delayed pasting temperature min of shearing followed by centrifugation, the yield of starch (1.3% and increased paste consistency in the amylograph compared to starch protein) was 70%, based on oat flour. Two bases were used to isolate isolated by high shear or calcium hydroxide. The same phenomena was oat starch at different concentrations and stirring times. Stirring for 60 observed in wheat starch isolated with 0.01 M sodium hydroxide but not min at pH 10.5 with 0.01 M sodium hydroxide (pH 10.5) or 0.03M calcium in corn or rice starch. Dry milling of oat groats yields approximately 35% oat bran and 65% oat flour. When the demand for oat bran is high, a surplus of oat flour results. Separating oat flour into starch and protein is complicated by strong binding between the two components and by the presence of f3-glucan. Oat starch has been isolated with sodium carbonate (Paton 1977) or sodium hydroxide (Wu et al 1973) at low shear and with water at high shear (Meuser et al 1985). No reports have appeared on the use of protease or cellulase to release oat starch, nor has a comparison been made of the use of sodium and calcium hydroxides. The objectives of this investigation were to compare 1) the yield and purity of oat starch isolated from oat flour using low shear with alkali, protease, and/or cellulase treatment and high shear with water and 2) the pasting properties of oat, wheat, corn, and rice starches isolated with sodium and calcium hydroxides. MATERIALS AND METHODS General Oat flour was obtained from the ConAgra Flour Milling Co., Omaha, NE. The flour contained 10.3% moisture, 6.8% protein, 80.0% starch, 3.1% lipid, 0.6% ash, and 0.5% /8-glucan. Hard red winter wheat, dent corn, and long-grain rice were commercial samples. Moisture, protein, ash, lipid, and starch were determined by AACC methods (1983) 44-18, 46-13, 08-01, 30-26, and 76-11, respectively. The 18-glucan content was determined using a ,B-glucan test kit (Biocon, Inc., Rockville, MD). Starch lipids were determined gravimetrically after extraction with propanol/ water (3:1, v/v) at 1000 C (Morrison and Coventry 1985). All chemicals were reagent grade. Protease (from Aspergillus oryzae, Bacillus subtilis, Streptomyces griseus, and Rhizopus sp.) and cellulase (from Penicillium funiculosum) were purchased from Sigma Chemical Co. (St. Louis, MO). Cellulase from Trichoderma reesei (Celluclast) was from Novo (Danbury, CT). One unit of protease activity was defined as the amount of enzyme that liberated 1.0 ,umol of tyrosine per minute from casein at pH 7.5 and 370C. One unit of cellulase activity was defined as the amount of enzyme that released 1.0 ,umol of glucose from cellulose in 1 hr at pH 5.0 and 400 C.