SWELLING AND GELATINIZATION OF OAT STARCHES

A comparison was made between the structure and physicochemical proper ties of starches extracted from five normal and one naked cultivar of oat. There was little difference in the molecular size or polydispersi ty of the native amylose and amylopectin determined by gel permeation chromatography (GPC), or in the unit chain distribution of isoamylase- debranched amylopectin, where three peaks were resolved at modal degre e of polymerization of 15, 23, and 46. Apparent, total, and Delta-amyl ose (difference between apparent and total amylose due to lipid comple xing) contents ranged from 19.7 to 22.0%, 27.5 to 29.8%, and 7.1. to 8 .1, respectively, with lipid content, as fatty acid methyl esters, ran ging from 0.66 to 0.75% on a dry basis and comprising the following fa tty acids: 46.6% C16; 2.1% C18; 15.0% C18:1; 35.3% C18:2, and 0.7% C18 :3. The naked oat starch had the lowest lipid content and Delta-amylos e. Lintner type solubilization in 2M HCl (six days of incubation at 35 degrees C) ranged from 56.6 to 60.0% of the original dry alpha-glucan . The 80 degrees C swelling factor corresponding to postgelatinization swelling (determined by a blue dextran dye exclusion method) ranged f rom 8.6 to 10, with the naked oat being at the top of the range. At th is temperature, the amount of alpha-glucan leached from the granules r anged from 4.1 to 6.6% (dry basis), where the highest value correspond ed to the naked oat. Amylose (determined colorimetrically) accounted f or 42.1-47.6% of the alpha-glucan in the leachate. No intermediate mat erial could be detected by GPC. Damaged starch levels were very low in the starches analyzed (1.9-2.2% on a dr) basis). The high proportion of branched alpha-glucan in the leachate was confirmed by GPC and was attributed to the fragile nature of the gelatinized oat starch granule s. Gelatinization parameters by differential scanning calorimetry were 44.7-47.3, 56.2-59.5, and 68.7-73.7 degrees C for T-o, T-p and T-c re spectively, with Delta H ranging from 8.1 to 9.5 J/g. The mean diamete r of native granules, determined by Coulter Counter, ranged from 4.96 to 5.63 mu m, with the naked oat starch being at the low end.