title: Effects of annealing on the polymorphic structure of starches from sweet potatoes (Ayamurasaki and Sunnyred cultivars) grown at various soil temperatures.
abstract: Starches extracted from the sweet potato cultivars Sunnyred and Ayamurasaki grown at 15 or 33 degrees C (soil temperature) were annealed in excess water (3 mg starch/mL water) for different times (1, 4, 8 or 10h) at the temperatures 2-3 degrees K below the onset melting temperature. The structures of annealed starches, as well as their gelatinisation (melting) properties, were studied using high-sensitivity differential scanning calorimetry (HSDSC). In excess water, the single endothermic peak shifted to higher temperatures, while the melting (gelatinisation) enthalpy changed only very slightly, if any. The elevation of gelatinisation temperature was associated with increasing order/thickness of the crystalline lamellae. The only DSC endotherm identified in 0.6 M KCl for Sunnyred starch grown at 33 degrees C was attributed to A-type polymorphic structure. The multiple endothermic forms observed by DSC performed in 0.6M KCl for annealed starches from both cultivars grown at 15 degrees C provided evidence of a complex C-type (A- plus B-type) polymorphic structure of crystalline lamellae. The A:B-ratio of two polymorphic forms increased upon annealing due to partial transformation of B- to A-polymorph, which was time dependent. Long heating periods facilitated the maximal transformation of B- to A-polymorph associated with limited A:B ratio.
authors.affiliation: Institute of Biochemical Physics, Russian Academy of Sciences, Kosygina str. 4, 119991 Moscow, Russia.
authors.forename: Natalia K
authors.initials: NK
authors.lastname: Genkina
authors.forename: Lyubov A
authors.initials: LA
authors.lastname: Wasserman
authors.forename: Takahiro
authors.initials: T
authors.lastname: Noda
authors.forename: Richard F
authors.initials: RF
authors.lastname: Tester
authors.forename: Vladimir P
authors.initials: VP
authors.lastname: Yuryev
mesh_terms: D002152:Calorimetry, Differential Scanning; D002236:Carbohydrate Conformation; D003460:Crystallization; D006358:Hot Temperature; D027723:Ipomoea batatas / Q000737:chemistry* / Q000378:metabolism; D011110:Polymorphism, Genetic; D011189:Potassium Chloride / Q000737:chemistry; D012987:Soil; D013213:Starch / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D012987:Soil; D011189:Potassium Chloride; D013213:Starch