Some factors determining the thermal properties of amylose inclusion complexes with fatty acids

✍ Scribed by John Karkalas; Song Ma; William R. Morrison; Richard A. Pethrick

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 851 KB
• Volume: 268
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(94)00336-e

✦ Synopsis

The thermal properties of water-insoluble amylose-stearic acid (18:0) complexes prepared under various conditions were studied by differential scanning calorimetry (DSC). Complexes were studied normally at a concentration of 5% in water at pH ~ 7. Type I complexes formed at < 60°C had dissociation temperatures (T m) in the range 96-104°C. Type IIa polymorphs formed at > 90°C had T m = 114-121°C. Various ratios of types I and IIa were formed at 80°C depending on the duration of heating, but no intermediate form was detected. Annealing of the type IIa complex at 105°C and at 115°C gave rise to increasing proportions of type lib polymorphs with T m = 121-125°C and dissociation enthalpies of 32-34 J/g of amylose, depending on the temperature and time of annealing. Conversion into the higher polymorphs was retarded at a higher concentration (10%) of the complex under identical conditions, and was delayed at pH ~ 4.7. The dissociation temperatures of amylose complexes with the cis-unsaturated fatty acids oleic (18:1), linoleic (18:2), and linolenic (18:3) also depended on the temperature of formation, and three distinct types were obtained (I, IIa, and lib). Significant decreases in the T m of the three polymorphs were observed for each double bond in the fatty acid guest molecule. When type I and type II complexes were made using various proportions of 18:0 and 18:2, mixed acid complexes were obtained with T m values intermediate between those of the monoacid complexes. The origin of the endothermic transitions on heating the three types of complexes is discussed.