Presence of Amylose Crystallites in Parboiled Rice

• Published in: Journal of agricultural and food chemistry 2009-04, Vol.57 (8), p.3210-3216
• Main Authors: Lamberts, Lieve, Gomand, Sara V, Derycke, Veerle, Delcour, Jan A
• Format: Article
• Language: English
• Subjects: Amylopectin - analysis; amylose; Amylose - analysis; amylose-lipid complexes; Biological and medical sciences; Calorimetry, Differential Scanning; Cereal and baking product industries; Chemical Changes Induced by Processing/Storage; crystallites; Crystallization; differential scanning calorimetry; Food industries; free amylose; Fundamental and applied biological sciences. Psychology; Hot Temperature; Hydrolysis; melting point; Oryza - chemistry; parboiling; rice; Seeds - chemistry; X-Ray Diffraction
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf803385m

Mildly, intermediately, and severely parboiled Jacinto [16% free amylose (FAM) content] and Puntal (26% FAM content) rice samples were submitted to differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). DSC thermograms revealed ungelatinized starch only in mildly parboiled rices and retrograded amylopectin in all parboiled samples. Amylose crystallites were present in intermediately and severely parboiled samples but could not be detected due to their high melting temperature. Nonparboiled and parboiled rice DSC profiles showed only type I and type II amylose−lipid complexes, respectively. Intermediately and severely parboiled rice showed a clear Vh-type (crystalline amylose−lipid complexes) with a superimposed B-type (retrograded amylopectin and/or amylose crystallites) pattern. The mildly parboiled samples showed a mix of A- (native starch crystallites) and Vh-type patterns (Puntal) and A-, Vh-, and B-type patterns (Jacinto). Mild acid hydrolysis destroyed the acid labile retrograded amylopectin crystallites and increased the relative abundance of amylose crystallites. Indeed, acid-hydrolyzed intermediately and severely parboiled samples of both cultivars showed a clear B-type diffraction pattern conclusively showing, for the first time, the presence of amylose crystallites. The melting temperature of the amylose crystallites was ca. 135 °C, and melting peaks were visible in the DSC thermograms of the intermediately and severely parboiled samples. Their levels depended on the degree of parboiling and FAM content.