Phase transitions in amylose and amylopectin under the influence of Ca(OH)(2) in aqueous solution

Amylose (A(1)) and amylopectin (A(2)) are the two main constituent substanc es of most starches (75-80% in dry cornstarch). Endosperm of corn kernel co ntains, in general, 28% A(1) and 72% A(2). During cooking of corn starch in food preparation, specially those solved in water, the mixture of A(1) and A(2) experiences a phase transition from a pasty and weak-tied wet masa to a completely consistent dry material (gelatinization). Cooked corn tortill as, from dough prepared with 0.25% of Ca(OH)(2) in weight (Mexico and Centr al America), have better mechanical, structural and rheological properties, beside a more accepted flavor. In order to understand the mechanism of pha se transformation of wet dough of corn starch under the Ca(OH)(2) presence, A(1), A(2) and 28%A(1)+72%A(2) (A(3)) samples were prepared with and witho ut Ca(OH)(2), which afterward were boiled. During this process part of Ca i s incorporated in cooked samples. X-ray diffraction (XRD) analysis and ther mal diffusivity (alpha) measurements were carried out in six samples: Three including Ca(OH)(2) and other three without it. Thermal diffusivity data w ere achieved by means of a photoacoustic system. XRD patterns show a more s tructured material when Ca2+ is present in the molecular structure of mater ial. alpha data evidence an increase when Ca2+ is present in A(1) and A(2) samples, however, improves notably for the A(3). This result can indicate t hat Ca2+ enhances the crosslinking of polymeric chains, contributing to a b etter heat conduction.