Gelatinisation of starches of different amylose/amylopectin content. A study by differential scanning calorimetry

Abstract

Differential scanning calorimetry has been used to study the gelatinisation of waxy maize, wheat and potato starches as a function of water content. Despite the good straight-line plots obtained when the data were fitted using the Flouy-Huggins equation, some doubt exists over the applicability of this equation, since it is unclear whether melting of the ‘last’ crystallite occurs (effectively) at equilibrium or is controlled by plasticisation of the amorphous regions of the granules as a result of a glass transition. The gelatinisation of these three starches and, in addition, amylomaize starch, was examined at an intermediate water content (v 1 0·67, 57 % water). The most appropriate model for gelatinisation includes a glass transition, perhaps due to plasticisation of the amorphous amylose fraction, and two phase transitions within amylopectin; M1, assigned to the disordering of amylopectin crystallites, preceded by G due to the disordering of ‘double-helices’ associated with short-range order. The enthalpies of gelatinisation of amylomaize, wheat and waxy maize starches ranked in order of amylopectin content. In contrast, potato starch had the largest gelatinisation enthalpy of all the starches even though its amylopectin content was similar to that of wheat starch. The reason for this may lie in a high proportion of ‘double helical’ material with only short range order for this starch, compared with other starches.