Influence of dehydration rate on the vitrification of corn protein

This article deals with the physicochemical mechanisms involved during the desiccation of cereals, to understand the basis of their endosperm structure: vitreous endosperm is compact and floury endosperm is porous, giving the endosperm its hard and soft textures, respectively. Dehydration of zein (the most abundant protein in the vitreous region of the corn endosperm) was investigated for water contents ranging from ~ 50% to 10% (wet basis). A system of partial confinement of zein pills was optimized to compare both slow and rapid dehydration on two separate domains of the same sample. Macroscopic observations, porosity analysis, and scanning electron microscopy showed that either a compact or porous structure is obtained, depending on the dehydration rate. The glass transition temperature (Tg) of zein, which varies from 160°C for dry zein to about 15°C for zein with 25% water content, is mainly dependent on water content. A state diagram of the zein/water system, including ice melting, was determined from calorimetric measurements of state and phase temperature changes. The different porous and compact structures observed on vitreous zein are discussed in terms of collapse and dehydration rate.