FACTORS AFFECTING EXPANSION OF CORN MEALS WITH POOR AND GOOD EXPANSION PROPERTIES

Two corn meals, one with good and one with poor expansion properties, were used to study the critical factors responsible for poor expansion during corn curl extrusion. Screening tests revealed that the corn me al with poor expansion had a slightly larger particle size. This sampl e also had a larger proportion of opaque particles compared to the cor n meal with good expansion. Extrusion of coarse corn grits showed that larger particle size alone could cause poor expansion. Water diffusio n tests showed that the sample containing more opaque particles was mo re competitive for water. As a result, in corn that contained both opa que and vitreous particles less water was available to the vitreous pa rticles. The underplastisized (dry) vitreous particles remained glassy (unmelted) during extrusion, resulting in reduced expansion of the ex trudates. The results suggest that addition of water to the conditioni ng cylinder of the extruder would overcome poor expansion.