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Investigation of Growth and Shrinkage Mechanisms in Vapor-Induced Expansion of Extrusion-Cooked Corn Grits

Horvat, Mario, Schuchmann, Heike P.
Food and bioprocess technology 2013 v.6 no.12 pp. 3392-3399
cooking, corn grits, extrusion, image analysis, linear models, prediction, shrinkage, temperature, water content
The development of expansion models with good predicting capabilities requires experimental data and a more fundamental understanding of the vapor-induced expansion behavior in extrusion cooking. In this study, we used a conventional and also a high-speed camera to observe the radial and axial expansion behavior of extrusion-cooked corn grits. Image processing was performed with an automated evaluation code. The experimental setup consisted of a novel high-speed extruder, which enabled the determination of the influence of high screw speeds of up to 1,200 rpm on extrudate growth and shrinkage. In addition to optical measurement of the expansion, moisture content and temperature development during growth and shrinkage were determined. Three distinct stages of expansion were observed: extrudate growth, short-term shrinkage, and long-term shrinkage. The initial extrudate growth rate fitted well with a linear regression. Especially the second stage of shrinkage occurring in a time range of 24 h after the experiment showed that shrinkage is often underestimated in existing models. Furthermore, total shrinkage increased at higher screw speeds. The data obtained deliver new insight into expansion phenomena and can support the development of predicting models. ©Springer Science+Business Media New York 2012.