Microstructural and chemical changes in corn protein bodies and alpha-zeins during processing and their effect on texture
Abstract
The overall goal of this project was to investigate the role of corn zein on the texture of processed, corn-based ready-to-eat (RTE) food products by studying the microstructural and chemical changes of zeins in cornflakes and extrudates, as well as assessing textural changes due to corn protein in extrudates. First, changes in protein body shape, and release of encapsulated α-zeins as a result of cornflake processing (conventional pressed and extruded flaking) were investigated. It was found that cooking caused zeins to form large, protein polymers, but had no effect on the structure of protein bodies. In conventional, pressed cornflakes, the protein bodies were flattened, partially fused together, and α-zeins were only slightly released, whereas in the extruded flakes, protein bodies were completely disrupted, and α-zeins dispersed. This indicated that zeins in cornflakes particularly extruded ones, are not confined to the rigid constraints of protein bodies, but can interact to some degree with each other and other components in the system. In the second study, microstructural analysis of corn flour extruded from mild [low specific mechanical energy (SME)] to harsh (high SME) processing conditions showed that an SME of approximately 100 was the point at which protein bodies started to break apart and release zein. Chemical analysis showed protein in extrudates was less soluble than that in unprocessed flour. This was speculated to be due to zein aggregation upon processing, and prevalence of hydrophobic interactions and disulfide bonds. In the third study, various amounts of commercial zein or corn gluten meal (CGM) were mixed with starch, and extruded at various SMEs. Chemical and microstructural analysis on the extrudates revealed that commercial zein forms large aggregates and becomes less soluble during extrusion compared to extrudates containing CGM. Textural analysis revealed that low levels of commercial zein increased extrudate strength, while CGM decreased extrudate strength as measured by Kramer shear cell and three-point bend tests. Overall, these studies demonstrate that in corn, zeins are released from protein bodies during certain processing conditions and appear to form protein fibrils. Zein proteins influence textural parameters in processed, RTE corn-based foods.
Degree
Ph.D.
Advisors
Hamaker, Purdue University.
Subject Area
Food science
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.