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ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Plant Polymer Research » Research » Publications at this Location » Publication #106392
Title: MICROSTRUCTURAL CHANGES IN ZEIN PROTEINS DURING EXTRUSION

Author
item BATTERMAN-AZCONA, SHERI - PURDUE UNIVERSITY
item Lawton Jr, John
item HAMAKER, BRUCE - PURDUE UNIVERSITY

Submitted to: Scanning
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Extrusion is used in the food industry to produce a wide variety of ready-to-eat (RTE) breakfast cereals. Corn is one of the major cereals used in the production of these items. Traditional cornflakes were made on flaking machines, where the whole grit was flaked. Now corn is processed through extruders and then flaked. Traditional flaking does not release zein from the protein bodies, whereas extrusion processing does. Despite advances in cornflake processing, manufactures still have difficulties making consistent, high quality cornflakes. Most research has been focused on the effect starch has upon the texture of RTE breakfast cereals. No research has been done which addresses the effect that protein has upon the texture of RTE breakfast cereals. Model systems were used to study the effect of extrusion processing on two types of corn protein: commercial zein and corn gluten meal (CGM) combined with starch. Zein is incased in protein bodies in CGM, whereas zein has been released from the protein bodies in commercial zein. Scanning electron micrographs show that the greatest dispersal of zein occurred in the CGM/starch extrudate. Under harsh extrusion conditions, the protein bodies in the CGM were completely disrupted and the dispersed zein appeared to form fibrils. The micrographs show that the zein/starch extrudate contain large protein aggregates. Protein fibrils produced during extrusion may effect the texture of corn-based breakfast foods.

Technical Abstract: Changes in proteins during extrusion may influence the texture of ready- to-eat (RTE) corn-based extruded foods. This study focused on microstructural changes and dispersal patterns of corn storage proteins, zeins, that occur during extrusion processing. Model systems were used that consisted of two types of corn protein: commercial zein and corn gluten meal (CGM), combined with corn starch. Commercial zein is not encased in protein bodies, whereas CGM is comprised of zeins encapsulated in protein bodies. Mixtures were extruded under conditions that resulted in different specific mechanical energy (SME). The microstructure of the resulting extrudates was analyzed using transmission electron microscopy (TEM) with immunogold labeling of the alpha-zein storage protein. The micrographs showed that the greatest zein dispersal occurred in CGM/starch extrudates, especially under high SME conditions. The micrographs also showed that, at both mild and harsh extrusion conditions, commercial zein/starch extrudates contained large protein aggregates. Under mild extrusion conditions, protein bodies in the CGM/starch extrudates partially retained their spherical shapes, but during harsher processing, protein bodies were disrupted and dispersed zein appeared to form fibrils. Such protein fibrils may influence texture and/or quality of extruded corn-based snacks and breakfast foods.