Physical characteristics of genetically-altered wheat related to technological protein separation

Authors: Robertson, George; Blechl, Ann; Hurkman Ii, William; Anderson, Olin; Cao, Trung; Tanaka, Charlene; Gregorski, Kay; Orts, William

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2012
Publication Date: 1/1/2013
Citation: Robertson, G.H., Blechl, A.E., Hurkman II, W.J., Anderson, O.D., Cao, T., Tanaka, C.K., Gregorski, K.S., Orts, W.J. 2013. Physical characteristics of genetically-altered wheat related to technological protein separation. Cereal Chemistry. 90(1):1-12.

Interpretive Summary: Specific native wheat proteins and novel new ones may be attenuated or enhanced in the grain to produce materials of potential interest in biobased products. This report initiated the examination of technological problems in the processing of these grains from several wheat lines genetically altered to produce high amounts of native proteins and in one case a high amount of a novel extra long protein. Conventional methods of separation were unsuccessful and physical structures visible by special microscopic methods suggested a lack of interprotein networking. Poor mixing properties, higher protein transition temperature and resistant milling behavior suggested greater structural rigidity at sub-microscopic and molecular levels in the modified lines. A successful chemical method for enrichment was tested. This work impacts the ability to repurpose grain proteins for evaluation as a protein polymer component with potentially unique properties for biobased products.

Technical Abstract: Wheat protein is a technologically challenging substrate for food and non-food applications because of its compositional diversity and susceptibility to denaturation. Genetic modification could be used to create cultivars capable of producing more uniform or focused and novel protein compositions targeted to non-food uses. These lines could serve as expression systems for specific high molecular weight protein polymers and would be new crops leading to more diverse agricultural opportunities. However, fundamental changes to the molecular architecture in such wheat seeds could also result in separation and processing issues, such that conventional methods of protein enrichment may need modification or even reinvention. Enriched gluten protein fractions were prepared from Bobwhite lines modified to overproduce HMW glutenin subunits Dx5 and/or Dy10. These lines serve as experimental models to test various approaches that may be taken for protein polymer enrichment. However, conventional wheat gluten enrichment based on the glutomatic as a small model of industrial methods was incapable of producing enrichment for any of the tested meal or flour, including that from the non-transformed parent Bobwhite. Mixing in the mixograph or farinograph failed to produce standard patterns for whole kernel meal and straight run flour, and the normal cohesiveness of dough expected from these devices was not observed. Microscopy of stained dough samples revealed severely limited formation of normal protein networks, a capability crucial to conventional separation technology. Particle size analysis of whole kernel meal revealed a higher resistance to milling for the altered lines. Higher drying rates, lower farinograph moisture absorption, and increased thermal transition temperatures were observed. These data suggested that the native architecture of these new forms was more tightly constructed with reduced capacity for alteration by hydration and input of mechanical energy. An alternative enrichment method featuring solvation in SDS and precipitation in acetone produced coagulated (Bobwhite) or partially coagulated protein (transgenic lines producing Dx5 or Dy10) enriched to 78-85% protein with high yield.