Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2011
Publication Date: 9/1/2011
Citation: Schober, T., Bean, S., Tilley, M., Smith, B.M. and Ioerger, B.P. 2011. Impact of different isolation procedures on the functionality of zein and kafirin. Journal of Cereal Science. 54(2):241-249.
Interpretive Summary: Producing high quality baked products such as bread from corn and sorghum is challenging due to the fact that the native proteins of these grains do not form dough when mixed with water. Previous research has shown that commercially isolated corn proteins will form dough however. Laboratory isolated corn and sorghum proteins however, did not have the same functionality as the commercial corn samples. Modifying extraction procedures to enrich isolated proteins with a specific component of corn proteins improved the functionality of the lab isolated proteins. Likewise, by modifying the extraction conditions, functionality of isolated sorghum proteins was improved. Understanding the factors necessary to make isolated corn and sorghum proteins function more like wheat will provide the necessary knowledge to produce fully functional sorghum flours for the wheat-free food market.
Technical Abstract: Commercial corn prolamin (zein) aggregates in water above room temperature into an extensible, viscoelastic gluten-like substance. This specific functionality of zein can be used in the production of superior gluten-free bread. The present study examined laboratory-scale isolation of such functional zein from dry-milled corn. RP-HPLC indicated that successful isolation procedures resulted in relatively pure alpha-zeins, with a maximum ratio of (beta + gamma)/alpha-zeins of about 10%. In the present study, such functional zeins were obtained by using 70% ethanol as the extractant, without added alkali or reducing agent in the main extraction step. In contrast, films could be cast from a wider range of zein isolates, also with higher ratios of (beta + gamma)/alpha-zeins. Isolation of the analogous prolamin (kafirin) from dry-milled sorghum required a more hydrophobic extractant like 83% isopropanol to achieve some functionality. Such kafirin was able to aggregate in warm water, preferably when a reducing agent was added. However, it quickly became very firm and lost its extensibility. The present study suggests that hydrophobic interactions rather than disulfide links are the key to gluten-like functionality of zein and kafirin.