ARS | Publication request: PREFERENTIAL BINDING OF SORGHUM TANNINS WITH GAMMA-KAFIRIN AND THE INFLUENCE OF TANNIN BINDING ON KAFIRIN DIGESTIBILITY AND BIODEGRADATION

Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 2006
Publication Date: July 1, 2007
Citation: Taylor, J., Bean, S., Ioerger, B.P., Taylor, J. 2007. Preferential binding of sorghum tannins with gamma-kafirin and the influence of tannin binding on kafirin digestibility and biodegradation. Journal of Cereal Science. 46:22-31.

Interpretive Summary: Tannins, phenolic compounds that bind to proteins, are present in some sorghum lines and confer important agronomic benefits to sorghum such as insect, bird, and mould resistance and cross-linking of sorghum protein films using tannins improves their quality. Thus the objective of this study was to investigate the binding of sorghum tannins to sorghum proteins. Binding assays and analysis of protein-tannin complexes by SDS-PAGE, RP-HPLC, and HPCE showed that tannins preferentially bound gamma kafirins. Sorghum proteins bound to tannins had lower digestibility than unbound proteins and protein films made from tannin-protein complexes had longer life. The use of tannins in the production of biodegradable protein films may improve the quality of such films and understanding the binding of tannins to sorghum may lead to improved methods to disrupt such binding in food products, thereby improving their nutritive value.

Technical Abstract: The binding of different kafirin species with sorghum condensed tannins was investigated. Analysis by chemical assay and by SDS-PAGE, RP-HPLC, and FZCE, showed that gamma-kafirin bound more condensed tannins than the other kafirin species. SDS-PAGE suggested that the '-kafirin bound tannins were in the form of aggregates of molecular size >200 k. RP-HPLC and FZCE revealed that sample preparation and drying the kafirins prior to the binding assays had a significant impact on '-kafirin solubility. The effect of tannin binding on kafirin and kafirin film digestibility and film biodegradation was determined. Kafirins bound to tannins had lower digestibilities than unbound kafirins. Films made from tannin-bound kafirin had much lower digestibility and were less biodegradable than films made from unbound kafirin. The increase in kafirin film life by tannin modification appears to be due to a decrease in protein digestibility caused by kafirin-tannin binding.