Kafirin structure and functionality

The structural and functional properties of kafirins are reviewed. Three classes of kafirin: the α, β and γ forms have been identified at the protein level and one, the δ, has been identified only at the gene and transcript levels. All forms show high homology with the equivalent zein proteins. By analogy with the zeins it is believed that the α-kafirins probably have an extended hairpin structure in solution, comprising elements of α-helix, β-sheet and turns folded back on itself. Kafirins are the most hydrophobic of the prolamins as shown by their solubility, and calculated hydration free energies. The proteins exhibit extensive cross-linking by disulphide bonds and on cooking form indigestible aggregates which are not solubilised by reduction of disulphide bonds. In spite of continuing studies, the reasons for the low digestibility of the protein remain uncertain and there may be several factors involved. Other research has shown that kafirins may have non-food uses and may be used to form films.