Do kafirin bioplastic materials have unique functional characteristics?

Abstract

BACKGROUND AND OBJECTIVES : There is considerable interest in kafirin, sorghum prolamin, as a bioplastic material because it apparently produces bioplastics with superior functional properties. This review evaluates the evidence, focussing on research directly comparing the properties of kafirin bioplastics (films and elastomers) with those from zein and gluten. FINDINGS : Kafirin and zein are more hydrophobic than gluten but there is little difference in hydrophobicity between them. Kafirin and zein films have better moisture barrier properties than gluten films. Films made from total kafirin (α-, β-, and γ-kafirins) are stronger and take up less moisture than films from commercial zein (essentially α-zein). However, total kafirin- and total zein films have similar moisture uptake. Also, there is little difference in oxygen barrier properties between total kafirin- and commercial zein films. Total kafirin elastomers have better elastic recovery than commercial- and total zein elastomers and similar elastic recovery to gluten. CONCLUSIONS : The better functional properties of kafirin bioplastics compared to commercial zein bioplastics seems to be largely due to the greater disulfide bonded polymerization of kafirin polypeptides, involving the cysteine-rich β- and γ-kafirin classes. SIGNIFICANCE AND NOVELTY : This work should stimulate research into disulfide-bonded polymerization of prolamins to improve their bioplastic functionality.