Adhesive potential of marama bean protein

Marama bean is an underutilised indigenous Southern African oilseed legume with protein content similar to soya bean. In this study, the adhesive potential of marama protein was explored. At 45% moisture content, marama protein was very sticky with a force of adhesion (6.5 N), which was about twice that of soya and 5 times that of gluten. Marama protein adhesive prepared using a standard procedure described for soya, had better adhesive properties when applied on a wooden substrate than did soya in terms of strength and resistance to delamination in water. The shear strength of marama protein (36–173 kg/cm2) was about 1.5 times higher than that of soya over the protein concentrations: 1.2–3.6 mg protein/cm2. When 2.4 mg protein/cm2 was applied on the wood, about 47% of glued wood pieces were delaminated for marama compared to 90% for soya after 2 cycles of 48 h soaking. Marama protein contained more β-sheet structure (54%) than soya (47% β-sheet), which was increased by approx. 12% in marama protein adhesive compared to 3% in soya protein adhesive. By AFM, marama protein adhesive presented a rough surface without holes compared to soya, which was rough but with many holes within its structure. Thus, the high β-sheet conformation and surface structure of marama protein are most likely responsible for its better adhesive behaviour compared to soya.