Residual Polyphenols, Phytate and In-vitro Protein Digestibility of Extruded Sorghum-Bambara Groundnut Blends

Aim: This study was designed and implemented to produce instant breakfast cereals from the blends of sorghum and Bambara groundnut flour through extrusion cooking as a strategy to reduce phytic acid and polyphenol and improve the protein digestibility and solubility.

Methodology: In this study, different blends of Bambara groundnut (10%, 20% and 30%) and sorghum flour were extruded at 20%, 22.5% and 25% moisture levels and 120°C, 140°C and 160°C barrel temperatures using a single-screw extruder. Response surface methodology with central composite face-centered design (CCFD) was used to model the residual phytic acid and polyphenols, protein solubility and protein digestibility of the extrudates.

Results: Increasing the barrel temperature caused a reduction in protein solubility, residual polyphenols and phytic acid but increased the in vitro protein digestibility of the extrudates. The coefficients of determination (R2) were 0.96, 0.83, 0.95 and 0.94 for polyphenols, phytic acid, protein solubility and protein digestibility respectively with non-significant lack of fit in all cases. Barrel temperature had the most effect on the responses.

Conclusion: Extrusion cooking in combination with dehulling significantly increased the protein digestibility of sorghum-Bambara groundnut extrudates. The second order polynomial was found appropriate for the prediction of polyphenols, phytic acid and protein digestibility of the sorghum-Bambara groundnut extrudates. The optimum levels of the response variables attainable were 11.32%, 70.0%, 48 mg/100 g and 63.11 mg/100 g respectively for protein solubility, digestibility, residual polyphenols and phytate content.