The Effect of Fermentation and Extrusion on the Anti-nutritional Composition and Digestibility of Millet and Soybean Flour Blends

Abstract

Aims: To investigate the effect of fermentation and extrusion on the anti-nutritional properties, starch and protein digestibility of millet and soybean flour. Methodology: Four combinations (100, 90:10, 80:20, and 70:30) of millet and defatted soybean flour blends were separated into two batches. A batch of the combination was extruded in a laboratory single screw extruder. The other batch was separately hydrated, preconditioned and extruded. The raw flour blends and extrudates were subjected to antinutritional analysis, starch and protein digestibility, using standard methods. Results: Tannin, saponin, trypsin inhibitor, and phytate contents significantly changed in all the extrudates. However, the fermented-extruded (FE) blends recorded highest reduction in all antinutrients. Saponin contents observed a change from 11.65 -13.08% (raw flour blends), to             4.98-6.54% (extruded (E) blends), and 2.13-3.19% (FE blends). Tannin contents changed from 0.1235-0.1412 mg/g (raw flour blends) to 0.0988-0.1083 mg/g (E blends) and 0.0838-0.0962 mg/g (FE blends). Trypsin inhibitors changed from 50.13-56.02% (raw flour blends) to 34.10-37.76% (E blends) and 32.98-41.89% (FE blends). Phytic acid contents also changed from 9.311-10.600 mg/g (raw flour blends) to 6.810-7.416 mg/g (E blends) and 4.944-6.361 mg/g (FE blends). In vitro starch digestibility was significantly higher (P<0.05) from 0.2615-0.3509 mg/g (raw flour blends) to 0.3246-0.4204 mg/g (E blends), and 0.3877-0.4699 mg/g (FE blends). As compared to the raw flour blends, protein digestibility significantly changed from 0.0298-0.0328 mg/g (raw flour blends) to 0.0817-0.0665 mg/g (E blends) and 0.0931-0.0753 mg/g (FE blends). Conclusion: From the results of this research, it is evident that fermentation and extrusion will produce acceptable products and increase the nutritional and sensory attributes of the product.