Effect of Fermentation on Antinutritional Factors and in Vitro Protein Digestibility of Bambara Nut (Voandzeia subterranean L.)

Abstract

Bambara nut (Voandzeia subterranean L.) has better nutritive values than most other legumes. However, it is being underutilized due to long cooking time, antinutritional constituents and dehulling constraints. Fermentation as a unit operation has been able to address most of the factors responsible for the underutilization of some legumes. In this study, a full factorial block design comprising of time (0, 12, 24, 36, 48, 60 and 72 h) and Rhizopus combinations (A, B, C, AB, AC, BC and ABC) were used. Three species of Rhizopus (R. oligosporus (A), R. oryzae (B) and R. nigricans (C)) and their combinations were used in the fermentation for 3 days. Fermented samples that were collected at 12 hourly intervals were blanched, dried and milled to Bambara Flour (BF).  The BF was evaluated for tannin, oxalate, phytate, trypsin inhibitors and in vitro protein digestibility (IVPD). The results show that fermentation significantly (p < 0.05) reduced the antinutritional factors and enhanced IVPD of bambara nut. Ranges of values for antinutritional factors were tannin (0.35 – 0.02), oxalate (1.54 – 0.39), phytate (35.20 – 10.70) and trypsin inhibitor (3.22 – 0.49mg/g) while in vitro protein digestibility were 21.70 – 66.14%. Therefore, fermented bambara nut flour could be useful to supplement starchy foods.

Key words: Antinutritional factors, in vitro protein digestibility, Rhizopus, bambara flour