EFFECTS OF FERMENTATIONAND EXTRUSION ON THE NUTRIENT AND ANTI-NUTRIENT CONTENTS OF COWPEA AND UNRIPE PLANTAIN FLOUR BLENDS

Abstract

The effects of fermentation and extrusion cooking on the nutrient and anti-nutrient composition of the raw, fermented, fermented-extruded and unfermented-extruded blends of cowpea(Vigna ungiculata L. Walp) and unripe plantain (Musa parasidiaca) flours were evaluated. Cowpea flour was blended with plantain flour at various ratios of 100:0 (A), 80:20 (B) and 60:40 (C) (unripe plantain flour: cowpea flour) and the flour blends were subjected to solid state fermentation for 72 hours. The proximate composition, minerals, anti-nutrients, invitro protein and starch digestibility as well as organoleptic properties of all the samples were determined using standard methods. The bacterial population of all the samples during fermentation increased between 0 and 48 hours but decreased between 48 and 72 hours. There was no fungal growth observed in all the samples until after 24 hours. A total of 18 isolates were obtained; 11 bacteria, 4 moulds and 3 yeasts. The pH and total titratable acidity (TTA) significantly varied during fermentation. The results of the chemical composition of the fermented and extruded flour blends showed a significant difference as compared with the raw flour blends. The moisture content was highest in fermented unextruded A (13.00 ± 0.03%) and least in the raw sample sample C (4.00 ± 0.03%). The protein content increased from 2.62- 8.75% in the raw flour blends and from 3.06- 12.10% in the fermented extruded blends. The carbohydrate content was highest in the raw flour blends (82.80-88.88%) and least in fermented unextruded samples (60.27-72.47%). There was no significant difference in the fibre content of all the flour blends. The fat content was highest in the fermented unextruded blends (4.89-5.80%) and least in raw blends (1.19-1.99%). There was no significant difference in the ash content of all the flour blends. All the minerals reduced in the unfermented extrudates and fermented extrudates, however increased in the fermented unextruded samples. Fermentation and extrusion significantly increased the in-vitro starch digestibility of the flour blends with fermented extruded samples having the highest value ranging from 49.62-52.67mg/100g and fermented unextruded samples had the least values (41.32-46.91mg/100g). The in-vitro protein digestibility was significantly increased with the raw samples having the least values (5.02-11.84mg/100g) and fermented extruded samples having the highest values (18.48-21.47mg/100g). Fermentation and extrusion significantly reduced the phytate, oxalate, tannin, phenol and trypsin inhibitor content of the samples. The sensory evaluation of the unfermented extrudates indicated a good preference in terms of colour, texture, aroma and overall acceptability. The nutritional properties of cowpea and unripe plantain flour blends were enhanced by fermentation and extrusion.