EFFECTS OF FERMENTATION AND EXTRUSION ON THE NUTRITIONAL COMPOSITION OF SWEET POTATO (IPOMOEA BATATA L) AND BENISEED (SESAMUM INDICUM L) BLENDS

Abstract

The effects of fermentation and extrusion on the nutritional composition of fermented, fermented-extruded, unfermented-extruded and raw blends of sweet potato (Ipomea batata .L) and beniseed (Sesamum indicum .L) flour were evaluated. The sweet potato flour was blended with beniseed flour at manifold proportion of 100:0 ,70:30, 60:40 and 50:50 (sweet potato flour : beniseed flour) and these flour blends were subjected to solid state fermentation for 72 hours. The proximate, mineral, vitamins and anti-nutrient composition, 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 and48hours but decreased between 48 and 72hours. The fungi growths were observed after 72hours. A total of 11 isolates were obtained: 6 bacteria, 5 moulds and 1 yeast. The pH and total titratable acidity (TTA) varied significantly during fermentation. The result of the chemical composition of the fermented and extruded flour blends showed a significant difference as compared with raw flour blends. The moisture contentwas highest in fermented- extruded (13.00± 0.02%) and least in raw (4.00± 0.14%). The protein content increased from (8.04± 0.09% -18.61±0.02%) in fermented-extruded while it has a lower value (3.21±0.02% - 2.23±0.01%)in raw . The carbohydrate was highest in the unfermented-extruded flour blends (74.72± 0.02%-79.50±0.02%) and least in fermentedflour blends (53.97± 0.07%-65.19± 0.09%). The fibre content showed slight difference in all the blends. The fat content was highest in the fermented flour blends (14.50±0.16%-22.00±.021%) and least in fermented-extruded (2.00±0.12%-5.00±0.09%). There was no significant difference in the ash content of all the flour blends. All the mineral content of the flour blends showed increased in fermented and fermented-extruded samples but decreased in unfermented-extruded and raw samples. Also the vitamins content of all the flour blends showed the highest in fermented and fermented-extruded however reduced in unfermented-extruded and raw samples. Fermentation and extrusion significantly increased in the invitro –starch digestibility of the flour blends with fermented-extruded samples having the highest values ranging from 220.74±0.39mg\g-265.44±0.39mg\g andraw samples had the least values from 170.24±0.39mg\g- 180.81±mg\g. The invitro-protein digestibility showed a significant difference with highest in fermented extrudates values 80.30± 10.36mg\g-88.62±12.30mg\g and raw sample having the least (31.84±28.53mg\g-33.17± 20.11mg\g).Fermentation and extrusion significantly reduced the anti-nutrient content (phytate, oxalate, tannin, saponin and trypsin inhibitor) of the samples. The sensory quality rating (UFE-50:50) of the unfermented extrudates showed a good preference in terms of colour, texture, taste and overall acceptability. The nutritional properties of sweet potato and beniseed flour blends were improved by fermentation and extrusion.