Cyanide Reduction, Functional and Sensory Quality of Gari as Affected by pH, Temperature and Fermentation Time

Abstract

The effects of control pH, temperature and fermentation time on the cyanide reduction, functional and sensory properties of gari were investigated. Freshly harvested cassava roots (local variety) were peeled, washed and grated into a mash. The meal was divided into five equal portions and mixed thoroughly with already prepared buffer solutions from citric acid, sodium orthophosphate, -analytical grade (10% by weight buffer and kept in stainless containers to ferment at room temperature (30^oC). Samples were withdrawn at intervals of 12, 24, 36, 48 and 72 h, dewatered, sifted and toasted into gari and packaged in cellophane bags. The process was again carried out at 35 and 40^oC. The product gari was subjected to functional analysis (swelling index, pH, titrable acidity, water absorption capacity and residual cyanide) and sensory evaluation (appearance, taste and general acceptability) for the uncooked gari. The results obtained show that the buffer treated samples had high pH than the control sample. The highest mean pH was recorded for the BS = 8.0, (7.19), followed by BS = 7.0 (6.55) and BS = 6.0 (5.97), while the control had the lowest 4.5. The highest Swelling Index (SI) (17.45 ml/ml) was obtained for BS = 5.0 and closely followed by BS = 6.0 (17.14 ml/ml) while BS = 8.0 recorded the least 16.91 ml/ml. The buffer at pH 7.0 reduced the cyanide content to 7.69 mg HCN/kg, which is lower than the safe level of 10 mg HCN/kg. Moreover the gari from BF = 5.0 (5.4) and BF = 6.0 were the preferred in terms of general acceptability while the gari from the control BF = 0.0 (4.8) was rated the least. The buffer treated samples also performed better than the control in bulk density and general acceptability as rated by the panelists. Therefore controlling the process variables (pH, temperature and fermentation time) while fermenting cassava mash for gari production is sure way to enhance product quality and safety.