ABSTRACT

Aerial yam (Dioscorea bulbifera) and cocoyam (Xanthosoma sagittifolium) were evaluated for the proximate, functional, anti-nutrient properties and volatile constituents as affected by processing treatments. The proximate, functional and anti-nutritional properties of the processed flour showed significant (p<0.05) variations. The proximate results ranged as follows: protein (5.54-7.92%), fat (2.29-3.53%), fibre (1.53-2.41%), ash (1.93-3.72%), moisture (6.52-10.17%) and carbohydrate (75.34-80.22%) respectively. There were significant increases in the fat and ash contents of the roasted flour (1.40 and 2.40%). The functional property values ranged as follows: bulk density (0.49-0.74 g/mL), water absorption capacity (1.79-2.13 ml/g), oil absorption capacity (1.32-1.74 g/ml), foam capacity (10.23-15.35 ml/ml) and gelatinization temperature (60.52-75.63⁰C) respectively. The result of the anti-nutritional factors (oxalate, alkaloid, tannin, and saponin), reveals that the boiled flour samples had lower values (aerial yam; 0.09-1.95%, cocoyam; 0.02-1.46%) while the unprocessed flour samples had the highest values (aerial yam; 0.49-2.93%, cocoyam; 0.33-2.30%). Volatile constituents of Dioscorea bulbifera and Xanthosoma sagitifolium play an important role in the flavour quality characteristics of these roots and tubers. In this study, volatile aroma components of Dioscorea bulbifera and Xanthosoma sagitifolium were analyzed using gas chromatography-mass spectrometry (GC-MS). A total of 150 volatiles were identified in raw, boiled and roasted Dioscorea bulbifera and Xanthosoma sagitifolium. The compounds identified were amines, acid and esters, hydrocarbons, alkanes, carboxylic acids, amides, aldehydes, ketones, alcohol compounds and other additional compounds. The predominant volatile compounds in the two cultivars (unprocessed, roasted and boiled) were the alkanes followed by hydrocarbons, carboxylic acids, acid and esters, ketones, alcohol, aldehyde, amine, amide and other additional volatiles. Methylene chloride, Acetic acid, dichloro, Methane-d, trichloro, Octane. 2-methyl, 1, 10-diaminodecane and Propanoic acid, 2-hydroxy-2-methyl- were detected in all the samples studied. These volatile components had different retention times with different percentage peak area. Propanoic acid, 2-hydroxy-2-methyl- had 3.555mins, 3.557mins, 3.563mins, 3.566mins and 3.566mins retention time, at percentage peak area of 0.22, 0.68, 0.32%, 0.26% and 0.30% respectively for aerial yam and cocoyam (Ede uhie) samples. The major volatile components obtained for the unprocessed Dioscorea bulbifera and unprocessed Xanthosoma sagittifolium are the Methylene chloride and Acetic acid, dichloro, which increased consistently at different retention times.