Effect of Pretreatments on Color, Functional and Pasting Properties of White (Dioscorea rotundata) and Yellow Yam (Dioscorea cayenensis) Varieties

The effects of blanching, sulfiting and cooking pretreatments on color, functional and pasting characteristics of flours of Dioscorea rotundata (Abuja, Amula, Gbangi) and Dioscorea cayenensis (Alo) cultivars were investigated. The L* (71.45–79.98), a* (2.36–4.72), b* (19.96–25.71), ΔE (0–6.68), ΔC (0–5.75) and hue angle (78.99–84.77) varied significantly with pretreatment and yam variety. Also, loose (0.44–0.77 g/cm³) and packed (0.79–0.97 g/cm³) bulk densities, water (13.5–22.0%) and oil (10.0–19.0%) absorption capacities, and solubility (13.40–59.10%) and paste transparency (44.50–61.90%) varied with pretreatment and variety. Average peak viscosity of cooked and sulfited yams of Abuja, Amula, Gbangi and Alo was 19.58 and 16.96, 35.33 and 131.84, 92.18 and 79.00, and 61.88 and 163.92 rapid visco analyser, respectively. Peak, trough, breakdown and setback viscosities of pretreated yams were significantly lower than the untreated control. Flours of pretreated Alo and Gbangi varieties showed higher values of peak, trough, breakdown and setback viscosities than Amula and Abuja varieties. PRACTICAL APPLICATIONS: Huge postharvest losses are often recorded during handling and storage of yams as a result of the high moisture content, sprouting and activities of external agents, such as insects, rodents and moulds. However, drying of yams and the subsequent milling into flour has been found to increase the utilization and production of value‐added yam flours that could easily be reconstituted and consumed or used as raw materials for further processing. The need to determine the effect of appropriate pretreatments prior to the drying of yams is germane to the production of high quality and acceptable flours for highly demanding consumer is necessary. The determination of physical, functional and physicochemical properties of flours of pretreated yams would be a pointer to the quality indices.