Drying Characteristics, Physicochemical and Functional Properties of Yam (Dioscorea spp.) Flours: Influence of Air Drying Temperature

Abstract

This study investigated the effect of air drying temperature on drying characteristics, chemical composition and functional properties of yam flours. Prior to drying, peeled yam tuber was blanched in boiling water containing 2% NaCl and 1% citric acid and drying was conducted in a cabinet hot air dryer at 50oC, 60oC, 70oC and 80oC. The time required for the lowering the moisture content of yam slices from initial 74.44 % (wb) to a constant moisture content (9.34 to 11.33 %) was varied between 420 to 730 min, depending on the temperature used and drying took place entirely in the falling rate period. Drying led to a significant (P < 0.05) reduction in the moisture (9.34 to 11.33 %) and total phenolic content (9.68 to 10.74 mgGAE/100g) of yam flours, whereas the protein (4.24 to 5.42 %), ash (4.64 to 5.99 %), fat (0.45 to 0.95 %), fiber (0.75 to 1.33 %), total carbohydrate (77.41 to 79.23 %) and total starch content (56.46 to 65.57 %) increased significantly (P < 0.05) compared to fresh yam. Both chromatic parameters (L, a, b, h, C and whiteness index) and browning index were affected by drying temperatures, which contributed to the discoloring of some yam flour sample. Moreover, the functional properties of yam flours in terms of bulk density (0.84 - 1.15 g/ml), swelling power (2.10 - 2.63), water absorption index (132 - 176%), water solubility index (13.59 – 27.16%), iodine affinity of starch (196.66 - 353.33 ppm) and starch gelatinization point (77.67 - 85.31°C) was found to be varied significantly (P < 0.05). The results of this study concluded that flours obtained from yam tubers by drying in cabinet dryer at various temperatures gave excellent overall nutritional quality and functional properties. These flours could be used to make a higher quality product that is more attractive to product developers and consumers