Influence of Soaking Method on the Chemical and Functional Properties of Trifoliate Yam (Dioscorea dumetorum) Flours

Abstract

The effect of soaking method on the chemical and functional properties of trifoliate yam flour was evaluated in Nigeria. The freshly harvested trifoliate yam tubers (white and yellow cultivars) were divided into two portions. Portion A was washed, drained, peeled, sliced, dried, milled and sieved to obtain the raw flour while portion B was washed, peeled and soaked in warm water (60oC) for 10 minutes and then left in hot water for 12 h, sliced, dried, milled and sieved. Alkaloid and carotenoid profiles, pasting and functional properties of the flours were evaluated. Raw white trifoliate yam flour had higher peak viscosity (210.21 RVU), holding strength (155.50 RVU) and final viscosity (236.09 RVU). The viscosities were drastically reduced in the soaked flours. The major carotenoid in yellow trifoliate yam flour was carotene followed by  Î²-cryptoxanthin. Total carotenoid contents of the flour ranged from 94.95 to 102.57 mg 100g-1. The major alkaloid in trifoliate yam was dioscorine followed by dihydrodioscorine. Total alkaloid was higher (0.58 mg 100g-1) in the raw white trifoliate flour but these values were lower in the processed flours. Raw yellow trifoliate yam flour had higher bulk density (0.88 g cm-3) while the least values was observed in the soaked yellow flour (0.73 g cm-3). The soaked flours had higher swelling power and water absorption capacities. Raw and soaked trifoliate yam flour could be used in food industry for baking and stiff dough production.