Effect of Pre-Cooking and Particle Size Distribution on the Pasting and Functional Properties of Trifoliate (Dioscorea dumetorum) Yam Flour

Aims: The effects of pre-cooking and particle size distribution on the pasting and functional properties of trifoliate yam flours were evaluated.
Study Design: 2 x 2 x 5 factorial experimental design was used for this study.
Place and Duration of Study: The study was carried out in the Department of Food Science and Technology, Osun State Polytechnic, Iree, Osun State, Nigeria, between April 2011 and March 2012.
Methodology: Freshly harvested trifoliate yam (white and yellow cultivars) were peeled, washed, diced, dried, milled and packaged while the precooked flour was cooked for 10 min, dried, milled and packaged. The flour was separated into different particle sizes using sieves 150, 212, 315, 425 and 500 μm. Pasting and functional properties such as bulk density, water absorption capacity, swelling power of the flour samples were evaluated.
Results: Larger percentage of raw flour samples were recovered on sieve size 315 µm and 500 µm respectively while pre-cooked flour samples were retained on the sieve <150 µm and 315 µm respectively. The peak viscosities of the pre-cooked flours were lower than the raw flours and these decreased with increase in particle size. Bulk density and water absorption capacity ranged from 0.67 to 1.00 g/cm3 and 1.50-4.90 mL H2O/g respectively. Pre-cooked yellow trifoliate yam flour had higher bulk density value than the raw yellow flour at 212 µm but no significant difference (p = 0.05) exists between them. The highest water absorption capacity (4.9 mL H2O/g) was observed in the pre-cooked yellow trifoliate yam flour at 315 µm size sieve. Pre-cooked flour of white trifoliate yam had higher swelling power (9.86) at 150 µm particle size and 80ºC. The swelling power of the raw and pre-cooked flours increased with increase in temperature.
Conclusion: The pre-cooked trifoliate yam flours with 150-315 μm particle sizes produced flours with higher pasting and functional properties.