Effect of soaking and boiling treatments on the quality of winged bean seed

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Abstract
Winged bean (Psophocarpus tetragonolobus (L) DC) seeds were soaked for 24 h in distilled water, 30 or 50 g litre−1 rice husk ash suspension or solutions of 10 or 20 g litre−1 baking soda, or 5 or 10 g litre−1 NaHCO3. Seeds were then boiled for 30 min in these solutions, then either washed and resoaked in distilled water or peeled, washed for 24 h and resoaked for 24 h in distilled water. The pH and level of leached solids increased during boiling. The colour of the bean cotyledon remained light when boiled in distilled water or rice husk ash suspension, but became darker when boiled in the alkaline solutions. Boiling in distilled water or rice husk ash suspensions did not render the bean sufficiently soft, whereas boiling in the alkaline solutions produced adequately soft seeds. There was no significant difference in tenderness of beans given further processing by resoaking or peeling and resoaking compared with boiling. The nature of the cooking liquid had no significant effect on the protein content of the seeds.