Air-drying characteristics of fresh and pretreated (African Oil Bean) Pentaclethra macrophylla benth. cotyledons

Abstract

Processing of African Oil Bean Cotyledons (AOBC), a valuable source of protein has been a bottleneck because of the associated drudgery. In addition, the shelf life of the processed bean is very short; the cotyledon turns green shortly during storage due to putrefaction. On the basis of the above, there is a need to produce shelf-stable cotyledons which could be rehydrated when needed. Three portions were separately soaked in each solution of sodium chloride (3 %), sodium meta-bisulfite (300 ppm), ascorbic acid (300 ppm) for 1h, and one portion were subjected to natural fermentation for three days, while the other was used as control. All the samples (single and double cotyledons) were oven-dried at 50, 60, 70, and 80^o C to constant weight. The dehydration rate of AOBC decreased gradually until the water activity of the oil bean cotyledon reduced to less than one. Moisture diffusivity increased from 4.9061×10-10 – 2.091 × 10-9 m²/s, and varied with drying temperature, thickness, and pretreatments. Midilli and Kucuk model (R² = 0.9702 - 0.9940) showed a better fit than other drying models. Effective moisture diffusivity is direct of the samples is reliant on air-drying temperature and can be described by the Arrhenius equation. The activation energy of drying of the African Oil Bean cotyledon was in the range of 10.29 – 27.12 kJ/mol. Finally, the addition of preservatives proved to be highly effective on the drying rate and the other studied parameters as well as the shelf stability of the AOBC.