ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 91 Number 1
Effect of soaking on some mechanical properties and dehulling efficiency of cowpea (Vigna unguiculata). (21)
Cowpea is gradually becoming an industrial raw material with the production of powdered cowpea; hence, there is need for research into proper mechanization of its processing. This study focused on effect of soaking time on moisture content, coefficient of static friction, dehulling efficiency, and selected mechanical properties of three varieties of cowpea. The cowpeas were soaked in water at ambient temperature 29 ± 2oC for 0, 5, 10, 20 and 30 minutes. Moisture content of the soaked samples was determined using oven method. Also determined were coefficient of static friction, some mechanical properties, and dehulling efficiency. Five replicates of the treatments were carried out, and mean values were recorded as data obtained. Data were subjected to descriptive analysis and ANOVA at 5% level of significance using SPSS package. Moisture content of the cowpeas ranged from 13.84 to 70.81%, 13.76 to 60.54% and 15.56 to 65.12% for IT 98-4914, IT 93K 625 and IT 98K 1312, respectively. Significant differences were recorded among the water absorption rate of the cowpea varieties at 5% level of significance. After 20 minutes of soaking time, coefficient of static friction was uniform (0.22) for wood, rubber and steel. Deformation, strain at yield and peak increased with increase in soaking time. The lowest efficiency of 37.58% was obtained for mild steel at zero soaking time. While 53.38% was the lowest efficiency recorded when rubber was used as surface of rubbing plate. The highest efficiency (70.14%) was the same for both mild steel and rubber. A quadratic model was fit to predict the effect of soaking time on dehulling efficiency of cowpea using mild steel and rubber surface. Appropriate soaking duration for the three varieties of cowpea (IT 98-4914, IT 93K 625 and IT 98K 1312) was 20 minutes. Rubber-rubbing surface produced best dehulling efficiency, thus its use is recommended as rubbing pad in cowpea dehulling machine.
Keywords: Cowpea varieties, soaking time, mechanical properties, dehulling efficiency