Influence of ultrasound pretreatment on the nutritional quality of yellow cassava during convective drying

Abstract

Yellow cassava were pretreated in ultrasound with distilled water (DWU) and ultrasound with osmotic dehydration (UOD) before hot air drying in order to  determine its effect on some physico-chemical qualities of the dried yellow cassava. The ultrasound frequency of 20 kHz, power of 600W and  pretreatment time of 10 min was applied during ultrasound pretreatment. Yellow cassava samples without ultrasound pretreatment served as the  control. The treated and the untreated samples were further subjected to hot air drying at 50, 60 and 70^oC. Proximate analysis was carried out on the  fresh, untreated and treated dried samples. The result showed that the highest total colour change was observed at DWU samples dried at 70^oC. Also, at 70^oC UOD samples had the lowest amount of protein. For fibre, there was no significant difference between the samples treated with ultrasound and the  fresh samples, but samples treated with ultrasound (DWU and UOD) were significantly higher than the untreated dried sample. In the case of carotenoid  content, DWU samples were significantly higher than that of the untreated and UOD after drying at 70^oC. This work showed that incorporation of  ultrasound pretreatment before convective drying could help to retain some nutritional qualities after drying.