Abstract The response surface method (RSM) has an important application in formulation of new products. This study determined the effect of electric hot-air drying on the functional properties of flour made from orange-fleshed sweet potato (OFSP). Flour from the cultivars Bophelo (B) and Impilo (IM) were treated with 13 temperature-time combinations designed by STAT EASE software version 8.01.0. Bophelo flour dried at 70 °C for 8.6 hrs and Impilo at 70 °C for 14.4 hrs showed the lowest gelatinization temperatures and enthalpy of gelatinization (ΔH), indicating ease of cooking. The highest swelling power of 12.45 g/g for Bophelo and 8.16 g/g for Impilo were significantly higher than the remaining samples. Flours for Bophelo and Impilo at drying temperatures and times at 70 °C for 4.4 hrs, 56 °C for 6.5 hrs and 60 °C for 6.5 hrs indicated favourable gelling properties and cost of drying, implying that these can be used at household level and in food industries as thickeners from both cultivars.

Abstract Drying characteristics of Cleome leaves in an oven dryer was studied. The impact of oven drying temperature (50, 60 and 70 °C) on moisture composition of the plant at a uniform air speed was considered. Eight drying models, namely, simple exponential, Page, Verma, modified Henderson and Pabis, Lewis, two term exponential, Newton, logarithmic, and Wang and Singh were fitted to drying data. Modified Henderson and Pabis model satisfactorily depicts the drying behaviour of Cleome leaves. Effective moisture diffusivity of Cleome ranged from 1.03 × 10−6 to 1.77 × 10−5 m2/s. Reliance of the calculated effective diffusivity on oven temperature was unavoidable. The required activation energy for oven drying of Cleome leaves was found to be 24.46 kJ/mol. The colour characteristics of Cleome leaves in terms of L*, a* and b* were determined. Based on the colour characteristics results, drying condition of 70 °C 90 min was found to be optimum for oven drying of Cleome leaves.

AbstractOptimization of microwave drying conditions of Luvhele and Mabonde banana varieties were studied using response surface methodology. The drying was performed using a central composite rotatable design for two variables: microwave power level (100, 200 and 300 W) and drying time (40, 26, and 12 min.) for Luvhele; (100, 200 and 300 W) and (42, 27, and 12 min) for Mabonde. The colour and texture (hardness) data were analyzed using ANOVA and regression analysis. The fitness of the models obtained was good as the lack of fit for each of the models was not significant. The coefficient of determination R2 of the models was relatively high, hence the models obtained for the responses were adequate and acceptable. Drying conditions of 178.76 W, 12 min. drying time were found optimum for product quality at a desirability of 0.91 for Luvhele; while 127.67 W, 12 min. with a desirability of 0.86 was predicted for Mabonde. The result of this study could be used as a standard for microwave processing of Luvhele and Mabondebanana varieties.