Mathematical Modelling and Color Characteristics of Purslane (Portulaca oleraceae L.) Leaves Using Different Drying Methods
The effects of microwave (180, 360, 540, 720 and 900 W), convective (100, 160 and 220 °C), and combined microwave (180 and 540 W) and convective drying (100, 160 and 220 °C) on drying time, drying rate and color degradation of purslane (Portulaca oleracea L.) leaves were investigated. The drying data were applied to nine different mathematical models, namely, the Newton, Page, Henderson and Pabis, Logarithmic, Wang and Singh, Diffusion Approach, Verma, Two-Term Exponential and the Midilli-Kucuk Equation Model. The performances of these models were compared based on the coefficient of determination (R²), the standard error of estimate (SEE) and the residual sum of squares (RSS), between the observed and predicted moisture ratios. The Midilli-Kucuk model described the drying curve best in all drying methods (R²= 0.9996–1.0000, SEE = 0.0014–0.0208, RSS = 0.0001–0.0047). After the drying process, the color of the samples was determined in terms of CIE L*, a*, b*, Chroma* and α values. The color quality of products dried using 180 W microwave drying alone, 160 °C convective drying alone, or combined microwave-convective drying 180 W-100 °C was the best compared with that of the other treatments.
Key Words: color, drying, modelling, Portulaca oleracea L., purslane