EFFECT OF GEOMETRICAL SHAPES AND SIZES ON THE DRYING CHARACTERISTICS OF CARROT (Daucus carota L.) TUBERS

Abstract

This study was concerned with the effect of geometrical shapes and sizes on the drying characteristics of carrot tubers. Carrot tubers were procured and sliced into 30 mm diameter circular shapes of 3, 5, 8 and 10 mm thickness and cubic shapes of 3, 5, 8 and 10 mm3, other tubers were prepared into 2 and 5 mm shredded carrot and carrot pomace from juice extraction. Thin layer drying experiment of the carrot samples was carried out at a constant temperature of 60 oC and air velocity of 1.2 m/s in a hot air cabinet dryer. The dependence of drying rate constant on the shapes and sizes of carrot was investigated and ten (10) existing mathematical models were tested to fit the drying data of the carrot samples. The whole drying process of carrot samples took place in a falling rate period except a very short accelerating period at the beginning. It was observed that as the size of the samples increases the average drying rate decreases while the drying time and effective moisture diffusivity increases. The average drying rates for both circular and cubic shapes ranges from 0.0041 – 0.0028 kg/hr, the average drying rates for 2 and 5 mm shredded carrot were 0.0042 and 0.0039 kg/hr respectively and 0.0040 kg/hr for carrot pomace. Nutritional and colour analysis of the fresh and dried samples of carrot and pomace were carried out to ascertain the nutrient composition of the samples. The mathematical models were compared based on their coefficients of determination (R2), root mean square error (RMSE), reduced chi-square (χ2) and modeling efficiency (EF) between the experimental and predicted moisture ratios. Consequently, the Hii et al. (2009) model was selected as the best mathematical model for describing 3, 5 and 8 mm circular shapes, 3, 5 and 10 mm3 cubic shapes and carrot pomace. The Page model was selected for prediction of 10 mm circular shape and 8 mm3 cubic shape, and the Midilli and Kucuk model for the 2 and 5 mm shredded carrot samples