MATHEMATICAL MODELLING OF THIN LAYER DRYING KINETICS OF PRE-TREATED DATE FRUITS (Phonenix dactylifera L.)

Abstract

Date palm (Phoenix Dactylifera L.) is consumed locally as staple food in Nigeria. Date fruit contain high moisture content and is very susceptible to deterioration due to lack of preservation techniques. There is need to develop efficient preservation method which can ensure the nutritional safety of biological products and effective storage at local level. Drying is used in many countries to improve shelf life, reduce packaging costs, enhance appearance, retain original flavour and maintain nutritional value of food products. Different forms of pre-treatment have been reported to effect drying characteristics of food materials. In this study, effect of thermal pre-treatment on the two local varieties of date fruits, this-layer kinetics of pre-treated and un-treated date fruits under oven and cabinet drier at varying drying temperatures 500C, 600C and 700C and to fit into the best dry models were investigated at three drying temperatures following standard procedures. This study is aimed at modelling the drying characteristics of pre-treated date-red and yellow varieties Thin-layer drying experiments were conducted at varying drying temperatures ranging from 50, 60, 700C using laboratory oven with a constant air velocity of 1.4m/s and cabinet dryer for un-blanched samples and blanched samples at 500C for 2, 5, and 10minutes. Models were proposed to simulate the drying process, non-linear regressions was used to establish coefficient of determination (R2), sum of square error (SSE) and root mean square error (RMSE) for each model to determine the model of best fit. The result indicated that moisture removal at the initial stage of drying process was high and there was a rapid decrease as drying continue until equilibrium was reached. Also, the drying time reduced as the drying temperature increases from 50, 60 to 700C for both blanched and un-blanched red and yellow date fruits samples. The drying data were fitted into thirteen different mathematical thin layer drying models to establish best thin-layer mathematical drying model for predicting the drying kinetics of red and yellow date fruits using relevant statistical tools. The drying curve showed that blanched red and yellow date fruits had higher drying rate than the un-blanched samples. The results showed four thin layer drying models: modified Henderson and Pabis, diffusion approach, Verma eal. and two term models were satisfactory in describing the drying kinetics of the red and yellow date fruits. The best model selected for the oven drying of red date fruit was the diffusion model while modified Henderson and Pabis model was selected for cabinet dried red and yellow date fruits. The oven dried yellow date fruits had three models, the modified Henderson and Pabis and Verma et al. models. The effective moisture diffusivity of the oven and cabinet dried red date fruits increases with increasing temperature, while the cabinet dried yellow samples decreased with increasing temperature with values ranging from 1.29-11 to 9.87-12. This study established drying models for predicting the drying kinetics of blanched and un-blanched date fruits with a view to promote utilisation in food value addition through productive and processing system.