Modeling the kinetics, energy consumption and shrinkage of avocado pear pulp during drying in a microwave assisted dryer

Drying kinetics, energy utilization (EU) and shrinkage level of avocado pear pulp during drying were investigated and modeled to determine the condition that enhances the quality of the dried product. Drying was carried out using a microwave assisted dryer with data lodger. The system was set at a constant power of 200 W, air velocity of 1.4 m/s, and temperatures of 50, 60 and 70 degrees C with pulp thickness being 5 mm. Fifteen thin-layer drying models, five non-linear shrinkage models and ANN methods were tested for describing the drying behaviour of avocado pulp using statistical parameters. The results revealed that drying took place in the falling rate period with the above temperatures reducing the moisture content of the pulp from 64.12 to 2.16 % wet basis within 15,360, 11,520 and 5,130 s, respectively. The drying rate and effective diffusivity increased with increase in temperature and ranged from 6.05 x 10-3 to 1.70 x 10-2 kg/kgs and 3.11 to 9.34 x 10-9 m2/s, respectively. The activation energy of the pulp was 50.34 kJ/mol. Among the drying models tested, Page and Aghashilo models provided the best statistical parameters for describing the drying behaviour of the pulp, while ANN demonstrated great ability to predict MR and SR more accurately with high and low R2 and RMSE. A non-linear shrinkage model developed also had the best fit qualities for describing the shrinkage behaviour of the pulp. The energy utilized (EU), specific energy utilized (S EU ), heat transfer coefficient (h tc ) and mass transfer coefficient (M tc ) of the pulp ranged from 7.36 to 3.19 kWh, 11.21 to 5.76 x 10-2 Wh/kg, 0.1054 to 7.98 x 10-7 W/mK and 2.06 to 4.28 x 10-6 m/s respectively and were statistically (5 %) influenced by temperature. The EU model developed had the best description behaviour of the energy relationship with other factors, having high R2 and low RMSE and SSE values.