Thin layer modeling for drying of nutmeg mace (Myristica fragrans) in reverse air flow dryer

Abstract

Nutmeg and mace are the two important spices derived from the same fruit of nutmeg (Myristica fragrans). Nut is the seed of the fruit and mace is the outer aril surrounding the nut. The mace from the freshly harvested fruit is removed from the nut and processed separately. Drying of two treatments of nutmeg mace ie. blanched and unblanched mace from nutmeg variety ‘Viswasree’ was done at temperatures of 50, 55 and 60 oC in a reverse air flow, natural convection mechanical dryer. Blanching was done by dipping in boiling water for 1 min. The experimental data for moisture loss was converted to moisture ratios and fitted to five thin layer drying models to describe the drying process mathematically. The results were compared for their goodness of fit in terms of coefficient of determination (R2), root mean square error (RMSE), mean bias error (MBE) and mean square of deviation (2). Page model was found most suitable to describe the drying process of nutmeg mace. The unblanched mace took 330, 240 and 210 min and blanched took 300, 210 and 180 min to dry from moisture content of 186.5 to 5.2% (db) at air temperatures of 50, 55 and 60 oC respectively. The effective moisture diffusivity varied from 1.59 × 10-08 to 2.82 × 10-08 m2s-1. The activation energy was higher for unblanched than for blanched nutmeg mace and was found to vary from 47.56 to 52.77 kJ/mol.