Modeling the convective drying kinetics of coconut chips pretreated with osmotic dehydration

Abstract

The aim of this research was to evaluate the kinetics of drying and quality indicators of coconut chips (Cocos nucifera L.) dried by osmoconvection. Coconut is rich in potassium, protein and fatty acids, especially medium chain saturated fatty acids. Osmoconvective drying of the coconut chips at 50, 60 and 70°C required 80, 75 and 60 min, respectively, to reduce the moisture content from 30.09% m/m after osmosis to 5% m/m.

Fresh coconut had an initial humidity of 46.28% m/m, which decreased by 16% m/m after osmotic dehydration. The most suitable model to represent the kinetics of the moisture ratio of the coconut chips corresponded to that of modified Midilli.

Effective diffusivity of the water was 6,48 × 10−10, 8,11× 10−10 and 9,73 × 10−10 m2/s, for 50, 60 and 70°C, respectively, in the convective drying. The differences with other similar investigations can be given by the type of energy transfer, the operational parameters of the drying, the species used, semi-thickness of the sample and that, at high drying temperatures, due to the fast evaporation rate, it is possible to obtain higher effective diffusivity values. The activation energy of the drying process was 18.74 kJ/mol, which is in the range for food products. The colorimetric parameters were affected with the increase of the drying temperature and it is evident that non-enzymatic browning reactions occur during drying. Samples dehydrated at 50°C were those with the greatest defects in appearance and texture. The sample was chosen at 60°C, as the most accepted taking into account its organoleptic quality.