Effect of pretreatment and drying method on drying kinetics of ackee (blighia sapida) arils

Abstract

Ackee (Blighia sapida) is a tropical fruit known for its nutritional content and health benefits, but its high perishable nature limits its shelf life. The research investigated the effect of different pretreatments and different drying methods on drying kinetics of ackee fruit arils. Freshly harvested ackee aril were portioned and subjected to pretreatments of blanching at 85 ? for 3 min, dipping in salt (NaCl) solution of 1, 2 and 3% w/v for 5 min and untreated samples served as control. The aril samples were dried at different temperatures (50, 60, 70 ?, solar and sun drying) monitored at intervals, until constant weight was obtained, and they were subsequently analyzed for drying kinetics, effective moisture diffusivity (D_eff), activation energy (Ea), using standard methods. The drying was observed to take place in a falling rate period. The moisture content of the ackee aril before drying was found to be 62.847% wet basis and at the end of the drying experiment, the moisture content reduce to less than 3% in the dried samples. The moisture loss was at a fast rate in aril dried at 70 ? compared to 60 and 50 ? which could be due to an increase in the energy of water molecules with increased temperature resulting in quick evaporation of water from the sample. The effective moisture diffusivity (D_eff) increased with increase in drying temperature from 50 to 70 ?. The overall highest effective moisture diffusivity was found to be 2.07 ×10^-4 m²/s at oven drying temperature of 60 ?, 1% salt solution pretreatment, while the lowest was found to be 4.23 × 10^-6 m²/s at oven drying temperature of 70 ?, 3% salt solution pretreatment. The activation energy obtained falls within the range of (106.10 – 125.29 kJmol^-1) which indicates that the ackee aril processed is highly sensitive to temperature. The obtained drying data were fitted into five different thin layer drying mathematical models using coefficient of determination (R²), least values of Chi Square (?2), Root Mean Square Error (RMSE) and Mean Biased Error (MBE). Pretreatment had significant effect (p?0.05) on the drying of ackee arils. Midilli and Kucuk model described the drying behaviour of ackee aril pretreated with 1% salt (NaCl) solution and oven-dried at 70 ? satisfactorily having the R² values of 0.999.