Osmg-convectwe Dehydration of Aonla Suces: Influence of Operatins Parameters on Process Kinetics

Abstract

A study was undertaken on osmotic dehydration and osmo-convective drying of Spherical shaped aonla slices (1.7x3.7 em). These slices were osmotically dehydrated in different sugar solution concentrations (50, 60 and 70°Brix), solution to fruit ratio (4, 5 and 6), process temperature (35, 50 and 65 °C} for 60,150 and 240 minutes of duration of osmosis. Response Surface Methodology (RSM) Box-Behnken design was used to analyse osmotic dehydration process. The osmosed and unosmosed aonla slices were dried in tray drier at 65, 70 and 75 °C drying air temperatures. The effect of process parameters during osmotic dehydration such as duration of osmosis, sugar concentration solution to fruit ratio and process temperature of syrup on water loss, mass loss, solute gain and moisture content were studied. It was found that the rate of solute gain and water loss decreased with increase of sugar concentration while solute gain and water loss increased with increase in process duration and also increased with increase in process temperature. It was found that osmosis as a pre-treatment prior to convective air drying was able to decrease drying time and increased the total dehydration process. Drying curves were affected by the drying air temperature and osmotic dehydration as a pre-treatment. Increase in the air temperature caused a decreased in the drying time. It was observed that drying rate increased with increase in drying temperature from 65°C to 75°C (tray) and constant rate drying period was absent throughout the drying process of aonla slices dried under all drying air temperatures. The values of rehydration ratio, coefficient of rehydration and rehydrated moisture content of conventionally tray dried samples increased with increase in drying air temperatures. The osmo-convective dehydrated samples were found more acceptable than convective dried ones. Air temperature and pre-treatment as osmotic dehydration had a significant effect on sensory evaluation