Effects of different pre-treatments on drying characteristics of banana slices

Abstract

The effects of different pretreatments and temperature on the drying characteristics of ripe Gros Michel banana slices were investigated. 5 and 7 mm thick slices of bananas were pretreated with four different pretreatments such as ascorbic acid, lemon juice, salt solution, honey dip and a control for 10 minutes, each replicated three times. Pretreated banana slices were dried in a cabinet oven dryer using a completely randomized design at 60°C and 70 o C and their drying characteristics such as rate of drying, moisture diffusivity, re-hydration ratio, and coefficient of re-hydration were studied. The moisture content of the fresh ripe bananas for both the untreated and treated samples was found to be in the range of 75-77 % (w b) which reduced to 16.8 to 27% after oven drying for various thicknesses and temperatures of air drying for 16 hours. The moisture diffusivity during oven drying varied from 7.89E -5 to 14.94E -5 m/s 2 , and increased with drying air temperature. The 5 mm thick slices at a drying air temperature of 70°C dried better than the others and resulted in about 13% savings in time. The minimum re-hydration ratio of 1.215 was obtained for 7 mm thick slices treated with ascorbic acid and the maximum re-hydration ratio of 1.716 was obtained for lemon juice samples. This means that the lemon juice treated dried bananas will reconstitute more moisture when exposed to air.