摘要：Ambul banana (Musa mysore) is a popular variety in Sri Lanka and it has short postharvest shelf life. Postharvest
losses of banana are estimated to be more than 25%. An optimum drying system for the preparation of quality
dehydrated products is cost effective as it shortens the drying time and cause minimum damage to the product. The
process of osmotic dehydration followed by hot air drying was studied and modeled for ambul banana preservation.
Preliminary trials were done to identify the correct total soluble solid content, thickness and diameter of banana slices
for the dehydration. Three antibrowning pretreatment were evaluated for banana slices. They are 0.1M ascorbic (A),
0.1M citric (B) and 0.1 M ascorbic citric (50:50) combination(C).Samples were immersed in 60° brix sucrose solution
in 1:30 solid to solution ratio at room temperature (30°C) until it became equilibrium. The effective diffusion
coefficients for water and sucrose transport were determined according to predictive mathematical model based on
Fick’s 2nd law. The osmotically pretreated banana slices of sucrose solution were convectively dried in a tray dryer at
air temperatures of 50, 60 and 70°C at constant velocity. Color attribute of final dried banana slices were evaluated by
“image J” software (version IE 6.0 java). Changes in vitamin C content with time were determined by using a
titrimetric method. The moisture content in ambul banana was 75.47% in wet basis. Preliminary study showed the
optimum thickness, diameter and soluble solid content of banana slices were, 5 mm, 21mm and 16° respectively.
According to predictive mathematical model effective diffusion coefficients of A, B and C pretreated samples were 5.65
× 10-10, 5.86 ×10-10 and 6.74 × 10-10 m
2
/s respectively. Solid gain observed in samples were not correlated linearly with
the time, solid gain in nine hours osmotic process maximum in A and C pretreated samples (17.94%) whereas the
lowest solid gain was observed in B pretreated sample (16.41%). In the hot air drying process moisture content
decreased in a nonlinear manner with time at all three temperatures. It was faster in the initial period of drying and
then the rate decreased. The surface color (browning index) increased with drying temperature while vitamin C content
decreased when increased drying time and temperature. The dried banana prepared by 9 hours osmosis in 60° Brix
with C pretreatment and subsequent drying at 50°C hot air for eight hours showed better color, appearance and
moisture content.
关键词：Ambul banana; effective diffusion coefficient; Fick’s law; hot air drying; osmotic dehydration
