Effects of edible coatings on convective drying and characteristics of the dried pineapple

Abstract

The influence of two different edible coatings on air-drying kinetics and characteristics of pineapple slices was evaluated. Samples were osmotically dehydrated in aqueous solution containing 50 % of sucrose, 4 % of calcium lactate, and 2 % of ascorbic acid for 1 h. Osmo-treated pineapple slices coated with pectin, uncoated, and coated with a mix of whey protein isolate (WPI) + locust bean gum (LBG) + glycerol were hot-air-dried at 60 and 70 A degrees C. Moisture and vitamin C content were evaluated before and after each treatment. Water activity and color were evaluated before and after drying. A simplified model based on Fick's Law was used to estimate the effective diffusion coefficients during air-drying. The results showed that the impregnation pretreatment resulted in high vitamin C levels in dried pineapples. Pectin and WPI-LBG coatings did not affect the drying behavior of the samples and both coatings were effective in vitamin C retention during hot-air-drying. Water diffusion coefficients were strongly affected by temperature, whereas they were slightly affected by coatings. The coatings differently affected the lightness of the samples during air dehydration, and pectin coating showed the slightest change at this color parameter.