Solar drying characteristics of strawberry

Thin layer solar an forced drying experiments were conducted for strawberry (Fragaria Xananassa) variety chandler's. Different shapes of strawberry (whole, halves quarter, and 3 mm discs) pretreated with different solutions: (1) 1% sodium metabisulphite + 1% citric acid (Tr. A), (2) 1% ascorbic acid + 1% citric acid (Tr. B), (3) 1% citric acid (Tr. C), (4) 2% sodium metabisulphite (Tr. D). Air heated by the solar air heater was forced through the product by an electric fan. The best fit of the thin layer drying of strawberry is obtained by exponential equation or Newton model which fitted very well the experimental data at various shapes of strawberry indicated by high value of coefficient correlation (r) in the range of 0.97-0.98 and low values χ2 ranging from 0.0102 to 0.0046. According to the results, a (Newton) term drying model could satisfactorily describe the solar drying curve of strawberry. The drying constant (k) was greatly affected by product surface area, drying air temperature and ratio projected surface area to product mass. The required drying times were 28, 26, 20 and 24 h for whole, halves, quarter and discs strawberry, respectively. Pretreatment and slicing did not affect the chemical composition of strawberry. Increasing of the surface area increased the loosing of V.C. during drying. Halves, quarters and discs presoaked in 2% sodium metabisulphite had the highest (pH) and re-hydration ratio. Dried strawberry pretreated with solutions contained sodium metabisulphite can be added in preparing flavoured cakes by 3% without any significant (P ≤ 0.05) effect on the acceptability compared to the fresh. © 2005 Elsevier Ltd. All rights reserved.