Effect of chemical and physical pretreatments on the convective drying of cape gooseberry fruits (Physalis peruviana)

Drying of cape gooseberry fruits is a slow process because of the low permeability to moisture of the fruit's waxy skin. In this work, the effect of chemical pretreatments (sunflower oil/K2CO3 or olive oil/K2CO3 at 28 degrees C, and NaOH/olive oil at 96 degrees C) and physical pretreatments (blanching) to break down the waxy surface and accelerate moisture diffusion during drying, was assessed. Drying was carried out at 60 degrees C and 2 m/s air velocity for 10 h. The lowest moisture content (0.27 kg water/kg db), the highest vitamin C content (0.36 mg/g), and the greatest rehydration capacity (1.89) were obtained in fruits pretreated with olive oil (9.48%) and K2CO3 (4.74%). However, the greatest changes in color (Delta E* = 15.05) and chroma (Delta C* = 9.03) were also associated to fruits pretreated with olive oil and K2CO3. The effective diffusivity of water during drying was 737 x 10(-11) m(2)/s in pretreated samples compared with 6.61x10(-11) m(2)/s for untreated samples. (C) 2013 Elsevier Ltd. All rights reserved.