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 °C, and NaOH/olive oil at 96 °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 °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 (ΔE* = 15.05) and chroma (ΔC* = 9.03) were also associated to fruits pretreated with olive oil and K2CO3. The effective diffusivity of water during drying was 7.37 × 10−11 m2/s in pretreated samples compared with 6.61×10−11 m2/s for untreated samples.