The effect of abrasive pretreatment on the drying kinetics and phenolic compounds in goji berries (Lycium barbarum L.)

The paper investigated the effect of a physical surface abrasion of goji berries on drying kinetics and the evolution of phenolic compounds at 323, 333, and 343 K. A diffusion model was developed to describe the drying process. The effective diffusion coefficient estimated by the model ranged from 7.5 × 10–9 to 4.2 × 10–8 m2/s for cylinder and 2.0 × 10–9 to 1.15 × 10–8 m2/s for sphere for untreated samples (UTR). Higher values were found for treated samples (TR) (from 2.50 × 10–8 to 1.20 × 10–7 m2/s for cylinder and 8.0 × 10–9 to 2.70 × 10–8 m2/s for sphere). For the UTR samples, the values of activation energy were found to be 79.5 and 80.8 kJ/mol, respectively, in the cylinder and sphere models, which decreased to 72.0 and 55.8 kJ/mol for the TR samples. Catechins and cinnamic acids were the main phenols in goji berry. TR samples showed high antioxidant activity owing to the shorter exposure time to high temperatures and to oxygen. Practical applications: The fruit of Lycium barbarum is known for its nutritional properties and health benefits. Dried goji berries are consumed as a snack or they are added as ingredients in other foodstuffs. The drying of goji is difficult because the berry contains an outer layer of peeled wax, which does not allow moisture escape from the inside to the outside.The physical surface abrasion pretreatment here proposed before convective air drying helps in reducing the time and energy required for goji drying. The dried berries so obtained exhibit better nutritional quality and good appearance respect to the untreated ones. The use of this pretreatment combined with the best hot air drying conditions identified by the developed diffusion model, could represent an effective innovation in order to obtain dried products with high physicochemical properties. Furthermore, these dried goji berries have no sulfites added as a preservative.