The influence of berry perforation on grape drying kinetics and total phenolic compounds

Drying is one of the traditional methods used for the conservation of fruits. In recent years, different methods have been developed to obtain higher quality products. Chamber-drying methods with hot air at controlled temperature are reliable and easy to use. The effect of piercing the structure of grape berries on their drying time was studied experimentally during convective drying within a temperature range of 30-50 °C. Experimental moisture loss results were fitted to different mathematical models, evaluated for goodness of fit by comparing their respective R² , χ² , and root mean square error.

The Midilli et al. model provided a better prediction to describe the drying of whole grapes than the other models evaluated. However, punched grapes showed a better fit for the two-term model at 30 and 40 °C, and the approximation of diffusion model at 50 °C. The values of effective moisture diffusivity fluctuated between 8.04 × 10^-12 and 7.31 × 10^-11  m²  s^-1 . Activation energy was 56.49 and 54.43 kJ mol^-1 for whole and punched grapes, respectively. All the drying processes produced an increase of total phenolic compounds and antioxidant activity in grapes, these increases being higher in whole grape drying.

The drying of punched grapes was faster and the activation energy higher than with drying of whole grapes; however, whole grapes presented more total phenolic compounds and antioxidant activity. © 2019 Society of Chemical Industry.