Assessment of drying characterics of berry fruits under physical pretreatment

The drying process of berry fruits, i.e. grapes, cherries, redcurrant and blueberries is a more complex process compared to the dehydration of other agricultural materials. The drying can be difficult due to the wax layer surrounding the fruit (Tarhan S., 2007). The berry fruits are a rich source of phenolic compounds which contributes to their high level of antioxidant activity. However, these compounds of important health benefit will be degraded after the fruit undergo air drying processes because of long exposure to high temperatures (Kalt et al., 2000). Skin pretreatments are considered before drying in order to facilitate water diffusion (Esmaiili et al., 2007). The waxy layer removal has been so far carried out by using several chemical pretreatments. However, they cause heterogeneity in the waxes removal and problems during shelf-life (Carranza-Concha et al, 2012). In this paper an abrasive pretreatment (Cinquanta et al., 2002) for enhancing the drying rate and preserving the samples is applied to berry fruits. The abrasion of the fruit peel is carried out in a motorized shaker, the surfaces of which are covered by abrasive sheets with different grit range. The benefits of the physical pretreatment include low energy cost, low capital cost and no heat damage. We aim at investigating the effect of wax abrasive pretreatment on the convective drying of berry fruits. The factors that are taken into consideration include time, load and rotation speed. The drying characteristics of pretreated and untreated fruits are studied using a convective oven with the air temperature ranging from 40 to 70°C at air velocity of 2.3 ms-1. Fruit quality parameters such as color, texture, moisture content, water activity (aw), skin damage (i.e. by SEM analysis), polyphenols content and antioxidant activity are evaluated to optimize the drying process.