Effect of abrasive pre?treatment on drying rate of grape berries and raisin quality

Abstract

Drying of grapes for production of raisins is a slow and complex process. The prevalent chemical pre-drying treatment involves the use of chemicals which triggers the food safety issues and such a method also takes a longer drying time for grapes. A novel industrial scale abrasive pre-treatment system was developed and its operating parameters were optimized. The physical pre-treatment system consists of rotating drum with its inner surface of specific abrasive protrusions. Optimized parameters using Box-Bhenken Design of Response surface methodology as operating speed (15.13 rpm), treatment time (3.27 min) and sample size (8.45 kg), resulted in maximum treatment efficiency (97.76 %) and minimum drying time (65.5 h) for grape. Waxy cuticle layer was removed physically from the surface of grapes and hence drying rate found enhanced compared to chemical pre-treatment. Abrasive pre-treatment produced better quality raisins except slightly higher browning index (29.64?1.53) compared to chemical pre-treatment (26.19?0.93).