Convective, vacuum and freeze drying of black seedless raisins: Physicochemical properties

Abstract

Fresh black seedless grapes were dried by convective, vacuum and freeze drying in order to investigate and compare the physical (moisture content, water activity, total colour change and rehydration power) and chemical (total phenolic, flavonoids and monomeric anthocyanin content and antioxidant activity) properties of dried raisin samples. The optimal maximum and minimum values of all the investigated physicochemical parameters were obtained in vacuum dried samples. The vacuum dried sample (70 °C, 20 mbar and 11 h) was characterized as a sample with the most favourable physicochemical properties ( namely moisture content, water activity, rehydration power, total phenolic and flavonoid content), whereas convective and freeze dried samples were found to exhibit less favourable results relative to all the investigated physicochemical properties.

Keywords

• black seedless raisins
• convective drying
• vacuum drying
• freeze drying
• physicochemical properties