Effect of freeze, microwave-convective hot air, vacuum and dehumidified air drying on total phenolics content, anthocyanin content and antioxidant activity of jamun (Syzygium cumini L.) pulp.

Jamun (Syzygium cumini L.) pulp-skin paste was dried using four drying methods viz., microwave-convective hot air drying (MCD), freeze drying (FD), vacuum drying (VD), and dehumidified air drying (DAD) at different conditions. Except for FD, the drying temperatures of MCD (1, 2 and 3 W/g power density), VD (60, 160 and 260 mm Hg pressure) and DAD (1, 1.5 and 2 m/s of air velocity; 20% RH) were varied from 40 to 70 °C. The dried pulp-skin flakes were analysed for total phenolics content [TPC, gallic acid equivalent (GAE)], monomeric anthocyanin content [MAC, malvidin-3-glucoside (M3G)] and antioxidant activity [AA, butylated hydroxyanisole (BHA)]. This study aimed on selection of the best drying method based on the retention of the above functionalities. Compared to the fresh sample, TPC and AA of the dried samples increased for all the methods, whereas MAC showed mixed response. With the retention of 31.52 mg GAE, 11.99 mg M3G and 28.63 mg BHA per gram of dried sample (on dry basis), MCD (70 °C, 1 W/g) was selected as the most suitable method based on statistical analyses.