Microwave-convective hot air and vacuum drying of Syzygium cumini (L.) Skeels seeds and its effect on total phenolics content, vitamin C and antioxidant activity

Abstract

Seeds of (Syzygium cumini (L.) Skeels) are rich in medicinal values. In this work, the effect of drying on its total phenolics content (TPC), vitamin C (vit C) and antioxidant activity (AA) was studied. Seeds were dried at 60, 70, 80, and 100 °C using both microwave-convective hot air drying (MCD) at 1, 2, and 3 W/g, keeping air velocity fixed at 0.5 m/s, and vacuum drying (VD) at 60, 160, and 260 mm Hg. Dried seeds were powdered and evaluated. Statistically, MCD at 60 °C, 2 W/g was selected as the best drying method and condition that retained the highest functional properties. Compared to fresh seed powder, this drying condition retained 82% of TPC and ≈ 34% vit C and increased AA by about 52%. The drying curve at 60 °C, 2 W/g was fitted to four different mathematical models, viz., Lewis, Page, Henderson and Pabis, and Logarithmic. Logarithmic model was found to be best suited for characterising the drying profile. The final product was non-hygroscopic and free-flowing with a negligible degree of caking.