Effect of drum drying temperature on drying kinetic and polyphenol contents in pomegranate peel

The pomegranate peel, an agro-industrial waste, has a high content of antioxidant polyphenolic compounds with proven health-benefiting and technological properties. Polyphenol stability might be affected by heat treatments that are required during drying. Thus, the aim of this study was to analyze the drying kinetics of pomegranate peel dried by double drum drying and to evaluate its effect on polyphenolic compounds. Pomegranate peel was dried at 100, 110 and 120 °C using a constant clearance (2 mm); the processes were modeled and the physiochemical and antioxidant properties were analyzed. Drum drying at 100, 110 and 120 °C were very fast processes that required short drying times (422 s, 400 s and 257 s, respectively) to reach low moisture contents (5.0, 1.6 and 2.6 g water/100 g peel, respectively). At these short drying times, the total polyphenolic content and antioxidant activity were not significantly decreased at any temperature, and the hydrolysable tannins content was maintained by drum drying at 100 and 110 °C. Thus, the drum drying results demonstrate an efficient alternative to obtain a high quality product from pomegranate peel and thereby reuse and add value to this agro-industrial waste.