Effects of Drying Techniques on Murtilla Fruit Polyphenols and Antioxidant Activity

‘Murtilla’ (Ugni molinae Turcz) is a native Chilean species that belongs to the Myrtaceae family. It produces a small, globular fruit with pleasant flavor and recognized antioxidant activity. Convective hot-air and freeze drying are important techniques for fruit preservation, but their effect on murtilla fruit polyphenols and antioxidant activity has not yet been studied simultaneously. The objective of this study was to compare the effect of convective hot-air drying at 65 and 80 ºC and freeze drying on total polyphenol content (TPC), total anthocyanin content (TAC), polyphenols and anthocyanins of the Red Pearl-INIA variety of fresh murtilla fruits as measured by HPLC and antioxidant activity (DPPH and ABTS). The freeze dried fruit retained higher values for TPC (2192.4 mg/100 g d.w.), TAC (13.4 mg/100 g d.w.), polyphenols (79.02 mg/100 g d.w. by HPLC) and anthocyanins (0.188 mg/100 g d.w. by HPLC) than the murtilla dried by convective hot-air at both 65 and 80 ºC. The application of all treatments showed a positive increase in the DPPH (2945.4 to 3677.6 ?mol TE/100 g d.w.) and ABTS (2664.8 to 3397.2 ?mol TE/100 g d.w.) antioxidant activity of the dried murtilla compared to the DPPH (2111.1 ?mol TE/100 g d.w.) and ABTS (2247.8 ?mol TE/100 g d.w.) of the fresh fruit. Freeze drying was the best technique for the retention of polyphenols and antioxidant activity from the fresh murtilla fruit. Therefore, freeze drying is recommended over convective hot-air drying at 65 and 80 ºC when these bioactive compounds need to be preserved.