Effects of drying on the phenolics content and antioxidant activity of muscadine pomace

Three drying technologies [i.e., vacuum belt drying (VBD), hot air drying (HAD), and freeze drying (FD)] were evaluated for the processing of muscadine pomace in terms of their impact on drying time requirement, moisture content (MC), water activity (a(w)), total phenolics content (TPC), and antioxidant activity (AA). Muscadine pomace discs of two thicknesses (2 and 4 mm) were dried using 16 different time-temperature combinations for VBD, 12 different time-temperature and air velocity combinations for HAD, and one treatment for FD. The TPC and AA in lyophilised samples were 583 +/- 8 and 608 +/- 16 mu mol GAE/g d.w. and 2.21 +/- 0.15 and 2.30 +/- 0.17 mmol Fe2+ E/g d.w. for the 2 and 4 mm thick discs, respectively. The VBD treatment of 60-80-100-100 degrees C for 60 min (i.e., TV2) for 2 mm thick discs showed the highest TPC value, and no significant (P>0.05) differences were observed in AA of 2 mm thick discs dried by VDB and FD. The TPC and AA for the VBD treatment of 60-80-100-100 degrees C for 90 min and HAD treatment of 70 degrees C at 0.6 m/s for 3 h for the 2 mm thick discs were not significantly (P > 0.05) different compared to freeze dried samples. For 4 mm thick samples, the TPC and M for the VBD treatments of 60-80-100-100 degrees C, 60-90-120-120 degrees C, 70-90-110-110 degrees C, 80-90-100-100 degrees C, and 90-105-120-120 degrees C for 90 min as well as 70-90-110-110 degrees C for 60 min were not significantly (P > 0.05) different compared to those for freeze dried discs. VBD is a promising drying technology, as the resultant products possessed high TPCs and were dried in less than 1/4 of the time compared with that of FD. (C) 2011 Elsevier Ltd. All rights reserved.