Effect of Thawing Conditions on Polyphenol Content and Antioxidant Activity of Frozen Haskap Berries (Lonicera caerulea L.)

The effect of different thawing methods on three haskap berry (Lonicera caerulea L.) varieties, Tundra (T), Berry Blue (BB) and Indigo Gem (IG), was investigated. Methods included thawing the frozen berries at room temperature (25 ± 2 °C), refrigerated temperature (4 °C) and using a microwave oven. All the berry varieties were analyzed for their total phenolic content (TPC)/total reducing capacity (TRC), total anthocyanin content (TAC) and antioxidant potential (DPPH˙ radical scavenging activity). The TPC/TRC, TAC and DPPH˙ scavenging activity ranges in the fresh fruits were 6.17-8.42 mg GAE/ g FW, 4.49-6.97 mg C-3-G E/ g FW, and 78.70-89.55 %, respectively. Frozen storage for six months followed by consequent thawing at the standard conditions (room temperature) caused 35.85-44.73, 32.14-53.23, and 26.28-29.57 % reductions in the TPC/TRC, TAC, and DPPH˙ scavenging activity, respectively. The highest reduction occurred in the Berry Blue variety followed by that of Indigo Gem. Refrigerated thawing did not significantly improve the retention of phenolic compounds and anthocyanins. Microwave thawing could be achieved in significantly shorter time (17.31 min) as compared to room temperature (12.00 h) and refrigerated thawing (22.00 h) and could significantly improve the retention of phenolics, anthocyanins and antioxidant potential. The corresponding reductions in the TPC/TRC, TAC, and DPPH˙ scavenging activity of different varieties ranged from 24.97%-39.87%, 18.92%-47.22%, and 21.39%- 27.29 %, re-spectively. Thus, further investigation into the industrial application of microwave thawing is recommended to maximize the retention of bioactive compounds in products manufactured from frozen haskap berries.