Effect of frozen storage on polyphenol content and antioxidant activity of haskap berries (Lonicera caerulea L.)

BACKGROUND: Haskap berries (Lonicera caerulea L.) are processed into various products (e.g. juice, jam and chutneys). These fruits are rich in bioactive compounds, though losses can occur during frozen storage, affecting the nutritional content of the products. OBJECTIVE: To investigate the effect of freezing storage temperature (-18 and -32 degrees C) and steam blanching prior to freezing on the the total phenolic content (TPC)/total reducing capacity (TRC), total anthocyanin content (TAC) and antioxidant potential of three Haskap berry varieties; Tundra (T), Berry Blue (BB) and Indigo Gem (IG). METHODS: Berries were stored at -18 or -32 degrees C for six months, and analyzed monthly for TPC/TRC, TAC, and DPPH radical scavenging activity. Steam blanching prior to freezing was also evaluated. RESULTS: Frozen storage at -18 degrees C for six months reduced the TPC/TRC by 37.08 to 47.16%. TAC was also reduced, where the highest decrease was for BB (59.24%) followed by IG (46.34%), and DPPH scavenging activity decreased by 26.78 to 30.86%. Blanching prior to freezing improved the retention of bioactive compounds but storage at -32 degrees C did not yield significant improvements. CONCLUSIONS: Steam blanching prior to freezing followed by frozen storage at -18 degrees C is recommended for better retention of the bioactive components of haskap berries.