Effect of storage conditions on the biological activity of phenolic compounds of blueberry extract packed in glass bottles.J Agric Food Chem. 2007 Apr 04; 55(7):2705-13.JA
Recent research suggests that blueberries are rich in total polyphenols and total anthocyanins. Phenolic compounds are highly unstable and may be lost during processing, particularly when heat treatment is involved. There is no systematic study available providing information on the fate of phenolic compounds during storage and how that affects their biological activity. We provide a systematic evaluation of the changes observed in total polyphenols (TPP), total anthocyanins (TACY), Trolox equivalent antioxidant capacity (TEAC), phenolic acids, and individual anthocyanins of blueberry extract stored in glass bottles and the ability of blueberry extract to inhibit cell proliferation. The extract was stored at different temperatures (-20 +/- 1, 6 +/- 1, 23 +/- 1, and 35 +/- 1 degrees C). Two cultivars, Tifblue and Powderblue, were chosen for the study. The recoveries of TPP, TACY, and TEAC in blueberry extract after pressing and heating were approximately 25, approximately 29, and approximately 69%, respectively, for both cultivars. The recovery of gallic acid, catechin, and quercetin was approximately 25%. Ferulic acid was not detected in the final extract in both Tifblue and Powderblue cultivars. The recovery of peonidin, malvidin, and cyanidin glycosides was approximately 20% in the final extract in both cultivars. Losses due to storage were less when compared with initial losses due to processing. At -20 degrees C, no statistically significant loss of TPP, TACY, and TEAC was observed up to 30 days (P < 0.05). At 6 degrees C storage, there was a significant loss observed from 15 to 30 days. Similar results were obtained at 23 and 35 degrees C (P < 0.05). There was retention of more than 40% of ellagic and quercetin after 60 days at 35 +/- 1 degrees C. Anthocyanins were not detected after 60 days of storage at 35 +/- 1 degrees C. Significant retention (P < 0.05) was obtained for malvidin (42.8 and 25.8%) and peonidin (74.0 and 79.5%) after 60 days of storage at 23 +/- 1 degrees C in glass bottles for Tifblue and Powderblue, respectively, when compared with other individual anthocyanins. A linear relationship was observed between TEAC values and total polyphenols or total anthocyanins. A cell viability assay was performed using HT-29 cancer cell lines and anthocyanins extracted from 30, 60, and 90 days of stored extract at 6 +/- 1 and 23 +/- 1 degrees C. A significant cell proliferation inhibition percentage was observed in 30 days, although this was reduced significantly after 30-90 days. These results suggest that heating and storage conditions significantly affect the phenolic compounds and their biological activities. Frozen and low temperature storage are suggested for blueberry extract in order to retain the bioactive components.