Antioxidant activity, organic acids and bioactive compounds of Andean blackberries (Rubus glaucus Benth)

Andean blackberries are considered an important source of vitamins, minerals and different phytochemicals due to their high content in polyphenols, including anthocyanins, ellagitannins and phenolic acids, which present beneficial effects in human health and prevent chronic diseases. Among other factors, harvest maturity and postharvest conditions may affect the concentration of phenolics and the antioxidant activity of the berries. In this study, the effects of harvest maturity and storage temperature on antioxidant activity, organic acids and, polyphenols and anthocyanins concentration of Andean blackberries were evaluated. Blackberries were harvested at maturity stages 3 (light red) and 5 (dark purple), packed in PET clamshells (200±10 g) and stored under room temperature (18±2°C) and cold storage (8±1°C). Organic acids (citric, malic, ascorbic) and total anthocyanins were determined by HPLC, total phenolic content with the Folin-Ciocalteu method and antioxidant activity by the DPPH method. The analyses were performed on day 1 and every 3 d during storage. At harvest, similar total organic acids, polyphenols and antioxidant activity were observed in the fruit from both maturity stages while the anthocyanins were significantly higher in the more mature fruit. What's more, some differences in the individual acids were observed. During storage and regardless of temperature, total organic acids, total anthocyanins and polyphenols content, and antioxidant activity increased in the fruit harvested at maturity stage 3. On the other hand, in the blackberries harvested at maturity stage 5, a decrease in the organic acids was observed while the anthocyanins, the phenolic compounds and the antioxidant activity remained unchanged. According to the Ecuadorian Quality Standard, blackberries can be harvested as soon as they reach the stage maturity 3. However, at this stage the fruit presented a 5-fold lower anthocyanin content and could result unacceptable for consumers due to undeveloped full color.