Physicochemical, antioxidant and anti-cancer activity of a Eucalyptus robusta (Sm.) leaf aqueous extract

Abstract Eucalyptus robusta (Sm.) (ER) is a widely distributed tree native to the east coast of Australia, which has also been established in numerous other countries. ER leaves contain high levels of essential oils and are rich in total phenolic compounds (TPC), which have been linked with health benefits; however, there is limited information on the bioactivity of ER leaf extracts. This study aimed to optimise water extraction conditions for TPC, prepare a spray-dried powdered extract and test its physicochemical, antioxidant and anti-proliferative properties. The results showed that optimal water extraction conditions for TPC were 85 °C, 15 min and a water-to-leaf ratio of 20:1 mL/g. Under these conditions, spray-dried powdered extract was prepared with a recovery yield of 85%. The extract was water-soluble and had a TPC level of 407 mg GAE/g. It also possessed potent antioxidant capacity, comparable to pure ascorbic acid, but higher than pure α-tocopherol. In addition, the powdered extract demonstrated significant activity against a panel of cancer cell lines, which included cancers of the pancreas, breast, lung, brain, skin, colon and ovary. Of note, the ER extract exerted a more significant toxic effect on pancreatic cancer (PC) cells compared to gemcitabine, the first line chemotherapeutic agent for PC. We suggest that future studies should purify individual bioactive compounds from ER for further investigation of its potential health promoting and anti-cancer activity.