Study on extraction of natural antioxidants from old tea leaves
Abstract
Natural antioxidants are of great interest in food industry recently from the aspect of their ability to replace synthetic antioxidants whose usehas been restricted. Tea is well known as the source of many antioxidant compounds, but there are few studies on the use of fresh old tea leaves, although they are abundant in Vietnam as well as the surrounding area of Da Nang. Using DPPH method to evaluate the radical scavenging activity and HPLC to monitor the EGCG level, the old tea leaves from Da Nang were proven to contain large amount of antioxidants, which could be retrieved for production of natural antioxidant additive. From the result of the designed experiment, we found the best conditions for extraction of antioxidants with ethanol, according to which at temperature of 82.2oC,ethanol concentration of 72.5o, extraction time of 32.2 min, the EGCG level in the extract was maximum, meanwhile at temperature of 82.2oC, ethanol concentration of 75o, extraction time of 32.2 min, the extract had the highest antioxidant activity. Also in this study, we proposed the procedure for obtaining antioxidant extract in form of powder, which was cleaned almost completely from impurities and was stable during storage with absence of air and light.