evaluation of factors effecting on extraction of the green tea polyphenols and antioxidant properties

introduction: tea (camellia sinensis), is the most widely beverage after water across the world. the most important chemical composition in tea is phenolic compounds (catechins) that have antioxidant and anticarcinogenic properties and are benefited for cardiovascular disease. there are two major kinds of tea, black tea and green tea. green tea, is originated in china and dates back to several thousand years ago. in the production of green tea, young leaves are rolled and oxidized to decreasing oxidation but in production of black tea, tea leaves are oxidized (fermented) for 90-120 min after rolling and then catechins are converted to complexe compounds (theaflavins and thearubigins). the conventional method for extraction of green tea polyphenols compounds are heating, boiling, cold and heathing refluxe extraction, with long extraction periods and low extraction efficiency. in this study 3 techniques for extraction of polyphenol compounds from green tea leaves were investigated and compored together.the main objective of this study was to determine the effects of differrent extraction conditions, temperature ( 40, 60, 80 and 100° c), different time ( 15, 30, 45 and 60 min ), microwave power (300, 600 and 900 % ) and ultrasound amplitude (40, 60, 80 and 100 w) on green tea polyphenol content and antioxidant activity in three methods including heat reflux extraction(hre), microwave assisted extraction(mae) and ultasound assisted extraction(uae). materials and methods: dried green tea leaves (supplied from lahijan (iran))were grinded for increasing the contact surface area between the solvent and solute. 1 g of green tea was extracted with 100 ml of water at various methods, heathing reflux extraction(hre), microwave assisted extraction(mae), by microsynth laboratory system (milestone-act-36-rev01) at 50 hz and output 2450 mhz with adjustable power output (100-1000 w), temperature 180° c and ultrasound assisted extraction (uae) in double jacket vessel by using a 25 khz ultrasonic system (model vcx 750, sonics & materials, inc., usa), at a maximum nominal power output of 750w. all measurements were carried out in triplicate. the results were analysed statistically using the minitab 16 program to determine the average value and standard error. variance analysis, with a significant level of α= 0.05% was performed to determine the effect of time, temperature, microwave power and ultrasound amplitude on polyphenols content and antioxidant activity. total phenol were determined spectrophotometerically by folin-ciocalteu method at 765 nm )hewlett- packard spectrophotometer model 8452a, rockville). the antioxidant activity evaluated with the dpph test spectrophotometrically at 517 nm. results and discussion: these results showed that polyphenol content is increased with increasing the time, temperature, ultrasound amplitude and microwave power of extraction. by increasing temperature to 80°c , time to 45 min, ultrasound amplitude from 40 to 80 and microwave power from 300 to 600, polyphenol content and antioxidant activity was increased and after that was constant. these results showed that, h.r.e require long extraction time and have low efficiency. polyphenol compounds are thermally unstable and maybe degredate in thermal processing. also, the best method for extraction was mae, because of higher yield, higher contents of pol-yphenol and shortend time and this method was very efficient in the extraction of polyphenl compounds. the efficiency of extraction by uae method is higher than hre and lower than mae method. conclusion: uae method compared to hre method is enhanced the extraction of polyphenol, facilating solvent peneteration and increase the product releasing from intracellular. this method agitated the solvent to material and increased the contact surface between material and solven, and peneteration of solvent in to the green tea leaves. uae canbe carried out at a lower temperature than hre and decreased thermal damage.