The grape seeds were washed with excess water to remove adhering materials and sun-dried. Powder form of grape seeds were homogenizd with a mixer (MC-811C,Novita,Korrea) at high speed. Two forms of grape seeds (2.0g) - whole and powder forms -were placed single layer in a Pyrex Petri dish (8.0 cm dimeter) and roasted at 50,100,150 or 200度C for 10,20,30,40,60,90 or 120 min, respectively (43 treatments including contorl), in an electric muffle furnace (Mode DMF-802 , Daeil Engineering , Korea).
2.3 Prearation of 70% ethanol extracts of grape seeds
Raw or heat treated grape seeds (0.1g) were extracted overnight whit 10mL of 70%ethanol solution in a shaking incubator(100rpm) at room temperature. Then the extracts were centrifuged at 1000g for 15 min. The supernatans were filtered through a Whatman No.1 filter paper. The 70%ethanol extracts of whole(WGSE) or powder grape seeds (PGSE) were diluted 5-fold with 70% ethanol and used for the determination of antioxidant activity.
2.4. Total phenolic contents
antioxidtive and radical scavenging activity of proanthocyanidins had been reported(Ariga,Koshiyama,& Fukushima,1998;Ricardo da Silva, darmon, Fenandez,& Mitjavila,1991.These results indicated that phenolic compounds in GSE were liberated by heat treatments. Our previous studies(Jeong et al.,2004a;Jeong et al.,204b showed that simple heat treatment converted insoluble phenolic compounds to solubie phenolics but could not cleave covalently bound phenolic compounds from rice hull. This indicates that phenolic compounds of plants should present in different bound froms depend on species. Thus, effective processing step for liberating antioxidant from different plant species may not be the same.