Effect of thermal treatment on phenolic composition and antioxidant activities of two celery cultivars

Various thermal processing treatments (blanching 3 min, boiling 10 min or steaming 10 min) of Shengjie celery (Apium graveolens L.) and Tropica celery (Cryptotaenia japonica Hassk.) were studied for the effects on the levels of caffeic, p-coumaric, ferulic acid, apigenin, luteolin, kaempferol and total phenolics (TPC) as well as on the antioxidant capacity by the DPPH (1, 1-diphenyl-2-picrylhydrazyl) and ABTS+ [2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonate)] methods. Significant (p < 0.05) losses were found in boiled celery in TPC, 41.2%; DPPH, 40.6% and ABTS+, 35.2% on average. Blanching gave less extensive reductions in TPC, 37.8%; DPPH, 21.0% and ABTS+, 27.7% on average. Steaming had the most modest effect. The two cultivars exhibited different responses. Steaming did not cause losses in TPC and DPPH in Tropica celery. A significant positive correlation between antioxidant capacity (DPPH and ABTS+) values and the contents of flavonols or total phenolics acids was observed in this study.