Effects of temperature and time on polyphenolic content and antioxidant activity in the pressurized hot water extraction of deodorized thyme ( Thymus vulgaris ). http://dx.doi.org/10.1021/jf3027759

Abstract

The effects of temperature (50 − 200 ° C) and contact time (5 − 30 min) on the pressurized hot water extraction of deodorized thyme were explored for antioxidant activity, polyphenol pro fi les, and total antioxidants. Six not previously reported polyphenolic compounds were identi fi ed in thyme. An inverse correlation was found between the antioxidant activity and totalantioxidants with the amount and diversity of polyphenols. The highest total extract yield and antioxidant activity were obtained at 200 ° C, although maximum polyphenol extraction yields of hydroxycinnamic acids, fl avones, fl avonols/ fl avanones, and total polyphenols were detected at 100 ° C and 5 min. Higher temperatures and longer exposure times reduced extract polyphenoldiversity. Dihydroxyphenyllactic acid was the only phenolic compound for which extraction yield increased with temperature, probably as a product of the thermal degradation of rosmarinic acid. Consequently, for extracting phenolics from thyme, 100 ° C and 5 min would be appropriate operating conditions, whereas antioxidant-active nonphenolic compounds were favored at highertemperatures and exposure times.