The impact of digestion and gut bioavailability, in vitro, on the polyphenolic associated activity of cooked culinary herbs
Culinary herbs, the use of which has increased significantly in the last decade, are known to possess health promoting properties, which are attributed mainly to their polyphenols. However, despite the fact that such herbs undergo some form of cooking prior to consumption, there is a paucity of data concerning the effects of cooking on their properties. Furthermore, little is known of the disposition of these polyphenols following digestion and absorption, and thus it is not known whether these herbs have the potential to be significant contributors of dietary polyphenols at amounts used domestically. Thus the aim of this study was to investigate: the impact of cooking processes on the polyphenolic antioxidant activity (AA) of parsley, rosemary, sage and thyme; the impact of digestion in vitro on the AA of the herbs post cooking; the role of the gut on the AA of these herbs using the Caco-2 model of intestinal transport; and whether the AA of these herbs, contributes to their anti-inflammatory and antimicrobial activities. Results showed that cooking significantly increased the AA of these herbs. AA was further enhanced following in vitro digestion with rosmarinic acid identified as the predominant polyphenol. Polyphenolic activity was detected post absorption in vitro but, possibly due to the dilute nature of the samples used, individual polyphenols were not identified. Anti-inflammatory activity of the herbs investigated was significantly associated with their AA. However, there was no association between AA and the anti-microbial activity of aqueous extracts of herbs. Some oil extracts possessed anti-microbial activity, which was enhanced by cooking. In conclusion, this study suggests that the culinary herbs investigated have the potential to contribute to dietary polyphenol intake and thus their health promoting properties. However, the biological significance of this contribution in vivo is yet to be established.