Antioxidant and pro-oxidant factors in oregano and rosemary gourmet olive oils

Abstract

The study was carried out to examine the presence of antioxidants and pro-oxidants in oregano and rosemary gourmet oils. Dry, ground plant material (5% w/w) was infused to olive oil for 24, 48 and 72 hours and then it was removed by filtration. All preparations were found acceptable using a panel test. The total polar phenol content increased 3.5 and 1.7 times in oregano and rosemary gourmet oils with respect to that of the control sample. A qualitative enrichment of the methanol:water fraction of olive oil with phenolic compounds from herbs were found using HPLC. No rosmarinic acid was detected in the gourmet oils. Vanillic acid was only found in the rosemary gourmet oil. The presence of flavonoids was assessed using TLC. a-Tocopherol content of the oil matrix was not changed after herb infusion. A significant increase was found in pheophytin, a,b-carotene and lutein content of oregano flavoured oils. The oxidative stability of gourmet oils was greater to that of the control using the Rancimat test. In photo-oxidation, oregano flavoured oil was less stable than the rosemary one. Total chlorophyll content may be a critical factor for the shelf life of these preparations. Suitable labelling suggesting avoidance of light may be useful for a safe domestic use.