Dandan Tao, Ling Pan and Yan Zhang

In this investigation, the antioxidant activity of rosemary extract in peanut oil (PO) and flaxseed oil (FO) during accelerated storage has been studied and compared. Rosemary extracts were prepared in two forms, i.e. powdery rosemary extract (PRE) and oily rosemary extract (ORE). The changes of fatty acids composition during 24 days of storage were measured, and the correlations between unsaturated fatty acids (18: 3, 18: 2 and 18:1) and parameters of oil oxidation (PV, p-AV and TBARS) were analyzed, respectively. PRE was more effective than ORE in stabilization of both PO and FO samples. PO samples showed significantly higher oxidative stability than FO samples during 24 days of storage. Negative correlations were found in 18:3 vs. peroxide value in PO and FO samples. Positive correlations were found in 18:1 vs. p-AV and TBARS in PO and FO samples, and in 18:2 vs. p-AV and TBARS only in FO samples. Hence FO samples were more susceptible to oxidation than PO samples because of its significantly higher content of 18:3. Moreover, rosemary extract effectively inhibited the oil oxidation potentially by retarding the decomposition of 18:1 for PO samples, while by retarding the decomposition of 18:2 and 18:1 for FO samples.

Practical applications: Oxidation of unsaturated fatty acids is one of the major concerns in oil consumption and storage. The addition of natural antioxidants is a potential way to retard the oxidation of oils and thus to extend the shelf life of oil products. Rosemary extract has been reported to show good antioxidant activity and could act as a good resource to inhibit oil oxidation. The results in this study not only confirmed the effectiveness of rosemary extract in stabilizing oil during storage, but also suggested different anti-oxidative pathways in different oil system in relation to their different fatty acid compositions. Therefore, rosemary extract may have great market potential as food antioxidant in edible oils.