Fluorescence screening of antioxidant capacity in pumpkin seed oils and other natural oils

Plant oils provide a rich source of dietary polyunsaturated fatty acids (PUFAs) and mostly lipophilic antioxidants. PUFAs are both in their free form and as components of glycerolipids preferred targets of free radical‐induced oxidation, leading to the formation of highly atherogenic compounds. Thus, stabilization of polyunsaturated lipids by radical scavengers in the oils is important in order to avoid pathophysiological side effects of these essential components of our diet. To determine lipid oxidizability and its inhibition by endogenous antioxidants, we developed a simple fluorescence technique. It is based on solubilisation of the oils in aqueous buffer, labeling of the resulting emulsions with a suitable reporter fluorophore, which reflects lipid oxidation, and continuous monitoring of the decomposition process. Using this method, we found that oxidizability of the oils depended only to a limited extent on the content of lipophilic antioxidants. In addition, a smaller fraction of polar (phenolic) compounds showed comparable protective effects, especially in pumpkin seed oil, which is a non‐refined product therefore containing antioxidative components that are removed from most other edible oils during processing. Therefore, the contribution of these “minor” compounds has to be taken into account when potential biological effects of plant oils are evaluated.