Studies of the correlation between antioxidant properties and the total phenolic content of different oil cake extracts

► Cakes from linseed, rapeseed, camelina and white mustard are sources of antioxidants. ► Different cakes possess different activities, depending on antioxidant assay used. ► No correlation was found between antioxidant activity and phenolic content. ► Phenolics are not the only contributors to the antioxidant activities of the cakes. ► Methanolic extracts are better reductants, radical scavengers and chelators than ethanolic ones that were more active in emulsion. In this work, quantitative correlations between the antioxidant properties and the total phenolic content (TPC) of different oil cake extracts were studied. The oil cakes from camelina (Camelina sativa), linseed (Linum usitatissimum), rapeseed (Brassica napus), and two varieties of white mustard (Sinapis alba) were analysed as potential sources of antioxidant compounds. Two solvents of different polarity were used to obtain the extracts, resulting in great variation in antioxidant activity. The highest phenolic content was observed for white mustard, followed by camelina, rapeseed and linseed. The antioxidant properties were evaluated by determination of their reducing capacity, free radical scavenging activity and metal chelating ability, by the β-carotene bleaching method and as the effectiveness of inhibition of conjugate diene and triene formation in the bulk oil. The methanolic extracts exhibited higher reducing power (max. rapeseed), 2,2-diphenyl-1-picrylhydrazyl (DPPH·) scavenging activity (max. rapeseed) and chelating ability (max. linseed), while the ethanolic extracts were more efficient in the β-carotene bleaching test (max. camelina). White mustard extracts inhibited conjugate diene and triene formation the most. These various antioxidant activities were compared to the synthetic antioxidant butylated hydroxytoluene (BHT). A lack of positive correlations among the different antioxidant activity assays and total phenolic contents was observed.