Natural Antioxidant Enrichment of Linseed Oil: Ultrasound-Assisted Maceration with Mullein Flowers (Verbascum thapsus L.)

Abstract This study investigated the effect of natural antioxidants from mullein flowers ( Verbascum thapsus L.) on the quality and oxidative stability of linseed oil ( Linum usitatissimum L.). Ultrasonic-assisted maceration was optimized by evaluating the effects of extraction time, ultrasonic power, and flower concentration. The optimal conditions for maximising oil oxidative stability were identified as 3.31 min of ultrasound, 40 W power, and 8.56% (w/w) flower content. Under these conditions, the oxidative stability of the oil improved significantly, with an average protective factor of 1.74. Although slight increases in hydrolysis and oxidation were observed, the oils remained within acceptable quality and safety limits. Maceration also enhanced oils’ bioactive compounds content, increasing phenolic content from 68.82 to 92.57 to 368.65–419.02 mg GAE/100 g and flavonoids from 6.24 to 8.87 to 34.54–38.20 mg QT/100 g. Additionally, the macerated oils had higher antioxidant activity, chlorophyll, and carotenoid levels. While the maceration process led to a reduction in individual fatty acid groups, the loss was less pronounced than that caused by ultrasound treatment alone. Overall, ultrasonic maceration with mullein flowers effectively improved both the bioactive properties and oxidative stability of linseed oil.