The chemical composition of cold-pressed oils plays a crucial role in determining their oxidation rate, which is influenced by factors such as the composition of fatty acids, the presence of antioxidant and prooxidizing compounds, and external conditions, including storage time, temperature, scattered radiation, access to oxygen, and light. Natural antioxidants obtained from herbs can inhibit the process of fat oxidation. Mullein flowers (Verbascum L.) are used in many medicines due to their rich composition of bioactive compounds and high antioxidant activity. The aim of the study was to analyze the influence of lyophilized mullein flowers (Verbascum nigrum L.) addition on the oxidative stability and antioxidant activity of cold-pressed oils. Oils (rapeseed, chia seed, linseed, camelina, hemp seed) before and after the maceration process assisted by ultrasound (35°C, 30 minutes, 40 kHz) were analyzed for basic quality characteristics, fatty acid composition, a colour difference (CIELab), oxidative stability, phenolic compounds content and antioxidant activity of lipophilic and hydrophilic fraction, tocopherols, sterols and phenolic acids. Furthermore, based on obtained oxidative stability results, kinetics parameters were calculated. The conducted research has shown that mullein flower bioactive compounds increases the oxidative stability of all analyzed oils. The protection factor ranged from 1.07 to 1.63. Oils after maceration were characterized by higher oxidation activation energy (Ea) and lower constant rate of oxidation (k) almost twofold. Consequently, the calculated shelf was twice longer. The maceration process affected the oils’ initial quality, causing an increase in the level of primary and secondary products of oxidation, while not exceeding the level of Codex Alimentarius. The oils after the maceration process were characterized by a higher content of carotenoids, which resulted in a change in their colour, to the greatest extent in the case of chia seed oil (∆E=58). The oils after the maceration process were characterized by over higher content of phenolic compounds, from 351.5 to 657.0 mg GA/100g of oil. The oils were enriched mainly in gallic acid, protocatechuic acid and p-coumaric acid. The antioxidant activity of oils after maceration was found to be higher, both in the hydrophilic and lipophilic fractions, with notably greater differences observed in the lipophilic fraction. The total antioxidant activity of oils determined by the DPPH method ranged from 1.45 to 2.13 mM TEAC/ml for oils before maceration, and from 1.82 to 2.71 mM TEAC/ml for oils after maceration. On the other hand, for the ABTS method, from 1.14 to 3.13 and from 2.41 to 5.45 mM TEAC/ml, respectively. In summary, the findings from this research strongly support the conclusion that the addition of mullein flowers can substantially enhance the oxidative stability of cold-pressed oils. However, further investigation is warranted to deepen our understanding, optimize the maceration parameters, and conduct in-depth analysis of the bioactive compounds involved. These areas of research hold promising potential for further advancements in this field.
Keywords: antioxidant activity, cold-pressed oils, mullein, oxidative stability.