Growing consumption of cold-pressed plant oils and a wider range of available oil types have been observed on the market over the last few years. Currently, the most popular are olive oil, palm oil, rapeseed oil, soybean oil, and sunflower seed oil, but less common oils such as evening primrose seed oil, hemp seed oil, flaxseed oil, milk thistle seed oil, nigella seed oil, and pumpkin seed oil are gaining in importance. The global cold-pressed oil market value was $24.62 billion in 2018 and is expected to reach $36.40 billion by 2026, which is a 5.3% CAGR¹. The reasons are the growing health awareness of the human population, increasing knowledge of the bioactive compounds detected in various oilseeds and their contribution to diet-related and skin disease prevention and treatment. Cold-pressed oils retain most of their bioactive and nutritional value since the oil’s temperature during the pressing process lies below 50 °C. Therefore, for health benefits, nutritionists advise regular diet supplementation with small amounts (1–3 tablespoons per day) of cold-pressed oils, due to higher yields of pro-healthy compounds over refined oils. They may regulate the blood lipid profile and insulin level, as well as offer anticancer and antioxidant activity^2,3. Another trend observed is the modification of food products and nutraceuticals to improve their nutritional composition and positive impact on human health through the addition of edible oils^3,4. In particular, in animal food products, the partial replacement of the fat or meat fraction with a plant oil/protein fraction is more frequent^4,5.

Oilseeds are rich in n-3 and n-6 essential fatty acids, protein, carbohydrate, fibre, vitamins, minerals, and many small bioactive components belonging to different classes, including phytosterols, tocopherols, phenolic compounds, flavonoids, carotenoids, and bioactive peptides. For instance, hemp oil has a high content of antioxidants, such as phenolic compounds, tocopherols, and phytosterols as well as flavonoids, including flavanones, flavanols, flavonols and isoflavones. Milk thistle oil is a source of silymarin and mixtures of various flavonolignans, i.e. silydianin, silychristin, silybin, and isosilybin, and flaxseed oil is rich in phenols, flavonoids, α- and δ -tocotrienol, and carotenoids, including lutein and β-carotene^6–8. The presence of proteins and peptides in cold-pressed oils is less commonly discussed, though they are an important component that may influence the oils’ stability and also cause an allergenic response in sensitive consumers^2,3.

The use of cold-pressed oil by the food industry is anticipated to reach the highest growth rate in the next few years. The oils’ online retail distribution channel is also expected to grow considerably¹. Since unprocessed oils reach high prices and are a desirable commodity on the market, they are products susceptible to counterfeiting^9,10. Therefore, there is an urgent need to implement modern and sophisticated analytical methods to detect adulterations of high-price cold-pressed oils derived from various oleaginous seeds and fruits. Many advanced untargeted approaches have been introduced recently to address authenticity issues of edible oils, based on liquid or gas chromatography mass spectrometry (LC–MS or GC–MS) techniques for measuring various polar, nonpolar, and volatile compounds, as well as spectroscopic techniques including nuclear magnetic resonance (NMR) spectroscopy, near-infrared spectroscopy (NIR), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), or fluorescence, where the result is achieved by analysing the whole spectrum of oils and development of statistical models^11–14.

When food fraud is considered in terms of food safety issues, and related, for example, to food allergenicity, a targeted approach based on identifying specific proteins and peptide markers could be a method of choice. From this aspect, MS-based proteomic analysis has the advantage of detecting the adulteration of unrefined oils and tracing potential allergenic proteins present in the sample, simultaneously during one MS run. Depending on the type of oil, the method of protein extraction and assessment methodology, the protein content of edible oils varies from 0.01 to 14.8 ppm^2,15. Allergenic proteins, such as cruciferin (11S globulin) and napin (2S albumin) have been identified in rapeseeds (Brassica napus) but also in unrefined rapeseed oil using a gel-based LC–MS method; however, these allergens have not been shown in refined rapeseed oil¹⁶. Moneret-Vautrin et al.¹⁷ found that the residual allergenic proteins, i.e. Ara h1, in peanut oil can cause an allergic reaction in infants with atopic dermatitis sensitive to peanut, whereas, Blom et al.¹⁸ estimated the risk of allergenic reactions to refined peanut oil as extremely low.

This study aimed to identify the unique peptide markers specific to oilseed species and proteins present in cold-pressed oils using proteomic techniques. An additional goal was to assess the presence of allergens. The protein and peptide composition of oils produced from 10 oilseeds, namely coconut, evening primrose, hemp, flax, milk thistle, nigella (also known as black cumin), pumpkin, rapeseed, sesame, and sunflower seeds, was analysed using ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF–MS/MS). The markers identified could be useful for the detection of adulteration.