Oak Acorns as Functional Foods: Antioxidant Potential and Safety Assessment.

Abstract

With the growing interest in natural and health-supporting foods, oak acorns (Quercus robur) are gaining renewed attention for their nutritional and antioxidant potential. This study explored how different processing methods affect bioactive compounds in three acorn-based products: raw acorn flour, roasted "coffee," and washed-and-roasted "super coffee." Extracts were obtained using methanol, acetone, and hexane to evaluate total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity via ABTS, DPPH, CUPRAC, FRAP, and TRP assays. Methanol proved to be the most effective solvent, extracting up to 66.53 mg GAE/g dw of phenolics in raw flour and 76.50 mg GAE/g dw in roasted "coffee," reflecting a 15% increase in TPC after thermal treatment. However, the same treatment resulted in a 17% decrease in flavonoid content, from 181.5 mg RE/g dw in raw flour to 150.67 mg RE/g dw in "super coffee." Antioxidant activity followed a similar pattern, with methanol extracts showing the highest values, up to 584 mg TE/g dw in the CUPRAC assay and 126.7 mg TE/g dw in ABTS. Safety was also assessed through the quantification of 16 priority polycyclic aromatic hydrocarbons (PAHs). The total PAH levels in the roasted "coffee" and "super coffee" samples were 222 ng/g dw and 290 ng/g dw, respectively. Importantly, PAH4 compounds, used as key safety indicators in EU regulations, were present in low concentrations, primarily as benzo[a]anthracene (34.3-39.8 ng/g), and none exceeded the maximum limits established for cocoa-based products. Benzo[a]pyrene, a major carcinogen, was not detected. The results confirm that acorns of Quercus robur, especially in their native flour form, are rich in antioxidants, naturally gluten-free, and safe when thermally processed, making them a strong candidate for use in functional foods.