A novel silver nanoparticle-based (AgNP) method and two modified procedures, ferric reducing antioxidant power (FRAP) and 2,2'-diphenyl-1-picrylhydrazyl (DPPH), were used for determination of antioxidant capacities of the ethanolic, methanolic, methanolic-aqueous (1 : 1 v/v) and aqueous extracts of rapeseed and its products. The AgNP method based on the electron-transfer reaction between silver ions and antioxidants in an optimized ammonium buffer medium (pH = 8.4) and determination of silver nanoparticle formation has been elaborated. The novel AgNP method was validated using sinapic acid, gallic acid, caffeic acid, ascorbic acid and quercetin as standard antioxidant solutions in concentration ranges of 0.03-0.21 µmol mL(-1), 0.02-0.20 µmol mL(-1), 0.01-0.18 µmol mL(-1), 0.03-0.30 µmol mL(-1) and 0.001-0.009 µmol mL(-1). The calculated detection (DL = 0.01, 0.02, 0.009, 0.02 and 0.0004 µmol mL(-1) for sinapic, gallic, caffeic, ascorbic acids and quercetin, respectively) and quantification limits (QL = 0.04, 0.06, 0.03, 0.08 and 0.001 µmol mL(-1) for sinapic, gallic, caffeic, ascorbic acids and quercetin, respectively) confirm linearity concentration ranges for determination of antioxidant capacity by AgNP assay. The average antioxidant capacities of the studied rapeseed samples ranged between 14.7 and 126.2 µmol sinapic acid per gram for the proposed AgNP method, 7.4-112.7 µmol sinapic acid per gram for the FRAP method and 39.1-339.8 µmol sinapic acid per gram for DPPH assay. The methanol-water mixture (1:1 v/v) was the most efficient solvent for extraction of antioxidants from the studied rapeseed samples. There are significant, positive correlations between the novel AgNP and the modified FRAP, DPPH and FC methods for all extracts of the studied rapeseed samples (r = 0.7564-0.8516, p < 0.001). Satisfactory values of precision (RSD = 1.2-4.4%) and accuracy (recovery = 95.6-104.6%, except methanolic extracts) demonstrate the benefit of the proposed AgNP method for analysis of the antioxidant capacity of rapeseed samples. Results of the principal component analysis (PCA) indicate that there are differences between the total amounts of antioxidants in rapeseed samples extracted by different solvents.

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Ultrasound-assisted extraction (UAE) and conventional solid–liquid extraction were applied to extract total antioxidants from two rapeseed varieties. The antioxidant capacities (AC) of winter and spring rapeseed cultivars were determined by four different analytical methods: ferric reducing antioxidant power (FRAP), cupric reducing antioxidant capacity (CUPRAC), 2,2′-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS). The average AC of the studied rapeseed cultivars ranged between 4.21–10.03 mmol Trolox (TE)/100 g, 7.82–10.61 mmol TE/100 g, 8.11–51.59 mmol TE/100 g, 22.48–43.13 mmol TE/100 g for FRAP, CUPRAC, DPPH and ABTS methods, respectively. There are positive correlations between total phenolics (TPC = 804–1625 mg sinapic acid (SA)/100 g) and AC of the studied rapeseed extracts (r = 0.2650–0.9931). Results of the principal component analysis (PCA) indicate that there are differences between the total amounts of antioxidants in rapeseed samples extracted by different extraction techniques. Rapeseed extracts obtained after 18 min of ultrasonication revealed the highest content of total antioxidants. The UAE is a very useful, efficient and rapid technique of oilseed samples preparation for determination of AC by different analytical methods.

Physicochemical characteristics, antioxidant capacity (AC), and sensory quality of rapeseed oils available on the Polish market were analyzed and compared. The fatty acid composition (saturated fatty acids = 6.91–7.58%, monounsaturated fatty acids = 64.14–66.14%, and polyunsaturated fatty acids = 27.22–30.17%), color (T420 = 54.5–83.8%), amounts of free fatty acids (0.02–0.07%), primary (PV = 0.04–2.04 meq O2 kg−1) and secondary (AV = 1.02–3.21) oxidation products, phosphorus (0.38–1.62 mg kg−1), chlorophyll (0.002–0.068 mg kg−1), and polycyclic aromatic hydrocarbons (Σ4PAH = 0.00–2.50 μg kg−1) in the commercial rapeseed oils meet the requirements of the European Food Regulation and Codex Alimentarius standards. Moreover, total phenolic content (TPC = 40.3–467.9 mg SA kg−1) in the studied oils significantly differs from each other. However, the AC of rapeseed oils was analyzed using the novel iron oxide nanoparticle‐based (IONP = 5552.1 − 18,510.2 μmol TE/100 g) method and the modified ferric reducing antioxidant power (FRAP = 55.7–280.3 μmol TE/100 g), cupric reducing AC (CUPRAC = 79.6–784.0 μmol TE/100 g), 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH = 185.7–516.7 μmol TE/100 g), and 2,2′‐azinobis‐3‐ethylbenzothiazoline‐6‐sulfonic acid (ABTS = 465.6–2142.6 μmol TE/100 g) assays. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied for discrimination of the refined rapeseed oils based on fatty acid composition, physicochemical parameters, AC, and sensory properties.

Two electron transfer (ET) reaction-based methods, ferric reducing antioxidant power (FRAP) and Folin-Ciocalteu (FC) reducing capacity, were used for the determination of total antioxidant capacity of vegetable oils (rapeseed, palm and extra virgin olive oils), meat samples (poultry and pork) and potatoes before and after the frying process under domestic frying conditions. Before frying, potatoes had the highest FRAP value (276.7 μmol Trolox/100 g), whereas extra virgin olive oil revealed the highest FolinCiocalteu Index (FCI=443.2 μmol Trolox/100 g). Antioxidant capacity of methanolic extracts of raw meat (9.0-9.4 μmol Trolox/100 g and 135.7-160.1 μmol Trolox/100 g for FRAP and FC methods, respectively) was lower than FRAP (133.4-149.6 μmol Trolox/100 g) and FCI (156.2-443.2 μmol Trolox/100 g) of unheated rapeseed and extra virgin olive oils. However, antioxidant capacity of the studied food samples changed after frying process. Positive correlations (correlation coefficients ranged between 0.5742 and 0.9942) were found between the two analytical methods used to determine the antioxidant capacity of unprocessed and processed food products. The results of principal component analysis (PCA) indicate that there are differences between total amounts of antioxidants in raw and fried food products.