Development of a novel gold nanoparticle-based method to determine antioxidant capacity of Brassica oilseeds, white flakes and meal.

Antioxidant capacity (AC) of Brassica oilseeds, white flakes and meal was determined by a new spectrophotometric method. The proposed assay (AuNP) based on the formation of gold nanoparticles (AuNPs) in an acetic buffer medium (pH=4.6) was compared with the previously described silver nanoparticle-based (AgNP), ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and Folin-Ciocalteu (FC) procedures. The novel AuNP method was validated using standard antioxidants such as phenolic acids and quercetin. The AC of rapeseed, white flakes and meal varied from 10.0 to 86.7µmolsinapicacid(SA)/g, 26.5-160.3µmolSA/g, 6.8-103.0µmolSA/g, 23.0-259.3µmolSA/g and 6.9-92.1µmolSA/g for AuNP, AgNP, FRAP, DPPH and FC methods, respectively. The proposed AuNP method is simple, precise (intra-day RSD=0.27-2.11% and inter-day RSD=2.05-4.87%) and accurate (recovery=96.2-104.3%) and can be useful in the routine analysis of the AC.

Optimisation of ultrasound-assisted extraction of natural antioxidants from mustard seed cultivars.

BACKGROUND: Modified mustard varieties can produce edible oil with reduced amounts of erucic acid and glucosinolates and enhanced antioxidant potential. Therefore, this work focused on the optimisation of the ultrasound-assisted extraction of compounds with high antioxidant capacity from three white mustard seed cultivars using response surface methodology. RESULTS: The predicted optimum solvent polarity (57.2, 56.5 and 57.6) and ultrasound power-to-sonication time ratio (4.5, 4.8 and 4.3 W min(-1)) resulted in antioxidant capacities determined by the ferric-reducing antioxidant power (FRAP) assay [54.37, 65.75 and 68.55 mmol Trolox equivalent (TE) kg(-1)] and the 2,2'-diphenyl-1-picrylhydrazyl (DPPH) method (141.65, 175.26 and 185.10 mmol TE kg(-1)) and total phenolics content (23.70, 27.16 and 11.29 mg sinapic acid g(-1)) for extracts obtained from one traditional and two modified mustard seed varieties. The highest FRAP and DPPH values (69.51 and 197.73 mmol TE kg(-1)) revealed 50% methanolic extract prepared from modified mustard seed cultivar without erucic acid and glucosinolates treated with ultrasound for 30 min (ultrasound power/ultrasound time = 4 W min(-1)). CONCLUSION: Ultrasound-assisted extraction was found to be a more rapid, convenient and appropriate extraction method with higher yield of antioxidants, shorter time and lower solvent consumption in comparison to conventional extraction.

Antioxidant Capacity of Rapeseed Extracts Obtained by Conventional and Ultrasound-Assisted Extraction.

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.

Comparison of a silver nanoparticle-based method and the modified spectrophotometric methods for assessing antioxidant capacity of rapeseed varieties.

The antioxidant capacity of 15 rapeseed varieties was determined by the proposed silver nanoparticle-based (AgNP) method and three modified assays: ferric reducing antioxidant power (FRAP), 2,2'-diphenyl-1-picrylhydrazyl (DPPH) and Folin-Ciocalteu reducing capacity (FC). The average antioxidant capacities of the studied rapeseed cultivars ranged between 5261-9462, 3708-7112, 18864-31245 and 5816-9937 µmol sinapic acid (SA)/100g for AgNP, FRAP, DPPH and FC methods, respectively. There are significant, positive correlations between antioxidant capacities of the studied rapeseed cultivars determined by four analytical methods (r=0.5971-0.9149, p<0.05). The comparable precision for the proposed AgNP method (RSD=1.4-4.4%) and the modified FRAP, DPPH and FC methods (RSD=1.0-4.4%, 0.7-2.1% and 0.8-3.6%, respectively), demonstrate the benefit of the AgNP method in the routine analysis of antioxidant capacity of rapeseed cultivars. The principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used for discrimination the quality of the studied rapeseed varieties based on their antioxidant potential determined by different analytical methods. Three main groups were identified by HCA, while the classification and characterisation of rapeseed varieties within each of these groups were obtained from PCA. The chemometric analyses demonstrated that, rapeseed variety S13 had the highest antioxidant capacity, thus this cultivar should be considered as the richest source of natural antioxidants.

A silver nanoparticle-based method for determination of antioxidant capacity of rapeseed and its products.

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.