Abstract
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.
Highlights
Rapeseed (Brassica napus) is cultivated predominantly as winter or semi-winter form in Europe and Asia, respectively,J Am Oil Chem Soc (2014) 91:2011–2019 whereas spring-sown canola types are more suited to the climatic conditions in Canada, northern Europe and Australia
The antioxidant capacities (AC) and total phenolics content (TPC) in the studied rapeseed cultivars were determined by the ferric reducing antioxidant power (FRAP), cupric reducing antioxidant capacity (CUPRAC), DPPH, ABTS and Folin– Ciocalteu (FC) methods, respectively
The Pearson correlation test was used to calculate the correlations between AC determined by different analytical methods and TPC
Summary
Rapeseed (Brassica napus) is cultivated predominantly as winter or semi-winter form in Europe and Asia, respectively,J Am Oil Chem Soc (2014) 91:2011–2019 whereas spring-sown canola types are more suited to the climatic conditions in Canada, northern Europe and Australia. It is known that, rapeseed gives a considerable yield of oil (around 45 %). Rapeseed cultivars classified as winter (requiring vernalization) and spring (without vernalization) differ in the vernalization requirements for flowering, which would affect the yielding and antioxidants content in seed and oil [1,2,3,4]. Cultivars strongly reduced in erucic acid and glucosinolates (00 quality), but rich in bioactive compounds give one of the healthiest vegetable oils for human consumption. Production of rapeseed oil with modified fatty acid composition and rich in antioxidants is possible through breeding of new double low rapeseed varieties and genetic engineering techniques. Improved knowledge on the AC analysis of rapeseed varieties would assist in modernization of technological process of rapeseed oil with high content of bioactive compounds
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