Abstract
Brassica napus L. is rich in phenolic components and it has natural antioxidant characteristics which are important to human health. In the present study, the total phenolic and flavonoid contents of developing seeds of yellow- and black-seeded B. napus were compared. Both phenolic and flavonoid contents were significantly higher at 5 weeks after flowering (WAF) in black seeds (6.44 ± 0.97 mg EE/g phenolics and 3.78 ± 0.05 mg EE/g flavonoids) than yellow seeds (2.80 ± 0.13 mg/g phenolics and 0.83 ± 0.01 mg/g flavonoids). HPLC–DAD–ESI/MS analysis revealed different content of 56 phenolic components between yellow and black-seeded B. napus, including kaempferol-3-O-glucoside, isorhamnetin-3-O-glucoside, quercetin-3-O-sophoroside, procyanidin B2 ([DP 2]), which were significantly reduced in yellow seeds compared with black seeds. Applying the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical assay, we found maximum clearance of DPPH and ABTS in the late developmental stages of yellow and black seeds. Additionally, the ferric reducing antioxidant power (FRAP) value maximized at 5 WAF in black seeds (432.52 ± 69.98 μmol Fe (II)/g DW) and 6 WAF in yellow seeds (274.08 ± 2.40 μmol Fe (II)/g DW). Generally, antioxidant ability was significantly reduced in yellow-seeded B. napus compared to black rapeseed, and positive correlations between antioxidation and flavonoid content were found in both yellow- and black-seeded B. napus.
Highlights
Rapeseed (Brassica napus L.) is the most broadly cultivated Brassica species in the world for its high oil (~50%) and protein (~25%) content [1]
Comparison of Total Phenolic and Flavonoid Content in Developing Seeds of Yellow- and Black-Seeded. We found that both total phenolic and flavonoid content in black rapeseed maximized at 5 weeks after flowering (WAF) and declined thereafter, whereas, total phenolic and flavonoid content continued to increase as the yellow seeds developed (Figure 1)
Qu et al reported that polymeric phenolic compounds started accumulating at 21 days after pollination (DAP), and a significant difference between yellow and black rapeseed was observed from 28 DAP to 49 DAP [25]
Summary
Rapeseed (Brassica napus L.) is the most broadly cultivated Brassica species in the world for its high oil (~50%) and protein (~25%) content [1]. Yellow-seeded B. napus has been evaluated as having significant advantages over black rapeseed, such as improved nutrients (oil and protein), and reduced anti-nutrients (phenolic compounds, lignin and fiber). These anti-nutrients are not Molecules 2018, 23, 1815; doi:10.3390/molecules23071815 www.mdpi.com/journal/molecules. In Aronia prunifolia hybrids, cyanidin glycosides have been proved to inhibit HeLa human cervical tumor cell proliferation [21] These chemicals greatly reduce the quality of rapeseed oil and meal [22]. The comprehensive accumulation pattern of phenolic compounds in developing rapeseeds, accompanied by analysis of the correlation between phenolic content and antioxidant activity, will help to elucidate the character of yellow rapeseeds, the variation in seed color related gene expression, and provide guidance for rapeseed breeding
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