Antioxidant activities and total phenolic contents of various extracts from defatted wheat germ
Research highlights
► 70% ethanol extract showed the best DPPH radical scavenging power. ► 100% ethanol extract showed the highest ABTS+ scavenging activity and reducing power. ► Total phenolic contents of DWGEs were inconsistent with their antioxidant activities.
Introduction
Natural antioxidants, which are ubiquitous in fruits, teas, vegetables, cereals, and medicinal plants, have received great attention and have been studied extensively, since they are effective free radical scavengers and are assumed to be less toxic than synthetic antioxidants, such as butylated hydroxyanisole (BHA) and butylated hydroxyltoluene (BHT), which are suspected of being carcinogenic and causing liver damage (Ratnam, Ankola, Bhardwaj, Sahana, & Kumar, 2006). It is believed that an increased intake of food, which is rich in natural antioxidants is associated with a lower risk of degenerative diseases, particularly cardiovascular diseases and cancer (Perez-Jimenez et al., 2008).
Wheat is one of the major cereals and food ingredients across the world. Wheat kernel is composed of bran, germ, and endosperm morphologically. The antioxidants in wheat include carotenoids, tocopherols, flavonoids and phenolic acids. In the past years, the antioxidant activities of whole wheat and milling fractions (Liyana-Pathirana and Shahidi, 2007, Vaher et al., 2010, Zhou et al., 2004) have been widely studied. Antioxidant rich extracts have been obtained from wheat using various solvents including water, ethanol, methanol, an aqueous ethanol solution, and an aqueous methanol solution (Vaher et al., 2010, Zielinski and Kozłowska, 2000). Some studies have also reported on the antioxidant activity of roasted defatted wheat germ (Gelmez et al., 2009, Krings et al., 2000), wheat germ oils (Malecka, 2002), and wheat germ protein hydrolysates (Zhu, Zhou, & Qian, 2006b).
Defatted wheat germ (DWG), the main by-product in the wheat germ oil extraction process, contains many nutritional ingredients, such as proteins, carbohydrates, B vitamins, pigments, and minerals and some functional microcomponents (Ge et al., 2000, Zhu et al., 2006a). However, few systematic studies have been found on WG antioxidants. Furthermore, the phenolics in WG have been less treated in terms of their contents and contribution to the overall antioxidant activities of WG. As a matter of fact, due to the complex nature of phytochemicals, their antioxidant activity should be evaluated using several commonly accepted assays.
In the present study, defatted wheat germ extracts (DWGEs) were obtained using water, aqueous ethanol solutions and ethanol as solvents, and each determined for its antioxidant activities by in vitro methods, including DPPH scavenging assay, ABTS scavenging assay, reducing power, and antioxidant activity in a linoleic acid system, and for its total phenolic contents by the method of Folin–Ciocalteu reagent.
Section snippets
Materials and chemicals
Raw wheat germ (RWG) was a gift from Huai’an Xinfeng Flour Mill (Jiangsu, China). 2,2′-azinobis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) were purchased from Sigma Chemical Co. (St. Louis, USA). Linoleic acid was from Zhongchuang Bio-engineering Co., Limited. Other chemicals were of analytical grade.
Preparation of defatted wheat germ flour (DWGF)
After being removed of contaminants, RWG was defatted with n-hexane until the supernatant was colourless, and then the resulting DWG was consecutively
Extraction yields and total phenolic contents of extracts
Extraction is an important step for obtaining extracts with acceptable yields and strong antioxidant activity (Moure et al., 2001). In this experiment, the yields of DWGE ranged from 5.16% for the ethanol extract to 48.03% for the aqueous extract (Table 1), depending on the extraction solvent in the following order: water > 30% ethanol > 50% ethanol > 70% ethanol > 100% ethanol. The yield of 50% ethanol extract did not show significant difference with the 30% and 70% ethanol extracts; but the yield of
Conclusions
In this study, all the DWGEs exhibited antioxidant activities in the DPPH radical scavenging assay, the ABTS radical scavenging assay, the reducing power assay, and inhibition of linoleic acid peroxidation. The yields of the aqueous and aqueous ethanol extracts were acceptable, but the antioxidant activity of aqueous extract was low. Among the various extracts, all aqueous ethanol extracts and the ethanol extract showed high antioxidant activity, while the ethanol extract was low in yield.
Acknowledgements
This work was supported by the Fundamental Research Funds for the Central Universities (JUSRP10922) and the Agricultural Key Technology R & D Program of Jiangsu (BE 2009361-1).
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