Original Research ArticlePhytochemical composition and antiproliferative activities of bran fraction of ten Maryland-grown soft winter wheat cultivars: Comparison of different radical scavenging assays
Introduction
Wheat and its products are an important part of the human diet. Wheat is the third most important field crop in both planted acreage and gross farm receipts, behind corn and soybeans in US (USDA, 2012). It is one of most important agricultural product commodities consumed globally. Wheat bran, a byproduct of the flour milling industry, is an important, inexpensive and readily available source of dietary fiber. It has primarily been used as animal feed, but wheat and other cereals bran have gained importance in various food product formulations and dietary supplement markets due to high fiber and bioactive constituents (Doty, 2012). This has been attributed to the recent epidemiological studies with whole grain foods which suggest that whole grains provide health-promoting protective effects against certain types of cancers, cardiovascular diseases and type-2-diabetes (de Munter et al., 2007, Mellen et al., 2009, Schatzkin et al., 2007). Most of the health beneficial effects of the whole grains are due to bioactive phytochemicals, vitamins, minerals, and fiber present in high concentration in the bran fraction of the grain.
The bran fraction constitutes approximately 15–20% of dry grain weight. It usually comprises the outermost portion of the grain composed of several layers (pericarp, testa, and hyaline) that are characterized by distinct structures and composition. The inner layer is composed of aleurone cells, and it constitutes approximately 6–7% of the bran. The percent values for bran fractions vary with the type of wheat cultivar (Hemery et al., 2012).
There have been large numbers of peer-reviewed publications on antioxidant capacity of wheat bran fraction in recent years. Significant antioxidant capacity and phenolic compounds have been detected in wheat, wheat bran and wheat-based products (Liyana-Pathirana and Shahidi, 2007, Moore et al., 2005, Moore et al., 2006a, Zhou et al., 2004a, Zhou et al., 2004b, Zhou et al., 2005). In addition, phenolic acids exist in both soluble and insoluble bound forms in wheat grains, and around 90% of total phenolic acids are in insoluble forms, tightly bound to cell wall polymers. Thus, it is difficult to extract all the forms of phenolic compounds that are responsible for antioxidant capacities from wheat grains. Moreover, the wide variations in the reported antioxidant capacity values of these compounds stems from the differences in procedures used for the assay of antioxidants and the methodologies used for extraction of antioxidants (Luthria, 2006). Recently, researchers have developed a new procedure to measure the antioxidant capacities of insoluble bound phenolic acids in foods and cereal grains (Celik et al., 2013, Gokmen et al., 2009, Serpen et al., 2008, Tufan et al., 2013). Apak et al. (2007) utilized the QUENCHER-CUPRAC method for assaying total antioxidant capacity, whereas Serpen et al. (2007) measured antioxidant capacity in the insoluble portion of the food by QUENCHER procedure using ABTS+ or DPPH.
In previous publications by Zhou et al. (2004b), the authors described phytochemicals and antioxidant properties of 7 wheat varieties from 4 countries. In another study the same group carried out antioxidant capacity and phytochemical analysis of hard red winter wheat varieties (Zhou et al., 2004a). In a very recently published study, the authors reported phytochemicals composition, antioxidant activities, and antiproliferative activities of 10 wheat flour samples (Lv et al., 2012). In a continuation of our research on wheat, we report here a systematic comparison of 3 classes of phytochemicals (phenolic acids, tocopherols, and carotenoids) from bran fraction of 10 soft red winter wheat (Triticum aestivum L.) varieties commonly cultivated in the mid-Atlantic region of the United States. In this study, we examine the scavenging activities against hydroxyl (HO), 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′azinobi-3-ethylbenzothiazoline-6-sulfonic acid (ABTS+), and peroxyl radicals along with total phenolic content by commonly used Folin-Ciocalteu assay. In addition, reduction of oxidative stress in human liver cancer Hep G2/C3A cells, and antiproliferative activities in HT-29 and Caco-2 human colon cancer cells of soft winter wheat bran samples are also investigated.
Section snippets
Wheat samples
Ten soft red winter wheat (Triticum aestivum L.) varieties, SS520, SSMPV57, SS5205, USG3555, USG3665, USG3315, Branson, Shirley, Jamestown and Chesapeake, representing a sample of elite commercial cultivars currently grown in the mid-Atlantic region of the United States, were grown in the field at Clarksville (MD, USA) in yield trial plots 4 m long × 1 m wide at a density of approximately 350,000 plants ha−1. Plots were planted following a crop of corn on October 2010. Plots were fertilized with a
Analysis of ferulic acid
Ferulic acid was the predominant phenolic acid identified in all bran fractions. Similar results were reported in previous studies on wheat bran (Mateo Anson et al., 2008, Zhou et al., 2004b). The concentration of total soluble (free and conjugated) ferulic acid ranged from 4.48 μg/g in SS MPV57 wheat bran to 7.02 μg/g in USG 3665 wheat bran sample (Table 1). The concentration of total soluble (free and conjugated) ferulic acid in all samples was less than 1%. Over 99% of the ferulic acid was
Conclusion
In summary, bran samples of all 10 Maryland-grown soft winter wheat varieties contained significant levels of phytochemicals, namely ferulic acid, α- and δ-tocopherols, lutein, zeaxanthin, and β-carotene. All bran extracts showed significant radical scavenging capacity. Both phytochemical contents and radical scavenging capacities were higher for bran samples than the soft winter wheat flour samples. Insignificant correlations between different radical scavenging activities with identified
Acknowledgements
This research was partially supported by a grant from the Joint Institute for Food Safety and Applied Nutrition (JIFSAN), a grant from Maryland Grain Producers Utilization Board (MGPUB).
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