International Journal of Food Science and Technology 2015, 50, 2509–2518
Review Composition and functionality of wheat bran and its application in some cereal food products Oluwatoyin O. Onipe,* Afam I. O. Jideani & Daniso Beswa Department of Food Science and Technology, School of Agriculture, University of Venda, Private Bag X5050, Thohoyandou 0950, Limpopo Province, South Africa (Received 10 May 2015; Accepted in revised form 11 July 2015)
Summary
Production of wheat bran (WB) for human consumption is estimated to be about 90 million tonnes per year. WB is a cheap and abundant source of dietary fibre which has been linked to improved bowel health and possible prevention of some diseases such as colon cancer. It also contains minerals, vitamins and bioactive compounds such as phenolic acids, arabinoxylans, alkylresorcinol and phytosterols. These compounds have been suggested as an aid in prevention of noncommunicable diseases such as cardiovascular disease. This article discusses WB extraction, its nutritional properties, potential health benefits, effects on quality and sensory properties of some cereal foods, and its application in some baked products as well as in fried cereal snacks, as an additive for oil reduction and fibre enrichment.
Keywords
Antioxidants, dietary fibre, extraction, fried cereal snacks, functionality, nutritional composition, Wheat bran.
Introduction
Wheat (Triticum aestivum) is a leading cereal crop which is mainly utilised for human consumption and livestock feed. A wheat kernel comprises three principal fractions – bran, germ and endosperm. The outer layers are all parts of the bran (Fig. 1). The bran fraction is a by-product of milling and has food (Curti et al., 2013) and nonfood applications (Apprich et al., 2013). The use of wheat bran (WB) for human consumption has increased gradually over the years. Globally, the number of WB-incorporated food products increased from 52 in 2001 to approximately 800 in 2011 (Pr€ uckler et al., 2014). WB is rich in minerals, fibre, B vitamins and bioactive compounds which are known to possess health-promoting properties (Reisinger et al., 2013). Treatment processes to assess the functional ingredients from WB have been studied (Rosa et al., 2013). The awareness of consumers and their demand for healthier foods led to the exploration and incorporation of ingredients from natural sources in food production. As indicated by Pr€ uckler et al. (2014), of all bran-incorporated food groups categorised, bakery and cereals topped the chart with approximately 60% market share. Over the years, WB has received more attention in baked foods and recently in fried cereal foods. This article examines the *Correspondent: E-mail:
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nutritional composition of WB, effects of WB inclusion on quality and sensory properties of cereal foods, and possible application of WB in fried cereal snacks as a potential functional ingredient that can serve as a barrier layer which could reduce oil migration into food during frying. Extraction of wheat bran
Bran makes up about 13–19% of total wheat grain weight depending on the milling process (wet or dry) used for its extraction (Hossain et al., 2013). The dry milling process involves separation of bran from the endosperm – which is further ground into fine flour. Extraction of bran from wheat grains is achieved at a highly efficient rate using a roller mill. Before milling, the wheat grains are first tempered through spraying of water to about 15% moisture content (De Brier et al., 2014) and later transferred into tempering bin. Tempering duration is dependent on the hardness of the wheat. During this conditioning process, the pericarp and germ layer of the kernel absorbs water, and the endosperm is softened for the extraction process. Conditioning also prevents the bran from breaking during separation from the endosperm. In the roller mill, the conditioned grains are passed through counter-rotating corrugated metal rolls where the kernels are cracked open, and the endosperm and germ are removed from the pericarp (Serna-Saldivar, 2010). The
doi:10.1111/ijfs.12935 © 2015 The Authors International Journal of Food Science & Technology published by John Wiley & Sons Ltd on behalf of Institute of Food, Science and Technology (IFSTTF) This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
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Wheat bran use in cereal food products O. O. Onipe et al.
Figure 1 Wheat grain structure. Adapted from Surget & Barron (2005) and Brouns et al. (2012) with permission.
cracked grains are then separated into germ, endosperm and bran fractions (Apprich et al., 2013). Bran is considered a major by-product from flour milling, and about 90% is used as a livestock feed while only 10% is used in food industry as fibre source in bakery, fried foods and breakfast cereals (Hossain et al., 2013). The extracted bran can be used as food supplement and livestock feed. It can also be milled with the rest of the wheat kernel components for whole wheat flour (Serna-Saldivar, 2010), but this takes more mechanical energy and resources. Other bran extraction processes are pearling, peeling and bran fractionation which yield bran with enhanced nutritional quality (De Brier et al., 2015). The removal of the outer layers of wheat kernel by friction and abrasion is known as ‘pearling’. This process is used with durum wheat and rice milling, but not frequently employed with the common wheat. Pearling can be used to extract aleurone-rich wheat bran, in order to enrich flour and other wheat-based food products (De Brier et al., 2014). Nutritional composition of wheat bran
Wheat bran (WB) is subdivided into three distinct layers, viz testa, aleurone and pericarp. WB is composed of about 53% dietary fibre (xylans, lignin, cellulose, and galactan, fructans). Other components include vitamins and minerals (Table 1) and bioactive compounds such as alkylresorcinols, ferulic acid, flavonoids, carotenoids, lignans and sterols (Apprich et al., 2013; Andersson et al., 2014; De Brier et al., 2014). The pericarp is divided into outer and inner
International Journal of Food Science & Technology 2015
layers, which contains insoluble dietary fibre as well as phenolic acids in bound state. (Apprich et al., 2013). The hyaline layer is also known as the nucellar tissue, and it belongs to the intermediate layer of the bran. Alkylresorcinol is primarily localised in the testa layer (Rebolleda et al., 2013). The aleurone layer is the innermost layer of the bran, and it is partly shared by the endosperm. It contains a rich stock of lignans and proteins with balanced amino acid content, bioactive compounds, phytic acid, antioxidants, vitamins and minerals (Javed et al., 2012). Aleurone has gained increasing research attention, and it is still currently being studied as functional ingredient in cereal foods. The rich stock of nutrients in aleurone culminates in the healthy added value of WB and whole-grain cereals consumption in the prevention of some diseases. This nutritional composition translates into WB having functionality in cereal foods. Minerals found in WB include iron (Fe), zinc (Zn), manganese (Mn), magnesium (Mg) and phosphorus (P). About 80% of P in mature cereal seeds is stored as phytates which forms complexes with other minerals such as Fe, Zn and Mg. This complex formation reduces bioavailability of these minerals. Over the years, successful attempts to reduce phytic acid in WB include hydrothermal treatment, size reduction, enzymatic treatment, malting, soaking and fermentation (Aivaz & Mosharraf, 2013; Coda et al., 2014). The action of endogenous phytase in the grain and exogenous phytase from yeast and sourdough fermentation can also release the phytic acid complexed minerals (Brouns et al., 2012).
© 2015 The Authors International Journal of Food Science & Technology published by John Wiley & Sons Ltd on behalf of Institute of Food, Science and Technology (IFSTTF)
Wheat bran use in cereal food products O. O. Onipe et al.
Table 1 General composition of wheat bran
Bran component
Range % dm
Dietary fibre Moisture Ash Protein
33.4–63.0 8.1–12.7 3.9–8.10 9.60–18.6
Total carbohydrates Starch
60.0–75.0 9.10–38.9
Phytochemicals
lg g
Reference
1
Alkylresorcinol Phytosterols Ferulic acid
489–1429 344–2050 1376–1918
Bound phenolic compound
4.73–2020
Flavonoids
3000–4300
Micronutrients
mg per 100 g
Phosphorus
900–1500
Magnesium Zinc Iron
530–1030 8.3–14.0 1.9–34.0
Manganese
0.9–10.1
Vitamin E (Tocopherols/tocotrienol) B Vitamins Thiamin (B1) Riboflavin (B2) Pyridoxine (B6) Folate (B9)
Curti et al. (2013) Curti et al. (2013) Curti et al. (2013) Curti et al. (2013); Yan et al. (2015) Javed et al., 2012; Curti et al. (2013); Yan et al. (2015)
0.13–9.5
0.51–1.6 0.20–0.80 0.30–1.30 0.088–0.80
Luthria et al. (2015) Fardet (2010) Kim et al. (2006); Brouns et al. (2012) Kim et al. (2006); Brewer et al. (2014) Fardet (2010); Brewer et al. (2014)
Fardet (2010); Brouns et al. (2012) Brouns et al. (2012) Brouns et al. (2012) Fardet (2010); Brouns et al. (2012) Fardet (2010); Brouns et al. (2012) Fardet (2010)
Fardet (2010) Fardet (2010); Brouns et al. (2012) Brouns et al. (2012) Fardet (2010)
Dm, dry matter.
Functional and potential health properties of wheat bran
Bran plays a key role in the overall health benefits of whole grains. Although not elucidated, WB in clinical trials and epidemiological studies show that consumption of foods high in fibre has been linked with reduced risk of diseases such as colon cancer, diabetes, obesity and cardiovascular disease probably due to the phytochemicals (phenolic acids, sterols, alkylresorcinol, vitamin E, minerals) and fibre which are embedded in the bran (Andersson et al., 2014; Pr€ uckler et al., 2014). These bioactive compounds in WB tissues vary because of cultivar, genetic and environmental factors (Hossain et al., 2013). Studies have shown that WB is one of the cereal bran with strong anticancer effect
(Prinsen et al., 2014; Sang & Zhu, 2014). The mode of action of WB in cancer prevention is more than its fibre content, or a particular phytochemical, but rather the cumulative effect of the diverse bioactive phytochemicals in the bran (Liu et al., 2012). Some WB components are discussed below, and their potential health benefits are highlighted in Table 2. Dietary fibre
Whole-grain foods are a rich stock of dietary fibre (DF) – a complex compound consisting of cellulose, hemicellulose and pentosan polymers based on xylose and arabinose attached to proteins (Apprich et al., 2013). DF has been defined as remnants of edible plant cell polysaccharides, lignin and other substances which escape hydrolytic enzymatic digestion in the upper gastrointestinal tract. It is the indigestible carbohydrates of plant origin with a heterogeneous chemical structure that is resistant to the effects of digestive enzymes in the human gut (Almeida et al., 2013). WB is high in DF and it ranges from 33.4% to 63.0%; it can be classified as ‘soluble’ or ‘insoluble dietary fibre’ based on their solubility in water. Soluble dietary fibre (SDF) in WB is
