Improving the Health Benefits of Bread
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F Improving the health benefits of bread by Peter Shewry, Distinguished Research Fellow, Department of Plant Biology and Crop Science, Rothamsted Research, UK The development of roller milling in the 19th Century of improved “patent” breads, the most well known being “Hovis” made white bread affordable to all social classes for which is enriched in wheat germ. Despite the compulsory the first time, leading to a love affair with white bread, production of high extraction and wholemeal breads in the which remains in many countries to the present day. UK during the two World Wars, white bread has remained the favourite for much of the British population, and in many other countries. ecause bread has long been the staple Although those who promoted improved breads in the 19th food in temperate countries, this Century recognised the importance of fibre and protein, the health led to massive changes in diet, with benefits were not soundly established until the early 20th Century, coarse wholemeal or brown breads with the discovery of vitamins and the recognition that these being almost completely replaced by are depleted when the bran and germ are removed to produce white products in the UK by 1880. white flour. Since then, many studies have been reported positive Although the science of nutrition was relationships between flour extraction rate and the contents of then in its infancy, concerns were “beneficial” components in flour, including B vitamins, Vitamin nevertheless expressed about the E, minerals, fibre and “bioactive” phytochemicals, with the impact of this change in diet on the nutrition and health of the differences in concentrations of these components between population. Foremost among the critics of white bread in the UK wholemeal and white flour exceeding ten-fold in some cases. were May Yates and Thomas Allinson. Allinson qualified as a doctor in 1879 and established a Wholegrain and health Bpractice in London. He believed that diet was crucial for health, Recent interest in the relationship between wheat and health and particularly advocated the consumption of stone ground has been stimulated by the wholegrain movement, which can wholemeal wheat. He was frequently in dispute with orthodox be dated from the approval granted by the US Food and Drugs medicine and was “struck off” (disqualified from practicing) in Administration in 1999 that “Diets rich in whole grain foods 1892, having been found guilty of “infamous conduct” (self- and other plant foods and low in total fat, saturated fat, and promotion). In the same year he purchased a stone mill and cholesterol, may help reduce the risk of heart disease and certain established a milling and baking company that continues to cancers." This has stimulated interest from both industry and produce wholemeal bread to the present day. academics and the establishment of bodies to promote wholegrain By contrast, May West was not trained as a scientist but became consumption, such as the Whole Grains Council, Grains for convinced of the benefits of wholemeal bread during a visit to Health Foundation and Healthgrain Forum. Sicily. She founded the Bread Reform League in 1880 and spent The role of vitamins and minerals in health is well established 40 years campaigning for the use of high extraction (about 85 but recent attention has focussed on dietary fibre. There is strong percent) flours. The late 19th Century also saw the introduction scientific evidence that increased consumption of cereal fibre, 40 | November 2015 - Milling and Grain F UK Scientific Advisory Committee on Nutrition. Although, the roles and benefits of “bioactive” phytochemicals remain to be established, few would dispute that increasing flour extraction rate could have a significant impact on the health of consumers. starchy endosperm Wheat grain structure and milling In botanical terms the wheat grain is a single-seeded fruit, called a caryopsis. It consists of three main parts, which have different Aleurone functions and compositions. The central part of the grain is the endosperm, which accounts for about 90 percent of the total grain. This is essentially a storage tissue, being packed with starch and protein, which are digested to support the growth of the seedling during germination. However, the outer layer of endosperm cells differ from the others, being rich in dietary fibre, protein, oil, B vitamins, minerals and phytochemicals. These outer aleurone cells account for about 6.5 percent of the grain. The embryo is relatively small, accounting for about 3 percent of the total grain, pericarp and testa and develops into the seedling on germination. It is similar in composition to the aleurone, except for a lower proportion of dietary fibre. Outside of the embryo and endosperm germ are the seed coat (testa) and the fruit coat (pericarp)) which provide protection to the grain (see figure). These outer layers are very rich in fibre and associated phenolic acids but not in other beneficial components. Conventional milling has been developed to separate the starch-rich cells of the central endosperm (called particularly in wholegrain, results in reduced risk of a range of the starchy endosperm) from the outer layers, aleurone and germ, chronic diseases including type two diabetes, stroke and some which are together recovered as bran. types of cancer (notably colorectal). The scientific evidence The process is remarkably effective, with the yield of white for the role of dietary fibre and other cereal carbohydrates in flour approaching 80 percent of the total grain. However, as health has been reviewed in detail in a recent report from the flour yield approaches and exceeds 80 percent there is increasing Milling and Grain - November 2015 | 41 F in the white flour. These proteins are therefore diluted by about 25 percent in wholemeal, and to a correspondingly lesser extent in high extraction flours. It is therefore necessary to use grain of higher protein content and/or protein quality, or to supplement low protein flour with “vital gluten” produced by the industrial separation of starch and gluten from flour. New approaches to producing enhanced flours Two recent multinational projects supported by the European Union have focused on developing new technologies to improve the quality and acceptability of whole grain and high extraction rate bread. One option, which was explored, is to eliminate the more unpalatable fibre-rich outer layers of the bran while retaining the “contamination” with bran tissues, particularly with the aleurone, inner bran, which includes the nutrient-rich aleurone layer. This which adheres tightly to the outer starch-rich cells (figure). cannot be achieved by simple abrasion (debranning) of whole Hence, the concentrations of beneficial components increase grain because of the oval shape and the presence of a crease. significantly as extraction rate rises. The Health grain programme (2005-2010) therefore developed a process in which the grain was pearled twice, initially to remove Challenges to increasing flour extraction rate for bread the outer bran (approx three percent dry wt) and then the inner making bran (up to 15 percent original dry wt). The first fraction was Increasing the flour extraction rate poses challenges for food discarded while the second fraction, which was enriched in the processing and for the consumer acceptability of the products. aleurone layer, retained. Although the pearling removed most of Increasing the content of bran in bread-making flour reduces the bran some remained in the crease region. The debranned grain the acceptability to consumers accustomed to consuming white was therefore milled and sieved using conventional procedures bread, due to the grittiness associated with bran particles and to and the white flour recombined with an appropriate proportion the colour and flavour (more wheaty and bitter with an aftertaste) of the second pearling fraction to give “Healthflour” which was associated with the presence of proanthocyanidin pigments in the enriched in beneficial components and had improved processing testa of the “red” grained types of wheat which are largely used properties and higher acceptability. for bread making. Alternative approaches in the same project were to mechanically In theory, the latter problem is easy to eliminate as “white” separate the aleurone layer using different types of mills to grained wheats are available which lack the pigment and produce “aleurone powder” as an ingredient, and to finely grind associated flavour. However, white wheats are highly susceptible the bran (micronisation) prior to fractionation by electrostatic to “pre-harvest sprouting” when subjected to cool and wet separation. Miconisation also has the advantage that it increases conditions at harvest, leading to loss of value as sprouted grain the bioavailability of minerals, vitamins and phytochemicals. cannot be used for food processing. Hence, white wheats are Following on from Health Grain, the Healthbread project not widely cultivated and the grain is too expensive to be used (2012-2014) developed a range of concentrates from aleurone except for premium products. It has not been possible to separate and wholegrain, which were successfully used by commercial the red colour from the resistance to sprouting by conventional partners using either long fermentation or sough dough systems. plant breeding but work in progress on understanding the precise There is no doubt that such new approaches can be used to relationships between the two seemingly