Wheat. Peter R. Shewry
among the critics of white bread in the UK were May Yates (née Mary Corkling) (1850–1938) and Thomas Allinson (1858–1918). Allinson qualified as a doctor in 1879 and established a practice in London. He believed that diet was crucial for health, and particularly advocated the consumption of stone ground wholemeal wheat. He was frequently in dispute with conventional medicine and was struck off (disqualified from practicing) in 1892, having been found guilty of infamous conduct (self‐promotion). In the same year he purchased a stone mill and established a milling and baking company that continues to produce wholemeal bread to the present day. By contrast, May Yates was not trained as a scientist but became convinced of the benefits of wholemeal bread during a visit to Sicily. She founded the Bread Reform League in 1880 and spent 40 years campaigning for the use of high extraction (about 85%) flours. The late nineteenth century also saw the introduction of improved patent breads. The most well‐known of these, and the only one still produced today in the UK, is Hovis, which is enriched in wheat germ.
Despite the compulsory production of high extraction and wholemeal breads in the UK during the two World Wars, white bread remained the favourite for much of the British population, and in many other countries. It is not difficult to understand why this is the case; factory‐produced white bread stores well (with a shelf life of up to a week), while its mild flavour and soft texture means that it has high consumer acceptability and combines well with other foods. By contrast, wholemeal products are more expensive, strongly flavoured, may have a coarse texture, and store less well.
Nevertheless, it is now recognized that the bran fractions are rich in fibre, minerals, vitamins, and phytochemicals and, therefore, that white flour is depleted in beneficial components compared to whole grain (e.g. Wang et al. 2013). As its health benefits have been promoted, the consumption of wholemeal has increased in some countries over the last decade. The catalyst for this increase was the approval in 1999 by the US Food and Drug Administration (FDA) of an application to ‘use the following claim on the label and in labelling of any product that meets the eligibility criteria described in the notification: Diets rich in whole grain foods and other plant foods and low in total fat, saturated fat, and cholesterol, may help reduce the risk of heart disease and certain cancers’ (USFDA 1999). The FDA further defined whole grain foods as containing 51% or more whole grain ingredient(s) by weight, meaning that the amount of fibre required to qualify could be below 6% (based on whole grain containing 11% fibre). This was followed by the approval of several health claims for whole grain fibre by the European Food Safety Authority (EU 2006, 2012) (see Chapter 9). These approvals have provided an economic stimulus to the production and marketing of wholegrain products.
The marketing of wholegrain products has, however, been confusing for the consumer because of the use of different definitions. Although the FDA minimum of 51% is clearly not equivalent to the whole grain, the omission of only a small proportion of the bran fraction can have a significant impact on palatability and consumer acceptability without seriously compromising the health benefits. The consortium of the HEALTHGRAIN EU project therefore launched a series of discussion meetings that resulted in an agreed definition (van der Kamp et al. 2014), which should facilitate the development and acceptance of whole grain products in the future. This states that:
1 Whole grains shall consist of the intact, ground, cracked, or flaked kernel after the removal of inedible parts such as the hull and husk. The principal anatomical components – the starchy endosperm, germ and bran – are present in the same relative proportions as they exist in the intact kernel.
2 Small losses of components, that is, less than 2% of the grain (< 10% of the bran), that occur through processing methods consistent with safety and quality are allowed.
1.4.5 Producing White and Wholemeal Flours by Roller Milling
Although there has been increased interest in recent years in the use of whole grain flour, most wheat‐based foods, including breads, pastries, cakes, cookies, noodles, and pasta, are still made from white flour. The art of the miller is to maximize the recovery of white flour by increasing the yields of the purest fractions and combining them to achieve a high total flour yield from a given weight of grain (i.e. the flour extraction rate). However, the purity of the combined flour will inevitably decrease as the extraction rate increases, with a trade off between yield and purity. The purity of the flour is often monitored as ash content, as ash is derived from minerals which are concentrated in the bran fractions. In addition to varying in purity, the white flour fractions produced by milling will also vary in their contents and compositions of other components, resulting from gradients in composition within the starchy endosperm (Chapter 8). Thus, although the > 20 fractions produced by modern roller milling do not correspond to precise regions of the starchy endosperm they do differ in their compositions (e.g. Gonzalez‐Thuillier et al. 2015). There is, therefore, an opportunity to combine selected mill streams to produce specialist flours differing in their compositions and properties for processing and health (Shewry et al. 2019).
Wholegrain flour is produced by combining all the milling fractions in the proportions that they are produced, rather than by grinding the whole grain as is often thought. However, it is also possible to combine fractions to give high extraction flours, in which a proportion of the bran, notably the aleurone, is included. These flours may correspond to an extraction rate of 85% or more and are enriched in the fibre, minerals, vitamins, and phytochemicals present in the bran. It is also possible to use milling to produce germ‐rich fractions that can then be incorporated into flours to increase the contents of B vitamins, as in the Hovis patent of 1887. The relationship between extraction rate and the presence of other tissues in white flour is illustrated in Figure 1.20, based on the analysis of durum wheat milling fractions using biochemical markers.
1.5 Grain Quality
1.5.1 Grain Size, Shape, and Specific Weight
Plump grain is preferred for milling because it gives higher flour yields than thin grain. The reason for this is simple; plump grain has a higher proportion of starchy endosperm to bran. Conversely, well filled, heavier grain tends to yield less bran (Figure 1.21). The proportion of endosperm to bran is relevant to animal feed and alcohol production as well as to milling, because high starch contents are related to energy contents and alcohol yields, respectively.
Some of the scatter in Figure 1.21 may be due to cultivar differences in grain shape rather than purely grain size. More rounded grain with a less pronounced crease should give higher flour extraction rates (Evers et al. 1990). Genetic analyses and molecular studies of grain size and shape have been reported (Gegas et al. 2010; Brinton and Uauy 2019). These should allow selection for grain size and shape in breeding programmes but direct selection for these qualities, as opposed to yield, is not usually carried out.
Figure 1.20 Determination, using phenolic acids as biochemical markers, of the grain tissues proportions (aleurone, pericarp, endosperm), as a function of total flour extraction rate (durum wheat grains, cv. Ardente).
Source: Redrawn from Hemery et al. (2007) with permission.