gluten

gluten The term ‘gluten’ comes from the Latin word for glue. The use of the word gluten to describe a sticky proteinatious component of dough was established by the middle of the nineteenth century. Mrs Beeton in her famous Book of household management observed that when flour and water were mixed and kneaded, an elastic dough was produced which was best using wheat flour, less satisfactory with rye flour, and inadequate with barley, maize (corn), oats, or rice. This sticky elastic substance, or gluten, is essential for making satisfactory leavened bread. Bubbles of carbon dioxide released from fermenting yeast are trapped by the visco–elastic protein, ensuring a light honeycombed texture for the dough. The elastic nature of gluten also holds particles of the dough together, preventing crumbling during rolling and shaping.

Wheat gluten can be extracted from wheat flour by adding sufficient water to make a kneadable dough which is then washed with a stream of cold water. The water-soluble protein and starch granules are thus flushed away, leaving a sticky mass high in structural plant protein. About 70% of the mass is water and 30% is protein. With drying, a pale, yellow-grey powder is produced. Gluten is poorly soluble in water, but the fraction known as ‘gliadin’ is soluble in aqueous alcohol. Two thirds of gluten protein is in the form of glutenins, which are insoluble in ethyl alcohol but soluble in a mixture of ethanoic acid, urea, and cetrimide. There are more than 40 different gliadin proteins, which traditionally have been separated by starch gel electrophoresis. The fraction with the fastest mobility is known as alpha gliadin, with progressively slower mobility groups classified as beta, gamma, and omega. These proteins have molecular weights between 30 000 and 40 000. The glutenin proteins are much larger units, mostly around 2 000 000 molecular weight. The glutenin protein chains form a three-dimensional net when hydrated (mixed with water) and this gives the elastic properties to gluten.

Not all sticky plant cereals in our diet contain gluten. A type of rice grown in the Far East known as glutinous or sticky rice contains no proteinatious gluten and owes its sticky nature to a waxy carbohydrate.

The sticky nature of gluten has been utilized as a paper and fabric glue, as in making papier-mâché and wallpaper paste. Wheat gluten has also been used as a cattle feed and as a starting point for the manufacture of the food flavour enhancer, monosodium glutamate.

Although the presence of gluten in wheat flour has been utilized to create a variety of pasta shapes, such as noodles, spaghetti, and tagliatelle, gluten is not an essential human nutrient. There is however, some experimental work to suggest that dietary gluten may be protective against some toxic substances. For example, gluten in the diet of rats reduces the liver toxicity of a known toxic chemical, D-galactosamine.

Gluten and coeliac disease

The importance of gluten in the human diet however, relates to the fact that 1 in 200–300 of the European Caucasian population are intolerant to wheat, barley, and rye gluten.

The lining cells of the small intestine become damaged and the patients develop a condition known as coeliac disease or permanent gluten-induced enteropathy. The classical presentation was of a pre-school child with diarrhoea and weight loss. Possibly due to nutritional campaigns to delay the introduction of gluten to infant diets, an insidious onset later in childhood, with anaemia and poor growth in height, is now more frequently seen. Onset in adult life may occur, with anaemia, infertility, and vitamin D deficient bone disease amongst the possible presenting features, although gastrointestinal symptoms and weight loss may, as in children, be the main complaints.

Although this medical condition was described in the first century ad by Aretaeus and accurately, clinically, delineated by a London physician, Dr Samuel Gee, in the late nineteenth century, its cause and cure were not discovered until the 1940s. Dr W. K. Dicke, an astute Dutch physician, noticed that in Holland children with coeliac disease were temporarily cured and improved in health during the World War II famine created by Nazi occupation. He then observed the relapse in their condition when wheat flour was flown in by the Swedish authorities. Subsequent work by Dicke and colleagues and later investigators identified the toxic factor to be an oligopeptide in alpha gliadin.

The practice of cereal cultivation by man started first in the Middle East around 8000 years bc. There was subsequently a gradual spread north and westward. Cereal cultivation arrived late in southwest Ireland, at around 3000 years bc, and wheat was not a staple food until after the potato famine of 1847. The majority of patients suffering from gluten-induced enteropathy (coeliac disease) are of tissue type HLA B8. The incidence of coeliac disease in southwest Ireland, particularly Galway, is amongst the highest in Europe, and there is correspondingly a high prevalence of HLA B8 tissue type. It has been suggested that when populations consume large quantities of gluten from wheat cereals the susceptible HLA B8 individuals develop disease and are at a reproductive disadvantage compared with those not genetically predisposed to the disease, leading to a reduced proportion of B8 individuals in subsequent generations.

Many commercially-prepared foods in Europe contain gluten. Wheat flour is added as a bulking agent in many items of confectionery, as thickeners in sauces, to give bulk and to reduce the cost of meat products, such as sausage meat, and even in some pharmaceutical preparations. It is therefore difficult without a detailed knowledge of the constituents of manufactured foods for an individual to adhere strictly to a gluten free diet. Some food labels indicate the product is gluten free, either in words or as a symbol — an ear of wheat with a cross through it. ‘Gluten free’ flour and bread are available and usually contain starch from maize (corn) or rice, with some of the elastic properties of gluten being provided by guar gum or similar substances.

T. J. Evans

See also alimentary system; diets.