Avenin

The oat (''Avena sativa''), sometimes called the common oat, is a species of cereal grain grown for its seed, which is known by the same name (usually in the plural, unlike other cereals and pseudocereals). While oats are suitable for human consumption as oatmeal and rolled oats, one of the most common uses is as livestock feed. Oats are a nutrient-rich food associated with lower blood cholesterol when consumed regularly.

Avenins are oat gluten proteins, similar to gliadin in wheat. They can trigger celiac disease in a small proportion of people. Also, oat products are frequently contaminated by other gluten-containing grains, mainly wheat and barley.

Origin

The wild ancestor of ''Avena sativa'' and the closely related minor crop '' A. byzantina'' is '' A. sterilis''. ''A. sterilis'' is a wild oat that is naturally hexaploid. Genetic evidence shows the ancestral forms of ''A. sterilis'' grew in the Fertile Crescent of the Near East. Oats are usually thought to have emerged as a secondary crop, i.e., derived from a weed of the primary cereal domesticates, then spreading westward into cooler, wetter areas favorable for oats, eventually leading to their domestication in regions of the Middle East and Europe.

Cultivation

Oats are best grown in temperate regions. They have a lower summer heat requirement and greater tolerance of rain than other cereals, such as wheat, rye or barley, so they are particularly important in areas with cool, wet summers, such as Northwest Europe and even Iceland. Oats are an annual plant, and can be planted either in autumn/fall (for late summer harvest) or in the spring (for early autumn/fall harvest).

Production

In 2017, global production of oats was , a 13% increase over 2016. Production was led by Russia with 21% of the total and Canada with 14% (table). Other substantial producers were Australia, Poland, China, and Finland, each with over .

Uses

Oats have numerous uses in foods; most commonly, they are rolled or crushed into oatmeal, or ground into fine oat flour. Oatmeal is chiefly eaten as porridge, but may also be used in a variety of baked goods, such as oatcakes, oatmeal cookies and oat bread. Oats are also an ingredient in many cold cereals, in particular muesli and granola. Oats are also used for production of milk substitutes ("oat milk").

Historical attitudes towards oats have varied. Oat bread was first manufactured in Britain, where the first oat bread factory was established in 1899. In Scotland, they were, and still are, held in high esteem, as a mainstay of the national diet.

In Scotland, a dish was made by soaking the husks from oats for a week, so the fine, floury part of the meal remained as sediment to be strained off, boiled and eaten. Oats are also widely used there as a thickener in soups, as barley or rice might be used in other countries.

Oats are also commonly used as feed for horses when extra carbohydrates and the subsequent boost in energy are required. The oat hull may be crushed ("rolled" or "crimped") for the horse to more easily digest the grain, or may be fed whole. They may be given alone or as part of a blended food pellet. Cattle are also fed oats, either whole or ground into a coarse flour using a roller mill, burr mill, or hammermill. Oat forage is commonly used to feed all kinds of ruminants, as pasture, straw, hay or silage.

Winter oats may be grown as an off-season groundcover and ploughed under in the spring as a green fertilizer, or harvested in early summer. They also can be used for pasture; they can be grazed a while, then allowed to head out for grain production, or grazed continuously until other pastures are ready.

Oat straw is prized by cattle and horse producers as bedding, due to its soft, relatively dust-free, and absorbent nature. The straw can also be used for making corn dollies. Tied in a muslin bag, oat straw was used to soften bath water.

Oats are also occasionally used in several different drinks. In Britain, they are sometimes used for brewing beer. Oatmeal stout is one variety brewed using a percentage of oats for the wort. The more rarely used oat malt is produced by the Thomas Fawcett & Sons Maltings and was used in the Maclay Oat Malt Stout before Maclays Brewery ceased independent brewing operations. A cold, sweet drink called ''avena'' made of ground oats and milk is a popular refreshment throughout Latin America. Oatmeal caudle, made of ale and oatmeal with spices, was a traditional British drink and a favourite of Oliver Cromwell.

Oat extracts can also be used to soothe skin conditions, and are popular for their emollient properties in cosmetics.

Oat grass has been used traditionally for medicinal purposes, including to help balance the menstrual cycle, treat dysmenorrhoea and for osteoporosis and urinary tract infections.

In China, particularly in western Inner Mongolia and Shanxi province, oat ('' A. nuda'') flour called youmian is processed into noodles or thin-walled rolls, and is consumed as a staple food.

Health

Nutrient profile

Oats contain diverse essential nutrients (table). In a 100 gram serving, oats provide and are a rich source (20% or more of the Daily Value, DV) of protein (34% DV), dietary fiber (44% DV), several B vitamins and numerous dietary minerals, especially manganese (233% DV) (table). Oats are 66% carbohydrates, including 11% dietary fiber and 4% beta-glucans, 7% fat and 17% protein (table).

The established property of their cholesterol-lowering effects has led to acceptance of oats as a health food.

Soluble fiber

Oat bran is the outer casing of the oat. Its daily consumption over weeks lowers LDL and total cholesterol, possibly reducing the risk of heart disease.

One type of soluble fiber, beta-glucans, has been proven to lower cholesterol.

After reports of research finding that dietary oats can help lower cholesterol, the United States Food and Drug Administration (FDA) issued a final rule that allows food companies to make health claims on food labels of foods that contain soluble fiber from whole oats (oat bran, oat flour and rolled oats), noting that 3.0 grams of soluble fiber daily from these foods may reduce the risk of heart disease. To qualify for the health claim, the food that contains the oats must provide at least 0.75 grams of soluble fiber per serving.

Beta-D-glucans, usually referred to as beta-glucans, comprise a class of indigestible polysaccharides widely found in nature in sources such as grains, barley, yeast, bacteria, algae and mushrooms. In oats, barley and other cereal grains, they are located primarily in the endosperm cell wall. The oat beta-glucan health claim applies to oat bran, rolled oats, whole oat flour and oatrim, a soluble fraction of alpha-amylase hydrolyzed oat bran or whole oat flour.

Oat beta-glucan is a viscous polysaccharide made up of units of the monosaccharide D-glucose. Oat beta-glucan is composed of mixed-linkage polysaccharides. This means the bonds between the D-glucose or D-glucopyranosyl units are either beta-1, 3 linkages or beta-1, 4 linkages. This type of beta-glucan is also referred to as a mixed-linkage (1→3), (1→4)-beta-D-glucan. The (1→3)-linkages break up the uniform structure of the beta-D-glucan molecule and make it soluble and flexible. In comparison, the indigestible polysaccharide cellulose is also a beta-glucan, but is not soluble because of its (1→4)-beta-D-linkages. The percentages of beta-glucan in the various whole oat products are: oat bran, having from 5.5% to 23.0%; rolled oats, about 4%; and whole oat flour about 4%.

Fat

Oats, after corn (maize), have the highest lipid content of any cereal, i.e. greater than 10% for oats and as high as 17% for some maize cultivars compared to about 2–3% for wheat and most other cereals. The polar lipid content of oats (about 8–17% glycolipid and 10–20% phospholipid or a total of about 33%) is greater than that of other cereals, since much of the lipid fraction is contained within the endosperm.

Protein

Oats are the only cereal containing a globulin or legume-like protein, avenalin, as the major (80%) storage protein. Globulins are characterised by solubility in dilute saline as opposed to the more typical cereal proteins, such as gluten and zein, the prolamines (prolamins). The minor protein of oat is a prolamine, avenin.

Oat protein is nearly equivalent in quality to soy protein, which World Health Organization research has shown to be equal to meat, milk and egg protein. The protein content of the hull-less oat kernel ( groat) ranges from 12 to 24%, the highest among cereals.

Celiac disease

Celiac disease (coeliac disease) is a permanent autoimmune disease triggered by certain gluten proteins. It almost always occurs in genetically predisposed people, having a prevalence of about 1% in the developed world. The provocative gluten types are present in wheat, barley, rye, oat, and all their species and hybrids and contains hundreds of proteins, with high contents of prolamins.

Oat prolamins, named avenins, are similar to gliadins found in wheat, hordeins in barley, and secalins in rye. These are all types of glutens which are commonly called "gluten" in lay speech. Avenins' toxicity in celiac people depends on the oat cultivar consumed because of prolamin genes, protein amino acid sequences, and the immunoreactivities of toxic prolamins which vary among oat varieties. Also, oat products are frequently cross-contaminated with other gluten-containing cereals during grain harvesting, transport, storage or processing. Pure oats contain less than 20 parts per million of gluten from wheat, barley, rye, or any of their hybrids.

Use of pure oats in a gluten-free diet offers improved nutritional value from the rich content of oat protein, vitamins, minerals, fiber, and lipids, but remains controversial because a small proportion of people with celiac disease react to pure oats. Some cultivars of pure oat could be a safe part of a gluten-free diet, requiring knowledge of the oat variety used in food products for a gluten-free diet. Determining whether oat consumption is safe is critical because people with poorly controlled celiac disease may develop multiple severe health complications, including cancers.

Use of pure oat products is an option, with the assessment of a health professional, when the celiac person has been on a gluten-free diet for at least 6 months and all celiac symptoms have disappeared clinically. Celiac disease may relapse in few cases with the consumption of pure oats. Screening with serum antibodies for celiac disease is not sensitive enough to detect people who react to pure oats and the absence of digestive symptoms is not an accurate indicator of intestinal recovery because up to 50% of people with active celiac disease have no digestive symptoms. The lifelong follow-up of celiac people who choose to consume oats may require periodic performance of intestinal biopsies. The long-term effects of pure oats consumption are still unclear and further well-designed studies identifying the cultivars used are needed before making final recommendations for a gluten-free diet.

Agronomy

Oats are sown in the spring or early summer in colder areas, as soon as the soil can be worked. An early start is crucial to good fields, as oats go dormant in summer heat. In warmer areas, oats are sown in late summer or early fall. Oats are cold-tolerant and are unaffected by late frosts or snow.

Seeding rates

Typically, about (between ) are sown, either broadcast or drilled. Lower rates are used when interseeding with a legume. Somewhat higher rates can be used on the best soils, or where there are problems with weeds. Excessive sowing rates lead to problems with lodging, and may reduce yields.

Fertilizer requirements

Oats remove substantial amounts of nitrogen from the soil. They also remove phosphorus in the form of P₂O₅ at the rate of 0.25 pound per bushel (1 bushel = 38 pounds at 12% moisture). Phosphate is thus applied at a rate of 30 to 40 kg/ha, or 30 to 40 lb/acre. Oats remove potash (K₂O) at a rate of 0.19 pound per bushel, which causes it to use 15–30 kg/ha, or 13–27 lb/acre. Usually, 50–100 kg/ha (45–90 lb/ac) of nitrogen in the form of urea or anhydrous ammonia is sufficient, as oats use about one pound per bushel. A sufficient amount of nitrogen is particularly important for plant height and hence, straw quality and yield. When the prior-year crop was a legume, or where ample manure is applied, nitrogen rates can be reduced somewhat.

Weed control

The vigorous growth of oats tends to choke out most weeds. A few tall broadleaf weeds, such as ragweed

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