Oat

Oats contain diverse essential nutrients (table). In a 100 gram serving, oats provide 389 kilocalories (1,630 kJ) 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[1] has led to acceptance of oats as a health food.[12]

Oat grains in their husks

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.[1][13] One type of soluble fiber contained in oats, beta-glucans, has been proven to lower cholesterol.[1]

After reports of research finding that dietary oats can help lower cholesterol, the United States Food and Drug Administration (FDA) issued a final rule[14] 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.[14]

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.[14]

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%.

Oats are the only cereal containing a globulin or legume-like protein, avenalin, as the major (80%) storage protein.[15] 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.[16] The protein content of the hull-less oat kernel (groat) ranges from 12 to 24%, the highest among cereals.

Avenins present in oats (proteins similar to gliadin from wheat) can trigger celiac disease in a small proportion of people.[17][18] Also, oat products are frequently contaminated by other gluten-containing grains, mainly wheat and barley.[18][19][20] Celiac disease is a permanent intolerance to certain gluten proteins in genetically predisposed people, having a prevalence of about 1% in the developed world.[21] Gluten is present in wheat, barley, rye, oat, and all their species and hybrids[17][21] and contains hundreds of proteins, with high contents of prolamins.[22]

Oat prolamins, named avenins, are similar to gliadins found in wheat, hordeins in barley, and secalins in rye, which are collectively named gluten.[17] 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.[18][19][23] Also, oat products are frequently cross-contaminated with other gluten-containing cereals during grain harvesting, transport, storage or processing.[19][23][24] Pure oats contain less than 20 parts per million of gluten from wheat, barley, rye, or any of their hybrids.[18][19]

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,[19][25] but remains controversial because a small proportion of people with celiac disease react to pure oats.[18][26] 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.[18][19] Determining whether oat consumption is safe is critical because people with poorly controlled celiac disease may develop multiple severe health complications, including cancers.[27]

Use of pure oat products is an option, with the assessment of a health professional,[18] when the celiac person has been on a gluten-free diet for at least 6 months and all celiac symptoms have disappeared clinically.[18][28] Celiac disease may relapse in few cases with the consumption of pure oats.[29] 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.[29][30][31] The lifelong follow-up of celiac people who choose to consume oats may require periodic performance of intestinal biopsies.[27] The long-term effects of pure oats consumption are still unclear[27][28] and further well-designed studies identifying the cultivars used are needed before making final recommendations for a gluten-free diet.[24][25]

Typically, about 125 to 175 kg/ha (between 2.75 and 3.25 bushels per acre) 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.

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.

The vigorous growth of oats tends to choke out most weeds. A few tall broadleaf weeds, such as ragweed, goosegrass, wild mustard, and buttonweed (velvetleaf), occasionally create a problem, as they complicate harvest and reduce yields. These can be controlled with a modest application of a broadleaf herbicide, such as 2,4-D, while the weeds are still small.

Oats are relatively free from diseases and pests with the exception being leaf diseases, such as leaf rust and stem rust. However, Puccinia coronata var. avenae is a pathogen that can greatly reduce crop yields.[32] A few lepidopteran caterpillars feed on the plants—e.g. rustic shoulder-knot and setaceous Hebrew character moths, but these rarely become a major pest. See also List of oat diseases.

Harvesting of oats in Jølster, Norway c. 1890
(Photo: Axel Lindahl/Norwegian Museum of Cultural History)

Harvest techniques are a matter of available equipment, local tradition, and priorities. Farmers seeking the highest yield from their crops time their harvest so the kernels have reached 35% moisture, or when the greenest kernels are just turning cream-colour. They then harvest by swathing, cutting the plants at about 10 cm (3.9 in) above ground, and putting the swathed plants into windrows with the grain all oriented the same way. They leave the windrows to dry in the sun for several days before combining them using a pickup header. Finally, they bale the straw.

Oats can also be left standing until completely ripe and then combined with a grain head. This causes greater field losses as the grain falls from the heads, and to harvesting losses, as the grain is threshed out by the reel. Without a draper head, there is also more damage to the straw, since it is not properly oriented as it enters the combine's throat. Overall yield loss is 10–15% compared to proper swathing.

Historical harvest methods involved cutting with a scythe or sickle, and threshing under the feet of cattle. Late 19th- and early 20th-century harvesting was performed using a binder. Oats were gathered into shocks, and then collected and run through a stationary threshing machine.

After combining, the oats are transported to the farmyard using a grain truck, semi, or road train, where they are augered or conveyed into a bin for storage. Sometimes, when there is not enough bin space, they are augered into portable grain rings, or piled on the ground. Oats can be safely stored at 12–14% moisture; at higher moisture levels, they must be aerated or dried.

Oat seeds

In the United States, No.1 oats weigh 36 pounds per US bushel (463 kg/m³); No. 2 oats must weigh 33 lb/US bu. No.3 oats must weigh at least 30 lb/US bu (386 kg/m³). If 27 lb/US bu (348 kg/m³), they are graded as No.4, and oats under 27 lb/US bu (348 kg/m³) are graded as "light weight".

In Canada, No.1 oats weigh 42.64 lb/US bu (549 kg/m³); No.2 oats must weigh 40.18 lb/US bu (517 kg/m³); No.3 oats must weigh at least 38.54 lb/US bu (496 kg/m³) and if oats are lighter than 36.08 lb/US bu (464 kg/m³) they do not make No.4 oats and have no grade.[33]

Oats are bought and sold and yields on the basis of a bushel equal to 32 pounds (14.5 kg or 412 kg/m³) in the United States, and a bushel equal to 34 pounds (15.4 kg or 438 kg/m³) in Canada. "Bright oats" were sold on the basis of a bushel equal to 48 pounds (21.8 kg or 618 kg/m³) in the United States.

Yields range from 60 to 80 US bushels per acre (5.2–7.0 m³/ha) on marginal land, to 100 to 150 US bushels per acre (8.7–13.1 m³/ha) on high-producing land. The average production is 100 bushels per acre, or 3.5 tonnes per hectare. Straw yields are variable, ranging from one to three tonnes per hectare, mainly due to available nutrients and the variety used (some are short-strawed, meant specifically for straight combining).

Avena sativa is an allohexaploid plant with 3 ancestral genomes ("A", "C" and "D").[34] The hexaploid genome is challenging to sequence and the oat genome seqencing project is focusing on diploid species at first. Species within Avena can hybridize and genes introgressed from other "A" genome species has contributed with many valuable traits, like crown rust resistance.[35]

It is also possible to do introgression of traits in oats from very wide intergeneric hybridization. In contrast to wheat, oats sometimes retain chromosomes from maize or pearl millet.[36][37] These wide crosses are typically made in order to generate doubled haploid breeding material where the rapid loss of the alien chromosomes from the unrelated pollen donor results in a plant with only a single set of chromosomes (a haploid). The addition lines with alien chromosomes can be used as a source for novel traits in oats, for example has research on Oat-Maize-Addition lines (OMAs) been used to map genes involved in C4 photosynthesis. In order to obtain mendelian inheritance of these novel traits, also radiation hybrid lines have been established, where maize chromosome segments have been introgressed in the oat genome. Interestingly, these techniques which potentially transfers thousands of genes from a species that is very distantly related is not considered a GMO according to the European Union definition, since sexual hybridization and radiation-induced introgression are explicitly excluded from the definition.[38]

Upon delivery to the milling plant, chaff, rocks, metal, oversized materials and foreign grains are removed from the oats. As different sized oats de-hull at differing velocities, once the raw oats have been removed of impurities, they are then separated by width and length into different classifications before de-hulling.

Centrifugal acceleration is used to separate the outer hull from the inner oat groat. Oats are fed by gravity onto the centre of a horizontally spinning impeller, which accelerates them towards an outer mill ring. Groats and hulls are separated on impact. The lighter oat hulls are then aspirated away, while the denser oat groats are taken to the next step of processing. Oat hulls can be used as feed or as a biomass fuel and are often used within the oat processing line to power solid fuel boilers for steam and power generation. Excess oat hulls are generally pelletised before being provided as feed.

The unsized oat groats pass through a heat and moisture treatment to balance moisture for optimal storage conditions and to deactivate self catalysing enzyme activity. Oat groats are high in fat (lipids) and once removed from their protective hulls and exposed to air, enzymatic (lipase) activity begins to break down the fat into free fatty acids, ultimately causing an off-flavour or rancidity. Depending on temperature, humidity and moisture content, de-hulled oats can begin to show signs of enzymatic rancidity rapidly if not stabilized. This process is primarily done in food-grade plants, not in feed-grade plants. Groats are not considered raw if they have gone through this process; the heat disrupts the germ and they cannot sprout.

Many whole oat groats break during the dehulling process, leaving the following types of groats to be sized and separated for further processing: whole oat groats, coarse steel cut groats, steel cut groats, and fine steel cut groats. Groats are sized and separated using screens, shakers and indent screens. After the whole oat groats are separated, the remaining broken groats get sized again into the three groups (coarse, regular, fine), and then stored. "Steel cut" refers to all sized or cut groats. When not enough broken groats are available to size for further processing, whole oat groats are sent to a cutting unit with steel blades that evenly cut groats into the three sizes above.

Three methods are used to make the finished product:

This process uses two large smooth or corrugated rolls spinning at the same speed in opposite directions at a controlled distance, before which the cut groats are conditioned for flaking via steam injection. After flaking, the oats are then dried to a sufficient moisture for storage and transport. Oat flake thickness is a key control point dependant of the type of oat flakes to be produced. Typically, the flakes produced are either instant, quick or traditional whole rolled oats and range in size from 0.4 mm to 1 mm.

This process takes the oat groats through several roll stands to flatten and separate the bran from the flour (endosperm). The two separate products (flour and bran) get sifted through a gyrating sifter screen to further separate them. The final products are oat bran and debranned oat flour.

This process takes oat groats straight to a grinding unit (stone or hammer mill) and then over sifter screens to separate the coarse flour and final whole oat flour. The coarser flour is sent back to the grinding unit until it is ground fine enough to be whole oat flour. This method is used often in India and other countries. In India, whole grain oat flour (jai) is used to make Indian bread known as jarobra in Himachal Pradesh.

Oat flour can be ground for small scale use by pulsing rolled oats or old-fashioned (not quick) oats in a food processor or spice mill.[39][40]