WHEAT

Family: Gramineae

Genus: Triticum (Tribe: Hordeae)

Species: aestivum (bread wheat), durum (macaroni wheat)

(i) General background on the plant

Wheats are freely tillering, usually robust grasses 60 - 120cm tall. All species are annuals. Leaves are usually softly hairy with two prominent hairy auricles. The leaf blades are narrow with approximately 12 veins. The inflorescence is a typical spike with with a single spikelet at each node. Each spikelet consists of a pair of stiff glumes and from one to nine florets borne on a very short rachilla. The upper one or two florets are sterile. The glumes are about the same size as the lemmas, are asymmetrical and with the side away from the rachis being larger. The lemmas are thinner than the glumes, awned or awnless. Grains are large and plump and naked in most species (shed out of lemma when threshed).

There are very many distinct types of wheat which have been named as species. They are separable into three groups - diploid, tetraploid and hexaploid. The most important wheats today are hexaploids, having six sets of chromosomes AABBDD, those of the tetraploid emmer wheat plus a further two which have been derived from another goat grass species, Aegilops squarrosa. Hexaploid wheats are in most cases larger and higher yielding than diploids and tetraploids but they also inherit adaptability to a wide range of climates from A. squarrosa, making them much more versatile than the essentially Mediterranean diploid and tetraploid wheats.

Triticum aestivum is by far the most important of all wheat species, the highest yielding and the widest ranging as well as the one most suited to bread making. Its centre of origin is thought to be somewhere south of the Caspian sea but its rise to prominence came only after wheat cultivation had spread to more humid areas. During the last two thousand years it has come to replace almost all other species and has spread to almost all parts of the world where wheat can be grown.

(ii) Details of quality characteristics

Worldwide, wheat is the most important cereal crop - 585 x10⁶ metric tonnes of grain produced in 1996, relative to 562 x10⁶ mt of rice. The comparatively high protein content of wheat grain makes it the most important source of human nutrition. Several by-products of wheat from the food industry have created outlets for technical and industrial applications, namely wheat germ oil, wheat gluten and wheat starch. Wheat straw also has application as a source of fibre.

Wheat germ oil is contained at 8 - 12% in the wheat germ which is 2% of total grain weight. Its fatty acid composition (%) is:

Due to its high level of linoleic acid (C18:2) wheat germ oil is used for dietary purposes and in cosmetic preparations.

Starch is one of the most abundant natural raw materials in nature and is consumed as a component of bread, pasta, rice, breakfast cereals, cakes, biscuits and potatoes. A large proportion is also consumed after conversion to ethanol in beverages. Starch is a polymer of a-D-glucose that can be chemically or physically modified, it can also undergo hydrolysis to yield a range of derivatives from glucose syrups to polyols.

Starch is produced by the Martin process or Slurry process. Raw starch milk streams are freed from insolubles (small gluten particles, fibres and insoluble pentosans) by rotating screens or jet refiners. These are used as slurry for feeding or are concentrated or dried together with concentrated solubles and bran as wheat gluten feed.

Wheat starch grains are bimodal in size, B-starch (15 - 20%) is 2 - 15mm diameter and the larger A-starch granules (80 - 85%) are 20 - 35mm. B-starch is always highly contaminated with pentosans, fine fibres, lipids and protein, and for this reason the two fractions are worked up separately and recombined after washing and concentration, the resulting concentrated starch milk is then ready for further processing.

Wheat gluten is the water-insoluble protein complex in the wheat endosperm. Commercially it is the term given to industrial by-products of wheat starch production via wet milling purposes. Its composition is: 70 - 80% crude protein, 6 - 8% crude lipids, 10 - 14% carbohydrates, 0.8 - 1.4% minerals. Wheat gluten is used for production of hydrolyzed vegetable protein and glutamic acid by acid hydrolysis.

(iii) Current production and yields

Source: FAO 1996

(iv) Constraints upon production

As with all monocultures, wheat is susceptible to a large number of diseases, breeding of resistant cultivars has overcome this for yellow and brown rusts, mildew, eyespot, loose smut and glume blotch. Other notable diseases are barley yellow dwarf virus, take-all, sharp eyespot, Fusarium rots/blights.

Improved overall yields of starch and reduced fresh water inputs are desirable developments.

(v) Markets and market potential

World wheat starch production occupies second position after corn starch, with yields in EC exceeding 1x10⁶ metric tonnes per year.

Applications of Starch and its Derivatives:

Source: Jacques Michaud, Cerestar, Belgium.

(vi) Other information

The agronomy of cereal production is well researched and well documented

RHM Technology - Longevity of Thatch in Relation to the surface Properties of Straw