THE OCCURRENCE OF STARCH

Starch makes up the nutritive reserves of many plants. During the growing season, the green leaves collect energy from the sun. This energy is transported as a sugar solution to the starch storage cells, and the sugar is converted to starch in the form of tiny granules occupying most of the cell interior.

The conversion of sugar to starch takes place by means of enzymes. Then, the following spring, enzymes are also responsible for the re-conversion of starch to sugar - released from the seed as energy for the growing plant.

WHEAT VARIETIES

Wheat is a cereal plant of the genus Triticum of the family Gramineae (grass family). Modern wheat varieties are usually classified as winter wheat (fall-planted) and spring wheat - most of the wheat grown is winter wheat. Some ancient varieties of wheat like einkorn (T. monococcum), emmer (T. dicoccum) and spelt (T. spelta) are still being cultivated for specialty purposes. Triticum aestivum is by far the most important of all wheat species.

Flour from hard varieties derived from bread wheat (T. aestivum) contains a high gluten content and is preferred in bakery products. The hardest-kernelled wheat is durum - macaroni wheat (T. durum); it is essential for the manufacture of pasta products.

WHEAT GLUTEN

Gluten is proteins of the wheat. Gluten forms long molecules insoluble in water. This gives dough its characteristic texture and permits breads and cakes to rise because the carbon dioxide released by the yeast is trapped in the gluten superstructure.

Gluten is particular important in the manufacture of starch from wheat because gluten is a most valuable by-product representing half the turnover. In fact the starch is by some manufacturers considered the by-product and gluten the main product.

If the gluten is extracted and gently dried in hot air at moderate temperatures it maintains it's characteristics. If so it is designated "vital gluten". Vital gluten may be added as a dry powder to flour otherwise low in gluten and thereby improve the baking qualities of the flour. The Danish and Scandinavian climate favours weak wheat of poor baking qualities. The gluten content is low and the texture of the gluten is short. A remedy is mixing it with French or Canadian wheat known for their better gluten quality. As an alternative the baking characteristics may be improved by mixing it with vital gluten powder.

Commercial gluten is dried to minimum 90% dry matter and a typical composition is:

• 70 - 80 % crude protein,
• 6 - 8 % crude lipids,
• 10 - 14 % carbohydrates,
• 0.8 - 1.4 % minerals.

Gluten in general is used as a meat extender in both food and feed. The fermentation industry consumes large amounts of gluten and by acid hydrolysis it is used for production of hydrolyzed vegetable protein and glutamic acid. A gluten based meat analogue was invented by the International Starch Group. It replaces up to one third of minced meat in popular meat balls. Another invention combines emulsifiers and gluten into a spray dried powder improving both baking quality of the flour and shelf life of the bread.

WHEAT STARCH

Wheat starch granules are divided in two groups by size, B-starch (15 - 20 %) is 2 - 15 µm diameter and the larger A-starch granules (80 - 85 %) are 20 - 35 µm. B-starch is contaminated with pentosans, fibres, lipids and protein to an extent requiring special treatment in the factory

WHEAT GERM OIL

Wheat germ oil is contained at 8 - 12 % in the fresh wheat germ which is 2½ % of total grain weight.
Its fatty acid composition (%) is:

C16:0 C18:0 C18:1 C18:2 C18:3
11-20% 1-6% 13-30% 44-65% 2-13%

Due to its high level of linoleic acid (C18:2) wheat germ oil is used for dietary purposes and in cosmetic preparations.
Wheat germ oil is expelled or extracted from the germ. Because the germ is removed from the endosperm during the dry milling it is not a by-product from the industrial wet milling of wheat.

RAW MATERIAL FOR STARCH

Wheat grain may be taken in as raw material as is the case with corn, but typically the starch manufacturer prefers to buy flour from a flour mill.

Composition of the wheat kernel

Bran 12½ %
Germ 2½ %
Endosperm 82 %

The number of parts by weight of flour that is produced from 100 parts of wheat is termed the extraction rate. Flour extraction ranges from 73 to 77 % resulting in an average mill feed production of about 25 %. It is apparent that the mill feed contains, in addition to the bran, a significant portion of the starchy endosperm.

Typical flour composition on dry matter basis

Moisture content: 13.5 %
Total protein content: 13 %
Fibre content: 1.0 %
Ash content: 0.75 %

The flour must be suitable for human consumption and it has to be milled to a specific particle size distribution.