| Sorghum | |
|---|---|
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Monocots |
| (unranked): | Commelinids |
| Order: | Poales |
| Family: | Poaceae |
| Subfamily: | Panicoideae |
| Tribe: | Andropogoneae |
| Genus: | Sorghum L. |
| Species | |
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About 30 species, see text |
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Sorghum is a genus of numerous species of grasses, one of which is raised for grain and many of which are used as fodder plants either cultivated or as part of pasture. The plants are cultivated in warmer climates worldwide. Species are native to tropical and subtropical regions of all continents in addition to the South West Pacific and Australasia. Sorghum is in the subfamily Panicoideae and the tribe Andropogoneae (the tribe of big bluestem and sugar cane).
Other names include Durra, Egyptian Millet, Feterita, Guinea Corn (Africa), Jwari, Jowar (India), Juwar, Milo (Spain), Kaolian (China), Shallu, Sudan Grass, Cholam, Jola, Jonnalu, Gaoliang, Great Millet, Kafir Corn (Africa), Dura, Dari, Mtama, and Solam. For more specific details on commercially exploited sorghum, see commercial sorghum, also known as milo.
Sorghum has been, for centuries, one of the most important staple foods for millions of poor rural people in the semi-arid tropics of Asia and Africa. For some impoverished regions of the world, sorghum remains a principal source of energy, protein, vitamins and minerals. Sorghum grows in harsh environments where other crops do not grow well, just like other staple foods, such as cassava, that are common in impoverished regions of the world. It is usually grown without application of any fertilizers or other inputs by a multitude of small-holder farmers in many countries.[1]
Grain sorghum is the third most important cereal crop grown in the United States and the fifth most important cereal crop grown in the world. In 2010, Nigeria was the world's largest producer of grain sorghum followed by the United States and India. In developed countries, and increasingly in developing countries like India, predominant use of sorghum is as fodder for poultry and cattle.[2],[3] Leading exporters in 2010 were the United States, Australia and Argentina; with Mexico as the largest importer of sorghum.
There is international effort to improve sorghum farming and to find additional applications of sorghum. Sorghum is now finding demand primarily as poultry feed, secondarily as cattle feed and in brewing applications.[4]
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Sorghum is a self-pollinating plant. It is more drought and temperature resistant than maize (corn), soybeans, wheat and other crops. The height of the plant depends on the breed and growing conditions, varying between 60 to 460 centimeters. The long, wide leaves grow off the stalk. Sorghum seed is small and round. A seed head is usually between 25 to 36 centimeters, present on the top of the stalk of a mature sorghum plant.[5]
Sorghum seed consists of three major anatomic sections - pericarp (outer layer), endosperm (storage organ) and the germ. The pericarp is made of three segments - epicarp, mesocarp and endocarp. The epicarp is the outermost layer covered with a thin waxy film. The mesocarp consists of a large amount of starch granules. Sorghum is claimed to be the only food staple that contains starch in this anatomical section of the seed. Sorghum's endosperm is composed of aleurone layer, peripheral, corneous and floury areas. The aleurone contains proteins (protein bodies and enzymes), ash (phytin bodies) and oil (spherosomes). The germ has two major parts: the embryonic axis and embryonic disc. The protein of the germ contains high levels of lysine and tryptophan that are of unusually good quality for human consumption, as well as for fodder.
Sorghum is native to the tropical areas in Africa. The oldest cultivation record dates back to 3000 B.C. in Egypt. The original variety of sorghum was purple or red and the seed coat was red.[5]
In the 1950’s, hybrid sorghums were developed for higher yields and it became a popular crop as yields increased dramatically. The hybrid variety also offered a color and taste preferred by consumers. Sorghum grown in the United States is usually this hybrid variety, which is white sorghum with white seed coat, champagne colored body and wheat colored head. In other parts of the world, red or purple variety of low yield sorghum continues to be grown. Sorghum is now a globally important commercial crop.
One species, Sorghum bicolor,[6] is an important world crop, used for food (as grain and in sorghum syrup or "sorghum molasses"), fodder, the production of alcoholic beverages, as well as biofuels. Most varieties are drought and heat tolerant, and are especially important in arid regions, where the grain is staple or one of the staples for poor and rural people. They form an important component of pastures in many tropical regions. Sorghum is an important food crop in Africa, Central America, and South Asia and is the "fifth most important cereal crop grown in the world".[7]
Some species of sorghum can contain levels of hydrogen cyanide, hordenine and nitrates lethal to grazing animals in the early stages of the plant's growth. Stressed plants, even at later stages of growth, can also contain toxic levels of cyanide.
Another Sorghum species, Johnson grass (S. halapense), is classified as an invasive species in the US by the Department of Agriculture.[8]
Sorghum vulgare var. technicum is commonly called broomcorn.[9]
Sorghum is about 70 percent starch and a good energy source. Sorghum starch consists of 70 to 80 percent amylopectin, a branched-chain polymer of glucose, and 20 to 30 percent amylose, a straight-chain polymer.
The digestibility of the sorghum starch is relatively poor in unprocessed form, varying between 33 to 48 percent. Processing of the sorghum grain by methods such as steaming, pressure-cooking, flaking, puffing or micronization of the starch increases the digestibility of sorghum starch. This has been attributed to a release of starch granules from the protein matrix rendering them more susceptible to enzymatic digestion.
On cooking, the gelatinized starch of sorghum tends to return from the soluble, dispersed and amorphous state to an insoluble crystalline state. This phenomenon is known as retrogradation; it is enhanced with low temperature and high concentration of starch. Amylose, the linear component of the starch, is more susceptible to retrogradation.
Certain sorghum varieties contain anti-nutritional factors such as tannins. The presence of tannins is claimed to contribute to the poor digestibility of sorghum starch. Processing in humid thermal environment aids in lowering anti-nutritional factors of sorghum.
Sorghum starch does not contain gluten. This makes sorghum a possible grain for those who are gluten sensitive.[5]
After starch, proteins are the main constituent of sorghum. The essential amino acid profile of sorghum protein is claimed to depend on the sorghum variety, soil and growing conditions. A wide variation has been reported. For example, lysine content in sorghum has been reported to vary from 71 to 212 mg per gram of nitrogen.[1] Some studies on sorghum's amino acid composition suggest albumin and globulin fractions contained high amounts of Iysine and tryptophan and in general were well balanced in their essential amino acid composition. On the other hand, some studies claim sorghum's prolamin fraction was extremely poor in Iysine, arginine, histidine and tryptophan and contained high amounts of proline, glutamic acid and leucine. These variations may be linked to the sorghum variety, soil and growing conditions. The digestibility of sorghum protein has also been found to vary between different varieties and source of sorghum. Digestibility values ranging from 30 to 70 percent have been reported.
A World Health Organization report suggests that the inherent capacity of the existing sorghum varieties commonly consumed in poor countries was not adequate to meet the growth requirements of infants and young children. The report also claims that sorghum alone may not be able to meet the healthy maintenance requirements in adults. A balanced diet would supplement sorghum with other food staples.
Sorghum's nutritional profile includes several minerals. This mineral matter is unevenly distributed and is more concentrated in the germ and the seed-coat. In milled sorghum flours, minerals such as phosphorus, iron, zinc and copper decreased with lower extraction rates. Similarly, pearling the grain to remove the fibrous seed-coat resulted in considerable reduction in the mineral contents of sorghum. The presence of anti-nutrition factors such as tannins in sorghum reduces its mineral availability as food. It is important to process and prepare sorghum properly to improve sorghum's nutrition value.
Sorghum is a good source of B-complex vitamins. Some varieties of sorghum contain ß-carotene which can be converted to vitamin A by the human body; given the photosensitive nature of carotenes and variability due to environmental factors, scientists claim sorghum is likely to be of little importance as a dietary source of vitamin A precursor. Some fat-soluble vitamins, namely D, E and K, have also been found in sorghum grain in detectable but insufficient quantities. Sorghum as it is generally consumed is not a source of vitamin C.
The following table shows the nutrient content of sorghum and compares it to major staple foods in a raw form. Raw forms of these staples, however, aren't edible and can not be digested. These must be prepared and cooked as appropriate for human consumption. In post-processed and cooked form, the relative nutritional and anti-nutritional contents of each of these grains is remarkably different from that of raw form of these grains reported in this table. The nutrition value for each staple food in cooked form depends on the cooking method (for example: boiling, baking, steaming, frying, etc.).
| Synopsis[10] ~ composition: | Cassava[11] | Wheat[12] | Rice[13] | Sweetcorn[14] | Potato[15] | Sorghum[16] |
|---|---|---|---|---|---|---|
| Component (per 100g portion, raw grain) | Amount | Amount | Amount | Amount | Amount | Amount |
| water (g) | 60 | 11 | 12 | 76 | 82 | 9.2 |
| energy (kJ) | 667 | 1506 | 1527 | 360 | 288 | 1418 |
| protein (g) | 1.4 | 23 | 7 | 3 | 1.7 | 11.3 |
| fat (g) | 0.3 | 10 | 1 | 1 | 0.1 | 3.3 |
| carbohydrates (g) | 38 | 52 | 79 | 19 | 16 | 75 |
| fiber (g) | 1.8 | 13 | 1 | 3 | 2.4 | 6.3 |
| sugars (g) | 1.7 | <0.1 | >0.1 | 3 | 1.2 | 1.9 |
| iron (mg) | 0.27 | 6.3 | 0.8 | 0.5 | 0.5 | 4.4 |
| manganese (mg) | 0.4 | 13.3 | 1.1 | 0.2 | 0.1 | <0.1 |
| calcium (mg) | 16 | 39 | 28 | 2 | 9 | 28 |
| magnesium (mg) | 21 | 239 | 25 | 37 | 21 | <120 |
| phosphorus (mg) | 27 | 842 | 115 | 89 | 62 | 287 |
| potassium (mg) | 271 | 892 | 115 | 270 | 407 | 350 |
| zinc (mg) | 0.3 | 12.3 | 1.1 | 0.5 | 0.3 | <1 |
| pantothenic acid (mg) | 0.1 | 2.3 | 1.0 | 0.7 | 0.3 | <0.9 |
| vitB6 (mg) | 0.1 | 1.3 | 0.2 | 0.1 | 0.2 | <0.3 |
| folate (µg) | 27 | 281 | 8 | 42 | 18 | <25 |
| thiamin (mg) | 0.1 | 1.9 | 0.1 | 0.2 | 0.1 | 0.2 |
| riboflavin (mg) | <0.1 | 0.5 | >0.1 | 0.1 | >0.1 | 0.1 |
| niacin (mg) | 0.9 | 6.8 | 1.6 | 1.8 | 1.1 | 2.9 |
In 2009, a team of international researchers announced they had sequenced the sorghum genome.[17][18]
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