Commercial Sorghum - Nutritional Profile

Nutritional Profile

Sorghum is about 70% starch, so is a good energy source. Its starch consists of 70 to 80% amylopectin, a branched-chain polymer of glucose, and 20 to 30% amylose, a straight-chain polymer.

The digestibility of the sorghum starch is relatively poor in its unprocessed form, varying between 33 and 48%. Processing of the 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 temperatures and high concentrations of starch. Amylose, the linear component of the starch, is more susceptible to retrogradation.

Certain sorghum varieties contain antinutritional factors such as tannins. The presence of tannins is claimed to contribute to the poor digestibility of sorghum starch. Processing in humid thermal environments aids in lowering the antinutritional factors.

Sorghum starch does not contain gluten. This makes it a possible grain for those who are gluten sensitive.

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. Some studies on sorghum's amino acid composition suggest albumin and globulin fractions contained high amounts of lysine 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 lysine, arginine, histidine and tryptophan and contained high amounts of proline, glutamic acid and leucine. The digestibility of sorghum protein has also been found to vary between different varieties and source of sorghum, ranging from 30 to 70%.

A World Health Organization report suggests 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 claimed 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 reductions in the mineral contents of sorghum. The presence of antinutrition factors such as tannins in sorghum reduces its mineral availability as food. It is important to process and prepare sorghum properly to improve its 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.