Nutritional aspects of cereal proteins and approaches to overcome their deficiencies

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Abstract
The inferior nutritional value of cereal protein is primarily because of the high content of the storage protein prolamin. These proteins are in general characterized by a very high content of proline and glutamine and a low content of lysine and other nutritionally essential amino acids. The cereals vary with respect to prolamin and lysine content. Rice and oats have a relatively low prolam in content, around 10% , and an acceptable lysine content. W heat and barley contain 40-45% prolamin and about 3.5% lysine, while maize and sorghum contain more than 50% prolamin in their seed protein, that results in a lysine content below 2.5% . Intensive screenings for changes in endosperm morphology, protein composition, or lysine content have led to the detection of a number of mutants with reduced prolamin content and increased content of lysine and other essential amino acids. These high-lysine and low-prolamin mutants have a considerably improved nutritional value of the seed protein. However, all the mutants found so far are also characterized by a reduced starch content and grain yield, and high-lysine varieties have only been grown to a very limited extent. The present main approaches studied to improve the nutritional value of cereal proteins are (i) the replacement of some of the prolamin with lysine-rich storage proteins present in low amounts in the seed, and (ii) the improvement of the nutritional value of prolam in by genetic engineering.