In an international context, the priorities for the application of plant biotechnologies for the quality improvement of food vary depending on whether or not the community is in the developed or developing world.
Overwhelming proportions of the world's population are dependent on plants as their principal, if not exclusive, source of food. In such populations, the incidence of disease due to vitamin deficiencies is widespread. It has been estimated that over 100 million children worldwide are vitamin A deficient and that improving the vitamin A content of their food could prevent as many as 2 million deaths annually in young children (14). This is apart from the deficiencies in iodine intake, resulting in goiter, and from iron-deficient anemia, which are estimated to affect millions in the developing world. There is also an important need to improve the amino acid content of legume proteins that are deficient in essential sulfur amino acids.
There is evidence that the problem of vitamin A deficiency in particular has increased as a consequence of the application of traditional plant breeding. While the focus on improving disease resistance and yields of rice has rid many of these communities of hunger, it has had an impact on the local traditions. Less effort has been placed on growing alternative crops that may well have provided a source of vitamin A but are more difficult to make money from or do not produce consistent yields under local circumstances. This is particularly true of legume crops. With the focus only on this one aspect of basic food production, the problems of malnutrition have not disappeared. Indeed, the incidence of nutritional deficiencies may have increased.
This is an area of crucial importance to the majority of the world's population and is covered in greater detail in Chap. 12. Whatever strategies are adopted, there will need to be assurance that the introduction of any foreign protein into a plant will not increase the risks of an allergic response through the introduction of allergic epitopes. For example, the strategy of introducing a methionine-rich protein into legumes from the Brazil nut had to be abandoned because of the risks of an acute allergic response by some consumers (15). Apart from this problem, the sulfur-containing amino acid content of the legumes is not substantially raised. Suppression of synthesis of other methionine-rich proteins in the legume occurs (16). More information about the control of gene expression by the amino acid supply is required.
The interest in reducing antinutritional factors in plants has been predominantly focused around improving the nutritional value of feeding stuffs. Phy-tates are present in many plant seeds and uptake of limit phosphorus or iron as well as other elements. The potential for introducing a phytase gene into feeding stuffs has been explored (17). However, there are other strategies that seem to be of greater overall value in human nutrition. Thioredoxin is thought to be an activator of the germination process in seeds (18). It is able to activate proteins to degradation by proteolysis and results in improved digestibility (19). It also has the potential advantage of being able to reduce allergenicity, presumably because of its capacity to break disulfide bonds by the action of the reduced thiol groups in the molecule and ensure that the tertiary structure of the protein is accessible to degradation by proteases (19). The insertion of the wheat thioredoxin gene into barley has produced a transgenic plant in which thioredoxin accounts for 7% of the total protein content in the barley and is a good source of sulphur amino acids (20).
In contrast to that in the developing world, the incidence of known nutritional deficiency disorders in the developed world is low. Even in the case of vegetarians, there appears to be no appreciable problem. Classical nutritional deficiency diseases have been avoided through the widespread fortification of food when it was realized that many staple crops contained insufficient concentrations of many essential vitamins and minerals. Fortification is also utilized to replace nutrients lost in the heat processing of staple foods and through oxidation. In addition, the consumption of nutritional supplements is becoming more widespread. Nonetheless, there is good evidence, as shown in Fig. 2, that even in a country such as the United States, where most nutritionally related disorders probably stem from over-nutrition, there is inadequate intake of micronutrients compared with what would be found in the plasma if recommended dietary allowances (RDAs) were consumed.
For selected nutrients (iron, calcium, selenium, iodine, vitamin E, vitamin B6, and vitamin A), the clinical and epidemiological evidence strongly
Antioxidant status of US population compared with idea! '5-a-day' intake of fruit and vegetables
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