Dwarf bunt of wheat, caused by the fungus Tilletia contraversa, is a pathogen historically limited in distribution by its very specific climatic requirements for establishment. In an effort to both address the need for adequate protection and eliminate unwarranted trade barriers, a number of countries have examined restrictions on importing milling wheat containing teliospores of T. contraversa. Pest risk analysis (PRA), under the guidelines of the World Trade Organization and Food and Agriculture Organization, has become an internationally accepted process for evaluating such issues. As a component of a dwarf bunt PRA, our objective was to develop a quantitative mathematical model to evaluate and communicate the potential risk of dwarf bunt establishment from the importation of U.S. milling wheat containing teliospores of T. contraversa. A T. contraversa–risk model (TCK-risk model) was developed using new data, historic literature, and industry statistics to estimate teliospore diversion from transport and milling processes, spore contamination levels, grain handling, and end-product usage. A climatic model was developed to identify potential regions where the environment was favorable for disease development. The likelihood of disease establishment and wheat yield loss was determined using the model to conduct Monte Carlo simulations of 100,000 wheat shipping-years. The model is dynamic in that individual components can be easily updated or modified in order to determine the effect of numerous scenarios (e.g., climate changes, shipping tonnage, contamination levels, mitigation strategies) on the probability of dwarf bunt establishment. TCK-risk model evaluation scenarios previously conducted for the People's Republic of China, Brazil, Mexico, and Peru are presented as examples.
The relative importance of gossypol and raffinose in binding and destruction of lysine and in impairing the nutritive value of cottonseed meals was studied with meals from glandless cottonseed. Nutritional evaluations with protein-depleted rats showed that: raffinose in cottonseed reduces lysine content and nutritive quality of the proteins when heat is applied; 1 % concentration of gossypol is not as effective as 10% of raffinose in destroying lysine in cottonseed meal; gossypol and raffinose at these same concentrations are comparable in reducing the level of free e-aminolysine in cottonseed proteins; and the nutritive index of cottonseed meals as determined by the rat repletion method is highly correlated with the free e-amino groups of lysine of the protein, and poorly correlated with total lysine. The nutritive quality of cottonseed meal is impaired when it is heated (5), partly because of the destruction of a portion of the lysine in the proteins (7, 77). The mechanism of this destruction is not known. It is possible that both carbohydrates and gossypol are
The work reported grew out of an interest in the effects of heat on the nutritive quality of plant proteins. Lysine is the limiting amino acid in most rations in which cereals are the source of energy. Because the chick pea, a typically starchy seed, is rich in lysine and is an important food crop, interest developed in the effects of heat on the nutritive quality of its proteins in comparison with typical oilseeds. About 25% of the chick pea is protein, rich in lysine (6.5 to 6.7%). The lysine content is reduced about 1 0% when the seeds are heated in the autoclave to 121 0 C. for 30 and 60 minutes. The reduction is greater the less the moisture content of the seed.Usually the nutritional quality of oilseed meal proteins is improved when heating of the seed during processing for oil is moderate ( 9), but amino acids, especially lysine, cystine, and arginine, are destroyed when heating is severe.
In addition to the soybean, many other sources of vegetable protein have potential to provide a broad spectrum of functional properties. Among these sources are cottonseed, peanut, sunflower, and rapeseed. As with soy, the functional characteristics vary with the type of product, e.g., flour, concentrate, or isolate. In this discussion, functionality is defined as the set of properties that contributes to the desired color, flavor, texture, or nutritive value of a product. Utilization of these alternate sources of vegetable proteins will depend upon availability, economics of the product in any given country, and on the uniqueness and desirability of the functional properties of the product.
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