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New Crops News, Spring 1993, vol. 3 no. 1

Edible Soybeans

A project researched as part of the New Crops Initiative was the development of soybeans with improved flavor that can compete effectively in the Oriental edible food industry. Niels Nielsen’s group at the Department of Agronomy has demonstrated that the removal of certain lipoxygenase enzymes from soybeans causes a substantial decrease in the beany off-flavor associated with soybean products. Subsequent evaluation of low lipoxygenase Century soybeans in the Japanese edible food industry revealed that they produced products that were too yellow. In addition, the tofu produced from soy milk extracted from low lipoxygenase Century soybeans was soft.

Extraction and characterization of compounds from soy milk that are responsible for the yellow color have revealed that the offending chemical is an isoflavone. A simple quantitative test has been developed to detect the presence of this compound early in the breeding program to generate new soybean varieties suitable for the Oriental market place. Moreover, genetic studies have demonstrated that it is reasonably easy to separate the low lipoxygenase trait from the yellow color that decreases substantially the value of soybeans in the edible food industry of the Orient.

Research has been aimed at developing a simple small-scale experimental method to rapidly produce tofu whose texture is equivalent to that of tofu produced commercially. A method has been perfected that results in the production of tofu from 80 grams of seed and that yields highly reproducible results. The method has been used to evaluate about 200 soybean varieties grown in the Midwest. Among these, a number were identified that could be used as parents in a breeding program. These parents have been hybridized with Japanese lines selected because they are commonly used in the tofu industry. Third and fourth generation selections from these crosses will be evaluated in the field and in the laboratory during the summer and fall of 1993. The nursery at the Purdue University Agronomy Farm used for these selections will grow 10 to 11 acres of specialty beans during summer 1993.

This issue of quality control is one that has received scant attention, but that will assume an increased importance as value added new crops begin to play a more prominent role in the seed industry. In anticipation of this problem, a simple and rapid immunological test was developed that permits quantitation of the lipoxygenase content of seeds. Monoclonal antibodies that specifically recognize each of the three lipoxygenases found in soybeans have been developed and are used in Enzyme-linked Immunosorbant Assays (ELISA). The test is being used to screen seeds from breeding populations to identify low lipoxygenase genotypes. It is also being used for quality control purposes. With the ELISA test we have developed, contamination of lipoxygenase at levels under 0.5% can be accomplished. The test is presently available to other researchers in the U.S. through the Indiana Crop Improvement Association, a not-for-profit organization associated with Purdue University.