New Crops News, Spring 1992, vol. 2 no. 1
As one example, processors in many parts of the world are demanding that a minimum protein content in soybeans be maintained. This demand is in part a consequence of the selection criteria that have traditionally been used for breeding efforts. Because yield is the primary selection criteria, and yield and protein content are in general inversely related in soybeans, a gradual reduction in seed total protein content has taken place, as higher yielding varieties have been released. As protein based co-products produced from soybeans increased in importance compared to oil, seed protein contents decreased below the minimum standards of some processors. To meet these demands, independently run, nonstandardized tests are being performed by some processors to monitor total oil and protein content. These events have raised serious concerns among American soybean producers, and there has been discussion about changes that might be introduced into quality standards used for commodity pricing.
Were the demands limited to increased total protein or oil in soybeans, changes to the quality standards would be an attractive solution. Unfortunately, however, the issues are far more complex than this because of the appearance of markets for identity preserved soybeans. One of the earliest example of such crops is soybeans destined for the edible food market in the Orient. Japanese soymilk and tofu makers discovered many years ago that not all soybeans grown in the United States are equally suitable for making these traditional Asian food products. As a consequence, a growing acreage of certain soybean varieties is being grown under contract for Japanese producers, and these varieties remain identity preserved from their point of origin to product manufacture. Often soybeans destined for the edible food market in the Orient are not among the highest yielding soybean varieties, but have other more important traits that make them more valuable to the consumer, such as product flavor and texture. The added value of these products not only must defray the expense of identity preservation, but farmer producers must be paid a premium to grow the varieties because their yield is usually substantially lower than adapted American varieties.
Although only a small part of the industry at present, new soybean crops that cater to specific niches can be expected to account for a considerably larger proportion of the total market than at present. New crops tailored to meet the demands of specific industries and generated either via the application of conventional breeding technology or by the use of nonconventional biotechnological approaches, are sure to make an appearance in the near term. Already, extensive efforts are underway to modify oil content so that this co-product of soybeans can compete in new market areas. As part of the efforts at the New Crops Center in the Purdue Agricultural Experiment Station, several new soybean lines are being evaluated that have altered oil contents. One of these lines contains 17% palmitic acid as compared to about 11% in normal varieties. The significance of the increased palmitic acid content relates to oils used as shortenings added to improve the texture of baked products. Presently, soybean oil is blended with cottonseed oil that has 25% palmitic acid to produce shortening with the desired qualities. Sufficient amounts of the high palmitic acid seed have been produced and are being evaluated to determine if that oil can be used as a shortening directly without blending in cottonseed oil to increase palmitic acid content.
Other experimental soybean lines have been generated in which the concentration of either the saturated or polyunsaturated fatty acids are reduced. Reduced amounts of saturated fatty acids in human diets is associated with improved cardiovascular health. In one experimental line palmitic acid is decreased from 11% to 8%, and this reduces the total saturated fatty acids from 14% to 11%. Polyunsaturated fatty acids, on the other hand, are associated with poor oil flavor and stability. Presently soybean oil is hydrogenated to overcome these flavor and stability problems. A soybean with only 3.5% linolenic acid (18:3) has been identified. Tests have demonstrated that oil with reduced linolenic acid content has improved stability, flavor, and odor, particularly when heated.
Another project actively researched as part of the New Crops initiative is the development of soybeans with improved flavor that can compete effectively in the Oriental edible food industry. Earlier it was demonstrated that the removal of certain lipoxygenase enzymes from the seed caused 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 soymilk extracted from low lipoxygenase 'Century' soybeans was soft. Extraction and characterization of compounds from soymilk that are responsible for the yellow color has revealed that the offending chemical is probably an isoflavone, and efforts are underway to develop a simple and rapid quantitative test to detect its presence early in breeding programs. Research has also 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 during the past year that results in the production of tofu from 80 grams of seed, and that yields highly reproducible results. In addition to being useful in evaluating soybean lines in breeding populations, the method has been used to evaluate nearly 200 American commercial varieties to identify those that might be useful as parents in breeding programs.
The issue of quality control is one that has received scant attention, but which will assume an increased importance as value added new crops begin to play a more prominent role in the soybean industry. In anticipation of this problem, a simple and rapid immunological test has been developed that permits quantitation of the lipoxygenase content of seeds. Monoclonal antibodies that specifically recognize each of the three prevalent lipoxygenases found in soybeans have been developed and are used in Enzyme-linked Immunosorbant Assays (ELISA). This test can be used to detect contamination of low lipoxygenase by normal soybeans at levels under 0.5%. In addition, the test has considerably improved both the speed and accuracy with which low lipoxygenase lines can be identified in breeding populations, and is not nearly as cost-prohibitive as earlier tests.
It is important that new soybean varieties with unique characteristics retain their identity if they are to find niches in the market where they are preferred over conventional varieties. Economics dictate that the added value associated with their production must exceed the additional expense of production. Techniques such as the ELISA assay for lipoxygenase are a fundamental requirement so that value added varieties can be produced and marketed under an identity preserved system. Processors need to be guaranteed that the soybeans purchased are not contaminated with seeds that lack the desirable quality characteristics.
Niels C. Nielsen