Protein content in soybeans

Seed composition is a very important trait in soybean. Since soybean is used for both oil and protein, breeders generally try to aim for 40% protein and 20% oil (on a dry matter basis). In most cases, to date, soybeans are not marketed on composition however, protein and oil content has been considered in the special purpose/food soybean market for many years. Recently, limited markets are available for commodity soybeans with specified oil and/or protein levels. Although both oil and protein levels are quantitative traits, breeding can readily alter them. As technology for rapidly, accurately, and inexpensively measuring oil and protein content in soybeans becomes available, seed composition will need to be a trait specifically selected for breeders. 

Wolf ( ) has pointed out that the soybean could be classified as a protein seed rather than an oilseed. Average proximate composition of presently grown varieties Is 40% protein and 20% oil depending upon variety and strain, protein content ranges between 34-49% and oil content ranges from 14-25% ( 2). Protein content In soybeans Is higher than In many meat products and about twice that of other food legumes on an as-ls basis. 

Zu, S., Riaz, M. N., and Lusas, E. W., Effect of different extrusion temperatures and moisture content on lipoxygenase inactivation and protein solubility in Soybeans, J. Agric. Fd. Chem., 44,3315-3318 (1996). 

One observation is that many individual amino acids increase as crude protein content increases. As is apparent from Table 6.8, as the protein content of soybean meal goes up (in this case from 44 to 48%), in all cases the percentage of each amino acid contained goes up, but not necessarily in the exact ratio of the protein increase. 

Depending on the stage of maturity, green vegetable soybeans have protein contents in the range of 11—16% and oil in the range of 8—11%, whereas on moisture-free... 

The protein content of sea lettuces varies with the species but generally present in high amoimts. For example, protein content in Ulva reticulata is 21.06% of the dry weight, whereas higher protein contents are recorded in Ulva lactuca 27.2% of the dry weight (Ortiz et ah, 2006 Ratana-arporn and Chirapart, 2006). These level are comparable to those foimd in high-protein terrestrial vegetables such as soybeans, in which protein make up 40% of the dry mass (Murata and Nakazoe, 2001). 

H. Abe. et al. Non-destructive determination of protein content in a single kernel wheat and soybean by near infrared spectroscopy In Near-Infrared Spectroscopy The Future Waves Proceedings of the Seventh International Conference on Near-Infrared Spectroscopy, A.M.C. Davies, PhU Wifliams co-eds. NIR Publications, Chichester, UK, 1996, p. 457 61. 

Soybeans contain about 40% protein (dry basis) and are rich in amino acids lysine and threonine. However, low content of the essential amino acid L-methionine hmits nutritive value of soy protein. Globulins, referred to as glycinin and conglycinin, are the most abundant protein types in soybeans. Health benefits of soybean proteins have been studied extensively. Positive effects of soybean proteins on hypertension and heart disease, osteoporosis, bone health and certain cancers have been reported (Friedman and Brandon, 2001). The US Food and Drug Administration (FDA) has authorized a health claim on the role of soy protein in reducing risk of coronary heart disease. The FDA rule permits a statement on the soybean containing product labels indicating that Diets low in saturated fat and cholesterol that include 25 g of soy protein a day may reduce the risk of heart disease (FDA, 1999). 

Soybean Protein Isolates. Soybean protein isolates, having a protein content of >90 wt%, are the only vegetable proteins that are widely used in imitation dairy products (1). Most isolates are derived from isoelectric precipitation, so that the soybean protein isolates have properties that are similar to those of casein. They are insoluble at thek isoelectric point, have a relatively high proportion of hydrophobic amino acid residues, and are calcium-sensitive. They differ from casein in that they are heat-denaturable and thus heat-labile. The proteins have relatively good nutritional properties and have been increasingly used as a principal source of protein. A main deterrent to use has been the beany flavor associated with the product. Use is expected to increase in part because of lower cost as compared to caseinates. There has been much research to develop improved soybean protein isolates. 

Nutrition research on winged bean has mainly focused upon the tough, mature seed, which is rich in protein and oil. The seeds are occasionally consumed in Indonesia and Papua NewGuinea (59, 60). A survey of 240 winged bean accessions from 16 countries showed that the protein and oil contents range between 20.7-45.9% and 7.2-21.5% respectively (13). Studies on the evaluation of seed flour as an alternative feed source for livestock has only recently begun. The two most commonly used plant protein sources in broiler (chicken) diets to date have been soybean and peanut cake (62). 

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