**7. Agronomic relations**

Amino acids concentrations in soybean are not only affected by their genetic potential. Agronomic properties greatly impact the final levels of amino acids. Agronomy encompasses all aspects of crop production including environmental effects, climatic variables, and abiotic factors. Perhaps the most considered agronomic factor is soil nutrient availability. Insufficient soil nutrient levels of nitrogen, potassium, phosphorous, sulfur, calcium, and magnesium create poor amino acid profiles in soybean plants [71]. Increased phosphorous rates have been shown to increase the percentage of methionine and tryptophan in seed but had no effect on protein content percentage [72]. Applications of sulfur, phosphorous, and nitrogen (individual and combined) produced a variety of different methionine and cysteine seed concentrations [73]. Sulfur deficiencies were also shown to inhibit the production of 11S proteins while almost eliminating methionine and cysteine in 7S proteins [74]. It is becoming more popular to also apply biological substances such as amino acids to plants through foliar and seed application. Amino acid uptake by soybean and wheat have been proven, and improved soybean growth rates and antioxidant effects have also occurred [75, 76]. Further research should be conducted to determine if biofortification solutions are possible through amino acid application.

exist including solvent extraction, screw pressing, and extruding [48, 82, 83]. All three processes have three final products: oil, meal (usually toasted to lessen anti-nutritional factors), and hulls. Over processing of solvent extracted soymeal has been shown to decrease lysine, cysteine, and arginine levels [84, 85]. Protein solubility and dispersibility measurements may be a useful indicator of over processing [86, 87]. Soybean hulls are sometimes added to livestock feed for additional fiber, however an increase in hull/meal ratios decrease the digestibility of amino acids [88]. While soybean is renowned for its protein and amino acid content,

Soybean Amino Acids in Health, Genetics, and Evaluation

http://dx.doi.org/10.5772/intechopen.89497

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All previously mentioned aspects of soybean production in regard to amino acid levels and human and animal nutrition depend on a single common denominator: amino acid quantification. Amino acids must be reliably, effectively, and accurately identified, measured and evaluated. A Google Scholar search of "amino acid analysis" will display over 1 million results. Several reviews have been published regarding the development of amino acid analysis [89–91]. In general, contemporary analysis of amino acids from any source will be performed by chromatography or near-infrared reflectance spectroscopy. Chromatography is the common method with specific techniques including ion exchange chromatography (IEC), high-performance liquid chromatography (HPLC), and gas chromatography (GC). HPLC is the more validated method for soybean amino acid analysis. It is more efficient than IEC, and it does not require the transformation into volatiles like GC [91–94]. Near-infrared reflectance spectroscopy (NIRS) is a more recent addition to amino acid analysis, and it has the potential to drastically improve the efficiency in soybean feed evaluation [19]. The inability to actually measure amino acid levels is main hindrance for NIRS amino acid analysis. NIRS methods must be developed from a calibration set of raw data (often from HPLC) [95–97]. Nonetheless, efficiency improvements should persuade researchers to continually explore future NIRS amino acid analysis applications.

Soybean is a valuable source of protein and amino acids for humans and livestock. Soybean's well-balanced amino acid profile provides all essential amino acids as well as most nonessential. However, there is much room for nutritional improvement. Proteinogenic sulfurcontaining amino acids, methionine and cysteine, are deficient in soybean and are especially needed in livestock rations. Increased levels of these amino acids would augment soybean meal value and lessen the need for synthetic amino acid supplements. Breeding efforts have made little progress in adjusting amino acid profiles thus far, however significant developments in understanding genomic control regions promise future success. Genetic engineering efforts have shown promising amino acid improvements, but regulations and public opinion made commercialization difficult. New gene-editing technology could be the key to unlock-

actual nutritional values can be decreased through certain processing methods.

**9. Evaluation methods**

**10. Conclusion**

ing true nutritional improvement.

Amino acid variation has also been shown to occur across environments [24, 59]. Specific correlations have emerged in response to temperature, solar radiation, and rainfall. One study shows that increased temperature leads to increased concentrations of all proteinogenic amino acids [77], while another concludes that only methionine and cysteine increase alongside temperature [78]. Increased solar radiation and greater available water appeared to have a negative relationship with amino acid content [77]. These favorable conditions would increase yield which has been shown to have a negative correlation with overall protein content [57]. The multitude of agronomic factors that affect amino acid profiles in soybean make it exceedingly important to compensate for variables when researching.
