Analysis of soybean protein-derived peptides and the effect of cultivar, environmental conditions, and processing on lunasin concentration in soybean and soy products

Soybean, an important source of food proteins, has received increasing interest from the public because of its reported health benefits. These health benefits are attributed to its components, including isoflavones, saponins, proteins, and peptides. Lunasin, Bowman-Birk inhibitor, lectin, and β-conglycinin are some of the biologically active peptides and proteins found in soybean. This article provides a comprehensive review on the recently used techniques in the analysis and characterization of food bioactive peptides, with emphasis on soybean peptides. The methods used to isolate and purify lunasin from defatted soybean flour were ion-exchange chromatography, ultrafiltration, and gel filtration chromatography. The identity of lunasin was established by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blot, matrix-assisted laser desorption ionization-time of flight, and liquid chromatography. The results on the effect of soybean cultivar and environmental factors on lunasin concentration are also reported. The highest lunasin concentration, 11.7 ± 0.3 mg/g flour, was found in Loda soybean cultivar grown at 23°C; the lowest concentration, 5.4 ± 0.4 mg/g flour, was found in Imari soybean cultivar grown at 28°C. Lunasin concentration was affected by cultivar-temperature, cultivar-soil moisture, and cultivar-temperature-soil moisture interactions. The variation on lunasin concentration suggests that its content can be improved by breeding, and by optimization of growing conditions. In summary, bioactive peptides can be accurately identified and quantified by using different techniques and conditions. In addition, lunasin concentration in soybean depends mainly on cultivar and to some extent on environmental factors, particularly temperature. Lunasin concentration in soy products was also affected by processing conditions.