Determination of protease inhibitors, glycinin and beta-conglycinin in soybeans and their relationships

Authors: CHANG, SAM - Mississippi State University; YANG, YU - Northeast Agricultural University; ZHANG, YAN - Mississippi State University

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2021
Publication Date: 2/10/2022
Citation: Chang, S., Yang, Y., Zhang, Y. 2022. Determination of protease inhibitors, glycinin and beta-conglycinin in soybeans and their relationships. Journal of Food Science. 87:1082-1095. https://doi.org/10.1111/1750-3841.16054.
DOI: https://doi.org/10.1111/1750-3841.16054

Interpretive Summary: Soybean has been cultivated in most Asian countries for more than 3000 years, is being extensively used as an important source of high-quality oil and protein for both humans and animals throughout the world. Soybean and soy products have evoked tremendous interest globally due to their diverse health benefits, including promotion of cardiovascular health and reduction of cancer risk during recent years. However, soybean also contains two protease inhibitors, which can produce significant anti-nutritive effects to the body. These inhibitors, if not inactivated by cooking, can cause the enlargement of the pancreas in rodents and hypersecretion of digestive enzymes, including trypsin and chymotrypsin, and result in a decrease body growth. Aside from their negative biological effects, these inhibitors can be extracted for use as positiver processing aids to reduce protein degradation in fish gel processing during cooking. Due to large number of soybean available for industrial selection or in breeding programs, determination speed is important. In general, enzymatic and immunological tests are slower than electrophoresis, by which, many samples can be analyzed in one experiment. In the current study, we determined the content of the two protease inhibitors in 93 soybean varieties from different sources and harvest years. A reliable numerical equation was developed to estimate protease activity through their contents derived by electrophoresis. In addition, in this study, two major storage proteins of soybean with gelling ability were determined. The results provided useful foundational information for the food industry or breeders to select soybean varieties with different protease inhibitory activities or protein contents for different food processing applications.

Technical Abstract: In order to search for suitable soybean varieties for different food applications, the protein contents of Kunitz trypsin inhibitor (KTI), Bowman-Birk trypsin inhibitor (BBI), glycinin (11S) and ß-conglycinin (7S) of 93 soybean samples from different sources and harvest years were quantified by sodium-dodecyl-sulfate polyacrylamide gel electrophoresis. Meanwhile, the protease inhibitory activities against trypsin and chymotrypsin were determined. Results showed that the individual protein contents and trypsin inhibitor activities differed significantly (p< 0.05) among soybean samples. KTI contents ranged from 5.25 to 14.60 mg.g-1; BBI contents ranged from 1.81 to 5.74 mg.g-1; 11S varied from 13.65 to 48.55% and 7S varied from 15.68 to 42.15% of total soluble protein; trypsin and chymotrypsin inhibitory activities were 8.93–20.95 mg TI.g-1 and 4.18 –12.79 mg CI.g-1, respectively. Excellent linear relationships existed between trypsin inhibitor contents and their activities. The regression equations offer a rapid method for estimating the activity of KTI or BBI in raw soybeans or uncooked soy materials.