Isolation of Nicotianamine from Soybean Broth and Changes in Its Content in the Soybean Steaming Process

Abstract

Soybean broth (SB), a by-product of miso, soy sauce and natto manufacturing, is discarded as an industrial waste. The change in the inhibitory activity of angiotensin I-converting enzyme (ACE) in the soybean steaming process was investigated to evaluate the use of SB as a functional food material. An ACE inhibitor was isolated from SB by ion-exchange and gel chromatography. The results of the chemical identification by TOF-mass, IR, and NMR spectra analysis corresponded to those of Kristensen et al. for nicotianamine. The yield of pure nicotianamine from SB was 0.037% (dry matter). In the soybean steaming process at 121°C for 30min, the ACE inhibitory activity was the same in both raw and soaked soybeans, but decreased to 30% of raw soybeans in steamed soybeans and 10% in SB. The same changes were found for the nicotianamine content as for the ACE inhibitory activity in the soybean steaming process. As the content of lipids and water-soluble high-molecular-weight proteins is low in SB, nicotianamine can be easily isolated. Therefore, SB may be a suitable source of nicotianamine.