Chemical inactivation of soybean protease inhibitors

et al. 2010

Ann Microbiol

The anti-Aspergillus flavus activity of trypsin inhibitor (TI) from cultivated and wild-type soybean (SBTI and WBTI) was investigated in order to confirm its ability to reduce the activity of endogenous α-amylase, protease enzymes and production of aflatoxin B 1 secreted by A. flavus. In the current study, it was demonstrated that purified SBTI/WBTI belonged to the family of Bowman-Birk TI, based on evidence from amino acid composition, the presence of two independent binding sites for trypsin and chymotrypsin, and a lysine residue as the active site for trypsin inhibition. Studying the inhibition of A. flavus showed that the effect of SBTI/SBTI on A. flavus α-amylase activity and aflatoxin B 1 production depended on TI concentration. However, no inhibitory effect was observed when sufficient exogenous α-amylase (EC 3.2.1.1, from Bacillus subtilis) was added. The resistance to A. flavus infection was partially due to the ability of SBTI/WBTI to inhibit α-amylase activity, thereby limiting the availability of hydrolyzed reducing sugar for fungal growth and further suppressing aflatoxin B 1 biosynthesis. In addition, the relationship between SBTI/WBTI levels and fungal protease expression revealed that A. flavus released a certain quantity of endogenous proteases into the culture medium, and the decreased activity of protease and production of aflatoxin B 1 suggested that the inhibition activity might also be mediated by SBTI/WBTI as A. flavus protease inhibitor activity.

Section: Resultssupporting

confidence: 82%

Section: Sbti and Wbti Inhibit α-Amylase Activity And Aflatoxin B 1 Pmentioning

confidence: 83%

Inhibition of endogenous α-amylase and protease of Aspergillus flavus by trypsin inhibitor from cultivated and wild-type soybean

Zhang

et al. 2010

Ann Microbiol

“…Another feeding trial showed that PER improved from 2.11 for rats fed soy flour treated with heat at 75°C alone to 2.49 (38% increase) for rats fed the flour treated with sodium sulfite at the same temperature [23]. Sessa and Nelsen [24] showed that trypsin inhibitors in model systems under 65-90°C with SMBS treatment can be reduced by 40-85% compared to the original activities. However, our proteins were treated at 55°C.…”

Section: In Vivo Digestibility Evaluated By Animal Feeding Testmentioning

confidence: 99%

Increased In Vitro and In Vivo Digestibility of Soy Proteins by Chemical Modification of Disulfide Bonds

Faris

et al. 2009

J Americ Oil Chem Soc

To improve protein digestibility of aqueously extracted soy proteins, an effective chemical treatment under mild conditions is needed. Soy proteins, including storage protein glycinin and antinutritional factors such as trypsin inhibitors, are rich in disulfide bonds. Reduction of these disulfide bonds by incubating soy proteins with sodium sulfite and sodium metabisulfite at 55°C showed no net increase of free sulfhydryl groups after dialysis to remove the residual reducing agent. However, the in vitro digestibility measured by trypsin hydrolysis using the pH-Stat method was significantly increased. Sodium metabisulfite (SMBS) was more effective in increasing in vitro digestibility than sodium sulfite at the same molar concentration. The digestibility of soy protein treated by 0.5 mmol SMBS/g soy flour at 55°C was more than doubled compared to that of the control without reduction treatment. Large-scale testing of soy proteins treated with SMBS for an in vivo animal feeding study showed similar in vitro digestibility by trypsin, e.g., the degree of hydrolysis of the treated sample was 8.5% compared to 1.6% of the control. These soy proteins were further evaluated using a chick growth model. The protein efficiency ratio (PER) increased by 57% when the chicks fed SMBStreated soy were compared to the chicks fed raw soy flour. SMBS-fed chicks did not display any pancreatic hypertrophy compared to those fed with raw soy control. These results indicate that there is great potential to use safe chemicals and mild temperature to inactivate the antinutritional factors in soybeans and thus improve digestibility of soy proteins that are extracted with low-temperature aqueous process.

“…It is believed by many researchers that the seven SS are responsible for the high heat stability. − Wu and Sessa used sodium metabisulfite to reduce the SS in BBI, and it was found that only approximately 16% of the original TIA remained . Sessa and Nelsen reported that steeping soybean flour in 50 mM Na 2 S 2 O 5 at 65 °C for 1 h could inactivate approximately 98% of the BBI and 95% of the KTI . Jiao et al used an NADP/thioredoxin system, dithiothreitol, and lipoic acid to treat BBI, and approximately 29.4, 11.1, and 87.5% of the original TIA remained, respectively …”

Section: Introductionmentioning

confidence: 99%

Effects of Disulfide Bond Reduction on the Conformation and Trypsin/Chymotrypsin Inhibitor Activity of Soybean Bowman-Birk Inhibitor

Kong

et al. 2017

J. Agric. Food Chem.

Soybean seeds contain three groups (A, C, and D) of Bowman-Birk inhibitors (BBIs). In this study, highly purified BBI-A (approximately 96%) was obtained from soybean whey at the 0.1 g level by the complex coacervation method. BBI-A has seven disulfide bonds (SS) and no sulfhydryl group and exhibits trypsin inhibitor activity (TIA) and chymotrypsin inhibitor activity (CIA). The X-ray structure has shown that BBI-A has five exposed SS and two buried SS. Because of steric hindrance, it was reasonable to consider that dithiothreitol first attacks the five exposed SS and then the two buried SS, which was supported by the results that SS reduction with dithiothreitol could be divided into quick and slow stages, and the critical point was close to 5/7. The effects of SS reduction on TIA and CIA could be divided into three stages: when one exposed SS was reduced, both TIA and CIA decreased to approximately 60%; with further reduction of exposed SS, CIA gradually decreased to 8% and TIA gradually decreased to 26%; with further reduction of buried SS, CIA gradually decreased to 2% and TIA slightly decreased to 24%. Far-ultraviolet (far-UV) circular dichroism (CD) spectra showed that the secondary structure of BBI-A was slightly changed, whereas near-ultraviolet (near-UV) CD spectra showed that the conformation of BBI-A was substantially changed after the five exposed SS were reduced; further reduction of buried SS affected the conformation to some extent. The results of Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and from a C8 column showed the same trend as near-UV CD spectra. BBI-A has a structural peculiarity in that two hydrophobic patches are exposed to the exterior (in contrast to typical soluble proteins), which was attributed to the seven SS by some researchers. These results support the hypothesis that hydrophobic collapse of the exposed hydrophobic patches into a regular hydrophobic core occurred after the reduction of SS in BBI-A.