Improving Functional Properties of Soy Protein Hydrolysate by Conjugation with Curdlan

ABSTRACT:  Soy protein hydrolysate was conjugated with curdlan through the naturally occurring Maillard reaction to extend its application in food processing. The gel-forming and emulsifying properties of soy protein hydrolysates were significantly improved ( P < 0.05) by conjugation with curdlan. The soy protein hydrolysate–curdlan conjugate (SPHCC)–soy protein isolate (SPI) mixed gel had a much thicker network than the soy protein hydrolysate and SPI mixed gel judged from scanning electron microscopic images. The improvement of gelling properties of soy protein hydrolysate by curdlan-conjugate was attributed to both the decrease in the repulsive forces among soy protein hydrolysates and the increase in the solubility. The covalent binding of soy protein hydrolysates and curdlan also showed a profound effect on the antioxidative activity of the soy protein hydrolysates. The higher antioxidative activity of SPHCC was related to the peptide reductants produced from the Maillard reaction and the higher emulsifying property of SPHCC. The conjugates of soy protein hydrolysate and curdlan can be used as a functional food additive having excellent gel-forming, emulsifying properties and antioxidative activity.     

Gel-forming Ability and Radical-scavenging Activity of Soy Protein Hydrolysate Treated with Transglutaminase

ABSTRACT: Gel-forming ability and 1,1-diphenyl-2-picrydrazyl (DPPH) radical-scavenging activity of the peptic hydrolysate from soy protein isolate (SPI) were investigated. The gel-forming ability of mixtures consisted of SPI and its hydrolysate decreased as the percentage of hydrolysate increased. The inferior gel-forming ability of the hydrolysate was shown to be related to both the low surface hydrophobicity of the hydrolysate and the drop in sulfhydryl exchange reactions during gelation. Although antioxidants in the SPI-hydrolysate mixture (SHM) could be helpful in enhancing the radical-scavenging activity of the peptide-based gel, they suppressed the oxidization of sulfhydryls in sulfhydryl group/disulfide bond interaction. As a result of this, antioxidants present reduced the gel-forming ability of the SHM. The addition of transglutaminase (TGase) improved the gel-forming ability of SHM. A mixture of 70% SPI and 30% hydrolysate in the presence of TGase resulted in a gel with good gelling property and high radical-scavenging activity.     

Isolation and characterisation of a novel angiotensin I‐converting enzyme‐inhibitory peptide derived from douchi,a traditional Chinese fermented soybean food

BACKGROUND: Douchi, a traditional fermented soybean food, has recently attracted a great deal of attention owing to its superior physiological activity. In the present study the angiotensin I‐converting enzyme (ACE)‐inhibitory activity of typical douchi procured from various regions of China was analysed. An ACE‐inhibitory peptide derived from the most potent douchi was also isolated and characterised. The pattern of ACE inhibition and resistance to hydrolysis by gastrointestinal proteases of this peptide are described. RESULTS: ACE‐inhibitory activities were detected in all douchi samples, with IC₅₀ values ranging from 0.204 to 2.011 mg mL^?1. Among the douchi samples, a Mucor‐type douchi exhibited the most potent ACE‐inhibitory activity (IC₅₀ = 0.204 mg mL^?1). A novel ACE‐inhibitory peptide was then isolated from this Mucor‐type douchi using ultrafiltration followed by Sephadex G‐25 column chromatography and reverse phase high‐performance liquid chromatography. The amino acid sequence of the purified peptide was identified by Edman degradation as His‐Leu‐Pro (IC₅₀ = 2.37 µmol L^?1). The peptide is a competitive inhibitor and maintained its inhibitory activity even after incubation with some gastrointestinal proteases. CONCLUSION: The present study shows that peptides derived from soybean fermentation during douchi processing could be the main contributor to the ACE‐inhibitory activity observed. Copyright © 2009 Society of Chemical Industry