Modification of emulsifying properties and metal-ion chelating ability of gluten hydrolysates by partial enzymatic hydrolysis

Abstract

Wheat gluten represents the major protein fraction present in wheat flour and as protein-rich material posses cohesive and viscoelastic properties which permit the retention of gas bubbles in the dough. It could be obtained as a by-product during the separation of starch from wheat flour and as such may be utilized like a functional protein additive in various non-bakery foodstuffs due to its desirable structure-enhancing properties. However, wheat gluten is hardly soluble in water, which limits their expanding utilization. In the regard, the aim of this research was to investigate the correlation between process parameters of wheat gluten hydrolysis and emulsification activity and stability of the prepared hydrolysates. The hydrolysates showing the greatest enhancement of the emulsifying properties which are closed correlated with solubility improvement was further separated by sequential ultrafiltration to obtain molecular weight distribution profile and peptide fraction with higher metal-ion chelating ability. The hydrolysis was performed by using commercial endopeptidase from Bacillus licheniformis and process was followed by monitoring the degree of hydrolysis, emulsifying properties and metal-ion chelating activity. The effects of some relevant process parameters such as gluten concentration (1-9% w/v), temperature (40-60 °C), pH (7-9), enzyme/substrate ratio (0.25-0.75 AU g-¹ of protein) and their interactions were investigated by the means of the four-factor Box-Behnken experimental design with 29 experimental points (5 central points). The obtained results showed that the second-order models developed for emulsification activity and stability of gluten hydrolysates were significant (p<0.05) with a high value of the coefficients of determination (0.965-0.995). The statistical analysis showed that each variable had a significant effect on the emulsifying properties of the tested system. In terms of emulsifying properties results showed that gluten concentration and temperature have had a positive effect on the increase of emulsification activity, while the enhancement of emulsification stability was achieved with the highest gluten concentration and pH 9. It appeared that the hydrolysate with great emulsifying properties had the highest percentage of peptides with medium molecular weight (3-10 kDa) which had the ability to strongly chelating prooxidant metal ions such as Fe2+ at level 99.3%. Results are substantial because they give useful information for the design an efficient process of gluten hydrolysis for production in high peptide yields with improved emulsifying properties. Also, may be suggesting that there are peptides with considerable size presenting a remarkable metal-ion chelating ability.