Emulsion properties of different protein fractions from hydrolyzed wheat gluten

S. R. DRAGO R. J. GONZÁLEZ AND M. C. AÑÓN

Gluten: Properties, Modifications and Dietary Intolerance.

Nova Science Publishers

Lugar: New York; Año: 2011; p. 113 - 132

Many protein sources that are found in the market are obtained as by-products and there is a great interest in using them as protein ingredients with adequate functionality for food formulation. Structure modification allows to add value and to diversify their uses. The viscoelastic properties of wheat gluten have restricted its use in baked products, and the diversification of gluten applications depends of the improvement of its solubility in a wider pH range. An alternative for that is the enzymic hydrolysis. The objective of this work was to evaluate emulsion properties of protein fractions obtained by extracting at 3 pH different hydrolyzed gluten samples. Hydrolyzates were made using two commercial enzymes (acid and alkaline proteases) to reach 3 different hydrolysis degrees (DH) for each enzyme. Extracts were obtained at 3 different pHs (4, 6.5 and 9) and were diluted to a protein concentration of 4 g/l. Each extract was used to make the corn oil: extract emulsions (25:75, W/W). Emulsion capacity was determined by measuring droplet size distribution and the stability using a vertical scan macroscopic analyzer. Regarding emulsion capacity, multifactor ANOVA (factors: pH and DH) made for droplet size distribution parameters showed that there were no differences between samples. Regarding stability evaluation, alkaline protease extract emulsions were more stable in particle migration phenomena by creaming, but showed higher coalescence rates than those corresponding to acid protease extract emulsions. It was also observed that for both enzymes, as DH increases, coalescence rates decrease for the 3 pHs extracts and creaming rates increase for pH 4 and 9 extracts. In the case of pH 6.5, acid protease extracts emulsions showed a clear creaming instability by flocculation, probably due to the electrical charges suppression of the peptides adsorbed at the interface, since 6.5 is a pH near the isoelectric point of gluten proteins. It is suggested that acid protease extract emulsions showed a certain degree of bridging flocculation. This caused higher creaming rates but a lower coalescence as a consequence of the bridging. We conclude that although pH of the extraction and DH did not affect emulsion capacity, emulsion stability depended on the pH, DH and the enzyme used.