Enzymatic hydrolysis of soft wheat flour: the effect of present solids on functional properties and allergenicity reduction

Abstract

Enzymatic hydrolysis of wheat gluten at high solids concentrations is beneficial from both an ecological and an economic viewpoint, since wheat gluten can be hydrolyzed by either using the raw fraction of wheat gluten or directly from the soft wheat flour (SWF). Thus, in this study, the possibility to hydrolyze SWF with high concentration of solids, which implies in this case high starch content and the effect of its presence was investigated. SWF was hydrolyzed with Alcalase (pH 8.0, 60 °C) at different SWF concentrations while the enzyme to substrate (E/S) ratio was kept constant at 5%. By increasing the starch content in the sample and therefore reducing the amount of available water, greater degrees of hydrolysis (DH) were achieved. SWF prepared at 15% (w/w) showed greater DH compared to 5% (w/w) and 10% (w/w) mixtures. At a DH of 23.49%, sample prepared as 15% (w/w) showed greatest reduction in gliadin content, resulting in 9.42 ± 1.5 ppm of gluten, tested by competitive ELISA test. SDS-PAGE electrophoresis confirmed the differences in gliadin content for all of the prepared wheat flour hydrolysates (WFH). Enzymatic hydrolysis has removed glutenin subunits (GS), x-HMW-GS (83-88 kDa) and y-HMW-GS (67-74 kDa) and ω5-gliadins (49-55 kDa). All WFHs had significantly improved antioxidant (> 60%) and metal-ion chelating (> 80%) properties compared to SWF. Also, techno-functional properties were improved after enzymatic hydrolysis. Emulsifying activity and emulsion stability were significantly improved after hydrolysis and therefore more stable emulsion systems were formed. Foaming properties were also improved after hydrolysis. The changes in the WFHs macromolecular conformations and changes induced by the Alcalase, were inspected using Fourier transformation infrared spectroscopy (FTIR) and surface measurements. FTIR spectra confirmed structural changes in the Amide I (1,700-1,600 cm-1) region. The changes in total zeta-potential and average particle size were in accordance with above-mentioned functional behaviors. The increase in the DH, with prolonged time of enzyme attack, affected the increase in the surface charge of the WFH molecules, suggesting that the stability and electrokinetic potential were maintained stable. The hydrolysis reaction was facilitated by the increase of the solids content since it interferes with the aggregation of gluten proteins, therefore less available water was proven beneficial for the enzymatic reaction. Regarding process feasibility on an industrial level, a more concentrated system may be used in order to produce WFHs with reduced allergenic and improved functional properties.