Factors impeding enzymatic wheat gluten hydrolysis at high solid concentrations

Abstract

Enzymatic wheat gluten hydrolysis at high solid concentrations is advantageous from an environmental and economic point of view. However, increased wheat gluten concentrations result in a concentration effect with a decreased hydrolysis rate at constant enzyme-to-substrate ratios and a decreased maximum attainable degree of hydrolysis (DH%). We here identified the underlying factors causing the concentration effect. Wheat gluten was hydrolyzed at solid concentrations from 4.4% to 70%. The decreased hydrolysis rate was present at all solid concentrations and at any time of the reaction. Mass transfer limitations, enzyme inhibition and water activity were shown to not cause this hydrolysis rate limitation up to 50% solids. However, the hydrolysis rate limitation can be, at least partly, explained by a second-order enzyme inactivation process. Furthermore, mass transfer impeded the hydrolysis above 60% solids. Addition of enzyme after 24 h at high solid concentrations scarcely increased the DH%, suggesting that the maximum attainable DH% decreases at high solid concentrations. Reduced enzyme activities caused by low water activities can explain this DH% limitation. Finally, a possible influence of the plastein reaction on the DH% limitation is discussed.

Starch facilitates enzymatic wheat gluten hydrolysis

“…approximately 30% starch) did not induce any mass transfer limitations. This is in line with a previous study, where no mass transfer limitations were observed in high-solid VWG hydrolysis up to 50% solids (Hardt et al, 2014). Similar observations were done in a high-solid cellulose hydrolysis, where it was shown that the addition of 15% (w/w) water-insoluble, non-hydrolyzable dextrans had no effect on the hydrolysis of 5% cellulose slurries (Selig et al, 2012), which is comparable to water-insoluble, nonhydrolyzable starch in gluten hydrolysis.…”

“…5 is related to a concentration effect present in protein hydrolysis: the DH% decreases for higher protein concentrations and at constant enzymeto-substrate ratio. This concentration effect has been reported for protein concentrations above 10% in wheat gluten hydrolysis (Hardt, Janssen, Boom, & van der Goot, 2014) and above 1% in whey protein hydrolysis (Butr e, Wierenga, & Gruppen, 2012), and is thus also present at relatively low wheat gluten concentrations of 3e10%.…”

“…5 demonstrates that the positive effect of starch on wheat gluten hydrolysis diminishes at higher wheat flour concentrations. Similar to high-solid VWG hydrolysis (Hardt et al, 2014), mass transfer limitations can explain why the positive effect of starch disappeared after 3 h and 6 h above 60% wheat flour. Additionally, we believe that the reduced water activity further impedes WFG hydrolysis at longer reaction times.…”

“…Additionally, we believe that the reduced water activity further impedes WFG hydrolysis at longer reaction times. Water activities below 0.98 can already reduce that enzyme activity (Hardt et al, 2014). Therefore, samples with a w 0.980 are denoted Fig.…”

Enhanced cellulase recovery without β‐glucosidase supplementation for cellulosic ethanol production using an engineered strain and surfactant

“…Another strategy involves the solution pH. Additionally, high solid loading is generally required to increase the ethanol concentration and to reduce water consumption (Hardt et al, 2014;Luterbacher et al, 2012;Modenbach and Nokes, 2012;Zhang et al, 2010). Thus, we developed a pH-trigged adsorption-desorption approach for cellulase recycling (Shang et al, 2014).…”