The Effect Of Deamidation On Wheat Gluten Susceptibility To Enzymatic Hydrolysis And The Hydrolysates’Properties

Wheat gluten is a byproduct of the wheat starch industry. Nevertheless, as a result ofinferior water dispersion property, the application of wheat gluten and its efficiency toenzymatic hydrolysis have been strongly under restriction and limitation in thefood-processing. Hydrochloric acid was one of the most effective acid catalysts usedfrequently for protein deamidation. In this study, hydrochloric acid was used to deamidate thewheat gluten with different deamidation degrees. We optimized the deamidation condition,enzymatic process and LAB fermentation process, then the structural features, susceptibilityand antioxidative activity of wheat gluten were investigated.We optimized the technology of HCl-deamidation to wheat gluten and the enzymatichydrolysis to deamidated wheat gluten. Results showed that the optimal deamidationcondition with HCl was24%wheat gluten with0.30mol/L HCl under65℃deamidating for24h; Pancreatin and PR23are the best enzymes to hydrolyze the wheat gluten, The optimumconditions of pancreation: substrate concentration12%(w/w), enzyne concentration0.024%(w/w), pH8.0,50℃and the optimum conditions of PR23: substrate concentration12%(w/w), enzyme concentration0.030%(w/w), pH3.2,50℃; Then PR2324h+pancreatin48h revealed the highest PR(94.43%) and DH(23.46%). At last, we also compared thesusceptibility of hydrolysates from HCl-deamidated wheat glutens which were under optimalcondition and hydrolyzed by Pancreatin, Flavor protease and Alkaline protease. Resultsshowed the wheat gluten hydrolysates of Panceatin reavealed the best hydrolysis efficiencyand susceptibility, which laid the foundation for the next chapter.The effect of the structural features of hydrochloric acid-deamidated wheat gluten withdifferent deamidation degrees (DD) on the susceptibility to enzymatic hydrolysis byPancreatin was investigated. The wheat gluten deamidated by hydrochloric acid with a DD of55%revealed the highest susceptibility to enzymatic hydrolysis. With the increasing DD from0%to60%, the peptides of hydrolysates below3000Da were observed increase. RamanSpectra suggested that wheat gluten had taken off the deamidation with different DDs anddisulfide bond had disrupted to sulfhydryl groups with different intensities, respectively.Results from FTIR spectra showed that the content of α-helix decreased and the content of in β-turn and β-sheet increased with the increasing of DD, which improved the molecularstructure and flexibility of wheat gluten. Scanning electron microscope (SEM) revealed thatimage of HDG-55%presented the smoothest surface and the least uniform pore, enabling thesample more susceptible to enzymatic hydrolysis.The antioxidant activities of the fermented wheat gluten hydrolysates were investigated toelucidate the impact of LAB fermentation on the wheat gluten hydrolysates. Prior to LABfermentation, wheat gluten was deamidated by hydrochloric acid and then hydrolyzed byPancreatin to12h and24h, respectively. Results showed that LAB fermentation improved thesusceptibility of wheat gluten. The hydrolysis efficieny reached maximum values whenfermenting with LAB for36h. The antioxidant activity analysis revealed a marked increaseand improvement in the scavenging activities of DPPH radicals, hydroxyl radicals and ORAC,while the scavenging activities of ABTS radical decreased as the fermentation time extended.Antioxidant activities and endogenous antioxidative compounds were determined infermented wheat gluten hydrolysates with different fermentation times. The antioxidantactivities analysis revealed a marked increase and improvement in the scavenging activities ofDPPH radicals and ORAC after LAB fermentation. The results showed that peptide contentand total phenolic content correlated significantly with DPPH radicals and ORAC (P <0.05)respectively, while LAB amount and the Maillard products co、ntent has no significantcorrelation (P>0.05) with antioxidant activities. Results from stepwise linear regressionfurther demonstrated that different antioxidative components responsible for antioxidantactivity were dependent on the assay used. The peptide compound is by far the mostantioxidative in fermented wheat gluten hydrolysates. Furthermore, the peptide content andtotal phenolic content together made a95.4-99.7%contribution to the antioxidant activities offermented wheat gluten hydrolysates.