Highly Efficient Deamidation of Wheat Gluten by Glucose-Citric Acid-Based Natural Deep Eutectic Solvent: A Potential Effective Reaction Media

Abstract

An efficient technique using citric acid and glucose based natural deep eutectic solvent (G-C-NADES) was developed to obtain ultrahigh deamidated wheat gluten (UDWG) (deamidation degree (DD) > 90%). FTIR and 1 H NMR indicated intensive hydrogen bonds (HBs) in G-C-NADES supermolecules. Quantum chemical calculations and molecular dynamic simulations demonstrated that 10 wt % diluted G-C-NADES still had a myriad of HBs. Physicochemical results showed UDWG had DD up to 92.45% after G-C-NADES deamidation, that is, 22% higher than citric-acid-DWG with a weak degree of hydrolysis (1.75%). Conformational characterization demonstrated the obvious conversion from α-helix to β-sheet via FTIR, the least amount of disulfide bonds by Raman spectra, and more exposure of tryptophan residues by fluorescence measurement for UDWG. It is proven that enhanced accessible conformation of WG reached with HBs of G-C-NADESs could contribute to the improvement on nucleophilic attack of deamidation, declaring that G-C-NADES might be a potential solvent for obtaining an ultrahigh deamidation for WG to successfully guarantee the safety of wheat gluten based cereal food regarding to lowering its allergy.

Molecular Transformation and Characterizations of Super-deamidated Wheat Gluten by a Tunable Hydrated Ternary Natural Deep Eutectic Solvent

“…Wheat gluten showed subunits classified as H/LMW-GS, α/β/ γ/ω-gliadin, and α-amylase trypsin inhibitors. 17 The loss of the bands at the top (>66.2 kDa) of lines 6−8 (G-DWG, B-DWG, and W-DWG) might be attributed to the aggregation of these subunits caused by the hydrothermal treatment, which were not collected in the supernatant. 40 The subunit bands of citric acid based DWGs (lines 1−5) showed no considerable change, whereas the density of HB 3 C 1 G 1 -N-DWG (line 1) was noticeably different from those of others.…”

“…However, an independent peak at 1714 cm −1 was observed for B 3 C 1 G 1 -N. This result was consistent with the citric acid−glucose NADES reported in our previous work. 17 The carboxylate peak (COO-, As shown in Figure 2b, the chemical shifts at 3.31 and 3.94 ppm corresponding to betaine were referred to as the -N(CH 3 )-and -CH 2 -groups, respectively. 30 In the case of citric acid, the peaks corresponding to the -CH 2 -of the C2 and C6 atoms appeared as a doublet of doublets (2.86−3.10 ppm).…”

“…Additionally, citric acid and glucose, as the HBA and HBD, respectively, presented in the clusters and also interacted with each other. 17 The charge delocalization of the compounds in the clusters further affected the electrification of the boundary atoms. The values corresponding to the boundary hydroxy H of glucose in B 1 C 1 G 1 -N and carboxylic H of citric acid in B 2 C 1 G 1 -N were increased to 50.22 and 64.17 kcal/mol, respectively, which implied that these atoms were more active in interacting with others through hydrogen bonds.…”

“…44 In the case of molecular flexibility (ratio of α-helix to β-sheet), the relatively small value of HB 3 C 1 G 1 -N-DWG (0.97) agreed with the trend in the βturn with the protein structure showing more plasticity. 17 Additionally, the amide I band (1570−1720 cm −1 ) located in the Raman spectrum was observed to characterize the secondary structure (Figure S6). The negative bands at 1591−1604 and 1641−1643 cm −1 were assigned to aggregates (AGR) and random coils (RC), respectively.…”

“…The intensity at 760 cm −1 (I760) and 2935 cm −1 (I2935) was attributed to the Trp band and -CH stretching vibrations, respectively. 17,46 The intensity ratio of the doublet bands (I850/I830) showed the local microenvironment around the Tyr residues. 47 According to Figure 5d, the I760 of HB 3 C 1 G 1 -N-DWG decreased from 0.54 to 0.22 compared to that of C-DWG.…”