Hydrothermal Treatments Cause Wheat Gluten-Derived Peptides to Form Amyloid-like Fibrils

Abstract

Formation of amyloid fibrils (i.e. protein structures containing a compact core of ordered β-sheet structures) from food proteins can improve their techno-functional properties. Wheat gluten is the most consumed cereal protein by humans and extensively present in food and feed systems. Hydrolysis of wheat gluten increases the solubility of its proteins and brings new opportunities for value creation. In this study, the formation of amyloid-like fibrils (ALFs) from wheat gluten peptides (WGPs) under food relevant processing conditions was investigated. Different hydrothermal treatments were tested to maximize the formation of straight ALFs from WGPs. Thioflavin T (ThT) fluorescence measurements and transmission electron microscopy (TEM) were used to study the extent of fibrillation and the morphology of the fibrils, respectively. First, the formation of fibrils by heating solutions of tryptic WGPs [degrees of hydrolysis 2.0% (DH 2) or 6.0% (DH 6)] was optimized using a response surface design. WGP solutions were incubated at different pH, times and temperatures. DH 6 WGPs had a higher propensity for fibrillation than did DH 2 WGPs. Heating DH 6 WGPs at 2.0% (w/v) for 38 hours at 85 °C and pH 7.0 resulted in optimal fibrillation. Secondly, trypsin, chymotrypsin, thermolysin, papain and proteinase K were used to produce different DH 6 WGPs. After enzyme inactivation and subsequent heating at optimal fibrillation conditions, chymotrypsin and proteinase K DH 6 WGPs produced small worm-like fibrils whereas fibrils prepared from trypsin DH 6 WGPs were long and straight. The surface hydrophobicity of the peptides was key for fibrillation. Thirdly, peptides from the wheat gluten components gliadin and glutenin fractions formed smaller and worm-like fibrils than did WGPs. Thus, peptides of both gluten protein fractions jointly contribute in gluten fibrillation.

Effect of Thermal Treatment on the Self-Assembly of Wheat Gluten Polypeptide

“…GPs with a greater DH (DH 6 and 10) had a higher fluorescence intensity than the GPs with a lower DH (DH 2). This is consistent with Lambrecht et al, who found that DH 6 wheat gluten-derived peptides had a higher propensity for fibrillation than DH 4 wheat gluten-derived peptides [ 23 ]. Smaller molecular weight peptides were more susceptible to driving forces, which might explain their greater fibrillation propensity.…”

“…This indicated that the smaller molecular weight was more favorable for fibrillation. In addition, Lambrecht et al found that trypsinized wheat proteins formed long and straight fibrils after 40 h of heating at 85 °C [ 23 ]. Ji et al found that soy protein isolates heated at 95 °C for 1 h formed short and dispersed fibers, but after 4 h, the fibers were long and straight [ 31 ].…”

“…The hydrolysis of the wheat gluten was carried out according to the method described by Lambrecht et al with some modifications [ 23 ]. First, 15 g of wheat gluten was dispersed in 300 mL of deionized water and heated in a water bath at 40 °C, and the pH was adjusted to 8.0 using 1 M sodium hydroxide.…”

Heating Wheat Gluten Promotes the Formation of Amyloid-like Fibrils

“…22 More recently, it has been shown that out of six peptidases, trypsin produces WG hydrolysates that are most successful for producing long (up to 1.3 μm) and straight protein fibrils. 23 Efforts have been made to identify the β-sheet aggregation regions in the fibril backbone. For instance, in contrast to glutenin tryptic hydrolysates, tryptic gliadin hydrolysates form cross β-sheet structures.…”

“…Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction data suggest that they contain cross β-sheet structures . More recently, it has been shown that out of six peptidases, trypsin produces WG hydrolysates that are most successful for producing long (up to 1.3 μm) and straight protein fibrils …”