Controlling wheat gluten cross-linking for high temperature processing

Abstract

a b s t r a c tThe high temperature blending of wheat gluten with other polymers for the manufacturing of bioplastics is associated with heat induced cross-linking reactions which can increase the viscosity and affect component miscibility. This work showed that a good level of control over the onset of cross-linking can be obtained during heating by adjusting the pH of the environment. Gluten was heated (>100 • C) in buffer solutions of different pH and protein polymerisation was monitored by various methods to assess the extent and nature of aggregation. In a sufficiently acidic environment (pH 2.5-3.0) during heating up to 153 • C, cross-linking was greatly hindered whilst protein degradation was not observed, provided 15 min heating time was not exceeded. Such conditions may well be suited to blend gluten with other polymers at relatively high temperatures in aqueous solvent. When hydrothermally treated gluten samples with large differences in protein cross-linking were compression moulded to produce plastic specimens, little differences in mechanical properties were observed.

Effect of heating and acidic pH on characteristics of wheat gluten suspension

“…The SE‐HPLC analysis was performed using a Prominence‐i, LC‐2030C instrument (Shimadzu, Kyoto, Japan). Samples were prepared by dissolving 1 mg of sample in 1 mL of 50 m m sodium phosphate buffer (pH 6.8) containing 2% SDS (extractability buffer) for 60 min followed by centrifugation (20 min at 10 000 g ) (Langstraat et al ., ). The supernatant (10 μL) was loaded onto a Yarra SEC 3000 column (Phenomenex, Torrance, United States) and eluted with 50 m m sodium phosphate buffer (pH 6.8) containing 300 m m NaCl at flow rate of 0.4 mL min −1 with detection set at 214 nm.…”

“…Wheat gluten (WG) is a heterogeneous mixture of gliadin and glutenin protein subunits which is produced as a by‐product of the wheat starch industry. It is widely used in a range of food (bakery products) as well as non‐food applications which includes production of bioplastics (Langstraat et al ., ) through to animal feeds and adhesives (Day et al ., ). Gluten can be hydrolysed to produce bioactive peptides with anti‐oxidant, anti‐microbial, anti‐cancer, opioid or anti‐hypertensive activities (Korhonen & Pihlanto, ; Shahidi & Zhong, ; Zhu et al ., ; Janković et al ., ; Garg et al ., ; Wu et al ., ).…”

“…At alkaline pH, the formation of lanthionine (Jansens et al ., ) and lysinoalanine (Rombouts et al ., ) leads to more aggregates due to cross‐linking. On the other hand, the ability of gluten to bind with other polymers is favoured under acidic pH as a result of reduced cross‐linking (Langstraat et al ., ) paving way for application of modified gluten in bioplastics. Reddy & Yang () reported the development of gluten based fibre with improved mechanical properties similar to that of wool.…”

Effect of adding a reactive plasticizer on the mechanical, thermal, and morphology properties of nylon toughened wheat gluten materials

“…Whilst synthetic polymers are fairly robust and can often be blended using solvent‐free routes such as melt compounding, natural polymers are not always suited to such energy intensive techniques. For example, WG proteins tend to degrade via peptide hydrolysis at temperatures in excess of 150 °C and so processing conditions have to be tailored accordingly . Furthermore, WG crosslinking reactions lead to a significant increase in viscosity which limits the possibility for extrusion at high temperatures without the aid of a plasticizer.…”

“…For example, WG proteins tend to degrade via peptide hydrolysis at temperatures in excess of 150 8C and so processing conditions have to be tailored accordingly. 15,16 Furthermore, WG crosslinking reactions lead to a significant increase in viscosity which limits the possibility for extrusion at high temperatures without the aid of a plasticizer. In this article, we investigate a method for blending WG with an aliphatic polyamide.…”