Enlarged Processing Window of Plasticized Wheat Gluten Using Salicylic Acid

Abstract

The temperature window for the extrusion of glycerol-plasticized wheat gluten was increased by the use of salicylic acid, a known scorch retarder and radical scavenger. It was possible to extrude 30 wt % glycerol-wheat gluten films with a die-head temperature as high as 135 degrees C, rather than 95 degrees C, by incorporating only 1 wt % salicylic acid. Small effects of shear-induced heating during extrusion at the higher temperatures suggested that the acid acted as a lubricant and viscosity reducer. The latter was suggested to originate primarily from the salicylic-acid-induced reduction in the degree of protein aggregation/cross-linking, as indicated by size-exclusion high-performance liquid chromatography and chemiluminescence. Electron paramagnetic resonance spectroscopy on extruded films indicated that the beneficial effect of salicylic acid was due to its radical scavenging effect. Tensile tests on extrudates revealed that the materials produced at the substantially higher processing temperature were still ductile. The complex shear modulus increased more slowly with increasing salicylic acid content above 110-120 degrees C, indicating that the aggregation/cross-linking rate was slower with salicylic acid, that is, that it did have a scorch-retarding effect, besides yielding a lower final degree/complexity of aggregation.

Injection-molded nanocomposites and materials based on wheat gluten

“…Interestingly, and in contrast to several other investigations carried out using compression-molded and extruded films [6,7], the lowest total solubility was obtained for the samples plasticated at the lowest temperatures. These results probably reflect the influence of a higher shear stress (high melt viscosity) at lower temperature and a corresponding higher protein aggregation.…”

“…wheat gluten is high due to its high molar mass and aggregated structure. Nevertheless, it has been shown, by us and others, that plasticized wheat gluten can be compression molded and extruded into films, troughs and plates [3][4][5][6][7][8]. These methods, however, provide rather limited ways of shaping the material/product into more or less complicated three dimensional (3D) items.…”

Structural Changes of Gluten/Glycerol Plastics under Dry and Moist Conditions and during Tensile Tests

“…31,32,34 Unless specifically mentioned, the term WG hereinafter refers to WG mixed with glycerol. The AH contents were 3, 5 and 10 %, all with 1.5 % of salicylic acid 30,31 (% refers to the total weight (WG + glycerol + AH/SA)) and the urea contents were 10, 15 and 20 % (% refers to the total weight (WG + glycerol + urea)). The samples were named accordingly as AHx (including SA) and Uy, where x and y are the contents.…”

“…25,27,28 Besides the plasticizers, additives, such as acids, bases and urea, have been used to improve the processability of WG. 26,[29][30][31] Interestingly, new tetragonal-packed and HCP nanostructures were discovered in the WG with NaOH and ammonium hydroxide (AH) 28 . A similar HCP structure was also reported in the presence of urea, which act as a combined protein denaturant and plasticizer.…”

Macromolecular changes and nano-structural arrangements in gliadin and glutenin films upon chemical modification

“…amount and type of plasticizer, processing temperature and the use of additives have an effect on the structural and functional properties of the final bioproducts [12]. The use of additives such as NaOH, NH 4 OH and salicylic acid (SA), contributes positively to functional properties of WG based films, by inducing changes in protein macromolecular structure [9,19,20]. Salicylic acid through its radical scavenging mechanism reduces/delays the disulfide crosslinking and increases the processing window of gluten proteins [9].…”