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Impact of Acid and Alkaline Pretreatments on the Molecular Network of Wheat Gluten and on the Mechanical Properties of Compression-Molded Glassy Wheat Gluten Bioplastics
- Jansens, Koen J. A., Lagrain, Bert, Brijs, Kristof, Goderis, Bart, Smet, Mario, Delcour, Jan A.
- Journal of agricultural and food chemistry 2013 v.61 no.39 pp. 9393-9400
- acid treatment, ambient temperature, crosslinking, cystine, ethanol, freeze drying, hydrochloric acid, mechanical properties, mixing, potassium hydroxide, sodium hydroxide, sulfuric acid, wheat gluten
- Wheat gluten can be converted into rigid biobased materials by high-temperature compression molding at low moisture contents. During molding, a cross-linked protein network is formed. This study investigated the effect of mixing gluten with acid/alkali in 70% ethanol at ambient temperature for 16 h followed by ethanol removal, freeze-drying, and compression molding at 130 and 150 °C on network formation and on types of cross-links formed. Alkaline pretreatment (0–100 mmol/L sodium hydroxide or 25 mmol/L potassium hydroxide) strongly affected gluten cross-linking, whereas acid pretreatment (0–25 mmol/L sulfuric acid or 25 mmol/L hydrochloric acid) had limited effect on the gluten network. Molded alkaline-treated gluten showed enhanced cross-linking but also degradation when treated with high alkali concentrations, whereas acid treatment reduced gluten cross-linking. β-Elimination of cystine and lanthionine formation occurred more pronouncedly at higher alkali concentrations. In contrast, formation of disulfide and nondisulfide cross-links during molding was hindered in acid-pretreated gluten. Bioplastic strength was higher for alkali than for acid-pretreated samples, whereas the flexural modulus was only slightly affected by either alkaline or acid pretreatment. Apparently, the ratio of disulfide to nondisulfide cross-links did not affect the mechanical properties of rigid gluten materials.