Synergistic impact of heat and salicylic acid pretreatment on gluten films: Characterization and functional properties

This study investigates how wheat gluten (WG) films in the presence of salicylic acid are influenced by thermal pretreatment. Unlike previous methods conducted at low moisture content, our procedure involves pretreating WG at different temperatures (65 °C, 75 °C, and 85 °C), in a solution with salicylic acid. This pretreatment aims to enhance protein unfolding, thus providing more opportunities for protein-protein interactions during the subsequent solvent casting into films. A significant increase in β-sheet structures was observed in FTIR spectra of samples pretreated at 75 °C and 85 °C, showing a prominent peak in the range of 1630-1640 cm-1. The pretreatment at 85 °C was found to be effective in improving the water resistivity of the films by up to 247 %. Moreover, it led to a significant enhancement of 151 % in tensile strength and a 45 % increase in the elastic modulus. The reduced solubility observed in films derived from pretreated WG suggests the development of an intricate protein network arising from protein-protein interactions during the pretreatment and film formation. Thermal pretreatment at 85 °C significantly enhances the structural and mechanical properties of WG films, including improved water resistivity, tensile strength, and intricate protein network formation.

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

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.

Edible packaging materials

Research groups and the food and pharmaceutical industries recognize edible packaging as a useful alternative or addition to conventional packaging to reduce waste and to create novel applications for improving product stability, quality, safety, variety, and convenience for consumers. Recent studies have explored the ability of biopolymer-based food packaging materials to carry and control-release active compounds. As diverse edible packaging materials derived from various by-products or waste from food industry are being developed, the dry thermoplastic process is advancing rapidly as a feasible commercial edible packaging manufacturing process. The employment of nanocomposite concepts to edible packaging materials promises to improve barrier and mechanical properties and facilitate effective incorporation of bioactive ingredients and other designed functions. In addition to the need for a more fundamental understanding to enable design to desired specifications, edible packaging has to overcome challenges such as regulatory requirements, consumer acceptance, and scaling-up research concepts to commercial applications.