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In the present study, we were able to produce composites of wheat gluten (WG) protein and a novel genetically modified potato starch (MPS) with attractive mechanical and gas barrier properties using extrusion. Characterization of the MPS revealed an altered chain length distribution of the amylopectin fraction and slightly increased amylose content compared to wild type potato starch. WG and MPS of different ratios plasticized with either glycerol or glycerol and water were extruded at 110 and 130°C. The nano morphology of the composites showed the MPS having semi-crystalline structure of a characteristic lamellar arrangement with an approximately 100 Å period observed by SAXS and a B-type crystal structure observed by WAXS. WG has a structure resembling the hexagonal macromolecular arrangement as reported previously in WG films. A larger amount of β-sheets was observed in the samples 70/30 and 30/70 WG-MPS processed at 130°C with 45% glycerol. Highly polymerized WG protein was found in the samples processed at 130°C vs. 110°C. Also, greater amounts of WG protein in the blend resulted in greater extensibility (110°C), and a decrease in both E-modulus and maximum stress at 110 and 130°C, respectively. Under ambient conditions the WG-MPS composite (70/30) with 45% glycerol showed excellent gas barrier properties to be further explored in multilayer film packaging applications.

Wheat gluten (WG) and potato protein (PP) were modified to a basic pH by NaOH to impact macromolecular and structural properties. Films were processed by compression molding (at 130 and 150 °C) of WG, PP, their chemically modified versions (MWG, MPP) and of their blends in different ratios to study the impact of chemical modification on structure, processing and tensile properties. The modification changed the molecular and secondary structure of both protein powders, through unfolding and re-polymerization, resulting in less cross-linked proteins. The β-sheet formation due to NaOH modification increased for WG and decreased for PP. Processing resulted in cross-linking of the proteins, shown by a decrease in extractability; to a higher degree for WG than for PP, despite higher β-sheet content in PP. Compression molding of MPP resulted in an increase in protein cross-linking and improved maximum stress and extensibility as compared to PP at 130 °C. The highest degree of cross-linking with improved maximum stress and extensibility was found for WG/MPP blends compared to WG/PP and MWG/MPP at 130 °C. To conclude, chemical modification of PP changed the protein structures produced under harsh industrial conditions and made the protein more reactive and attractive for use in bio-based materials processing, no such positive gains were seen for WG.

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Superabsorbent polymers (SAP) are a central component of hygiene and medical products requiring high liquid swelling, but these SAP are commonly derived from petroleum resources. Here, we show that sustainable and biodegradable SAP can be produced by acylation of the agricultural potato protein side-stream (PPC) with a non-toxic dianhydride (EDTAD). Treatment of the PPC yields a material with a water swelling capacity of ca. 2400%, which is ten times greater than the untreated PPC. Acylation was also performed on waste potato fruit juice (PFJ), i.e. before the industrial treatment to precipitate the PPC. The use of PFJ for the acylation implies a saving of 320 000 tons as CO2 in greenhouse gas emissions per year by avoiding the industrial drying of the PFJ to obtain the PPC. The acylated PPC shows biodegradation and resistance to mould growth. The possibilities to produce a biodegradable SAP from the PPC allows for future fabrication of environment-friendly and disposable daily-care products, e.g. diapers and sanitary pads.

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In this study, we combined two wheat proteins, gliadin (Gli)/glutenin (GT), and modified potato starch (MPS) into composites using extrusion. In the Gli/GT−MPS composites, we studied the structural dynamics of proteins and starch, protein−starch interactions, protein properties, and composite morphology in relation to mechanical and barrier properties. Materials with different ratios of Gli/GT and MPS were extruded using either glycerol or glycerol−water at 110 and 130 °C. For the first time, a hierarchical hexagonal structure of Gli proteins was observed in Gli−MPS composite at both extrusion temperatures. The higher temperature (130 °C) induced a higher degree of protein cross-links, an increase in the polymer size, and formation of β-sheets compared to 110 °C. The combination of plasticizers (glycerol and water) favored a micro-structural morphology with improved gelatinization of starch, processability, as well as strength, stiffness, and extensibility of GT−MPS composites. The highest amount of the oxidized proteins was observed in the samples with the highest protein content and at high extrusion temperature. The Gli-and GT−MPS (30/70) samples showed promising oxygen barrier properties under ambient testing conditions. These findings provide in-depth information for tailoring the structural−functional relationship of the Gli/GT-potato starch composites for their promising use in designing various green materials.