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The unique properties of wheat reside primarily in its gluten-forming storage proteins. Their intrinsic viscoelastic behavior is responsible for the characteristics of different wheat-based foods and for the use of wheat gluten proteins in different food products. Wheat-based food processing generally develops and sets the gluten protein network. Heat-induced gluten aggregation proceeds through cross-linking within and between its protein fractions. Prominent reactions include sulfhydryl (SH) oxidation and SH-disulfide (SS) interchange, which lead to SS cross-links. Other covalent bonds are also formed. Gluten functionality can be (bio-) chemically impacted. We focus on bread making, in which gluten proteins contribute to dough properties, bread loaf volume, and structure, and on pasta production, in which gluten proteins generate the desired cooking quality. Furthermore, it is speculated that the structure and texture of soft wheat products are also, at least to some degree, shaped by the heat-induced changes in the gluten protein fraction.

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The unique properties of the wheat grain reside primarily in the gluten-forming storage proteins of its endosperm. Wheat gluten's structural and functional properties have led to an expanding diversity of applications in food products. However, its viscoelastic properties and low water solubility also are very interesting features for nonfood applications. Moreover, gluten is annually renewable and perfectly biodegradable. In the processing and setting of gluten containing products, temperature plays a very important role. In this review, the structure and reactivity of gluten are discussed and the importance of sulfhydryl (SH) and disulfide (SS) groups is demonstrated. Wheat gluten aggregation upon thermosetting proceeds through direct covalent cross-linking in and between its protein groups, glutenin and gliadin. Predominant reactions include SH oxidation and SH/SS interchange reactions leading to the formation of SS cross-links. Additionally, thermal treatment of gluten can result in the formation of other than SS covalent bonds. We here review two main technological approaches to make gluten-based materials: wet processes resulting in thin films and dry processes, such as extrusion or compression molding, exploiting the thermoplastic properties of proteins under low moisture conditions and potentially resulting in very useful materials. Gluten bioplastics can also be reinforced with natural fibers, resulting in biocomposites. Although a lot of progress has been made the past decade, the current gluten materials are still outperformed by their synthetic polymer counterparts.

Plants developed a diverse battery of defense mechanisms in response to continual challenges by a broad spectrum of pathogenic microorganisms. Their defense arsenal includes inhibitors of cell wall-degrading enzymes, which hinder a possible invasion and colonization by antagonists. The structure of Triticum aestivum xylanase inhibitor-I (TAXI-I), a first member of potent TAXI-type inhibitors of fungal and bacterial family 11 xylanases, has been determined to 1.7-Å resolution. Surprisingly, TAXI-I displays structural homology with the pepsin-like family of aspartic proteases but is proteolytically nonfunctional, because one or more residues of the essential catalytical triad are absent. The structure of the TAXI-I⅐Aspergillus niger xylanase I complex, at a resolution of 1.8 Å, illustrates the ability of tight binding and inhibition with subnanomolar affinity and indicates the importance of the C-terminal end for the differences in xylanase specificity among different TAXI-type inhibitors.

Proteins play a crucial role in determining texture and structure of many food products. Although some animal proteins (such as egg white) have excellent functional and organoleptic properties, unfortunately, they entail a higher production cost and environmental impact than plant proteins. It is rather unfortunate that plant protein functionality is often insufficient because of low solubility in aqueous media. Enzymatic hydrolysis strongly increases solubility of proteins and alters their functional properties. The latter is attributed to 3 major structural changes: a decrease in average molecular mass, a higher availability of hydrophobic regions, and the liberation of ionizable groups. We here review current knowledge on solubility, water-and fat-holding capacity, gelation, foaming, and emulsifying properties of plant protein hydrolysates and discuss how these properties are affected by controlled enzymatic hydrolysis. In many cases, research in this field has been limited to fairly simple set-ups where functionality has been assessed in model systems. To evolve toward a more widely applied industrial use of plant protein hydrolysates, a more thorough understanding of functional properties is required. The structure-function relationship of protein hydrolysates needs to be studied in depth. Finally, test model systems closer to real food processing conditions, and thus to real foods, would be helpful to evaluate whether plant protein hydrolysates could be a viable alternative for other functional protein sources.