In 2012, the world production of starch was 75 million tons. Maize, cassava, wheat and potato are the main botanical origins for starch production with only minor quantities of rice and other starches being produced. These starches are either used by industry as such or following some conversion. When selecting and developing starches for specific purposes, it is important to consider the differences between starches of varying botanical origin. Here, an overview is given of the production, structure, composition, morphology, swelling, gelatinisation, pasting and retrogradation, paste firmness and clarity and freeze–thaw stability of maize, cassava, wheat, potato and rice starches. Differences in properties are largely defined by differences in amylose and amylopectin structures and contents, granular organisation, presence of lipids, proteins and minerals and starch granule size.

Starch-water, gluten-water, and flour-water model systems as well as straight-dough bread were investigated with (1)H NMR relaxometry using free induction decay and Carr-Purcell-Meiboom-Gill pulse sequences. Depending on the degree of interaction between polymers and water, different proton populations could be distinguished. The starch protons in the starch-water model gain mobility owing to amylopectin crystal melting, granule swelling, and amylose leaching, whereas water protons lose mobility due to increased interaction with starch polymers. Heating of the gluten-water sample induces no pronounced changes in proton distributions. Heating changes the proton distributions of the flour-water and starch-water models in a similar way, implying that the changes are primarily attributable to starch gelatinization. Proton distributions of the heated flour-water model system and those of fresh bread crumb are very similar. This allows identifying the different proton populations in bread on the basis of the results from the model systems.

In this paper, the current knowledge on properties of starch blends is critically reviewed. Nowadays, chemical modifications are commonly applied to modify starch properties. However, industry calls for alternatives for chemically modified starches to address the consumer's demand for natural food systems. A simple way to impact starch properties is by blending different starches. In some blends, interactions lead to unexpected gelatinization, pasting, gel texture, and retrogradation properties (non‐additive effect), while an additive effect occurs when the behavior of the blend corresponds to what can be expected based on the individual components. Analysis of different studies describing the physicochemical properties of blends brings insight into the role of botanical origin, amylose content, starch‐to‐water ratio, ratio of starches in the blend, etc. in the behavior of the blends. Gelatinization occurs mostly independently in excess water, while at intermediate water content more non‐additive behavior is recorded. Pasting, rheological, and textural properties show primarily non‐additive effects while retrogradation of starch blends occurs mainly in an additive way. Large differences in granule size and swelling power between the starches in a blend lead to uneven moisture distribution during heating of the starch suspension, which results in a different behavior of the blend than what would be expected based on the behavior of the individual starches.

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.

Wheat (Triticum aestivum) contains a previously unknown type of xylanase (EC 3.2.1.8) inhibitor, which is described in the present paper for the first time. Based on its >60% similarity to TLPs (thaumatin-like proteins) and the fact that it contains the Prosite PS00316 thaumatin family signature, it is referred to as TLXI (thaumatin-like xylanase inhibitor). TLXI is a basic (pI> or =9.3 in isoelectric focusing) protein with a molecular mass of approx. 18-kDa (determined by SDS/PAGE) and it occurs in wheat with varying extents of glycosylation. The TLXI gene sequence encodes a 26-amino-acid signal sequence followed by a 151-amino-acid mature protein with a calculated molecular mass of 15.6-kDa and pI of 8.38. The mature TLXI protein was expressed successfully in Pichia pastoris, resulting in a 21-kDa (determined by SDS/PAGE) recombinant protein (rTLXI). Polyclonal antibodies raised against TLXI purified from wheat react with epitopes of rTLXI as well as with those of thaumatin, demonstrating high structural similarity between these three proteins. TLXI has a unique inhibition specificity. It is a non-competitive inhibitor of a number of glycoside hydrolase family 11 xylanases, but it is inactive towards glycoside hydrolase family 10 xylanases. Progress curves show that TLXI is a slow tight-binding inhibitor, with a K(i) of approx. 60-nM. Except for zeamatin, an alpha-amylase/trypsin inhibitor from maize (Zea mays), no other enzyme inhibitor is currently known among the TLPs. TLXI thus represents a novel type of inhibitor within this group of proteins.

Results and DiscussionDuring storage of bread for 168 h, ∆H AP increased while the relative amount of FW decreased (Table 1). Water becomes unfreezable due to inclusion into the amylopectin crystals but also due to inclusion into the continuous, rigid amylopectin network. No amylopectin retrogradation was observed during drying. Crumb firmness increased during storage and drying ( Figure 1).The decreased crumb moisture content during storage did not result in an increased crumb firmness (Figure 1), showing that amylopectin retrogradation was largely responsible for crumb firming during storage. However, the increase in melting enthalpy levelled off after a couple of days of storage (Table 1), while crumb firmness increased further. This points to an additional phenomenon which contributes to crumb firmness.With 1 H NMR, changes in the distribution of protons from water and biopolymers can be observed. During storage of bread, the area of population A (rigid protons) increased due to formation of amylopectin crystals (Figure 2a). In addition, the mobility (T 2 relaxation time) and area of population E (mobile exchanging protons in the formed gel network) decreased during bread storage due to formation of a continuous, rigid amylopectin network and crumb to crust moisture migration (Figure 2a). Bread crumb firming is a complex process. It is generally accepted that amylopectin retrogradation is an important contributor to crumb firming during storage, but there is no direct cause and effect relationship between both processes 1 . Besides formation of amylopectin crystals 1 , water diffusion also affects crumb firmness during storage. Literature is scarce about the impact of such diffusion. It occurs on a macroscopic scale, i.e. from crumb to crust 2 , as well as on a molecular scale, i.e. from gluten to starch 3 . However, the relative importance of water redistribution and amylopectin retrogradation for bread firming is still under debate. Since water related phenomena are involved in crumb firming, the use of low resolution (LR) proton Nuclear Magnetic Resonance ( 1 H NMR) to examine bread crumb holds promise. the objective of this study was to investigate changes during bread storage, thereby distinguishing between the effect of crumb to crust migration and evaporation of water and the effect of amylopectin recrystallization with water incorporation into the resulting starch network. Introduction and Objective ReferencesBread making process Bread was made using a straight-dough method [100.0 g wheat flour (14.0% moisture), 5.3 g compressed yeast, 6.0 g sucrose, 1.5 g NaCl, 57.0 mL water] as described in Bosmans et al. (2012) 4 . Differential scanning calorimetry (DSC) measurementsThe melting enthalpy of retrograded amylopectin (∆H AP ) and the relative amount of freezable water (FW) were determined with DSC 5 . Firmness measurementsCrumb firmness was detected with an Instron 3342 (Instron, Norwood, MA, USA) on fresh, stored (for 168 h) and dried bread crumb 5 . H NMR measurementsProton relaxation measurement...

Research efforts on gluten-free bread making have rapidly increased during the last decade.A lot of different approaches are being used to improve the quality of these products. The techniques used in gluten-free bread making research vary widely. This review focuses on the methodological aspects of gluten-free bread making research and extracts relevant data from all Web of Science peer reviewed research articles on gluten-free bread published from 2010 to date. Recipes and methodologies are grouped by (main) starch source and list other ingredients, additives and treatments used. The focus lies on the experimental setups typically used to analyze batter/dough and end product. Small deformation rheological measurements are typically performed on gluten-free batter/dough, along with several other batter/dough properties, but there is no clear link between these characteristics and the bread quality which typically is determined by volume and texture analysis or sensory evaluation. Some more recent techniques that have already been used on wheat bread or other bakery products are discussed as well. Their application in gluten-free bread making research may help extend the current knowledge.

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