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.

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...

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The functionality of wheat flour lipids in sponge cakes prepared from flour, sugar, eggs and leavening agents only was investigated by altering their location or content in flour. Hexane (hex) or the more polar hexane:isopropanol (3:2 v/v) (hex:isoprop) were used to impact free flour lipid (FFL) or both FFL and bound flour lipid (BFL) fractions, respectively. Flour from which the FFLs were removed resulted in significantly improved cake volumes and crumb structures. Additional removal of part of the BFLs did not further impact cake quality. Prior contact of flour with hex:isoprop followed by gently removing the solvent broke native interactions between BFLs and starch or gluten and relocated more lipids than did hex. Cakes from flour with relocated lipids had coarse crumb structures. Our study demonstrates that FFLs and relocated flour lipids negatively impact sponge cake quality by disturbing air-liquid interface stabilization during mixing and the early phases of baking.

The presence of protein and lipid from wheat flour and eggs at the air-liquid interface (ALI) in sponge cake batter has been studied through a foaming protocol. Sponge cake batter was either prepared from flour, sugar, eggs and leavening agents only or from these ingredients and exogenous lipids (ELs, i.e. a combination of mono-and diacylglycerols and polyglycerol esters of fatty acids). The foaming protocol consisted of whipping diluted sponge cake batter into foam. The foam was considered to be a model for the ALI in sponge cake batter. Foam fractions were then isolated at multiple time points after whipping and chemically analyzed (i.e. lipid and proteins contents and their compositions).In absence of ELs, lipids were not enriched in the foam whereas proteins were. Under such conditions, proteins were more important for stabilizing the ALI than lipids. Size-exclusion high performance liquid chromatography profiles revealed that of all proteins in the system ovalbumin and wheat α-and γgliadins had the highest affinity for the ALI. Ovalbumin molecules unfolded and formed intermolecular disulfide bonds at the ALI. Furthermore, flour lipids had higher affinity for the ALI than egg lipids. When ELs were used, foam protein and lipid content and composition essentially remained constant over the experimental time period. In such case, they dominated the ALI and greatly contributed to its stability.Use of ELs decreased batter density and increased batter viscosity, cake volume and cake softness. Hence, it is clear that including ELs in the sponge cake recipe led to high batter and cake quality.

Gluten-free bread crumb generally firms more rapidly than regular wheat bread crumb. We here combined differential scanning calorimetry (DSC), texture analysis, and time-domain proton nuclear magnetic resonance (TD (1)H NMR) to investigate the mechanisms underlying firming of gluten-free rice and oat bread. The molecular mobility of water and biopolymers in flour/water model systems and changes thereof after heating and subsequent cooling to room temperature were investigated as a basis for underpinning the interpretation of TD (1)H NMR profiles of fresh crumb. The proton distributions of wheat and rice flour/water model systems were comparable, while that of oat flour/water samples showed less resolved peaks and an additional population at higher T2 relaxation times representing lipid protons. No significant crumb moisture loss during storage was observed for the gluten-free bread loaves. Crumb firming was mainly caused by amylopectin retrogradation and water redistribution within bread crumb. DSC, texture, and TD (1)H NMR data correlated well and showed that starch retrogradation and crumb firming are much more pronounced in rice flour bread than in oat flour bread.

When Bacillus stearothermophilus α-amylase (BStA), Pseudomonas saccharophila α-amylase (PSA), or Bacillus subtilis α-amylase (BSuA) was added to a bread recipe to impact bread firming, amylose crystal formation was facilitated, leading to lower initial crumb resilience. Bread loaves that best retained their quality were those obtained when BStA was used. The enzyme hindered formation of an extended starch network, resulting in less water immobilization and smaller changes in crumb firmness and resilience. BSuA led to extensive degradation of the starch network during bread storage with release of immobilized water, eventually resulting in partial structure collapse and poor crumb resilience. The most important effect of PSA was an increased bread volume, resulting in smaller changes in crumb firmness and resilience. A negative linear relation was found between NMR proton mobilities of water and biopolymers in the crumb and crumb firmness. The slope of that relation gave an indication of the strength of the starch network.

Three different crystalline amylose−glycerol monostearate (GMS) complexes with increasing thermal stability can be distinguished: type I, type IIa, and type IIb. All complexes consist of GMS-loaded amylose helices that pack hexagonally into lamellar habits. The complex melting points are proportional to the thickness of the lamellae and depend on the amount of water in the system. For type I complexes, SAXS experiments reveal folded amylose chains and a lamellar thickness governed by the presence of two stretched lipid molecules per amylose helix. In the conversion from type I to type IIa complexes, the short amylose chains unfold and assume a stretched conformation, which increases the number of aligned lipid molecules within the helices to four. In type IIb complexes, another pair of lipid molecules is added. The derived quantitative relation between crystal layer thickness, water content and melting point for amylose−GMS complexes also predicts the melting points of other amylose−monoacyl glycerol complexes.