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De rol van water-extraheerbare graanconstituenten in het stabiliseren van gascellen in brooddeeg

Year: 2025
Type: dissertation
Abstract: To produce a loaf bread with a high volume and a fine crumb structure, the gas cells that were incorporated during dough mixing must remain intact as they increase in size during dough fermentation and early baking. The ability of the gluten network to strain harden upon extension is the primary mechanism responsible for the stabilization of gas cells in dough. However, it has been hypothesized that gas cell expansion causes local rupturing of the gluten network and that from this moment on, a liquid film takes over gas cell stabilization (Gan et al., 1990; Janssen et al., 2021). This liquid film is hypothesized to be a part of the dough aqueous phase that contains water-extractable (WE) flour constituents. Such constituents may stabilize gas cells by either creating a strong interfacial layer at the gas cell air/water (A/W) interfaces or by stabilizing the thin liquid films in between gas cells against drainage. Previous research consistently shows that the WE fraction of flour affects bread volume. However, literature about the underlying gas cell (de)stabilization mechanisms remains lacking. Such mechanisms may be related to dough bulk effects (i.e., dough strain hardening), or gas cell A/W interfacial effects (i.e., A/W interfacial and/or thin liquid film stability). Moreover, not much is known about the role of WE proteins as well as their interplay with other constituents in determining bread volume. Thus, this PhD dissertation aimed to gain an in-depth mechanistic understanding of the role of WE flour constituents in bread dough gas cell stabilization, with a focus on proteins and their interplay with other constituents. The impact of adding water extracts prepared from various cereal flours to the recipes of model gluten-starch (GS) doughs, on the specific volume (SV) of the resulting breads was investigated. Additionally, the relationship of bread SV with dough extensional rheology and gluten network formation was assessed. An increase in GS bread SV was observed when including extracts from wheat or rye. This observation, however, was not explained by changes in the dough strain hardening behavior or in the chemical interactions between gluten proteins in the dough. Contrastingly, adding extracts from defatted oat flour drastically decreased the GS bread SV. This was ascribed to inferior dough strain hardening, which was in turn due to an impaired intermolecular disulfide bond formation. Due to the heterogeneity of the composition of the extracts, distinguishing the effects of WE flour proteins from those of other constituents was challenging. To mitigate this, the extract composition was modified to assess the contributions of different WE flour constituents to the bread SV, dough rheology, and air incorporation during mixing. Extracts were altered by dialyzing out (i) low molecular mass (MM) constituents or (ii) both low MM constituents and enzymatically hydrolyzed carbohydrates, resulting in extracts with progressively increasing protein content and distinct carbohydrate compositions. Irrespective of the extract modification, incorporating (un)modified wheat, rye, or oat extracts in a GS bread recipe resulted in comparable bread SVs, dough extensional behavior, and dough gas cell size distributions for the same cereal type. Since the extracts were added at a constant protein basis, this result suggests that dough and bread responses are likely driven by the WE protein fraction. Moreover, a heat-treated wheat extract had an opposite effect on bread SV as did a non-heated wheat extract, thus validating the role of WE wheat proteins in determining bread SV response. The poor dough strain hardening upon inclusion of oat (un)modified extracts in non-yeasted GS doughs was related to a much lower gas cell count and a higher heterogeneity of the gas cell size distribution compared to the control GS bread dough. The latter likely increased the susceptibility of gas cells in oat-containing GS doughs to gas cell destabilization events (i.e., coalescence and disproportionation). Next, the stability and evolution of gas cells in yeasted GS doughs were investigated in situ using time-resolved X-ray microcomputed tomography (µCT). Model GS bread recipes supplemented with the carbohydrate-hydrolyzed and dialyzed (CH,D) extracts of wheat (WCH,D) and oat (OCH,D) flour, i.e., the protein-enriched extracts, were studied. The changes in dough height were monitored by recording time-lapse videos during proofing and baking. Compared to the control, the yeasted GS dough containing OCH,D extract had higher median gas cell radii, heterogeneity in its gas cell size distribution throughout the 180-min fermentation period, and drastically lower height after proofing and oven spring. All these effects could be related to the poor dough strain hardening behavior of the OCH,D-containing GS dough, which possibly accelerated gas cell destabilization, subsequently leading to an early gas release during proofing and oven spring. The control and the WCH,D-containing yeasted doughs showed similar evolutions of the median gas cell radii and heterogeneities of the gas cell size distribution. Interestingly, after the oven spring, the dough height of the recipe containing WCH,D was significantly higher than that of the control. Thus, WE wheat flour constituents, primarily proteins, likely delayed gas cell destabilization by increasing the resistance of gas cell A/W interfaces to deformation and/or by stabilizing the liquid films between gas cells during oven spring. The ability of wheat extract constituents to stabilize A/W interfaces, thin liquid films (TLFs), and foams in model aqueous systems were evaluated to gain insight into their possible functionality in this regard in stabilizing gas cells in dough. A novel TLF balance setup was used to study TLF drainage dynamics. The mechanical strength of A/W interfaces, susceptibility to TLF drainage, and foam stability seemed to be driven by WE wheat proteins. In addition, dilatational and shear interfacial rheology, and TLF drainage dynamics experiments demonstrated that interactions between WE wheat protein and arabinoxylan increased the strength of A/W interfaces and TLFs. Foam stability and interfacial dilatational modulus were positively correlated, implying that the highly rigid A/W interfacial film composed of WE wheat proteins may have sufficiently delayed TLF drainage to prevent coalescence and disproportionation in the foams during the timescale investigated. Overall, it was demonstrated that various WE flour constituents have different effects on bread SV. Mechanistically, while dough strain hardening remains a key factor in determining bread dough gas cell stabilization, it cannot solely explain the observed bread SV changes. The findings obtained from dough rheology, time-resolved X-ray µCT, and time-lapse recordings during oven spring imply that A/W interfacial and/or TLF stabilization by WE flour constituents, especially during oven spring, could be important for bread dough gas cell stabilization. Still, advanced imaging techniques are necessary to visually prove the presence of the liquid film. Using a novel TLF balance setup, it was fundamentally exhibited that WE wheat proteins strongly influenced the stability of A/W interfaces and TLFs in model aqueous systems. This could facilitate further fundamental investigations not only in bread doughs but also in emerging research on plant-based, foam-type foods.
Author: Monterde, Viena
Language: English
Field: Nursing
Open Access status: green
OpenAlex ID: W7111501857
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