Periodic Reporting for period 1 - MECASTARCH (Mechanical contribution of starch granules in the stabilization/destabilization of cell walls during bread baking)
Reporting period: 2021-10-11 to 2023-10-10
The wheat market has been experiencing significant fluctuations in price and quality due to political issues and climate change. In this context of instability, the MECASTARCH project proposes the partial replacement of wheat flour in breadmaking with non-gluten flours containing starches of different properties, as a way of guaranteeing the price of products without significant losses in their quality, being valuable knowledge to society.
To that end, different botanical origins of starch (normal and waxy wheat and rice), with consequently different functionalities, were used to answer the question “can starch compensate the role played by wheat gluten in the stabilization of gas cell walls during baking?”. The research particularly focused on the softening conditions of the starch granules upon heating under limited water contents (conditions encountered in bread dough). Depending on the extent and the moment in the baking process, starch softening could alleviate the strain exerted on the gluten and delay the rupture in the gas cell walls, which governs the final bread crumb texture (doi: 10.1016/j.tifs.2021.01.032).
Based on this context, specific objectives were established. As a first step, starches likely to soften to a different extent upon heating in excess of water were collected, characterized and selected, and their mechanical properties upon heating and controlled hydration levels were acquired, to better understand their softening during bread baking. Then, the organization and morphology (deformation) of wheat starch granules in the gas cell walls were illustrated through different microscopic techniques (CLSM and NLOM), focusing on the proving and baking stages (dough and crumb).
To that end, different botanical origins of starch (normal and waxy wheat and rice), with consequently different functionalities, were used to answer the question “can starch compensate the role played by wheat gluten in the stabilization of gas cell walls during baking?”. The research particularly focused on the softening conditions of the starch granules upon heating under limited water contents (conditions encountered in bread dough). Depending on the extent and the moment in the baking process, starch softening could alleviate the strain exerted on the gluten and delay the rupture in the gas cell walls, which governs the final bread crumb texture (doi: 10.1016/j.tifs.2021.01.032).
Based on this context, specific objectives were established. As a first step, starches likely to soften to a different extent upon heating in excess of water were collected, characterized and selected, and their mechanical properties upon heating and controlled hydration levels were acquired, to better understand their softening during bread baking. Then, the organization and morphology (deformation) of wheat starch granules in the gas cell walls were illustrated through different microscopic techniques (CLSM and NLOM), focusing on the proving and baking stages (dough and crumb).
In general, the main objectives of the project were achieved. Structural analysis of the starch samples was combined with the characterisation of mechanical properties of these starches at moderate hydration (elasticity and viscosity). Mechanical testing was performed through compression-relaxation test using the method developed by Laridon et al. 2015 (doi: 10.1122/1.4922221) to estimate elasticity and viscosity. The morphology of starch granules imprisoned in the more or less thin gas cell walls of dough and crumb was evaluated by Confocal Laser Scanning Microscopy combined with staining of the protein fraction by Alexa, allowing the access in 3D to the morphology of starch granules by contrast.
The first results are available in the following paper (doi: 10.1038/s41598-023-39797-w) and three other papers will follow.
Attendance at 4 conferences and 3 workshops during the contract period also contributed to informing about the MECASTARCH initiative and disseminating the first results.
The first results are available in the following paper (doi: 10.1038/s41598-023-39797-w) and three other papers will follow.
Attendance at 4 conferences and 3 workshops during the contract period also contributed to informing about the MECASTARCH initiative and disseminating the first results.
As previously mentioned, the MECASTARCH has the potential to provide methodologies for rationalizing the blending of flours for breadmaking on the basis of starch functionalities which differ between botanical origins. In the context of an unstable wheat market situation, due to climate changes and political issues, this knowledge can be valuable to society, as it can help to decrease the wheat flour quantity on the bread (and thus decrease its overall cost) with controlled quality loss.
The results obtained are essential elements in building our understanding of starch transformation and the baking process. It was expected that MECASTARCH's contribution would be towards the academic world, and this is confirmed by the contribution to the knowledge in the cereal scientific community and the development of novel methodologies, such as: the continuous monitoring of loaf volume and local gas fraction during cooling using Magnetic Resonance Imaging (MRI); the mechanical testing of moderately hydrated starches upon heating (explored for the first time); the NLOM applied to bread dough for the first time too, with the potential of distinguishing granular and extragranular phases without any labeling, and exploring the gas cell wall in 3D; the morphological analysis of starch granules in gas cell walls, implying 3D acquisition with confocal laser scanning microscopy (CLSM) and 3D analysis with the AVIZO ® software. For each methodology, limitations have also been identified and will be shared with the scientific community, constituting tracks for future investigation and improvements of the methods.
As far as the results have been analyzed today (end of the contract), mechanical testing performed under moderate hydration levels encountered in dough showed that starch granules, even in the waxy form, do not soften enough to be deformed with the gluten. They also soften late (>75-80°C). In complement, microscopic observations of crumb with CLSM showed distortion of some starch granules, suggesting some deformability. This could be explained by the higher levels of hydration possible in the dough environment (flour constituents other than starch can hold water which can be mobilized for starch gelatinization upon heating). This finding was also consistent with the uneven access to water of individual starch granules in dough well recognized among the cereal scientific community. Consistently with the results from mechanical testing, little difference in granule size distribution was found at different extension levels of the gas cell walls from the crumb.
The results obtained are essential elements in building our understanding of starch transformation and the baking process. It was expected that MECASTARCH's contribution would be towards the academic world, and this is confirmed by the contribution to the knowledge in the cereal scientific community and the development of novel methodologies, such as: the continuous monitoring of loaf volume and local gas fraction during cooling using Magnetic Resonance Imaging (MRI); the mechanical testing of moderately hydrated starches upon heating (explored for the first time); the NLOM applied to bread dough for the first time too, with the potential of distinguishing granular and extragranular phases without any labeling, and exploring the gas cell wall in 3D; the morphological analysis of starch granules in gas cell walls, implying 3D acquisition with confocal laser scanning microscopy (CLSM) and 3D analysis with the AVIZO ® software. For each methodology, limitations have also been identified and will be shared with the scientific community, constituting tracks for future investigation and improvements of the methods.
As far as the results have been analyzed today (end of the contract), mechanical testing performed under moderate hydration levels encountered in dough showed that starch granules, even in the waxy form, do not soften enough to be deformed with the gluten. They also soften late (>75-80°C). In complement, microscopic observations of crumb with CLSM showed distortion of some starch granules, suggesting some deformability. This could be explained by the higher levels of hydration possible in the dough environment (flour constituents other than starch can hold water which can be mobilized for starch gelatinization upon heating). This finding was also consistent with the uneven access to water of individual starch granules in dough well recognized among the cereal scientific community. Consistently with the results from mechanical testing, little difference in granule size distribution was found at different extension levels of the gas cell walls from the crumb.