Structural formation during bread baking in a combined microwave-convective oven determined by sub-second in-situ synchrotron X-ray microtomography.

A new concept has been developed for characterizing the real-time evolution of the three-dimensional pore and lamella microstructure of bread during baking using synchrotron X-ray microtomography (SRµCT). A commercial, combined microwave-convective oven was modified and installed at the TOMCAT synchrotron tomography beamline at the Swiss Light Source (SLS), to capture the 3D dough-to-bread structural development in-situ at the micrometer scale with an acquisition time of 400 ms. This allowed characterization and quantitative comparison of three baking technologies: (1) convective heating, (2) microwave heating, and (3) a combination of convective and microwave heating. A workflow for automatic batchwise image processing and analysis of 3D bread structures (1530 analyzed volumes in total) was established for porosity, individual pore volume, elongation, coordination number and local wall thickness, which allowed for evaluation of the impact of baking technology on the bread structure evolution. The results showed that the porosity, mean pore volume and mean coordination number increase with time and that the mean local cell wall thickness decreases with time. Small and more isolated pores are connecting with larger and already more connected pores as function of time. Clear dependencies are established during the whole baking process between the mean pore volume and porosity, and between the mean local wall thickness and the mean coordination number. This technique opens new opportunities for understanding the mechanisms governing the structural changes during baking and discern the parameters controlling the final bread quality.

Effect of zein protein and hydroxypropyl methylcellulose on the texture of model gluten-free bread.

The influence of zein protein and hydroxypropyl methylcellulose (HPMC) on the texture and volume of gluten-free bread was investigated. The addition of HPMC to starch affected the dough viscoelasticity and it improved the bread volume during baking since it acts as an emulsifier. The addition of zein protein to gluten-free bread increased the crumb firmness and reduced the crust hardness within the range of concentrations investigated. No zein protein network could be observed in the bread crumb. The zein protein, cold mixed at low concentration, did not enhance the dough elasticity. Due to the lack of a protein network noncovalent interactions may stabilize the bubble structure stabilization within the crumb, rather than covalent links of the protein chain. With an optimized amount of zein protein and HPMC hydrocolloid, the gluten-free bread showed similar texture and staling behavior to that of model wheat bread. The optimized recipe, compiled into a spreadsheet, is available in the supporting information. The microstructural observations suggest that zein could be replaced with another protein for this recipe resulting in a similar bread texture.

Design of microcapsules with bilberry seed oil, cold-set whey protein hydrogels and anthocyanins: Effect of pH and formulation on structure formation kinetics and resulting microstructure during purification processing and storage.

Encapsulation of polar and non-polar bioactive compounds from bilberries was achieved by designing microcapsules with bilberry seed oil (BSO) distributed in an aqueous phase of anthocyanins (AC) stabilized by whey protein isolate (WPI). Non-thermal emulsification method (o/w/o) was developed and the effect of pH (3 or 4.5), concentration of WPI (8.4-10.8% w/w), addition of AC (72-216 ppm) and emulsifier on the structure-forming kinetics, resulting microstructure during storage and after centrifugation and washing was investigated. Agglomeration of BSO was observed in all microcapsules at pH 4.5 due to slow gelling process and in samples at pH 3 at low concentrations of WPI (≤8.4%). Capsules with pH 3 (9.6-10.8% WPI) had weak structures but as the gelling process was faster, it generated an even distribution of BSO droplets. All samples at pH 4.5 and samples with WPI concentration ≥10.8% at pH 3 exhibited intact structures after centrifugation and washing.

Effect of anthocyanins on lipid oxidation and microbial spoilage in value-added emulsions with bilberry seed oil, anthocyanins and cold set whey protein hydrogels.

The objective of this work was to explore the storage properties of a structured oil-in-water emulsion containing both water- and fat-soluble bioactive compounds from bilberries (Vaccinium myrtillus L.). Bilberry seed oil (BSO) was dispersed in a continuous aqueous phase of anthocyanins (AC) and whey protein isolate. The microstructure was evaluated using light microscopy and the effect of anthocyanins on lipid oxidation and microbial growth was investigated. The results showed that it was possible to generate a stable emulsion structure that resisted phase separation during 25 weeks of storage. Gas chromatography-mass spectrometry measurements of the fatty acids in the BSO during storage showed that AC had a protective effect against lipid oxidation. The AC did not have an antimicrobial effect against the investigated strains Zygosaccharomyces bailii (ATCC 42476) and Aspergillus niger (ATCC 6275 (M68)).

Interactions and diffusion in fine-stranded ß-lactoglobulin gels determined via FRAP and binding.

The effects of electrostatic interactions and obstruction by the microstructure on probe diffusion were determined in positively charged hydrogels. Probe diffusion in fine-stranded gels and solutions of ß-lactoglobulin at pH 3.5 was determined using fluorescence recovery after photobleaching (FRAP) and binding, which is widely used in biophysics. The microstructures of the ß-lactoglobulin gels were characterized using transmission electron microscopy. The effects of probe size and charge (negatively charged Na2-fluorescein (376Da) and weakly anionic 70kDa FITC-dextran), probe concentration (50 to 200 ppm), and ß-lactoglobulin concentration (9% to 12% w/w) on the diffusion properties and the electrostatic interaction between the negatively charged probes and the positively charged gels or solutions were evaluated. The results show that the diffusion of negatively charged Na2-fluorescein is strongly influenced by electrostatic interactions in the positively charged ß-lactoglobulin systems. A linear relationship between the pseudo-on binding rate constant and the ß-lactoglobulin concentration for three different probe concentrations was found. This validates an important assumption of existing biophysical FRAP and binding models, namely that the pseudo-on binding rate constant equals the product of the molecular binding rate constant and the concentration of the free binding sites. Indicators were established to clarify whether FRAP data should be analyzed using a binding-diffusion model or an obstruction-diffusion model.

Surface-directed structure formation of ß-lactoglobulin inside droplets.

The morphology of ß-lactoglobulin structures inside droplets was studied during aggregation and gelation using confocal laser scanning microscopy (CLSM) equipped with a temperature stage and transmission electron microscopy (TEM). The results showed that there is a strong driving force for the protein to move to the interface between oil and water in the droplet, and the ß-lactoglobulin formed a dense shell around the droplet built up from the inside of the droplets. Less protein was found inside the droplets. The longer the ß-lactoglobulin was allowed to aggregate prior to gel formation, the larger the part of the protein went to the interface, resulting in a thicker shell and very little material being left inside the droplets. The droplets were easily deformed because no network stabilizes them. When 0.5% emulsifier, polyglycerol polyresinoleat (PGPR), was added to the oil phase, the ß-lactoglobulin was situated both inside the droplets and at the interface between the droplets and the oil phase; when 2% PGPR was added, the ß-lactoglobulin structure was concentrated to the inside of the droplets. The possibility to use the different morphological structures of ß-lactoglobulin in droplets to control the diffusion rate through a ß-lactoglobulin network was evaluated by fluorescence recovery after photobleaching (FRAP). The results show differences in the diffusion rate due to heterogeneities in the structure: the diffusion of a large water-soluble molecule, FITC-dextran, in a dense particulate gel was 1/4 of the diffusion rate in a more open particulate ß-lactoglobulin gel in which the diffusion rate was similar to that in pure water.