Gas cells make up a significant proportion of bread’s volume and are responsible for a number of bread’s characteristics, making their size distribution throughout bread an important quality parameter. The number and size of cells affect the texture and volume of bread, the quantity of sauce mopped up, and how bright the bread appears. Gas cells are incorporated into bread dough during mixing and manipulated throughout the breadmaking process to obtain the desired cellular structure. Due to the fragile nature of bread dough, obtaining accurate quantitative data on its cellular structure is challenging. This thesis investigates the cellular structure of bread, as well as assessing the effect of sugar during breadmaking. Magnetic resonance imaging (MRI), microscopy and X-ray computerised tomography (X-ray CT) have been used throughout research in bread dough to visualise dough’s cellular structure. A non-destructive and non-invasive method giving a high resolution is X-ray CT, in particular when using a synchrotron light source. However, time on a synchrotron beamline is highly competitive, and can require applications more than two years in advance. Running costs of experiments from a synchrotron beamline are also high. This thesis details an alternative X-ray set-up to accurately visualise dough’s cellular structure using a conventional and therefore more easily accessible X-ray source. Three X-ray CT experiments were conducted to investigate dough’s cellular structure throughout mixing, during proving and in different sugar content doughs. The resolution of the scans varied from 7-11 µm. Industrial bread dough mixing is often conducted at a high pressure initially to improve oxygen availability, followed by a period of partial vacuum to favourably manipulate the cell size distribution. Using X-ray CT, dough cell size distribution was measured at different points throughout pressure-vacuum and constant pressure mixing. A simplified population balance model was fitted to the measured cell size distributions and the validity of the assumptions within the simplified model explored. It was shown that the dynamic changes in the cell size distribution within bread dough could be accurately measured during pressure step change mixing with a non-synchrotron X-ray source. Pressure-vacuum mixing was shown to give a finer cell distribution than constant pressure mixing and the observed decrease in cell number density was found to be much more short lived than the decrease in cell size. The model was found to provide a reasonably accurate characterisation of pressure-vacuum mixing. X-ray CT was also used to monitor dough’s changing cellular structure during proving by taking scans every 5 minutes over 145 minutes. Dough voidage increased from 3% to 66%, resulting in a volume increase from 544 mm3 to 1293 mm3. Cell growth was quickest between 40 and 140 minutes, where a steady increase in volume and significant changes in the cell structure occurred. A change in voidage distribution was observed, with greater proportions of gas located in larger cells over time. In addition, over the course of proving cell numbers dropped, a 156-fold increase in mean cell volume occurred, and mean cell Feret shape increased from 1.59 to 1.91. This in-situ method of X-ray imaging of bread dough provides higher resolution images than comparable data from conventional X-ray sources. In addition, the method has proved to be effective in obtaining high resolution and high contrast 3D images of the cellular structure of dough. This technique will help those wanting to investigate cellular changes in the dough dynamically, but without the waiting time and applications that are required with synchrotron X-rays. On investigating the effect of sugar during breadmaking, sugar was found to increase the gas free dough density and dough voidage, change the dough’s rheology, increase its proving time and produce denser bread. Application of a population balance model on the experimental results indicate that the decrease in steady state voidage as the sugar content increases is a result of an increase in disentrainment. This was reflected in the X-ray CT of sugared vs. non-sugared doughs through fewer and smaller cells present in sugared doughs. This is likely to be a result of a weaker dough structure, making cell rupture more likely. The Chorleywood Bread Process (CBP) is used industrially worldwide for the production of bread in less time and using inferior ingredients compared to the traditional bulk fermentation process, making it more cost effective. These results show that simply extending the pressure vacuum mixing used for the production of standard bread loaves in the CBP to sugared doughs should be avoided as aeration of sugared doughs differs to non-sugared doughs. The results suggest that to do so would be detrimental to the product quality.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:607398 |
| Date | January 2013 |
| Creators | Trinh, Linda |
| Contributors | Campbell, Grant; Martin, Peter |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/gas-cells-in-bread-dough(617b6c1d-273a-4223-a3f3-090d75ed7d0e).html |
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