Starch retrogradation is one of the main reasons bread goes stale. Freshly baked bread has a soft, moist and elastic crumb due to the gelatinisation of starch and presence of water. However, as the bread cools, starch polysaccharides (mainly amylose and amylopectin) start to reorganise themselves into a more crystalline structure. Over time, this makes the crumb firmer and causes the pore structure to shrink or collapse, leading to a drier, denser, less elastic texture. A moisture gradient is also formed during cooling. Differences in vapour pressure cause the migration of moisture from the crumb into the crust, resulting in lower crumb moisture and higher crust moisture1.
RSSL was asked to evaluate the extent of these changes in a white baguette, so our client could make the right formulation adjustments to maintain its freshly baked, light and airy texture for longer.
X-ray micro-CT (computed tomography) uses non-destructive X-rays to capture cross-sections of an object at different angles through 360° for later virtual reconstruction.
Visualisation of materials is based on their relative densities, with density of the material being inversely proportional to the measured intensity of X-ray photons. Scans were taken using Werth Metrology’s Tomoscope XS Plus. Once acquired, the datasets were processed in Avizo 2023 (3D image analysis software) before being exported to VGstudio Max for structural thickness and porosity analysis.
A white bread baguette was analysed at day 1 (T=0, fresh). To accelerate starch retrogradation, the baguette was then placed in a fridge before analysis on day 7 (T=1, stale). The structural thickness and pore size were calculated, as well as % porosity by total volume.
Based on inferred literature values, significant changes in moisture content and crystallinity would be observed in bread stored at 4°C2: