During the preparation of food products for consumers, factors such as flavor, texture, and shelf-stability are all influenced by the presence of air bubbles. For whipped products, the presence of air softens the mouthfeel of foods and reduces the calories contained in a similar size serving by volume. Micro-CT allows for non-destructive examination of air content in finished and in-process food products and monitoring changes over time may lead to information related to product stability.
X-Ray Microscopic Imaging of Whipped Food Products
This month we imaged both a traditional and a whipped cream cheese product of the same net weight using the SkyScan 1273 micro-CT. The large chamber allows for samples of many sizes to easily be positioned for imaging. The high-resolution flat panel detector provided us a detailed view of the air bubble shape and locations within the packaged product.
Figure 2: Planar 2D views of the reconstructed dataset for the standard (top) and whipped (bottom) varieties of cream cheeseAs shown in Figure 2, the SkyScan 1273 had sufficient resolution at the isotropic voxel size of 40 µm to detail the location of any air bubbles in either the standard or the whipped varieties of cream cheese examined in this study. As expected, we can see the apparent density of the standard cream cheese product is higher than the whipped product based on the higher average pixel brightness within the product data in the reconstructed images. Since the net weight of the two cream cheese products is identical, the increase in total volume of the whipped product arising from the incorporation of additional air into the product naturally leads to a lower effective density.
Exploring the data in 3D allows us to move through the dataset and to visually note the presence of small air bubbles, even in the standard product (Figure 3). These bubbles originated either during the filling process or during transportation and shelving of the product at the final retail location.
Examining the whipped product shows a vast increase in air content and CTVox allows for an overlay of color-coded size data of the bubbles obtained from CTAnalyzer (CTAn) (Figure 4). Using clipping shapes, we subtracted the volumetric data from the whipped cream cheese dataset while highlighting the location and size of the voids. While the product has a standard distribution of bubble diameters, a large void is also present at the base of the cup arising during the filling process in the manufacturing plant.
CTAn provides a quantitative assessment of air bubble diameter throughout our selected region of interest within the filled product volume. The histogram of bubble diameters compared against total volume fraction of air is shown in Figure 5. We see that the product has a normal distribution around the calculated nominal bubble diameter of 1.61 ± 1.84 mm with the large variance arising from the presence of the relatively few but very large voids from the filling and packaging process.
Ultimately, CTAn determined the whipped cream cheese to contain about 9% air within our examined region of interest.
Conclusion
The large sample chamber and fine movement capability of the micro positioning stage of the SkyScan 1273 was a perfect match for comparing the air content of standard versus whipped cream cheese examined in this study.
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Scan Specifications
| Sample | Cream Cheeses |
| Detector | Flat Panel |
| Voltage (kV) | 120 |
| Current (µA) | 300 |
| Filter | 0.5 mm Copper |
| Pixel Size (µm) | 40 |
| Rotation Step | 0.25 |
| Exposure Time (ms) | 99 |
| Scan Time (HH:MM:SS) | 02:21:06 |
These scans were completed on our SkyScan 1273 micro-CT system at the Micro Photonics Imaging Laboratory in Allentown, PA. Reconstructions were completed using NRecon while visualization and volumetric inspection of the 2D and 3D results were completed using Dataviewer and CTVox. CTan was utilized to segment and quantify air bubbles within the whipped cream cheese product.
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