X-ray Microscopic Examination of Chocolate

Figure 1: Volumetric rendering of caramel filled chocolate square imaged on the SkyScan 1272

The magic of chocolate is being unveiled by research investigating not its taste but its feel and texture. The study — published in the scientific journal “ACS Applied Materials and Interface” — demonstrates that fat plays a key function when a piece of chocolate is in contact with the tongue. This indicates that fat deeper inside the chocolate plays a limited role and could be reduced without having an impact on the feel or sensation of chocolate. Anwesha Sarkar, Professor of Colloids and Surfaces in the School of Food Science and Nutrition at Leeds, said: “Lubrication science gives mechanistic insights into how food actually feels in the mouth. You can use that knowledge to design food with better taste, texture or health benefits.”

X-Ray Microscopic Imaging of Chocolate

We took our own look inside chocolate bars and imaged two different formulations of chocolates using either the SkyScan 1272 micro-CT and the SkyScan 2214 nano-CT within the Micro Photonics Imaging Laboratory.

One chocolate bar containing a liquid caramel filling was sectioned down and imaged using the SkyScan 1272 at an isotropic voxel size of 10 micrometers. A second extra-dark formulation chocolate bar was also imaged on the SkyScan 1272 under the same imaging conditions before being further sub-sectioned and imaged at an isotropic voxel size of 500nm using the SkyScan 2214 nano-CT. The additional resolution provided by the nano-CT allows us to view individual pieces of ground chocolate and fillers within the bar which are not visible at the standard resolution used with the SkyScan 1272. Applying a single distance phase retrieval function to the nano-CT data further enhances the contrast present in the sample to highlight the components from one another despite all being similar in X-ray attenuation.

Figure 2: Planar 2D views of a caramel filled chocolate square section

As shown in Figure 2, the SkyScan 1272 micro-CT resolved the caramel filling as well as large salt crystals and air bubbles in the finished chocolate bar. The contrast between the caramel filling and the chocolate results from the slightly higher attenuation of X-ray energy by the caramel in comparison to the chocolate leading to the brighter coloration in the reconstructed dataset. Likewise, salt crystals show up as bright white spots in the dataset since inorganic materials attenuate an exponentially greater amount of X-ray energy compared to organic materials like the chocolate or caramel.

Figure 3: CTVox volumetric rendering through a portion of the caramel filled chocolate bar

CTVox allows us to interactively view the caramel filled chocolate bar dataset in 3D while having full control over the sample position and cutting planes (Figure 3). Since nice contrast exists between the caramel, salt, and chocolate components each can be artificially colored in CTVox using a careful tuning of the transfer function. While this produces remarkably useful data, the images can be further enhanced by exporting the dataset as a defined model before rendering using a more specialized third-party 3D software program as shown in Figure 1.

 

Figure 4: Clipped volumetric 3D rendering of the extra-dark chocolate formulation acquired on the SkyScan 1272

Imaging a second chocolate product with an extra-dark formulation using the SkyScan 1272 under the same conditions allows us to directly compare the two samples. The extra-dark formulation does not contain the caramel filing but does have a qualitatively higher porosity dispersed throughout the chocolate than the caramel filled product (Figure 4).

 

Figure 5: Planar views within the extra-dark chocolate formulation without (left) and with single distance phase retrieval applied (right)

Removing a small piece of chocolate from the larger segment imaged by the SkyScan 1272, the extra-dark formulation was also imaged using the SkyScan 2214 nano-CT for an enhanced view of the components within the chocolate bar (Figure 5). In reviewing the resulting reconstructed dataset, signs of small angle scattering were visible including the bright edges of the sample leading us to believe that application of a Paganin single distance phase retrieval function to our projection data could enhance our images. Using NRecon 2, we applied the function to a second copy of the dataset following the principles outlined in Bruker Method Note 133 and then reconstructed the resulting images producing the enhanced contrast seen above. While some resolution is ultimately lost during the phase retrieval process, in many cases the additional contrast which occurs in the sample is more important to interpretation and examination of the dataset.

Figure 6: Clipped volumetric 3D rendering of the extra-dark chocolate formulation acquired on the SkyScan 2214 nano-CT after single distance phase retrieval

Examining the volumetric data from the nano-CT dataset in CTVox allows us to see the relative scale and prevalence of bubbles in the formulation as well as individual components in the heterogeneous mixture which is a chocolate bar (Figure 6). 

Conclusion

The SkyScan 1272 is a versatile desktop instrument geared towards high-resolution imaging of medium and low density samples like the chocolates explored in this project. The SkyScan 2214 nano-CT provides an extra boost of resolution for samples where the finest details are needed.

We hope you found this Image of the Month informative and encourage you to subscribe to our newsletter and social media channels in preparation for the continuation of our Image of the Month series next month.

Scan Specifications

Instrument SkyScan 1272 SkyScan 2214
Voltage (kV) 70 40
Current (µA) 142 150
Filter 0.5 mm Aluminum None
Pixel Size (µm) 10 0.5
Rotation Step 0.2 0.2
Exposure Time (ms) 560 3500
Rotation Extent (deg.) 180 360
Scan Time (HH:MM:SS) 01:05:08 per length section 13:48:48

 

These scans were completed on our SkyScan 1272 micro-CT system and our SkyScan 2214 nano-CT system at the Micro Photonics Imaging Laboratory in Allentown, PA. Reconstructions were completed using NRecon 2.0 while visualization and volumetric inspection of the 2D and 3D results were completed using DataViewer and CTVox. Individual components were meshed using Synopsis Simpleware ScanIP* with the CAD Module (Synopsys, Inc., Mountain View, USA) before 3D rendering using Maverick Render Indie (Random Control, Madrid, Spain).

Would you like your work to be featured in our monthly newsletter? If so, please contact us by calling Seth Hogg at 610-366-7103 or e-mailing seth.hogg@microphotonics.com.

References

*Simpleware software enables you to comprehensively process 3D image data (MRI, CT, micro-CT, FIB-SEM…) and export models suitable for CAD, CAE and 3D printing. Use Simpleware’s capabilities to visualize, analyze, and quantify your data, and to export models for design and simulation workflows.

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