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Title: Possibilities of X-ray nano-CT for internal quality assessment of food products
Authors: Herremans, Els
Chassagne-Berces, Sophie
Chanvrier, Hélène
Atoniuk, Aleksandra
Kusztal, Robert
Bongaers, Evi
Verlinden, Bert
Jakubczyk, Ewa
Estrade, Pascal
Verboven, Pieter
Nicolai, Bart #
Issue Date: May-2011
Conference: ICEF edition:11 date:22-26 May 2011
Article number: FMS112
Abstract: Knowledge of food microstructure and how it changes during processing operations is essential to produce high quality food. X-ray CT (Computed Tomography) uses X-rays to look inside materials and produces 3-D images. While micro-CT (X-ray imaging at micrometer resolution) has become feasible over the last decade, many foods contain structural features (such as air spaces, cells, cell walls) that are manifested over a large range of dimensions, including the nanometer range. Up to date it has been nearly impossible to visualize structures on the nanoscale in 3-D with X-ray CT. As a consequence, it has been difficult to quantify the effects of these nanoscale features on important quality attributes such as texture or rehydration properties. While nano-CT (X-ray imaging at nanometer resolution) has recently become available, the applicability of this new method remains to be explored.

OBJECTIVE
The aim of this work was to visualize the 3-D structure of selected food products by advanced X-ray imaging at micro- and nanometer resolution. In particular, we wanted to determine the achievable representative sample size, resolution and contrast for imaging different types of foods by quantitative comparison of images acquired at different spatial resolutions.

METHODOLOGY
A diverse selection of moist and dry foods was used to explore the applicability range of nano-CT. Samples of different recipes of cereal products, a model food foam recipe with two distinct compositions and fresh apples were scanned using a nano-CT scanner with spatial resolution in the range of hundreds of nanometers. For micro-CT imaging, a high-resolution micro-CT system was used. Millimeter-sized samples were excised and moist tissues were wrapped in polymer foil to avoid dehydration. A source voltage ranging between 40 and 60 keV was applied for scanning these relatively ‘soft’ food materials. For high-resolution imaging, scan times typically ranged between 30 minutes and a few hours. The 3-D images were analyzed by the visualization software Avizo. Key microstructural features were quantified, including sample porosity (number and volume of individual pores) and connectivity (euler and fragmentation number).

RESULTS
X-ray CT was very effective for imaging the microstructure of these porous products. The distinct phases of the food (solid matrix and air spaces) could be segmented due to a high contrast in X-ray absorption. Nano-CT provided complementary structural information (in particular the pore size distribution) to micro-CT but care had to be taken to provide representative samples. Furthermore, small samples are easily subject to dehydration during lengthy scans, causing undesired artefacts. Nevertheless, X-ray nano-CT enabled the investigation of the 3-D microstructure of samples in a near-native state at unprecedented resolutions.

IMPLICATION
To make significant advances in delivering foods with excellent quality, the role of microstructure, and interactions with composition must be understood and used in the manufacturing process. This can only be achieved by accurate techniques that detect changes in the internal microstructure. On a longer term, this knowledge will contribute to improving nutritional quality (sugar- and gluten-free cereal products), sensory quality (texture) and safety (foreign material detection) of foods.
Publication status: accepted
KU Leuven publication type: IMa
Appears in Collections:Division of Mechatronics, Biostatistics and Sensors (MeBioS)
# (joint) last author

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