Use of X‐ray micro tomography to study the microstructure of loose‐packed and compacted milk powders

Abstract

SummaryThe use of X-rays to evaluate food microstructure has developed considerably in recent years. In this work we used X-ray micro tomography (XMT) to visualize the microstructure of loose-packed and compacted samples of spray-dried skim milk powder (SMP) and whole milk powder (WMP) and to quantify the proportion of both interstitial and occluded air voids in each sample. Visual scrutiny of the acquired XMT images showed details of the microstructure of the milk powders such as the spherical morphology of the particles, the size of the particles and internal air voids of various sizes. Within loose-packed powders, the proportion of air voids was higher (13% average) in WMP than in SMP. This was reversed in the compacted powders, in which the proportion of air voids was higher in SMP. The disparity in the proportion of air voids in both loose-packed and compacted samples of SMP and WMP was attributed to the size, shape and surface properties of the particles.

A Review of Particle Size Analysis with X-ray CT

“…Other studies have used a much lower limit, such as 8 or 10 voxels [ 37 , 45 ]. Assuming a sub-micrometre resolution X-ray CT system, an approximate smallest voxel size at the highest resolution is approximately 0.2 to 0.3 m. Using the 512 voxel cut-off limit, this means the smallest characterisable particle size is approximately 2 to 3 m. However, calculating the average amount of voxels across the smallest particles, in our survey of published research [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , ...…”

“…Over the last 20 years ( Figure 1 a), more than 60 publications [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ,…”

“…The digital data, collected with each scan, can feed directly into computed models about the particles and their behaviour in the granular assembly [ 27 , 47 , 48 , 54 ]. After early use of synchrotron beam lines [ 1 , 3 , 6 , 7 , 14 , 28 , 33 , 34 , 46 ], the emergence of laboratory X-ray CT instruments [ 2 , 4 , 8 , 9 , 10 , 11 , 12 , 13 , 18 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 30 , 31 , 32 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 47 , 48 , 49 , 50 , 51 , 52 , 54 , 55 , 57 , 58 , …”

“…Granulated organic materials, including foods, such as milk powder [ 12 ] or maltodextrin [ 24 ], pesticide-containing dust from seeds [ 20 ], and pharmaceutical powders (lactose, [ 51 ], hexamine [ 57 ], L-glutamic acid [ 55 ], acetylsalicyl acid [ 10 ]) have also been studied using X-ray CT.…”

Exploring the Developmental Progression of Endosperm Cavity Formation in Maize Grain and the Underlying Molecular Basis Using X-Ray Tomography and Genome Wide Association Study

“…The principle of X-ray μCT analyses is based on the differences in X-ray attenuation arising from differences in material density and composition ( Chawanji et al, 2012 ). The average attenuation of the sample is expressed in Hounsfield Unit (HU) or CT number ( Donis-González et al, 2014 ).…”