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Food Structure

Authors

B. E. Brooker

Abstract

Low temperature scanning electron microscopy in conjunction with X-ray microanalysis can be used to study not only the internal structure of intact bulk food systems but also the distribution of their constitutive chemical elements. However, the considerable practical problems that are usually encountered when performing X-ray analysis on frozen samples include: a) the controlled deposition of a good quality carbon film to prevent charging, b) producing digital elemental distribution maps of elements whose X-ray spectral energy peaks partially or completely overlap and c) controlling the plane of fracture through the specimen and ensuring that the resulting topography allows meaningful analysis to be performed.

The quality and control of carbon film deposition is greatly improved by the inclusion of a turbomolecular pump in the vacuum system and by using thickness monitoring of the carbon film during deposition. However, the complications of energy peak overlap in digital X-ray mapping can only be overcome by using a procedure which produces maps corrected for all of the spectrum processing routines normally available in quantitative programmes. Another advantage of this approach is that statistics such as FIT index {see appendix) and standard deviation are available for each pixel.

Problems associated with fracturing are avoided if the internal structure of materials is revealed using cryo-mi11ing. This procedure uses a rotating diamond cutting tool to produce a very flat surface on the frozen specimen which is ideal for X-ray analysis and for image analysis of structural components. Quantitative X-ray mapping of milled cocoa beans shows that this preparation procedure does not cause smearing of the chemical components across the surface of the specimen.

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