Protein Powder Refinements

Refining. After saccharification, the hydrolyzate is clarified by precoat filtration, or possibly membrane filtration, to remove traces of insoluble fat, protein, and starch. Treatment with powdered carbon, granular carbon, and/or ion-exchange resins is then used to remove residual trace impurities, color, and inorganic constituents. The refined hydrolyzate can be dried to a solid product, evaporated to a high dextrose syrup, or processed to crystalline monohydrate or anhydrous dextrose. A typical process for production of crystalline dextrose is shown in Figure 2(7). 

Foams. Refined lecithins have been employed as effective foam control agents. Examples include whipped toppings, ice creams, and many types of candies. Refined lecithin products have also been employed as effective defoaming agents in foams caused by powdered proteins in water. This is an excellent example of the system specificity of lecithin products (7). 

The view about line profile analysis given in this chapter is pessimistic, it is the consequence of the complexity of the Bragg peak shapes as they occur from poorly-crystallized material. More optimistic is the future of the main whole powder pattern fitting applications (decomposition or Rietveld methods) that have moved beyond the initial stages, enabling structure determinations (almost routinely) and refinements (routinely) of moderately complex structures to even complex crystal structures such as proteins (sometimes). 

The crystal structures of proteins represent an extreme in the number of atom positions needed to describe them compared to those structures more commonly studied by powder diffraction. For example, the well-known tetragonal crystal structure of hen egg white lysozyme has 1001 nonhydrogen atoms within the protein molecule another 100 or so water molecules and salt ions are also present. This gives over 3000 atomic x,j,z coordinates. Nonetheless, a Rietveld refinement of these structures from powder diffraction data can be performed by extending the suite of restraints to include all stereochemical features that show characteristic values.The suite of restraints given in Equation (24) is then ... 

Improvements in hardware have been accompanied by enhancements to software that facilitate the refinement of even more complex strnctures. Techniques that have been developed for powder diffraction and protein crystallography can now be applied routinely to single-crystal analysis and vice versa. For single-crystal studies, this has led to more reliable refinements of weak, low-resolution datasets that are unavoidable when, as is often the case in supramolecular chemistry, only microscopic crystals are available. 

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