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New methodology using synchrotron radiation to characterize fast events in food processing

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biology
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  1. Introduction.
  2. The problem.
    1. The mixing of ingredients at higher temperature.
    2. The engineer or scientist seeking to control a food process.
  3. Choice of method.
  4. XRD Technology.
    1. Production of X-rays.
    2. Detector technology.
    3. Applications to biological kinetics.
    4. Protein catalysis mechanisms.
    5. Protein structure/dynamics in solution.
    6. Applications to triglyceride crystallization.
    7. Classification of lipid crystals.
    8. Kinetics of lipid crystallization.
  5. Conclusion.

In a typical food process, a hot mixture is made, which is then cooled rapidly. A main result of cooling is a change in physical state and/or molecular structure. Often, a succession of physical changes occurs as the product cools. Events occurring at the more rapid cooling rates can be difficult to characterize using common laboratory methods, and there is a pressing need for faster laboratory measurement techniques. The goal of this chapter is to show that X-ray fluxes available today at synchrotron radiation sources make it possible to characterize rapid process events by X-ray diffraction (XRD). Currently, synchrotron X-ray fluxes are up by 3 to 4 orders of magnitude over the best conventional laboratory sources. When used in conjunction with fast electronic detector systems, synchrotron radiation beams can be used to study events occurring on millisecond time scales. Owing to on-going technical developments, the prospect is to be able to characterize events on a microsecond time scale in the near future. Many processed foods start with the mixing of ingredients at higher temperature, often with the formation of an emulsion during mixing. Typically, the mix is then cooled rapidly. In the sequence of heating and coohng, chemical changes may occur, such as disulfide bond formation in dairy products, or the major change may be simply a temperature-induced change of physical state, such as starch gelation, protein aggregation or fat crystallization.

[...] The radiation process is analogous to the emission of radio waves from a radio tower, but with a twist: Because of a relativistic effect, the radiation from the high- energy particles cannot go off in all directions, as for a radio antenna. Instead, the radiation goes off in the near-forward direction. The result is a highly directional X-ray beam. The X-ray beam so generated has been compared to the light coming from the headlamp of a locomotive moving around a bend in the tracks. [...]


[...] In order to introduce the technique of XRD using synchrotron radiation, this chapter will begin with a discussion of the technologies for generating and detecting X-rays. Then some examples of structural kinetics determined using XRD will be presented, which are drawn from the more mature areas of biological and biomedical studies; these areas are chosen because the materials studied are akin to foods. Finally, one of the first applications of synchrotron radiation to food science - the kinetics of fat crystallization - will be summarized. [...]


[...] Structural kinetics in phospholipid membranes Rapid crystallization events in phospholipid membranes have been characterized using synchrotron radiation. The events have been initiated by gradual heating and cooling, at rates of the order of 5 C/minute; or by a very rapid drop in pressure, which can have a similar effect to very rapid heating. Crystallization under shear A study of direct relevance to many food processes is crystallization under shear. Under conditions where a quiescent sample of plastic takes an hour to begin to crystallize, the process begins in seconds under even a low shear. [...]

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