Protein-based materials charged

A new ionization method called desorption electrospray ionization (DESI) was described by Cooks and his co-workers in 2004 [86]. This direct probe exposure method based on ESI can be used on samples under ambient conditions with no preparation. The principle is illustrated in Figure 1.36. An ionized stream of solvent that is produced by an ESI source is sprayed on the surface of the analysed sample. The exact mechanism is not yet established, but it seems that the charged droplets and ions of solvent desorb and extract some sample material and bounce to the inlet capillary of an atmospheric pressure interface of a mass spectrometer. The fact is that samples of peptides or proteins produce multiply charged ions, strongly suggesting dissolution of the analyte in the charged droplet. Furthermore, the solution that is sprayed can be selected to optimize the signal or selectively to ionize particular compounds. 

The development of "process flavors" based on proteins and other materials considered to have nutritional content or functional properties other than flavor became a major problem for the PMC. Their charge and professional view is that all these materials should be labeled. Labeling of flavor ingredients was exempted under a FDA decision. However, the USDA PMC considered diem non-flavor ingredients. This situation led to havoc in the flavor industry as companies had two labels for one flavor and in many instances a customer company would indicate the use of tiie flavor in a USDA product after being given an FDA label with disclosure of the protein or nutritional based materials used in making the "process flavor". 

Furthermore, the assumption of a uniform dielectric constant for all water structures interacting with protein-based machines and materials conceals the occurrence of competition for hydration between hydrophobic groups and charged groups. In the past there has been the practice of using a dielectric constant of 80 (that for bulk water) up to the surface of the protein and then decreasing the dielectric constant to 5 or less when within the protein. However, what Solomonic wisdom suffices for choice of dielectric constant to be used for ion-pair formation within the tortuous surfaces with clefts of varying shapes from acute to obtuse. As seen in Chapter 8, these clefts may reside inside the protein-based machine, as found in ATP synthase, or outside the protein-based machine, as occurs for the myosin II motor. 

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