INDEX milk proteins

J. A. B. Baptista and R. C. B. Carvalho, Indirect determination of Amadori compounds in milk-based products by HPLC/ELSD/UV as an index of protein deterioration. Food Res. Int, 37 (2004) 739-747. 

In principle, it would be logical to combine plots of the buffer index curves of each of the buffer components of milk and thus obtain a plot which could be compared with that actually found for milk. It is not difficult, of course, to conclude that the principal buffer components are phosphate, citrate, bicarbonate, and proteins, but quantitative assignment of the buffer capacity to these components proves to be rather difficult. This problem arises primarily from the presence of calcium and magnesium in the system. These alkaline earths are present as free ions as soluble, undissociated complexes with phosphates, citrate, and casein and as colloidal phosphates associated with casein. Thus precise definition of the ionic equilibria in milk becomes rather complicated. It is difficult to obtain ratios for the various physical states of some of the components, even in simple systems. Some concentrations must be calculated from the dissociation constants, whose... 

Clarification by removal of casein with such agents as calcium chloride, acetic acid, cooper sulfate, or rennin has often been employed to obtain a serum more suitable for refractometric measurements. Obviously the composition, and hence the refractive index, of such sera will depend on the method of preparation. Furthermore, some of the serum proteins may be precipitated with the casein by some of the agents used, particularly if the milk has been heated. Refractive index measurements of such sera are not generally considered as satisfactory as freezing point measurements for detection of added water (David and MacDonald 1953 Munchberg and Narbutas 1937 Schuler 1938 Tell-mann 1933 Vleeschauwer and Waeyenberge 1941). Menefee and Overman (1939) reported a close relation between total solids in evaporated and condensed products and the refractive index of serum prepared therefrom by the copper sulfate method. Of course, a different proportionality constant would hold for each type of product. 

Both the fat and protein of milk scatter light, the amount of scattering depending upon the number and size of the particles, the wavelength of the incident radiation, and the difference in refractive index between the different kinds of particles and the solvent (Ashworth... 

Since the PS reference sample is almost monodisperse, a cumulant analysis of that material would yield a very small Q, say Q < 0.03. That is, all the correction terms are negligible and Eqs. (17) collapse to Eqs. (12). But cumulant analysis is a useful way to handle practical samples such as pigments, inks, microemulsions, swollen micelles, globular proteins, and spherical virus particles, where there is a size distribution but one that is not very broad (say Q < 0.3). This analysis should be made for the milk data using a non-linem teast-squares fitting of Eq. (17a), neglecting /1.3 and all higher order terms. Report the F, D, and R values as well as the second cumulant /t2 aiid the polydispersity index Q. 

In pregnant women, there is a progressive increase in the erythrocyte glutathione reductase activation coefficient (an index of functional riboflavin nutritional status Section 7.5.2), which resolves on parturition despite the daily secretion of 200 to 400 /rg (0.5 to 1 /rmol) of riboflavin into milk. This suggests that the estrogen-induced riboflavin binding protein can sequester the vitamin for fetal uptake at the expense of causing functional deficiency in the mother. 

Changes in the aggregation state may result in insolubilization of the protein, or its binding (not necessarily through covalent bonds) to other insoluble components. Thus, disappearance of a specific protein from the pool of soluble proteins in a given food may be detected by any of the techniques discussed above, and taken as a reliable index of process damage. A prime example of this simple approach to defining food quality at the molecular level may be the detection of individual whey proteins to define the quality of heat-treated milk. 

Absorbed fat travels in the blood in particles of about 1 mp in diameter, termed chylomicrons. Like the fat in milk, they are stabilised by being surrounded by a protective protein layer. They may be enumerated microscopically, and afford an index of the rate of fat absorption and utilisation. The fat content of the systemic blood rises in one to three hours after a meal rich in fat, reaches a peak in six or seven hours, and gradually subsides. 

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