Caseins are the principal protein components in milk and an important ingredient in the food industry. In liquid milk, caseins are found as micelles of casein proteins and colloidal calcium nanoclusters. Casein micelles were isolated from raw skim milk by size exclusion chromatography and suspended in milk protein-free serum produced by ultrafiltration (molecular weight cut-off of 3 kDa) of raw skim milk. The micelles were imaged by cryo-electron microscopy and subjected to tomographic reconstruction methods to visualize the 3-dimensional and internal organization of native casein micelles. This provided new insights into the internal architecture of the casein micelle that had not been apparent from prior cryo-transmission electron microscopy studies. This analysis demonstrated the presence of water-filled cavities (~20 to 30 nm in diameter), channels (diameter greater than ~5 nm), and several hundred high-density nanoclusters (6 to 12 nm in diameter) within the interior of the micelles. No spherical protein submicellar structures were observed.

Milk proteins are very important ingredients to the food industry. As new uses and applications for these proteins are developed, it becomes more important to understand their physicochemical properties when they are subjected to different treatments. It has been reported that casein micelles dissociate when heated in the presence of ethanol. The changes to the hydrophobicity of milk proteins during that process were evaluated by using the fluorescent hydrophobic probe 1-anilinonaphthalene-8-sulfonic acid (ANS). Raw skim milk, pasteurized skim milk, and whey protein isolate samples with ethanol concentrations of 0 to 60% (vol/vol) were heated from 20 to 60 degrees C. The fluorescence of the samples with and without the addition of ANS was measured at an excitation wavelength of 390 nm and an emission wavelength of 400 to 500 nm. The results showed a decrease in the extrinsic fluorescence of the samples as the ethanol concentration and temperature increased, indicating competitive inhibition of the ANS-hydrophobic site interaction by ethanol. This inhibition was further enhanced by the addition of heat. This resulted in a reduction in the functional hydrophobicity of the milk proteins as ethanol rendered the hydrophobic sites unavailable for interaction.

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A new, simple and reliable technique .has been developed for the determination of functional α-2 Antiplasmin in plasma; It is based on the circular inhibition of lysis produced by a-2 Antiplasmin from a hole punched out in an agarose-fibrin plate in which Urokinase has been previously dissolved.Briefly: An Agarose-Fibrin plate is made with Agarose>(l%), Fibrinogen (0.5%) and Urokinase (0.5 U/ml). The components are mixed at 422 C and thrombinCO.25 U/ml is used to coagulate Fibrinogen. The mixture is poured on a horizontal glass, plate and left at room temperature. 30 min later a series of holes are punched out in the plate and the samples and controls are seeded in the holes.The plate is incubated during 18 hours at 37° C in a humid chamber. After that time, all the plate has been lysed by plasmin produced by Urokinase except a circular area around the holes where α-2 Antiplasmin has migrated from the border: A round opaque circle can be seen around the holes and the diameters are proportional in a log-log scale with the aα-2 Antiplasmin levels of the sample.A standard curve is constructed with a pool of plasmas and the diameters of each sample are referred to it in a log-log scale, determining in this way the levels of functional α-2 Antiplasmin as a percentage.The lysis inhibition circle is entirely due_ to α-2 Antiplasmin and not to any other Fibrinolysis inhibitor: This has been demonstrated incubating previosusly the samples with antibodies directed to α-2 Macroglobulin, α-1 antitrypsin and C-l Esterase Inhibitor with no change in the circle. But when samples were incubated with an antibody to α-2 Antiplasmin, the opaque lysis inhibition circle disapeared.This method presents a very good correlation with other functional methods (cromogenic substrate s-2251 Kabi:r=0.92 p(0.01) and is comparatively simpler.the sensibility of the method is 0.5 % and the reproductibility is 3% day by day and 1% in a same day.