Electron microscopy casein micelles

Association and shattering of micelles. Electron microscopy shows that the casein micelles aggregate initially, then disintegrate and finally aggregate into a three-dimensional network. 

Dalgleish, D. G., Spagnuolo, P. A., and Douglas Goff, H. (2004). A possible structure of the casein micelle based on high-resolution field emission scanning electron microscopy. Int. Dairy. 14,1025-1031. 

McMahon, D. J. and McManus, W. R. (1998). Rethinking casein micelle structure using electron microscopy. /. Dairy Sci. 81,2985-2993. 

Portnaya, I., Cogan, U., Livney, Y.D., Ramon, O., Shimoni, K., Rosenberg, M., Danino, D. (2006). Micellization of bovine p-casein studied by isothermal titration microcalorimetry and cryogenic transmission electron microscopy. Journal of Agricultural and Food Chemistry, 54, 5555-5561. 

Marchin, S., Putaux, J.L., Pignon, F., Leonil, J. (2007). Effects of the environmental factors on the casein micelle structure studied by cryo-transmission electron microscopy and small-angle X-ray scattering/ultra-small-angle X-ray scattering. Journal of Chemical Physics, 126, 45-101. 

Martin, A., Goff, H.D., Smith, A., Dalgleish, D.G. (2006). Immobilization of casein micelles for probing their structure and interactions with polysaccharides using scanning electron microscopy (SEM). Food Hydrocolloids, 20, 817-824. 

Figure 12 Transmission electron microscopy study of protein desorption in icecream mix containing emulsifiers and hydrocolloids, (a) Immediately after homogenization the fat globules (0 are stabilized by adsorbed partially dissociated casein micelles (arrows), (b) During ageing the mix at 5°C, the previously adsorbed protein film is released in the form of coherent protein layers (arrows) into the water phase (w). (c) After mechanical treatment in the ice cream freezer, desorbed protein layers are seen more often in the water phase without association to fat giobules (arrows). From reference 48, courtesy of Dr. W.Buchheim, Kiel, Germany.

The most thorough study of the formation of artificial casein micelles is that of Schmidt and co-workers (1977 1979 Schmidt and Koops, 1977 Schmidt and Both, 1982 Schmidt and Poll, 1989), who not only studied the properties of the casein aggregates but also attempted to relate them to the solution conditions under which they were formed. In the precipitation of calcium phosphate from solution, the means by which solutions are mixed together is of crucial importance Schmidt et al. (1977) described a method in which four solutions were pumped simultaneously into a reaction vessel while keeping the pH constant. As a result of careful, slow mixing, the reproducibility of the size distributions of particles, measured by electron microscopy on freeze-fractured and freeze-etched specimens, was very good. In the first series of experiments, the objective was to produce milk like concentrations of the most important ions while... 

On balance, electron microscopy appears to show a distribution of K-casein throughout the micelle and, less certainly, a preferential location toward the periphery. No support is given to those experiments with immobilized reagents that appear to show that K-casein is located overwhelmingly on the external surface of micelles. 

Figure 12.2. The structure of ice cream mix and ice cream. (A). Fat globules (F) in mix with crystalline fat within the globule and adsorbed casein micelles (C), as viewed by thin section transmission electron microscopy. (B). Close-up of an air bubble (A) with adsorbed fat, as viewed by low temperature scanning electron microscopy. (C). Air bubble (A) with adsorbed fat cluster (FC) that extends into the unfrozen phase, as viewed by thin section transmission electron microscopy with freeze substitution and low temperature embedding.

Fig. 7. The effect of adsorbed protein on structure of ice-cream mix, ice cream, and melted ice cream. A-B, ice-cream mix with no surfactant and with added surfactant, respectively, as viewed by thin-section transmission electron microscopy. f= fat globule, c = casein micelle, arrow = crystalline fat, bar = 0.5 pm. See Reference 24 for methodology. C-D, ice cream with no surfactant and with added surfactant, respectively, as viewed by low-temperature scanning electron microscopy, a = air bubble, f = fat globule, bar = 4 pm. See Reference 34 for methodology. E-F, ice cream with no surfactant and with added surfactant respectively, as viewed by thin-section transmission electron microscopy with freeze substitution and low-temperature embedding. a = air bubble, f= fat globule, c = casein micelle, fc = fat cluster, bar = 1 pm. See Reference 13 for methodology. G-H, melted ice cream with no surfactant and with added surfactant respectively, as viewed by thin-section transmission electron microscopy. f= fat globule, c = casein micelle, fn = fat network, bar = 1 pm in G and 5 pm in H. See Reference 24 for methodology.

IX were present in the casein micelle film in a weight ratio of 0.64 0.36. From the close-packing area of Fraction I, and the specific volume for caseins reported by Schultz and Bloomfield ]), we have calculated the average diameter of complexes in this fraction. The diameter is 9.1 nm, which is in agreement with results published by Pepper and Farrell on the diameter of the submicelles ( ) The submicellar structure of caseins has also been observed in electron microscopy studies. It has been reported that such submicelles could adsorb at fat-serum interface without becoming disrupted (17,25). 

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