Whole casein studies

Helstad, K., Rayner, M., van Vliet, T., Paulsson, M., and Dejmek, P. (2007). Liquid dropletlike behaviour of whole casein aggregates adsorbed on graphite studied by nanoindentation with AFM. Food Hydrocolloids 21, 726-738. 

Klostermeyer (1975) used an activated thiol-Sepharose 4B column with Tris-HCl buffer containing dithiothreitol to separate the K-and aa2-caseins from the aai-and /3-caseins in whole casein. More recently, Creamer and Matheson (1981) studied the fractionation of casein by hydrophobic interaction chromatography on octyl- or phenyl-Sephar-ose CL-4B columns. The whole casein was adsorbed onto the column from dilute phosphate buffers. A gradient of 0 to 40% ethylene glycol followed by 6 M urea was employed to desorb the protein. Optimum separation was obtained with an increasing urea gradient. Under all conditions, the major /3-casein component was eluted more readily than the asi-casein in spite of its higher hydrophobicity. 

Addeo, F., Chobert, J.-M. and Ribadeau-Dumas, B. 1977. Fractionation of whole casein on hydroxyapatite. Application of a study of buffalo kappa-casein. J. Dairy Res. 44, 63-68. 

It is difficult to obtain meaningful results on colloidal interactions unless the samples have low polydispersity. Studies of colloidal interactions between whole casein micelles can be affected by the polydispersity of native casein micelles. (Stothart,1987b). To circumvent the problem of polydispersity, the food system can be deposited on monodisperse silica spheres (Rouw and de Kruif,1989). 

Regarding the systems used in this study, we use the same proteins as in the previous section (whole casein and P -casein) and they are mixed with Tween 20, respectively. This is a low molecular weight surfactant used in the food industry, which is water soluble and nonionic. The different behavior of these two mixed systems is again discussed on the basis of fundamental magnitudes such as surface tension and foam film thickness. 

Maldonado-Valderrama, J. and D. Langevin. 2008. On the difference between foams stabUized by surfactants and whole casein or P-casein. Comparison of foams, foam films, and liquid surfaces studies. J. Phys. 

The distribution of essential and potentially toxic elements in different gross fractions is the preliminary step to study the particular chemical forms in which they are present in milk [105]. Multielemental distribution patterns in human, cow, and formula milks have been reported by the Sanz-Medel group [106]. Total elemental distributions in skimmed milk and/or milk whey samples were obtained after removing fat and/or caseins by ultracentrifugation. Then, in order to destroy the organic matter, each fraction (whole milk, skimmed milk, and milk whey) was digested by MW-assisted digestion for their minor and major elemental analysis. 

From the studies of Walstra and co-workers (2, ), it appears that the fat globules in homogenized milk are stabilized by apparently largely intact casein micelles although some smaller caseinate complexes can also be involved. However, homogenized milks differ in a number of respects from whole or skim milks. 

The separation of dairy proteins by CE has been generally carried out by CZE and has been exhaustively covered in several review papers, - - thus Table 30.8 only presents the key methodologies that offer the reader an overview of their most distinctive features. Basically, dairy protein analysis has been performed in whole milk for the simultaneous determination of caseins and whey proteins, or in fractions isolated from milk after casein precipitation. The first approach being used when the quantitative determination of the major proteins is required for the calculation of casein/whey protein ratios or for authentication purposes where an analysis of the whole protein profile is required. In both cases, accurate quantitative data must be derived. However, few studies have addressed the analysis of both groups of proteins in a single run by presenting quantitative data based on calibration curves constructed with analytical standards and good recovery of all proteins from milk samples. 

The peptide mixture prepared above (casein hydrolysate, 100 g) was mixed with glucose (100 g) in 0.2 M NaHC03 (1000 ml) and heated at 100° C for 2 h. The whole mixture was then lyophilized to powder to be used as a test sample in this study. 

Figure 2. Relationship between whole body rate of appearance (WB Ra) of glucose, metabolizable protein (MP) supply and lactose yield in studies involving casein infusion. Datafrom Clarket al., 1977, Galindo, 2010, mHaniganeXaX., 2004, KOnigeXaV, 1984 and A Lemosquet eXal, 2009a.

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