I am writing a chemistry essay about casein isolation using acid precipitation. I read that the casein micelle itself is constructed of more "mini" micelles, which are constructed of the constituents alpha-casein, beta-casein, kappa-casein and a few other caseins (however they are rather insignificant and negligible). In my experiment I used glacial (99%) acetic acid, i.e. ethanoic acid, to reach the isometric point of casein. Not only does the result in a reduction in pH, yet it also leads to the protonation of phosphate ions, such that they dissolve and the mini micelles are not held together anymore, enabling them to aggregate and come out of solution. Below is an image of the casein peptide being held together by the calcium phosphate bridges before acid addition. What reaction occurs exactly when the ethanoic acid is added?

Image of peptide held together by calcium phosphate "bridge"

What I have attempted/deduced thus far:

HPO4Ca2+ + 2CH3COOH → H3PO4 + Ca(CH3COO)2


https://www.researchgate.net/publication/226857525_Milk_and_Dairy_Products (p. 510)

  • $\begingroup$ In fact, I think I came up with the solution while writing the question. However, confirmation that my work is correct would be greatly appreciated. $\endgroup$ – Liam Apr 21 '19 at 3:43

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