This is to help me understand how milk-based bioplastic forms and how I can prepare a simplified instructional plan for younger students making sure the correct chemical principles are maintained.
It is pH-dependent. Casein is almost non soluble at neutral pH. Therefore, like many others proteins, Casein has amino and carboxyl groups on its terminal aminoacids. So at high pH values the acidic side chain (COO-) will be ionized making it easier to be soluble in NaOH solution. On the other hand, when the pH is low occurs the protonation of NH3+ making it soluble in strongly acidic condition.
What you must show to your students is that proteins solubility is minimum when it is close to the isoelectric point, in which the protein has a net charge of zero and so the material is insoluble. For casein the isoelectric point occurs when the pH is 4.
Dear Mangai Solomon Mahanan, please find details in the following link. My Regards
https://www.scientificamerican.com/article/bring-science-home-milk-plastic/
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