Precipitation of proteins from expired milk
Hello people,
I am back to extract chemicals from food waste. Today, we see the precipitation of proteins from expired milk. The procedure is very simple, proteins are precipitated out lowering pH of milk with vinegar. Let's
find out !
Procedure
1 liter of skimmed expired cow milk is poured into a large glass jar and brought to 65 C, under stirring on a hotplate. Once reached, 150 ml of 6%
vinegar is slowly added. The reaction mixture kept going for 45 minutes, when the jar is removed from hotplate, let standing until cooled down to room
temperature. A precipitate forms from whey. The suspension is filtered through cotton plug: filtrate, the whey is stored apart, while the semi-solid
white residue is redissolved in water and filtered again through tablecloth, pressed to remove as much water as possible, then in paper. Lastly, the
off-white product is treated with 200 ml of acetone, filtered through tablecloth, this pressed on cardbox, then let dry in open air.
50.42 g of skin-colored powder are obtained, which are almost quantitatively the amount of proteins declared on milk nutrition facts label.
 
Discussion
The proteins look like to oxidize in air. I repeated the procedure twice more with fresh sheep milk and long expired skimmed cow milk. Yield were
almost identical. Fresh milk proteins do not darken in air. The three type of proteins have been reacted with 33% formalin to form galalith, but
reaction failed, and just fresh milk proteins gave an harder product of reaction. That is because galalith is formed by casein only, instead here we
have all milk proteins not just casein.
Another test is performed with 60% nitric acid. 100 mg of each sample is added of few ml of acid and warmed a bit. After vigurous reaction, a yellow
color is obtained. That means positive test. From whey, lactose can be recovered.
As usual I link you to my YT video for more detailed procedure.
Thanks for attention,
palico
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