|MadSci Network: Biochemistry|
It all has to do with proteins! Milk contains apart from water and Calcium about 5% proteins. A large portion of this are the so-called caseins. These proteins are present in the milk as large aggregates named casein micelles, because of their ‘large’ size [200-500 nm] milk has that white appearance. These micelles remain in solution because ONE of the 4 different caseins (k-casein) has the particular characteristic to keep these aggregates in solution. What happens to milk when meat tenderizer is added is that proteins with a particular function [named proteolytic enzymes*] interact with that protecting k-casein and as a result it loses its protective function. Apart from that the acid value [pH] of the milk, which is usually around 6.7 will drop to lower values. Because of the combined action of the lowering in pH and the loss of protective action of k-casein, all proteins will precipitate - come out of solution - which is noted as the separation in curd and a liquid phase named whey. The last one is the one containing the so called whey proteins that are not sensitive to the the drop in pH. * Proteolytic enzymes are proteins that have the ability to hydrolyse - breakdown - other proteins. For this effect only very small amounts of enzyme are required, some bacteria as the ones used for yogurt and cheese production produce these enzymes in a natural way resulting in curd formation in the same way as described above.
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