If I want to keep milk samples in freezer for further tests on milk protein in near future, would freezing have impact on milk protein, change in its properties and quality after defrosting?
SUre, if you keep below -20C, then you can keep for 6 months for analysis, it is better if you can take out fat from it.
freezing would definitely have an impact on milk protein, and would result in change in its properties and quality after defrosting. Slow freezing of milk can cause a gradual precipitation of the caseinate system and an immediate destruction of the fat emulsion. Freezing, therefore, will cause a slow and gradual increase in the size of the casein aggregates but the change will be noticeable on advance freezing period.
In a study it was found that milk fat, total solids and dye-binding estimates were significantly affected by the freezing and thawing process, whereas milk fat, Golding bead, freezing point, micro-Kjeldahl, lactose and dye-binding estimates
were affected by length of frozen storage. The data indicated that accurate determination of chloride content could be made on frozen milk. Since correlation coefficients are large, micro-Kjeldahl values could be used to accurately rank animals for protein content if all milk was held in frozen storage the same
length of time; however, this would not be an accurate method to determine protein content due to the significant differences between the means. One should be careful in determining milk fat, total solids, dye-binding, freezing point and lactose on frozen milk, since the results may be quite different from those obtained on fresh milk. Some of these differences are undoubtedly due to coagulation when frozen milk is thawed and some may be due to degradation of constituents.
http://www.journalofdairyscience.org/article/S0022-0302(69)86833-5/pdf
Freezing would definitely have an impact on milk protein, and would result in change in its properties and quality after defrosting.
Freezing do have effect on proteins, especially casein and fat as well. Once milk is frozen, careful melting is required (slow and uniform rise in temperature). Sudden change in temperature causes heat soak, leading to destabilization of casein micelle and fat emulsion.
I am agree with the comments made by the above researcher. Destabilization of casein and milk fat emulsion will happen during freezing
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