The difference of skimming efficiency, threshold values of skimming, and composition of skimmed fractions between the buttermilk and butter serum can be attributed to differences in lipid structure in products to be treated.
Both containmilk fat particles (globules, fines…) which were removed by skimming but small milk fat globules, fragments of MFGM(mainly in buttermilk) and vesicles of milk polar lipids (in butter serum) remain in skimmed products, resulting in an increase in the polar lipids on total lipid ratio of skimmed buttermilks and butter serums.
Even if not totally efficient, the skimming step leads to a standardization of total lipid content of buttermilk and butter serum, leading to less variability in the lipid content of the products to be subsequently processed.
This study could be useful for a better control of the skimming step and for
the development of technological processes aiming at selecting polar lipids from by-products of the dairy industry such as industrial buttermilks and butter serums.
However it does not succeed in removing
small lipid fraction (fragments of membrane, lipid vesicles), which
results in a threshold of lipid content (7% fat in DM buttermilk; 20%
butter serum) under which the skimming is not efficient.