The lipid content and microstructure of industrial whole buttermilk and butter serum affect the efficiency of skimming

• The removal of all the lipids of buttermilks and butter serums was never obtained by centrifugation.
• The skimming of buttermilks and butter serums is inefficient under a threshold of lipid content.
• Skimming of buttermilk and butter serum removes milk fat globules having a diameter above 1 μm.
• Small milk fat globules, fragments of MFGM and polar lipid vesicles are not removed by skimming.
• Skimming efficiency can be predicted by particle size measurement.

The processes developed to valorize buttermilks and butter serums generally start by a technological step aiming at removing lipids by centrifugation. The efficiency of this skimming step has never been studied yet. The objective of this study was then to characterize the efficiency of the skimming of industrial buttermilk and butter serum and to determine its consequences on the lipid composition and microstructure of related products. This work clearly shows that the efficiency of the skimming step, operated both at pilot and industrial scales, is never complete and depends on the characteristics of the fluids to be treated. There exists a threshold of lipid content (7% total lipids in dry matter for buttermilk; 20% for butter serum) under which the skimming is not efficient. Above this threshold of lipid content, the skimming step removes all particles with a size larger than 1 μm (large fat globules, butter fines), but does not succeed in removing small size lipid fraction (fragments of membrane, lipid vesicles), which results in an increase in the polar lipids on total lipid ratio for both products (up to 20 ± 5% and 49 ± 6% for buttermilks and butter serums respectively). The difference of skimming efficiency, threshold values of skimming, and composition of final products between the buttermilks and butter serums could be attributed to differences in the microstructure of the lipids. Even if not totally efficient, the skimming step leads to a standardization of total lipid content of buttermilks and butter serums, useful for a better control of technological processes aiming at valorizing individual compounds of these dairy by-products.