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

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