Extraction of lipids from a specialist dairy stream

In this work a process for the extraction of neutral and complex lipids from the specialist dairy stream ‘beta-serum’ is described. Beta-serum is a proprietary product obtained from dairy streams containing greater than 60% fat that have been through phase inversion from an oil-in-water to a water-in-oil emulsion. It is an enriched source of milk fat globular membrane proteins and complex lipids, and is distinct from buttermilk in this respect. In the process described here a total lipid extract could be obtained from liquid beta-serum using a continuous near-critical dimethyl ether (DME) antisolvent fractionation process. Protein and water are precipitated from solution when mixed with the DME, whilst lipid and some water are extracted into the DME-rich phase. The extraction yield of lipids depended on the solids content of the feed and the feed to DME flow ratio, but did not depend on the lactose content. Lipids were also extractable from spray dried beta-serum powder, but only when the lactose content had been reduced below 45% by mass. A two step extraction process is described in which neutral lipids are extracted with supercritical CO2, and then polar lipids using near-critical DME. The polar lipid extract was enriched in phospholipids (∼70% by mass), which included phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and sphingomyelin. Other complex lipid components extracted included gangliosides and cerebrosides. Unlike the antisolvent process, proteins were not denatured during either CO2 or DME processing of the spray dried powders, and the de-fatted powders are therefore suitable for a range of functional foods. A polar lipid extract could also be produced from spray dried powder by extracting first with DME to obtain a mixed neutral/complex lipid extract, then re-extracting the lipid extract with CO2 to remove neutral lipids.