Evolution of phospholipid contents during the production of quark cheese from buttermilk

We report the evolution of phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylcholine (PC), phosphatidylserine (PS), and sphingomyelin (SM) contents during the production of quark cheese from buttermilk by successive ultrafiltration concentration, enrichment with cream, concurrent homogenization and pasteurization, fermentative coagulation, and separation of quark from whey by further ultrafiltration. Buttermilk is richer than milk itself in phospholipids that afford desirable functional and technological properties, and is widely used in dairy products. To investigate how phospholipid content is affected by end-product production processes such as ultrafiltration, homogenization, pasteurization or coagulation, we measured the phospholipids at several stages of each of 5 industrial-scale quark cheese production runs. In each run, 10,000L of buttermilk was concentrated to half volume by ultrafiltration, enriched with cream, homogenized, pasteurized, inoculated with lactic acid bacteria, incubated to coagulation, and once more concentrated to half volume by ultrafiltration. Phospholipid contents were determined by HPLC with evaporative light scattering detection in the starting buttermilk, concentrated buttermilk, ultrafiltrate, cream-enriched concentrated buttermilk (both before and after concurrent homogenization and pasteurization), coagulate, and quark, and also in the rinsings obtained when the ultrafiltration equipment was washed following initial concentration. The average phospholipid content of buttermilk was approximately 5 times that of milk, and the phospholipid content of buttermilk fat 26 to 29 times that of milk fat. Although phospholipids did not cross ultrafiltration membranes, significant losses occurred during ultrafiltration (due to retention on the membranes) and during the homogenization and pasteurization process. During coagulation, however, phospholipid content rose, presumably as a consequence of the proliferation of the inoculated lactic acid bacteria. In spite of these changes in total phospholipid content, the relative proportions of the phospholipids studied remain fairly stable throughout quark production (PE>PC>SM>PS>PI) and similar to those found in the milk of the region, except that SM content was lower than in milk.