Nitrogenous fractions during the manufacture of whey protein concentrates from Feta cheese whey

Samples taken from different manufacturing stages of Feta cheese whey protein concentrates (WPCs), with 65 and 35% total protein content, were analyzed by chemical methods and by reversed-phase HPLC and by size-exclusion chromatography. Mean total protein content of Feta cheese whey was 1.37%. 22% of total nitrogen (TN) was non-protein N (NPN) and 12% was proteose–peptone N (PPN). The mean native N (NN), NPN and PPN percentages of WPC 65 and 35%, were 63 and 71%, 10 and 14%, 0.08 and 0.08%, respectively. According to reversed-phase HPLC data, the percentages of β-Lg and α-La and their ratio were high; 56.5 and 59% of native proteins of whey and of WPC powders, respectively, were β-Lg. The respective α-La percentages were 13.1 and 14.1% and the respective caseino-macropeptide (CMP) percentages were 12.9 and 15.3%. Apart from ultrafiltration, the most critical stage for nitrogenous fraction composition was the evaporation process before spray drying.