• Egg yolk;
  • heat-induced gelation;
  • HPLC;
  • phospholipases;
  • rheological behaviour


Functional changes of hen’s egg yolk rheological behaviour as a result of processing (pasteurisation, freeze-drying) and modifying its phospholipids using phospholipase A1 (PLA1) and phospholipase A2 (PLA2) were studied. It could be shown how fermentation with phospholipases affects the different steps of heat-induced gelation of egg yolk. As a consequence of fermentation of native yolk with 0.1% PLA1, the first viscosity maximum was shifted from 79 to 97 °C. In fermented pasteurised yolk, the homogenous gel-like consistency from the first viscosity maximum was even stabilised up to 100 °C. The second viscosity ascent, which indicates solid gel structures (caused by aggregation of denatured proteins), was prevented entirely. In contrast to pancreatic PLA2, fermentation of egg yolk with microbial PLA1 resulted in a hydrolysis of approximately 78% of phosphatidylethanolamine and a significant change in flow behaviour (of yolk solutions).