Freeze-thaw stability of emulsions made with native and enzymatically modified egg yolk fractions

Frozen storage of food emulsions can increase their tenability and create possible applications in frozen food products. However, coalescence and phase separation can occur during freezing/thawing. In order to assess options for mitigating freeze/thaw-destabilization, egg yolk's emulsifying functionality in the form of whole egg yolk and its granula and plasma fractions was investigated. The fractions were enzymatically pretreated (phospholipase A₂) and their emulsifying functionalities were assessed in dependence of pH, salinity, freezing velocity and frozen storage time with oil droplet size and phase separation as measures. Mayonnaise-type oil in water emulsions of sunflower oil were prepared at pH 3, 4 and 6.5 with a salt content of 0.15 and 0.55 M NaCl with a colloid mill. The emulsions were frozen to −20 °C with varying freezing rates and stored up to 24 h. Egg yolk and plasma stabilized emulsions showed higher freeze/thaw stabilities than granule stabilized emulsions. Enzymatic treatment increased the stability of emulsions prepared with egg yolk and granula, but decreased the stability for plasma stabilized emulsions. The destabilization increased with longer frozen storage time. Very slow or fast freezing velocity resulted in higher destabilization effects than an intermediate freezing rate at low salt content. Increasing salinity from 0.15 to 0.55 M NaCl as well as increasing pH from 3 to 6.5 resulted in more stable emulsions and highest destabilization at the highest freezing rate.