Effect of cryogenic freezing on the rheological and calorimetric properties of pasteurized liquid egg yolk

Abstract

The egg yolk undergoes an irreversible gelation process when freezing to -6 °C or lower. In this experiment, liquid egg yolk (LEY) was frozen in liquid nitrogen and stored at -18 °C for 150 days. The measurement of pH and colour of LEY were performed. The examination of the rheological and calorimetric properties of samples was also carried out. The results indicated that the pH of LEY changed significantly during frozen storage, increasing from 6.37 ± 0.02 to 6.58 ± 0.03 over five months. The colour of the samples also showed a significant change compared to the fresh sample. The rheological properties of the LEY also changed significantly after 1 day of freezing and during frozen storage, with a clear increasing trend of the yield stress. The results of the calorimetric study showed that freezing and frozen storage did not affect the denaturation temperature, however, the denaturation enthalpy was reduced by about half after five months of frozen storage.

Keywords

• differential scanning calorimetry
• herschel-bulkley model
• frozen storage
• liquid nitrogen
• shear test