Determination of gelation mechanism and prevention methods of frozen-thawed hen egg yolk
Gelation of egg yolk during freezing and thawing has been a hurdle to food processors for decades, because of the reduced yolk functionality. Many studies have been performed in the past to understand the mechanism of gelation. However, this concept has not been fully elucidated. Currently, industry practices the addition of 10% salt or sugar to inhibit gelation. Although gelation is inhibited, this practice causes a significant change in flavor, which then limits the yolk application. It is therefore our objective to further study the gelation mechanism and identify the component(s) responsible for gelation through analyzing fractional mass distribution, protein distribution and rheological properties in four reconstituted yolk systems, so that alternative gelation prevention methods could be determined. Protein aggregation occurred as five weeks of freezing was induced in four recombined yolk systems containing different proportions of plasma and granule. All four frozen-thawed yolk systems had a significant increase (p<0.05) in the mass of granule fraction and an additional layer of floating lipidic fraction. Gel strength was shown to increase with increasing granule content in the system. This study showed that aggregations involved heterogeneous interactions between plasma and granule components, including LDL, HDL, and α-livetin. Ingredients that could reduce the degree of gelation were identified. Hydrolyzed carboxymethyl cellulose (HCMC), hydrolyzed egg white and yolk (HEW and HEY), and proline were able to significantly reduce (p<0.05) the hardness of the frozen-thawed yolk mixtures. The gelation-inhibiting mechanisms of these additives were assessed through differential scanning calorimetry (DSC), particle size distribution, and protein surface hydrophobicity as compared to salt and sugar.