Egg yolk undergoes a change in fluidity, termed gelation, when frozen below -6<sup>o</sup>C and thawed. This change is undesirable to food processors because of reduced yolk functionality. Previous studies suggested LDL aggregation as the main cause of gelation; however, very few studies discussed the role of HDL-rich granule fraction. In this study, gelation was induced through 5-week freezing of recombined yolk systems. Fresh hen egg yolk was fractionated into plasma and granular fractions, and the two fractions were recombined in different ratios to make 4 yolk systems that would mimic (1) whole egg yolk (78% plasma, 22% granules, db), (2) plasma fraction (100% plasma, db), (3) plasma mixed with 50% granule fraction (88% plasma, 12% granules, db), and (4) granule mixed with 50% plasma fraction (64% plasma, 36% granules, db). The objective of this research is to further study the mechanism of gelation, particularly to define the roles of plasma and granules in gelation. Mass balance (db) and protein distribution (SDS-PAGE) analyses on fractions obtained from the recombinant systems were performed to compare the changes that occurred before and after gelation, and to determine specifically what particular protein(s) was/were mainly responsible for gel formation. Rheological properties of the gelled yolk systems were also measured. Results confirmed the active participation of both the plasma and granular proteins during the gelation process. Significant increase in gel strength (p&lt;0.05) occurred with the increase of granule content. From the SDS-PAGE results, it was found that upon gelation, HDL proteins with molecular weights of 110, 47 and 31 kDa were released from granule (low optical density of PAGE band in gelled granule), and partitioned to the LDL fraction. LDL proteins with molecular weights of 11, 17, 93, 122 kDa, which are normally found in both LDL and livetin fraction, were completely separated from livetin and went to LDL fraction. These findings suggested disruption of HDL-containing granules and active participations of <u>both HDL and LDL</u> in protein aggregation during freezing and thawing of egg yolk. Overall, this study allows a better understanding of yolk gelation mechanism which may consequently lead to the design of innovative methods for preventing gelation.

Use of reconstituted egg yolk systems to study the roles of plasma and granules in yolk gelation induced by freezing-thawing

253rd National Meeting (2017)

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