Selene Gonzalez Toledo | ALES Graduate Seminar

Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Selene Gonzalez Toldeo. This seminar is open to the general public to attend.
Thesis Topic: Egg yolk-based emulsions as delivery systems of omega-3 fatty acids

Seminar Abstract: Omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are essential fatty acids with demonstrated health benefits. One way to increase omega-3 intake is to manipulate hen’s feed to produce omega-3 enriched eggs. However, there are many drawbacks to this approach: a high cost of production, wide variation in the amount of n-3 fatty acids, fishy taste, and shortened shelf life. Thus, the purpose of this research was to investigate the feasibility of using a processing approach to produce egg yolk with high content of n-3 LC-PUFAs and to test its use as an ingredient in food products.

The effects of fish oil concentration and esterification type, enzymatic modification, polysaccharide addition, and processing method on the ability of egg yolk to encapsulate EPA+DHA were investigated. Emulsions were characterized by their viscosity, particle size and distribution, and encapsulation efficiency. Moreover, their stability was evaluated during storage under different conditions. Consumer acceptance of n-3 LC-PUFAs fortified ice cream and cake, using selected emulsions or non-encapsulated fish oil (control) as ingredients, was evaluated using a 9-point hedonic scale.

We found that the apparent viscosity of the emulsions increased after treatment with phospholipase A₁ (PLA₁) and with the addition of gum guar. The native bimodal distribution of egg yolk, and its average particle size (169 nm) were affected by the concentration of fish oil, esterification type, and processing conditions. In the first chapter of this thesis, egg yolk proved to be an efficient carrier of 1 and 5% (w/w) fish oil, showing 100% encapsulation efficiency, and lack of significant peroxides and propanal formation after 4 weeks of storage at 4 – 6 °C. Results from our second and third studies showed that secondary homogenization (200 MPa) significantly increased the encapsulation efficiency (p < 0.05) of emulsions containing up to 50% (w/w on egg dry matter basis) fish oil, compared to those using raw egg yolk. Emulsions processed by secondary homogenization showed, overall, lower peroxides values, and propanal content during storage at 45 °C, compared to those found in non-encapsulated fish oil (up to 184.3 meq peroxide/kg oil and 9.7 mg propanal/g emulsion). None of the emulsions were toxic over 10 days of storage at 45 °C, whereas non-encapsulated fish oil decreased cell viability to 81%. In addition, the apparent permeability of EPA from emulsions in Caco-2:HT29 monolayers increased significantly (1.4 – 2.4 x10^-5) compared to that of non-encapsulated fish oil (0.1 x10^-5). Gum guar showed better stability than gum arabic in egg yolk/polysaccharide emulsions. Furthermore, emulsions combining PLA₁ treatment and secondary homogenization were the most stable under high temperature conditions; whereas gum guar improved stability after freeze-thaw cycle. A significant preference of ice cream samples containing EPA+DHA from emulsions (6.5 – 7.1 flavor liking score) over control samples (5.0 flavor liking score) was found. Consumers noted fishy taste, unpleasant aftertaste, and rancid notes in control samples. Moreover, no significant differences were found in consumer preference of cake samples.

This thesis conclusively shows that secondary homogenization can be successfully used to produce egg yolk emulsions with high content of EPA+DHA. The stability of emulsions can be enhanced by enzymatic modification of egg yolk or with polysaccharides addition. Our findings increase the scope of applications for egg yolk particularly for use as a functional food ingredient.

Selene Gonzalez Toledo – PhD with Dr. Jianping Wu