Functionality of egg yolk lecithin and protein and functionality enhancement of protein by controlled enzymatic hydrolysis

Date
2007-01-01
Authors
Wang, Guang
Major Professor
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Tong Wang
Committee Member
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Food Science and Human Nutrition
Abstract

Egg yolk lecithin (EYL) is a good source of phosphatidylcholine (PC) and phosphatidylethanolamine (PE), and it is different from soy lecithin (SL) in both fatty acid and phospholipid class composition. These factors may lead to different behavior in oxidative stability and emulsification properties in food systems. Therefore, these characteristics were investigated in this study. Emulsification properties were evaluated at two oil-to-water ratios, two emulsifier concentrations, two pHs, and with the addition of xanthan gum. The results showed that low concentration of EYL (2.5% in oil) gave poorer emulsion stability than did 5.0%, whereas emulsions with oil-to-water ratio of 50:50 were more stable than with a 20:80 ratio. Under neutral pH, EYL gave poorer emulsion stability than SL at both oil-to-water ratios and emulsifier concentrations. However, under acidic condition, EYL created a more stable emulsion than did SL. Adding xanthan (0.05%) increased stability of EYL emulsions and minimized stability differences caused by lecithin concentrations. Oxidative stability of egg yolk was determined in bulk and in emulsion. EYL showed better oxidative stability in both bulk and emulsion systems than did SL. Cupric ion did not accelerate oxidation of EYL in an emulsion system, but it did accelerate oxidation of SL.;Delipidated egg yolk protein (EYP) is produced as a co-product of egg yolk lecithin extraction. This EYP showed poor functionality possibly because of protein denaturation caused by ethanol treatment during lecithin extraction. Two food grade endo-proteases were used to produce EYP hydrolysates (EYPh) with two degrees of hydrolysis (DH), 3% and 6%. Protein solubility improved as DH increased, and both solubility profiles for EYP and EYPh were relatively less pH-dependent compared to soy protein. Except for foaming capacity, EYPh showed good improvement in foam stability, the speed of liquid being incorporated into foam, and maximal foam volume. Emulsion stability was improved for all EYPh treatments. Treatments at DH of 6% showed significant increase in emulsion capacity, but low DH of 3% gave reduced emulsion capacity in comparison with EYP and soy protein isolate. Overall, controlled enzymatic hydrolysis could be applied to ethanol-treated lipid-free EYP to increase the solubility, and improve the foaming properties and emulsification properties of EYP.

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