Lipid oxidation inhibited in oil-in-water emulsions by interface-adsorbed myofibrillar protein.
Comminuted meat products represent complex emulsion-type systems in which oil droplets are physically stabilized by a coating of myofibrillar proteins, with these proteins dispersed in an aqueous phase.
However, the steric role of these proteins in the oxidative stabilization of meat emulsions is poorly understood. Essentially, the steric effect relates to the spatial arrangement of atoms in the molecule, especially as the arrangement impacts a chemical reaction.
Scientists at the University of Kentucky tested their hypothesis that steric hindrance and interfacial myofibrillar proteins, when compared with the continuous phase, can more effectively protect oil droplets against oxidative changes.
The researchers prepared oil-in-water emulsions under high-pressure conditions--30 MPa--from a mixture of 10% soybean oil and a 90% buffer containing 25 mM phosphate and 0.6 M of sodium chloride, at pH 6.25, and using either 2% of Tween[R] 20, or 0.25%, 0.5% and 1% myofibrillar protein. The Tween 20 emulsion was then mixed with the proteins at the indicated concentrations.
The scientists subjected all of the emulsion samples to hydroxyl radical oxidation at 4 C for 0, 2 and 24 hours. They also monitored any oxidative changes in lipid and both adsorbed (membrane) and non-adsorbed proteins.
The myofibrillar protein, regardless of its location and concentration, was more readily oxidized than oil. However, the oxidized myofibrillar protein in the continuous phase stimulated lipid oxidation after 24 hours, sharply contrasting with the interface-adsorbed protein that inhibited TBARS formation at nearly 90%.
Desorbed protein from 2-hour-oxidized samples exhibited greater losses of fluorescence and more extensive polymerization of myosin than myofibrillar protein in the continuous phase, as detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis. This was presumably due to malonaldehyde-mediated cross-linking. Nonetheless, emulsions made of myofibrillar protein were prone to creaming, compared with the Tween 20 emulsions.
Results indicated that interface-adsorbed myofibrillar protein in general, and myosin in particular, provided both chemical--radical neutralization--and physical--steric--protection for the emulsions against oxidation. So, it is essential that meat processors apply the appropriate formulations to allow adequate interfacial protein coverage in emulsified meats.
Further information. Jiayi Yang, Department of Animal and Food Sciences, University of Kentucky, 900 W. P. Garrigus Building, Lexington KY 40546; phone: 859-257-2686; email: email@example.com.
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|Publication:||Emerging Food R&D Report|
|Date:||Nov 1, 2016|
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