Date Available

12-19-2018

Year of Publication

2016

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department/School/Program

Animal and Food Sciences

First Advisor

Dr. Youling Xiong

Abstract

This study investigated the progression of protein and lipid oxidation in different bi-phasic model systems: simple aqueous dispersions, liposome, and oil-in-water (O/W) emulsions. Varied concentrations of isolated pork myofibrillar protein (MFP) were mixed with free fatty acids (C18:1, C18:2, C18:3), lecithin, or vegetable oil to construct different lipid-protein dispersion systems, then subjected to hydroxyl radical stress at 4 °C. Comparison of the evolution of lipid oxidation with protein modification markers in all dispersion systems showed noteworthy attenuation of tryptophan fluorescence, protein carbonyl formation, and extensive polymerization of myosin in 2 h. This process preceded lipid oxidation which exhibited notable accumulations of thiobarbituric acid-reactive substances (TBARS) only after 2 h.

The study further explored the steric role of MFP in the oxidative stability of emulsions. Oxidized MFP in the continuous phase stimulated lipid oxidation in 24 h; sharply contrasting with interface-adsorbed MFP that inhibited TBARS formation nearly 90% in 24 h. Interfacial MFP from 2 h-oxidized samples exhibited attenuated tryptophan fluorescence but more pronounced myosin polymerization than MFP in the continuous phase. Due to the site distribution, interface-adsorbed MFP in general and myosin in particular provided accentuated protection of emulsions against oxidation. Similarly, soy protein isolate (SPI) and sodium caseinate (SC) acted as antioxidant barriers in O/W emulsions.

The effect of replacing pork fat by protein-stabilized soybean oil pre-emulsion on physical characteristics and oxidative stability of fresh sausages was subsequently investigated. Substitution (60%) of SC or partially denatured SPI pre-emulsified oil for fat improved sausage water-binding capacity (P < 0.05). During storage at 4 °C, cooked sausage formulated with partially denatured SPI-emulsified oil displayed a slower lipid oxidation rate throughout 14 days compared with control sausage, and SC-emulsified oil sausage had the lowest TBARS produced in the first 5 days. There was no significant difference (P > 0.05) in texture attributes (e.g., hardness, deformability, cohesiveness, and rupture force) between different formulations.

In summary, proteins as emulsifiers at the O/W interface are kinetically preferred targets of radicals compared to unsaturated lipids and proteins in the continuous phase. Such locality effect proves to be important for the physicochemical stability of emulsion-type foods.

Digital Object Identifier (DOI)

https://doi.org/10.13023/ETD.2016.528

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