Year of Publication

2016

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department

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

Available for download on Wednesday, December 19, 2018

Share

COinS