Effect of droplet size on lipid oxidation rates of oil‐in‐water emulsions stabilized by protein

Abstract

In emulsions lipid oxidation is mainly influenced by the properties of the interface. The aim of this work was to investigate the effects of droplet size and interfacial area on lipid oxidation in protein-stabilized emulsions. Emulsions, made of stripped sunflower oil (30% vol/vol) and stabilized by BSA were characterized by surface area values equal to 0.7, 5.1, and 16.3 m 2 ·cm −3 oil. The kinetics of O 2 consumption and conjugated diene (CD) formation, performed on emulsions and nonemulsified controls, showed that emulsification prompted oxidation at an early stage. On condition that oxygen concentration was not limiting, the rates of O 2 consumption and CD formation were higher when the interfacial area was larger. Protein adsorbed at the interface probably restrained this pro-oxidant effect. Once most of the O 2 in the system was consumed (6-8 h), CD remained steady at a level depending directly on the ratio between oxidizable substrate and total amount of oxygen. At this stage of aging, the amounts of primary oxidation products were similar whatever the droplet size of the emulsion. Hexanal and pentane could be detected in the headspace of emulsions only at this stage. They were subsequently produced at rates not depending on oil droplet size and interfacial area.Paper no. J10026 in JAOCS 79, 425-430 (May 2002).KEY WORDS: Conjugated dienes, droplet size, interfacial area, lipid oxidation in emulsions, oxygen, protein, volatile compounds.Many foods are oil-in-water emulsions stabilized by protein and lipid surfactants in a protein or polysaccharide matrix. In these systems, oxidation of unsaturated FA leads to the formation of volatile compounds, which are major contributors to the aroma or to undesirable off-odors and off-flavors (1). Oxidation in bulk and emulsified oils is influenced by several common factors, but additional factors are important in emulsions (2). These include the structure of the emulsions and the physicochemical properties of the aqueous phase and of the droplet membrane. The size of the oil droplets is often claimed as an important factor. On one hand, small droplet size signifies a large surface area, implying a high potential of contact between diffusing oxygen, water-soluble free radicals and antioxidants, and the interface. It also implies a high ratio of oxidizable FA located near the interface to FA embedded in the hydrophobic core of the droplets (3). Decreasing the size of the oil droplets is therefore expected to favor development of oxidation. On the other hand, when the droplet size decreases, the number of lipid molecules per droplet diminishes and the amount of surface-active compounds adsorbed at the interface is increased. This could limit initiation and propagation, as surface-active compounds may act as a barrier to the penetration and diffusion of pro-oxidants or even interfere with oxidation. For instance, homogenization is reported to protect milk fat from oxidation catalyzed by metal complexes (4) because casein, which adsorbs to the droplet surface, is an efficie...

Oxidative Stability of Egg and Soy Lecithin as Affected by Transition Metal Ions and pH in Emulsion

“…A general belief is that small particle size increases surface area and thus increases the chance of oil droplet being contacted with pro-oxidant transition metal ions, leading to fast lipid oxidation (2,17). Others reported that particle size of oil droplets did not affect lipid oxidation rate of o/w emulsion (18,19), or decreased particle size improved oxidative stability of various o/w emulsion (20). Our study seems to suggest that particle size did not significantly affect PL oxidation.…”

Meat Processing and Colon Carcinogenesis: Cooked, Nitrite-Treated, and Oxidized High-Heme Cured Meat Promotes Mucin-Depleted Foci in Rats

“…Development of oxidation was followed by measurement of oxygen consumption by the ground meat productemulsion mixtures kept in closed vials at 37°C in the dark. Oil-in-water emulsions were prepared with safflower oil (30 g oil; SICTIA) and 10 g/L bovine serum albumin (ICN Biochemicals, Inc.) in 0.1 mol/L sodium phosphate buffer (pH 6.0) and 0.2 g/L NaN 3 as previously described (27,28). The mean surface diameter (d 3,2 ) of droplets was ∼1 μm.…”

Mass Transport Phenomena in Lipid Oxidation and Antioxidation

“…These results suggest that the depletion of antioxidants, by itself, does not trigger the onset of oxidation; if it did, pure emulsified lipids would be instantaneously oxidized in the absence of antioxidants. Nevertheless, many studies in the literature have reported that lipid oxidation does start immediately under certain circumstances, especially when pro-oxidative catalysts are added (Sy et al 2015, Yoshida & Niki 1992 or when oxidative conditions, such as the combination of temperature and high-pressure homogenization, are used (Cuvelier et al 2003, Lethuaut et al 2002. Therefore, in practice, numerous reported examples of oxidation kinetics do not show the normal lag phase.…”