“…3 a), which indicated that additional oxygen consumption had taken place. This is in contrast to findings in previous work, where a closed oxygen balance for the oxidation of mayonnaise and bulk oil was found when applying the same methods to quantify oxygen consumption and lipid oxidation products as used in the present work 39 . In the present case, we used a substantial amount of Tween 20 to stabilise the emulsion, which is known to oxidise as well 40 – 42 .…”
Section: Resultscontrasting
confidence: 99%
“…It is difficult to find evidence in the literature for the stoichiometry of such a reaction, and thus to evaluate the potential contribution to the overall oxygen consumption. One previous study examined lipid oxidation, including oxygen consumption in Tween 20-based emulsions; however, in this example 37 , 39 , a much lower Tween 20-to-oil ratio was used compared the present work (12-fold lower ratio), which implies that the relative effect of Tween 20 oxidation compared to lipid oxidation was probably much smaller, and thus not pinpointed. Figure 3 ( a ) Measured oxygen consumption against calculated oxygen uptake in emulsions with small droplets (D 1,0 = 4.7 µm) (small, brown circles), intermediate droplets (D 1,0 = 9.1 µm) (intermediate, orange, circles), and large droplets (D 1,0 = 26.0 µm) (yellow, large circles).…”
Section: Resultsmentioning
confidence: 70%
“…The headspace oxygen content was monitored with a MOCON OpTech-O2 oxygen sensor (Ametek Mocon, Brooklyn Park, MN, USA) as previously described 39 . The initial amount of total available oxygen was calculated using a 1.35-mL headspace volume with 20.9% O 2 , 46.8 mg/kg oxygen concentration in the oil 55 , and 8.1 mg/kg oxygen concentration in the continuous phase 56 .…”
Section: Methodsmentioning
confidence: 99%
“…Lipid hydroperoxides (primary oxidation products) and aldehydes (secondary oxidation products) were quantified simultaneously by 1 H NMR spectroscopy, as previously described 39 , 58 . In brief, around 570 µL dry 5:1 CDCl 3 /DMSO‑ d 6 were added to a total of 30 µL extracted oil (section above) and transferred to 5-mm NMR tubes (Bruker, Billerica, MA, USA).…”
Section: Methodsmentioning
confidence: 99%
“…Epoxides (secondary oxidation products) were quantified using 1 H- 13 C heteronuclear single quantum coherence (HSQC) NMR spectroscopy, which was based on previous work 39 . Here, the protocol was modified to improve the spectral resolution.…”
Lipid oxidation in emulsions is hypothesised to increase with decreasing droplet size, as this increases the specific oil–water interfacial area, where lipid oxidation is expected to be initiated. In literature, however, contradictory results have been reported, which can be caused by confounding factors such as the oil droplet polydispersity and the distribution of components between the available phases. In this work, monodisperse surfactant-stabilised emulsions with highly controlled droplet sizes of 4.7, 9.1, and 26 µm were produced by microfluidic emulsification. We show that lipid oxidation increases with decreasing droplet size, which we ascribe to the increased contact area between lipids and continuous phase prooxidants. Besides, a significant amount of oxygen was consumed by oxidation of the surfactant itself (Tween 20), an effect that also increased with decreasing droplet size. These insights substantiate the importance of controlling droplet size for improving the oxidative stability of emulsions.
“…3 a), which indicated that additional oxygen consumption had taken place. This is in contrast to findings in previous work, where a closed oxygen balance for the oxidation of mayonnaise and bulk oil was found when applying the same methods to quantify oxygen consumption and lipid oxidation products as used in the present work 39 . In the present case, we used a substantial amount of Tween 20 to stabilise the emulsion, which is known to oxidise as well 40 – 42 .…”
Section: Resultscontrasting
confidence: 99%
“…It is difficult to find evidence in the literature for the stoichiometry of such a reaction, and thus to evaluate the potential contribution to the overall oxygen consumption. One previous study examined lipid oxidation, including oxygen consumption in Tween 20-based emulsions; however, in this example 37 , 39 , a much lower Tween 20-to-oil ratio was used compared the present work (12-fold lower ratio), which implies that the relative effect of Tween 20 oxidation compared to lipid oxidation was probably much smaller, and thus not pinpointed. Figure 3 ( a ) Measured oxygen consumption against calculated oxygen uptake in emulsions with small droplets (D 1,0 = 4.7 µm) (small, brown circles), intermediate droplets (D 1,0 = 9.1 µm) (intermediate, orange, circles), and large droplets (D 1,0 = 26.0 µm) (yellow, large circles).…”
Section: Resultsmentioning
confidence: 70%
“…The headspace oxygen content was monitored with a MOCON OpTech-O2 oxygen sensor (Ametek Mocon, Brooklyn Park, MN, USA) as previously described 39 . The initial amount of total available oxygen was calculated using a 1.35-mL headspace volume with 20.9% O 2 , 46.8 mg/kg oxygen concentration in the oil 55 , and 8.1 mg/kg oxygen concentration in the continuous phase 56 .…”
Section: Methodsmentioning
confidence: 99%
“…Lipid hydroperoxides (primary oxidation products) and aldehydes (secondary oxidation products) were quantified simultaneously by 1 H NMR spectroscopy, as previously described 39 , 58 . In brief, around 570 µL dry 5:1 CDCl 3 /DMSO‑ d 6 were added to a total of 30 µL extracted oil (section above) and transferred to 5-mm NMR tubes (Bruker, Billerica, MA, USA).…”
Section: Methodsmentioning
confidence: 99%
“…Epoxides (secondary oxidation products) were quantified using 1 H- 13 C heteronuclear single quantum coherence (HSQC) NMR spectroscopy, which was based on previous work 39 . Here, the protocol was modified to improve the spectral resolution.…”
Lipid oxidation in emulsions is hypothesised to increase with decreasing droplet size, as this increases the specific oil–water interfacial area, where lipid oxidation is expected to be initiated. In literature, however, contradictory results have been reported, which can be caused by confounding factors such as the oil droplet polydispersity and the distribution of components between the available phases. In this work, monodisperse surfactant-stabilised emulsions with highly controlled droplet sizes of 4.7, 9.1, and 26 µm were produced by microfluidic emulsification. We show that lipid oxidation increases with decreasing droplet size, which we ascribe to the increased contact area between lipids and continuous phase prooxidants. Besides, a significant amount of oxygen was consumed by oxidation of the surfactant itself (Tween 20), an effect that also increased with decreasing droplet size. These insights substantiate the importance of controlling droplet size for improving the oxidative stability of emulsions.
Lipid oxidation in food products is a crucial problem that causes undesirable changes in the food’s flavor, texture, and nutritional value. It should be carefully monitored as it can lead to the formation of potentially toxic compounds and in that way reduce the shelf life of the product. Liquid chromatography coupled to mass spectrometry is a powerful tool to monitor the formation of oxidized lipids. However, the presence of lipid species in both their non-oxidized and oxidized forms at distinctly different concentrations can hinder the detection and identification of the less abundant oxidized species, due to coelution. In this study, a flow injection mass spectrometry approach was used to selectively ionize oxidized triacylglycerols versus their non-oxidized precursors. Three mobile phase additives were investigated (ammonium formate, sodium acetate, and sodium iodide) at three different concentrations, and ion source settings (i.e., sheath gas temperature, capillary voltage, and nozzle voltage) were optimized. A fractional factorial design was conducted to examine not only the direct effect of the operating parameters on the selectivity of ionization for the oxidized lipid species, but also to assess their combined effect. Overall, selective ionization of oxidized versus non-oxidized lipid species was favored by the use of sodium-containing solvent additives. The application of specific ion source settings resulted in an increased ionization selectivity, with sheath gas temperature and capillary voltage having the most significant influence. A selectivity factor as high as 120 could be reached by combining 0.1 mg/mL sodium-containing additives, with 250 °C sheath gas temperature and 5000 V capillary voltage. These findings will contribute to future studies on fast detection and relative quantification of low abundant oxidized triacylglycerols and their possible impact on human health.
Graphical abstract
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