Unravelling mechanisms of protein and lipid oxidation in mayonnaise at multiple length scales

Raw dat

Tiny, yet impactful:Detection and oxidative stability of very small oil droplets in surfactant-stabilized emulsions

Hypothesis: The shelf life of multiphase systems, e.g. oil-in-water (O/W) emulsions, is severely limited by physical and/or chemical instabilities, which degrade their texture, macroscopic appearance, sensory and (for edible systems) nutritional quality. One prominent chemical instability is lipid oxidation, which is notoriously complex. The complexity arises from the involvement of many physical structures present at several scales (1–10,000 nm), of which the smallest ones are often overlooked during characterization. Experiments: We used cryogenic transmission electron microscopy (cryo-TEM) to characterize the coexisting colloidal structures at the nanoscale (10–200 nm) in rapeseed oil-based model emulsions stabilized by different concentrations of a nonionic surfactant. We assessed whether the oxidative and physical instabilities of the smallest colloidal structures in such emulsions may be different from those of larger colloidal structures. Findings: By deploying cryo-TEM, we analyzed the size of very small oil droplets and of surfactant micelles, which are typically overlooked by dynamic light scattering when larger structures are concomitantly present. Their size and oil content were shown to be stable over incubation, but lipid oxidation products were overrepresented in these very small droplets. These insights highlight the importance of the fraction of “tiny droplets” for the oxidative stability of O/W emulsions.</p

Characterization of hen phosvitin in aqueous salt solutions: Size, structure, and aggregation

Phosvitins is a key egg yolk protein and can often be found in food emulsions. It is highly phosphorylated and hence phosvitins contain a large number of negatively charged amino acid groups, for pH > pI. Due to the presence of these phophoserines, phosvitins bind to positively charged multivalent ions. Its amphipolar structure makes phosvitin also an efficient emulsion stabilizer. The ion binding and emulsifying abilities of phosvitins are influenced by environmental conditions such as pH and ionic strength. Various physicochemical properties of phosvitins such as size and charge under various conditions, and how they self-assemble via multivalent ions are not well-understood. To gain more insight into these physical characteristics, we performed high brilliance synchrotron small angle X-ray scattering (SAXS) on phosvitin solutions. The structure factor S(q) obtained from the SAXS profiles showed that the double layer interactions between charged phosvitin assemblies are strongly affected by pH and ionic strength of the buffer. The effects of multivalent ions (Mg2+, Fe3+) on the size and structure of phosvitin were also investigated. Our results revealed that the aggregation of phosvitin mediated by metal ions is induced by electrostatic attraction and only occurs beyond a threshold cation concentration, where phosvitin loses long-range electrostatic double layer repulsions. These findings help understanding the effects of metal ions and pH on phosvitin in more complex environments such as food emulsions

Real-Time Imaging of 2D and 3D Temperature Distribution: Coating of Metal-Ion-Intercalated Organic Layered Composites with Tunable Stimuli-Responsive Properties

Organic layered materials have intercalation and dynamic properties. The dynamic properties are tuned by the intercalation of the guests. In general, however, it is not easy to achieve the homogeneous and thin coating of the layered materials on substrates with complex shapes because of the two-dimensional anisotropic structures. In the present work, the layered organic composites were homogeneously coated on a variety of substrates for application to practical devices. The metal-ion-intercalated layered polydiacetylene (PDA-M^<i>n</i>+) with tunable stimuli-responsive color-change properties was coated on substrates, such as paper and cotton consisting of cellulose fibers. The homogeneous and thin coating of the precursor monomer crystal was achieved on the substrates through the controlled crystal growth. The intercalation and topochemical polymerization generated PDA-M^<i>n</i>+ on the substrates. The PDA-M^<i>n</i>+-coated devices visualized temperature distribution of two-dimensional surface and three-dimensional space in real time

Response to “Liposome vesicle cannot be formed in non-aqueous phase”

In a recent letter to the editor Prof Khosravi-Darani responded to our paper ‘’Unravelling mechanisms of protein and lipid oxidation in mayonnaise at multiple length scales’’. In our work, we observed liposomes in the continuous phase of mayonnaise. In the letter the objection was made that liposomes cannot be formed in a non-aqueous phase which, however, was not argued in our publication. As mayonnaise is an oil-in-water (O/W) emulsion and its continuous phase is aqueous, liposomes may be observed in this phase. Therefore, the objection from Prof Khosravi-Darani does not apply to our work.</p

Unravelling mechanisms of protein and lipid oxidation in mayonnaise at multiple length scales

In mayonnaise, lipid and protein oxidation are closely related and the interplay between them is critical for understanding the chemical shelf-life stability of mayonnaise. This is in particular the case for comprehending the role of low-density lipoprotein (LDL) particles as a main emulsifier. Here, we monitored oxidation and the concomitant aggregation of LDLs by bright field light microscopy and cryogenic transmission electron microscopy. We further probed the formation of protein radicals and protein oxidation by imaging the accumulation of a water-soluble fluorescent spin trap and protein autofluorescence. The effect of variation of pH and addition of EDTA on accumulation of spin trap validated that protein radicals were induced by lipid radicals. Our data suggests two main pathways of oxidative protein radical formation in LDL particles: at the droplet interface, induced by lipid free radicals formed in oil droplets, and in the continuous phase induced by an independent LDL-specific mechanism

Multi-scale imaging of protein oxidation in mayonnaise

In mayonnaise, lipid and protein oxidation are closely related and the interplay between them is critical for understanding the chemical shelf-life stability of mayonnaise. This is in particular the case for comprehending the role of low-density lipoprotein (LDL) particles as a main emulsifier. Here, we monitored oxidation and the concomitant aggregation of LDLs by bright field light microscopy and cryogenic transmission electron microscopy. We further probed the formation of protein radicals and protein oxidation by imaging the accumulation of a water-soluble fluorescent spintrap and protein autofluorescence. The effect of variation of pH and addition of EDTA on accumulation of spintraps validated that protein radicals were induced by lipid radicals. We observed protein radical formation at both the oil/water droplet interface and in the continuous phase. Our data suggests two main pathways of oxidative protein radical formation in LDL particles: at the droplet interface, induced by lipid free radicals formed in oil droplets, and in the continuous phase induced by an independent LDL-specific mechanism

Tunable stimuli-responsive color-change properties of layered organic composites

Stimuli-responsive properties of soft materials originate from dynamic structure changes. Layered polydiacetylene (PDA) shows color-change properties with the application of external stimuli, such as thermal and mechanical stresses. Layered organic materials possessing intercalation capabilities and dynamic properties have potentials for tuning their structures and properties by the intercalated guests. A variety of sensing and imaging devices can be developed by control of the stimuli responsivity. Here, the key structures, processes, and mechanisms for tuning the stimuli-responsive color-change properties of layered PDA are studied by in situ analyses with heating and cooling. The in situ analyses indicate that heating initiates thermal motion of the alkyl side chains of the PDA main chain in the host layers around 60 °C, regardless of the type of intercalated guests. Further heating induces torsion of the PDA main chain leading to color changes at different temperatures, depending on the types of the intercalated guest. Then, the layered structure is irreversibly deformed with lowering the crystallinity. The results indicate that the stimuli-responsive color-change properties are controlled by the rigidity of the layered structures consisting of the host layers and guests. The control strategy based on rigidity tuning can be applied to a variety of soft materials with stimuli responsivity