Plant antioxidants in food emulsions

Addition of free radical scavenging antioxidants (AOs) is one of practical strategies controlling the oxidative stability in food emulsions. Attention has been directed toward AOs derived from natural plant extracts with the capacity to improve health and well-being due to lack of consumers’ trust toward synthetic antioxidant in food. Nevertheless, antioxidant efficiency varies widely from one compound to another and the most abundant AOs in our diet are not necessarily those that have the best availability profile at the reaction place with free radicals. In this book chapter, we will provide a state-of-the-art summary of the uses of plant AOs in colloidal systems, ranging from their main structural features to their benefits for the human health and their antioxidant role in controlling the oxidative stress and, particularly, the oxidation of lipid-based food emulsions.Xunta de Galicia | Ref. ED431D-2017/18Ministerio de Educación y Ciencia | Ref. CTQ2006-13969-BQUMinisterio de Educación, Cultura y Deporte | Ref. FPU15/04849Xunta de Galicia | Ref. POS-B/2016/01

Understanding the metal distribution in core-shell nanoparticles prepared in micellar media

The factors that govern the reaction rate of Au/Pt bimetallic nanoparticles prepared in microemulsions by a one-pot method are examined in the light of a simulation model. Kinetic analysis proves that the intermicellar exchange has a strong effect on the reaction rates of the metal precursors. Relating to Au, reaction rate is controlled by the intermicellar exchange rate whenever concentration is high enough. With respect to Pt, the combination of a slower reduction rate and the confinement of the reactants inside micelles gives rise to an increase of local Pt salt concentration. Two main consequences must be emphasized: On one hand, Pt reduction may continue independently whether or not a new intermicellar exchange takes place. On the other hand, the accumulation of Pt reactants accelerates the reaction. As the reactant accumulation is larger when the exchange rate is faster, the resulting Pt rate increases. This results in a minor difference in the reduction rate of both metals. This difference is reflected in the metal distribution of the bimetallic nanoparticle, which shows a greater degree of mixture as the intermicellar exchange rate is faster.Ministerio de Economía y Competitividad | Ref. MAT2012-36754-C02-01Xunta de Galicia | Ref. 2013-04

Insight into the surface composition of bimetallic nanocatalysts obtained from microemulsions

The enhancement of catalysts efficiency of bimetallic nanoparticles depends on the ability to exert control over surface composition. However, results relating surface composition and feeding solution of bimetallic nanoparticles synthesized in microemulsions are controversial and apparently contradictory. In order to comprehend how the resulting surface can be modified under different synthesis conditions and for different pairs of metals, a computer simulation study was carried out. The resulting surface compositions are explained based on the relative rates of deposition of the two metals, which depend on the particular metal pair, the concentration of reactants and the microemulsion composition. This study provides a satisfactory understanding of experimental results and allows us to identify the main factors affecting the nanoparticle’s surface composition. Consequently, concrete and practical guidelines can be established to facilitate the experimental synthesis of bimetallic nanoparticles with tailored surfaces.Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGXunta de Galicia | Ref. ED431C 2017/22Xunta de Galicia | Ref. ED431E2018/08Fundación La Caixa | Ref. LCF/PR/PR12/110700

Tailored surface composition of Au/Pt nanocatalysts synthesized in microemulsions: a simulation study

Au/Pt nanoparticles show an optimized catalytic activity when compared with Pt nanoparticles because Pt activity is improved by the presence of Au on the surface. It was checked whether a controllable surface composition can be achieved by the simple strategy of varying the Au : Pt ratio. We present an in-depth kinetic simulation study on the influence of Au : Pt ratio on the formation of Au/Pt nanoparticles synthesized in microemulsions. This study is able to explain the resulting nanoarrangement as a function of kinetic parameters such as Au : Pt ratio and intermicellar exchange rate. The role of the micelles as a dosing pump of the Au precursor explains that a higher Au amount results in a Au reduction which takes place over a longer period of time. It implies that Au is deposited until longer stages of the synthesis, so Au is present at the nanoparticle surface. Micelles as reaction media produce a minor impact on Pt due to its slower reduction. These different kinetic behaviours of Au and Pt give rise to a surface composition which can be tailored by tuning the Au : Pt ratio. Numerical results on surface composition successfully reproduce experimental data and further support the outcomes of the degree of atomic mixing under different Au : Pt ratios.Xunta de Galicia | Ref. ED431E2018/08Xunta de Galicia | Ref. ED431C 2017/2