Influence of Interfacial Composition on in Vitro Digestibility of Emulsified Lipids: Potential Mechanism for Chitosan's Ability to Inhibit Fat Digestion

The objective of this study was to investigate the influence of interfacial composition and electrical charge on the in vitro digestion of emulsified fats by pancreatic lipase. An electrostatic layer-by-layer deposition technique was used to prepare corn oil-in-water emulsions (3 wt% oil) that contained droplets coated by (1) lecithin, (2) lecithin–chitosan, or (3) lecithin–chitosan–pectin. Pancreatic lipase (1.6 mg mL⁻¹) and/or bile extract (5.0 mg mL⁻¹) were added to each emulsion, and the particle charge, droplet aggregation, and free fatty acids released were measured. In the presence of bile extract, the amount of fatty acids released per unit amount of emulsion was much lower in the emulsions containing droplets coated by lecithin–chitosan (38 ± 16 μmol mL⁻¹) than those containing droplets coated by lecithin (250 ± 70 μmol mL⁻¹) or lecithin–chitosan–pectin (274 ± 80 μmol mL⁻¹). In addition, there was much more extensive droplet aggregation in the lecithin–chitosan emulsion than in the other two emulsions. We postulated that lipase activity was reduced in the lecithin–chitosan emulsion as a result of the formation of a relatively thick cationic layer around each droplet, as well as the formation of large flocs, which restricted the access of the pancreatic lipase to the lipids within the droplets. Our results also suggest that droplets initially coated by a lecithin–chitosan–pectin layer did not inhibit lipase activity, which may have been because the chitosan–pectin desorbed from the droplet surfaces thereby allowing the enzyme to reach the lipids; however, further work is needed to establish this. This information could be used to create food emulsions with low caloric level, or to optimize diets for individuals with lipid digestion problems.     

脉冲回波法研究微乳液体系的稳定性

本文主要以正庚炕（C71116）、水乳浊液（以span-80为表面活性剂）为模型体系,研究了脉冲回波法探测微乳体系结构稳定性的可能性,并进行了初步讨论。实验结果表明,超声衰减系数（a）与微乳体系配比、表面活性剂含量及微乳液制备时搅拌转速密切相关。微乳液体系在实验当中均出现了由油和水两相混合的状态到油和水分相的状态。微乳液体系的超声衰减系数在分相前后均保持着相对平稳的变化,但对应于不同条件下制备的溶液,分相时间都有所不同。且一般而言,当微乳液开始两相（水相和油相）分离时,超声衰减系数将发生明显变化。因此预计脉冲回波法有可能发展成为一种简单、可靠、非破环性的微乳体系稳定性检测新方法。     

Interfacial bioconjugation on emulsion droplet for biosensors

Interfacial bioconjugation methods are developed for intact liquid emulsion droplets. Complex emulsion droplets having internal hydrocarbon and fluorocarbon immiscible structured phases maintain a dynamic interface for controlled interfacial reactivity. The internal morphological change after binding to biomolecules is readily visualized and detected by light transmission, which provides a platform for the formation of inexpensive and portable bio-sensing assays for enzymes, antibodies, nucleic acids and carbohydrates.     

Stability of Lycopene in Oil‐in‐Water Emulsions

Lycopene can be dissolved within the oil phase of oil‐in‐water emulsions to increase bioavailability in water‐dispersible systems. It is sensitive to oxidative conditions and easily undergoes isomerization at high temperatures. Degradation kinetics and isomerization of lycopene in oil‐in‐water‐emulsions were investigated as a function of thermal treatment and oxygen content. Lycopene degradation was found to follow a first‐order kinetics and rate constants were determined. Higher temperatures are directly correlated with increasing lycopene losses. Moreover, thermal treatment leads to a significant decrease of the concentrations of all‐trans and 13‐cis isomer, while the concentration of the 9‐cis isomer increased. Oxygen‐free conditions reduce lycopene losses significantly.     

Emulsification in High‐Pressure Homogenizers

High‐pressure homogenizers are frequently employed for the homogenization of low‐viscosity emulsions containing a proportion of disperse phase which is not too high. High‐pressure homogenizers essentially consist of a high‐pressure pump and a homogenizing nozzle. The design of the homogenizing nozzle influences the flow of the emulsion in the nozzle itself and hence the results of droplet disruption. It is shown which mechanism in frequently used homogenizing nozzles is usually responsible for disruption. Experimental results reveal the effects of the dispersed phase content and the viscosity of the disperse and continuous phases in different nozzles. The results can be explained on the basis of the mechanisms of disruption. Finally, the homogenizing nozzles presented are directly compared with one another.     

Influence of Polydispersity and Thermal Exchange on the Flocculation Rate of O/W Emulsions

According to recent simulations [ Langmuir 16 , 7975 (2000)], the flocculation rate ( k f ) of concentrated oil in water (O/W) emulsions interacting through van der Waals forces, can reach values considerably higher than the one expected for a very dilute system of non-interacting spheres (5.49 2 10 -18 m 3 /s). Similar calculations at a volume fraction J =0.001 using 64 particles only, already show a k f =5.83 2 10 -18 m 3 /s, reasonably close to the theoretical prediction. In this report Brownian Dynamics (BD) simulations are used to study the effect of the volume fraction and the drop size distribution (DSD) on the flocculation rate. First, the dependence of k f with the maximum value of the thermal interaction between the particles and the solvent is studied. Following, the variation of the flocculation rate is studied as a function of polydispersity for J =0.15. As expected, there is a strong dependence of k f on J . Faster and slower aggregation rates are observed depending on the characteristics of the DSD.     

Designing Food Structure to Control Stability, Digestion, Release and Absorption of Lipophilic Food Components

The bioavailability of dietary lipophilic components may be either increased or decreased by manipulating the microstructure and/or physicochemical properties of the foods that contain them. This article stresses how knowledge of the molecular, physicochemical, and physiological processes that occur during lipid ingestion, digestion, and absorption can be used to rationally design food structures to control these processes and therefore impact the rate or extent of lipid digestion and/or absorption. These approaches include controlling the molecular characteristics of the lipid molecules, altering lipid droplet size or interfacial properties, and manipulating food matrix structure and composition. Improved knowledge of the molecular, physicochemical, and physiological processes that occur during lipid ingestion, digestion, and absorption will facilitate the rational design and fabrication of functional foods for improved health and wellness.     

A Simple Computational Technique for the Systematic Study of Adsorption Effects in Emulsified Systems. Influence of Inhomogeneous Surfactant Distributions on the Coalescence Rate of a Bitumen-in-water Emulsion

Abstract

In order to study the evolution of a bitumen-in-water (B/W) emulsion with time, a modification of a standard Brownian Dynamics (BD) algorithm was made. In these calculations, the 3-D movement of emulsion drops is mimicked by a combination of a steady DLVO (Derjaguin-Landau-Verwey-Oberbeek) inter-drop force and a random kick. The electrostatic component of the DLVO potential is allowed to depend on the surfactant population at the interface of each drop. Surfactant adsorption changes with the total surfactant concentration of the system, the available interfacial area, and the initial spatial distribution of amphiphilic molecules. Depending on these variables, the drops can flocculate and coalesce with either real drops or periodic-boundary images. As a consequence of coalescence, the interfacial area diminishes and surfactant is re-distributed among the surviving drops. The results are compared with well-known analytical equations developed for much simpler cases. With the present simulation technique, the exponential decrease of the number of drops with time reported for B/W systems can be reproduced. Evidence of a monotonic relationship between the total interfacial area of the surviving drops and the total surfactant concentration is also presented.