Interactions between β-lactoglobulin and dextran sulfate at near neutral pH and their effect on thermal stability

The effect of interactions between β-lactoglobulin (β-LG) and dextran sulfate (DS) on thermal stability at near neutral pH was investigated. Samples containing 6% w/w β-LG and DS (M_w = 5–500 kDa) at different biopolymer weight ratios, pH (5.6–6.2), and NaCl concentrations (0–30 mM) were heated at 85 °C for 15 min. Turbidity results showed that the presence of DS at appropriate biopolymer weight ratio and pH significantly lowered the turbidity of heated β-LG. Solutions containing DS:β-LG weight ratios of 0.02 or less showed improved heat stability as indicated by decreased turbidity. Analysis of the unheated mixture by size exclusion chromatography coupled with multi-angle laser light scattering (SEC–MALLS) showed an interaction between β-LG and DS. The size of the aggregates increased as pH decreased. The β-LG–DS aggregates had a greater negative charge as seen from electrophoretic mobility measurement. Addition of 30 mM NaCl inhibited complex formation and the effect of DS on reducing the turbidity of heated β-LG, suggesting that the interaction was electrostatic in nature. Other than charge property, the amount and size of native aggregates appeared to be the major factor in determining how DS altered heat-induced aggregation. The presence of DS decreased denaturation temperature of β-LG, indicating that DS did not improve thermal stability of β-LG by stabilizing its native state but rather by altering its aggregation. The results provide information that will facilitate the application of whey proteins and polysaccharides as functional ingredients in foods and beverages.     

Effect of thermal treatments on the properties of coconut milk emulsions prepared with surface-active stabilizers

Previously we have demonstrated improved stability of coconut milk emulsions homogenized with various surface-active stabilizers, i.e., 1 wt% sodium caseinate, whey protein isolate (WPI), sodium dodecyl sulfate (SDS), or polyoxyethylene sorbitan monolaurate (Tween 20) [Tangsuphoom, N., & Coupland, J. N. (2008). Effect of surface-active stabilizers on the microstructure and stability of coconut milk emulsions. Food Hydrocolloids, 22(7), 1233–1242]. This study examines the changes in bulk and microstructural properties of those emulsions following thermal treatments normally used to preserve coconut milk products (i.e., −20 °C, −10 °C, 5 °C, 70 °C, 90 °C, and 120 °C). Calorimetric methods were used to determine the destabilization of emulsions and the denaturation of coconut and surface-active proteins. Homogenized coconut milk prepared without additives was destabilized by freeze–thaw, (−20 °C and −10 °C) but not by chilling (5 °C). Samples homogenized with proteins were not affected by low temperature treatments while those prepared with surfactants were stable to chilling but partially or fully coalesced following freeze–thaw. Homogenized coconut milk prepared without additives coalesced and flocculated after being heated at 90 °C or 120 °C for 1 h in due to the denaturation and subsequent aggregation of coconut proteins. Samples emulsified with caseinate were not affected by heat treatments while those prepared with WPI showed extensive coalescence and phase separation after being treated at 90 °C or 120 °C. Samples prepared with SDS were stable to heating but those prepared with Tween 20 completely destabilized by heating at 120 °C.     

Real-Time 3D Head Pose Tracking Through 2.5D Constrained Local Models with Local Neural Fields

Tracking the head in a video stream is a common thread seen within computer vision literature, supplying the research community with a large number of challenging and interesting problems. Head pose estimation from monocular cameras is often considered an extended application after the face tracking task has already been performed. This often involves passing the resultant 2D data through a simpler algorithm that best fits the data to a static 3D model to determine the 3D pose estimate. This work describes the 2.5D constrained local model, combining a deformable 3D shape point model with 2D texture information to provide direct estimation of the pose parameters, avoiding the need for additional optimization strategies. It achieves this through an analytical derivation of a Jacobian matrix describing how changes in the parameters of the model create changes in the shape within the image through a full-perspective camera model. In addition, the model has very low computational complexity and can run in real-time on modern mobile devices such as tablets and laptops. The point distribution model of the face is built in a unique way, so as to minimize the effect of changes in facial expressions on the estimated head pose and hence make the solution more robust. Finally, the texture information is trained via local neural fields—a deep learning approach that utilizes small discriminative patches to exploit spatial relationships between the pixels and provide strong peaks at the optimal locations.

     

Effect of Liquid Oil on the Distribution and Reactivity of a Hydrophobic Solute in Solid Lipid Nanoparticles

The performance of solid lipid nanoparticles is often modified by the addition of small amounts of liquid oil. The effects of added liquid lipid (tetradecane, C14) on the distribution and reactivity of the spin probe 4-phenyl-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl nitroxide (PTMIO) in solid lipid nanoparticles (eicosane, C20) were investigated as a function of storage time and temperature. Emulsions prepared with blends of C14:C20 (100 % C14, 90 % C20, 99 % C20, and 100 % C20) and stabilized by sodium caseinate (1 wt%) were stored at 21.5 °C or 5 °C for 5 or 24 h prior to EPR analyses. In the liquid C14 droplets the PTMIO partitioned between the droplet and aqueous phases (70 and 30 %, respectively) independent of storage conditions. However, the proportion of probe in droplets decreased with increasing crystalline C20 concentration. The fraction of PTMIO in droplets containing C20 decreased in the following sequence: 5 h at room temperature >24 h at room temperature >24 h at refrigerated temperature and was lower in droplets with a higher proportion of C20. The residual PTMIO in semicrystalline droplets has higher polarity and lower mobility than PTMIO in liquid oil droplets suggesting it is in a layer surrounding the crystalline lipid core, and partly immobilized by interaction with the surface layer. The model of PTMIO distribution was consistent with the kinetics of PTMIO reduction by aqueous ascorbate ions.     

Encapsulation of Aqueous Components in Solid Fat Beads: Studies of a Model Dye and a Probiotic Culture

Solid fat beads containing aqueous droplets of either a water soluble dye (Brilliant Blue) or a suspension of viable probiotic bacteria (Bifidobacterium animalis ssp lactis) were produced by dropping a water‐in‐molten fat emulsion into cold water or onto a cold plate, respectively. Hydrogenated palm stearin beads containing 20 % dye solution were 4.6 ± 0.2 × 2.7 ± 0.4 mm and the average bead weighed 0.0103 ± 0.0003 g. The dye was completely released into an external aqueous phase after 24 h stirring at temperatures above the melting point of the fat but at temperatures where the fat was solid very little dye was released into an external aqueous phase. When a bacterial suspension was used as the internal phase of 20 % hydrogenated palm stearin/80 % palm kernel oil beads, the beads contained 8.44 log CFU/g. The encapsulated organisms were more resistant to acid stress than an unencapsulated control (loss of 0.7 versus 5.75 log CFU/g). This approach offers a way to protect probiotic bacteria during transit through the stomach. Practical application: by encapsulating bacteria in solid fat they become more resistant to acids. Small beads could be added to foods or swallowed as a pill as a way to deliver viable probiotic organisms to the lower digestive tract.     

Stability of Solid Lipid Nanoparticles in the Presence of Liquid Oil Emulsions

The dissolution of solid lipid nanoparticles (d ~200 nm, SLN) by mass transfer of lipid molecules from liquid oil emulsion droplets (d ~200 nm) was investigated by differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (NMR). The mass transfer of n-tetradecane to n-eicosane SLN resulted in the dissolution of the SLN over the course of several hours. The rate of dissolution increased with the tetradecane droplet to eicosane SLN ratio and was greater in the presence of a micelle forming surfactant (i.e., polyoxyethylene sorbitan monolaurate) compared to a protein (i.e., sodium caseinate). The rate of mass transfer was slower in a triacyglycerol system (i.e., liquid droplets of Miglyol and solid droplets of palm stearin, SLN) but could be accelerated by the presence of isopropanol (1.4%) in the aqueous phase. This work shows that even if SLN can be stabilized against aggregation, they may still dissolve due to diffusion of the lipids through the aqueous phase. Even a partial dissolution of SLN can dramatically change their functionality as delivery systems.     

Measurement of Steep Surfaces Using White Light Interferometry

Abstract:  Scanning white light interferometry (SWLI) is an increasingly popular method to measure the surface profile of miniature components. Although it is tolerant to step changes in profile, its capability to measure the large surface gradients that are characteristic of high-aspect-ratio surfaces is limited. This is in part due to the numerical aperture of the objective lens which restricts the spatial frequency content of both the illumination and recorded fields. More fundamentally, though, SWLI instrumentation neglects the effects of multiple scattering and assumes that the field which illuminates the object is that which would be present if the object were absent. Although this is a reasonable approximation for slowly varying surfaces, it is generally not true for those with steep gradients. In this paper the 3D theory of SWLI is presented and the approximations made by current instrumentation are discussed in this context. Using finite element methods (FEM), SWLI interferograms are calculated, for the cases of 2D Silicon V-grooves and step artefacts, and the effects of multiple scattering are illustrated. Methods to improve the capability of SWLI to measure large surface gradients, first by tilting the sample and subsequently by using an iterative FEM model to provide improved estimates of the illuminating conditions are introduced.