Modulation of thermal stability and heat-induced gelation of β-lactoglobulin by high glycerol and sorbitol levels

The influence of glycerol and sorbitol on the thermal stability and heat-induced gelation of β-lactoglobulin (β-lg) in aqueous solutions was investigated. The thermal stability of β-lg was characterized by measuring the thermal denaturation temperature (T_m) using differential scanning calorimetry, while its gelation properties were characterized by measuring the gelation temperature (T_gel) and final gel rigidity (G^∗) using dynamic shear rheology. All experiments were carried out using aqueous solutions containing 10% (w/w) β-lg, glycerol (0–70% w/w) or sorbitol (0–55% w/w), and 5 mM phosphate buffer (pH 7.0). No salt was added to these solutions so that there was a relatively strong electrostatic repulsion between the protein molecules, which usually prevents gelation. When the cosolvent concentration was increased from 0% to 50%, T_m increased from 74 to 86 °C for sorbitol, but only from 74 to 76 °C for glycerol, which indicated that sorbitol was much more effective at stabilizing the native state of the globular protein than glycerol. Protein solutions containing sorbitol (0–55%) did not form a gel after heating, but those containing glycerol formed gels when the cosolvent concentration exceeded about 10%, with G^∗ increasing with increasing glycerol concentration. We attribute these effects to differences in the preferential interactions of polyols and water with the surfaces of native and heat-denatured proteins, and their influence on the protein–protein collision frequency.     

Factors influencing the production of o/w emulsions stabilized by β-lactoglobulin–pectin membranes

A primary emulsion was prepared by homogenizing 10 wt% corn oil with 90 wt% aqueous β-lactoglobulin solution (0.5 wt% β-lg, pH 3 or 7) using a two-stage high-pressure valve homogenizer. This emulsion was mixed with aqueous pectin (citrus, 59% DE) stock solution (2 wt%, pH 3 or 7) and NaCl solution to yield secondary emulsions with 5 wt% corn oil, 0.225 wt% β-lactoglobulin, 0.2 wt% pectin and 0 or 100 mM NaCl. The final pH of the emulsions was then adjusted (3–8). Primary and secondary emulsions were ultrasonically treated (30 s, 20 kHz, 40% amplitude) to disrupt any flocculated droplets. Secondary emulsions were more stable than primary emulsions at intermediate pHs. Secondary emulsions prepared at pH 7 had smaller particle diameters (0.35 to 6 μm) than those prepared at pH 3 (0.42 to 18 μm) across the whole pH range studied, and also had smaller diameters than the primary emulsions (0.35 to 14 μm). Ultrasound treatment reduced the particle diameter of both primary and secondary emulsions and lowered the rate of creaming. The presence of NaCl screened the charges and thus the electrostatic interaction between biopolymer molecules and primary emulsion droplets. Secondary emulsions were more stable to the presence of 100 mM NaCl at low pHs (3–4) than primary emulsions. This study shows that stable emulsions can be prepared by engineering their interfacial membranes using the electrostatic interaction of natural biopolymers, especially at intermediate pHs where proteins normally fail to function.     

Nanoscale Nutrient Delivery Systems for Food Applications: Improving Bioactive Dispersibility,Stability, and Bioavailability

There has been a surge of interest in the development of nanoscale systems for the encapsulation, protection, and delivery of lipophilic nutrients, vitamins, and nutraceuticals. This review article highlights the challenges associated with incorporating these lipophilic bioactive components into foods, and then discusses potential nanoscale delivery systems that can be used to overcome these challenges. In particular, the desirable characteristics required for any nanoscale delivery system are presented, as well as methods of fabricating them and of characterizing them. An overview of different delivery systems is given, such as microemulsions, nanoemulsions, emulsions, microgels, and biopolymer nanoparticles, and their potential applications are discussed. Nanoscale delivery systems have considerable potential within the food industry, but they must be carefully formulated to ensure that they are safe, economically viable, and effective.     

The first panic attack: A neurobiological theory.

The authors extend a neurodevelopmental model of specific phobias (W. J. Jacobs and L. Nadel, 1985) to the etiology of an initial panic attack and its elaboration into panic disorder. An important difference between the initial panic attack and specific phobia is the developmental timing of critical emotional experience: Those occurring early in development lead to panic; those occurring later in development lead to specific phobia. By this account, sensory and emotional experiences that occur early in development are stored in a set of modules, each with a unique developmental trajectory. Reinstatement, which occurs during hormonal stress, produces an aggregate of sensory and emotional memories and the first experience of an unexplained panic attack. Panic disorder, which evolves from unexplained panic attacks, involves retrieval of a disaggregate set of sensory and emotional memory fragments supplemented by an inferential fitting of an explanatory context to this incomplete aggregate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of encapsulation of emulsified lipids with chitosan on their in vivo digestibility

The influence of interfacial composition on the in vivo digestibility of emulsified and encapsulated lipids was investigated. An electrostatic layer-by-layer deposition technique was used to prepare soybean oil-in-water emulsions that contained lipid droplets coated by lecithin or by lecithin–chitosan. Thirty six 4-week-old male mice were divided into four groups and fed treatment diets for 4 weeks; atherogenic diets supplemented with (A) non-emulsified fat, without chitosan (control), (B) non-emulsified fat, with chitosan, (C) emulsified fat, without chitosan, or (D) emulsified fat encapsulated by chitosan. There were no differences in body weights, food intake, major organ weights, or fecal fat contents between all treatment groups, where total fat absorption was >90%. The results suggest that encapsulation of lipids by chitosan does not inhibit their in vivo digestibility, even though previous studies indicate that chitosan does inhibit their in vitro digestibility. Consequently, it should be possible to use chitosan to microencapsulate lipids and lipid-soluble components without compromising their bioavailability, although further human studies are needed to confirm this.     

The effect of binary cosolvent systems (glycerol–sucrose mixtures) on the heat-induced gelation mechanism of bovine serum albumin

The influence of cosolvent composition on the thermal denaturation and gelation of bovine serum albumin (BSA) has been studied. Cosolvent composition was varied by changing the ratio of glycerol to sucrose in 40 wt% cosolvent solutions containing BSA. Differential scanning calorimetry measurements on 0.5 wt% BSA solutions showed that the thermal denaturation temperature of the protein increased with increasing sucrose content. Temperature scanning dynamic shear rheology and turbidity measurements on 4 wt% BSA solutions showed that the gelation temperature and final gel strength increased with increasing sucrose concentration. These observations were attributed to the fact that sucrose was more effective than glycerol at increasing the thermal stability and attraction between globular BSA molecules through a steric exclusion effect. The molecular origin of these effects is the tendency for the system to minimize the contact area of the protein molecules with the surrounding cosolvent solution.     

Characterization and optimization of Yb-doped photonic-crystal fiber rod amplifiers using spatially resolved spectral interferometry

Spatially resolved spectral interferometry is used to measure the mode content of a Yb-doped photonic-crystal fiber rod amplifier with a 2300 μm(2) mode area. The technique, known as S(2) imaging, was adapted for the short fiber amplifier at full power and revealed a small amount of a copolarized LP(11) mode. Simulations illustrate the potential for weak mode suppression in this fiber and agree qualitatively with the measurements of S(2) and M(2). Higher-order-mode content depends on the alignment of the input signal at injection and ranged from -18 dB for optimized alignment to -13 dB when the injection alignment was offset along the LP(11) axis by 30% of the 55 μm mode-field diameter.     

Risk assessment methodology for pipeline systems

The population increases along 8 km of a hypothetical 40 km pipeline system thereby necessitating the replacement of 8 km of pipe with thicker walled material. The effectiveness of replacing the old pipe is evaluated by comparing the risk between two gas pipeline systems; one wherein replacement has been effected and the other wherein the existing pipe is maintained. A Monte Carlo simulation is carried out to determine the relative probability of an occurrence of an ignited rupture for each scenario.     

Investigation of phase transitions in glyceride/paraffin oil mixtures using ultrasonic velocity measurements

A pulse echo technique has been used to measure the ultrasonic velocity of a number of 15% w/w glyceride/paraffin oil mixtures with increasing temperature (0–70 C). At the lower temperatures the glycerides are completely solid and there is a fairly steady decrease in velocity with temperature (ca. −3.8 ms⁻¹C⁻¹). As the temperature rises the glycerides become increasingly soluble in the paraffin oil and the velocity decreases more rapidly. Once the glyceride is completely soluble in the paraffin oil, a fairly steady decrease in velocity with temperature (ca. −3.3 ms⁻¹C⁻¹) resumes. The dependence of ultrasonic velocity on the amount of solid glyceride present means the technique can be used to investigate phase transitions in binary glyceride/oil mixtures.     

Effect of polysaccharide charge on formation and properties of biopolymer nanoparticles created by heat treatment of β-lactoglobulin–pectin complexes

Biopolymer nanoparticles can be formed by heating globular protein/polysaccharide mixtures above the thermal denaturation temperature of the protein under pH conditions where the two biopolymers are weakly electrically attracted to each other. In this study, the influence of polysaccharide linear charge density on the formation and properties of these biopolymer nanoparticles was examined. Mixed solutions of globular proteins (β-lactoglobulin) and anionic polysaccharides (high and low methoxyl pectin) were prepared. Micro-electrophoresis, dynamic light scattering, turbidity and atomic force microscopy (AFM) measurements were used to determine the influence of protein-to-polysaccharide mass ratio (r), solution pH, and heat treatment on biopolymer particle formation. Biopolymer nanoparticles (d < 500 nm) could be formed by heating protein–polysaccharide complexes at 83 °C for 15 min at pH 4.75 and r = 2:1 in the absence of added salt. The biopolymer particles formed were then subjected to pH and salt adjustment to determine their stability. The pH stability was greater for β-lactoglobulin-HMP complexes than for β-lactoglobulin-LMP complexes. The addition of 200 mM sodium chloride to heated complexes greatly improved the pH stability of HMP complexes, but decreased the pH stability of LMP complexes. The biopolymer particles formed consisted primarily of β-lactoglobulin, which was probably surrounded by a pectin coating at low pH values. AFM measurements indicated that the biopolymer nanoparticles formed were spheroid in shape. These biopolymer particles may be useful as delivery systems or fat mimetics.