Effects of heat-treated β-lactoglobulin and its aggregates on foaming properties

The effects on foaming properties of the aggregates formed by heating concentrate beta-lactoglobulin solutions (55 mg mL⁻¹, pH 6.8) at 85 °C from 1 to 15 min were investigated. Structural characteristics (size and molecular conformation), hydrophobicity and protein aggregates proportion were also studied. All tested methods pointed at 3 min of heating as a critical time, in terms of conformational changes and aggregation processes. At this time, the most significant conformational changes took place: non-native monomers were present and the greatest amount of dimers and trimers was produced, which was proved with the results of gel densitometry of SDS-PAGE, fluorescence quenching and circular dichroism tests. Foamability and foam stability were both improved by pre-heating the protein. A constant proportion among beta-lactoglobulin species (monomer 51%, dimer 33% and trimer 16%), regardless the protein concentration, led to the same results on foaming properties, confirming the link with structural changes. Aggregates formed by heating beta-lactoglobulin up to 10 min produced more stabilized foams, slowing down disproportionation, because of the formation of stiffer films. The increase in surface hydrophobicity was considered a decisive factor in the improved foamability and hydrophobic interactions improved the foam stability trough the rapid formation of a viscoelastic film.     

Microstructure of highly concentrated tomato suspensions on homogenisation and subsequent shearing

The changes in the microstructure of tomato paste suspensions have been investigated during homogenisation and subsequent shearing in suspensions with similar composition, at three tomato paste concentrations 10, 30 and 40%. The suspensions were characterised by the particle size distribution (PSD), volume fraction (ø), and dynamic rheological properties (G′, G″). All suspensions exhibit a solid-like behaviour with G′ > G″. Micrographs indicate that the process of homogenisation creates a smooth network of finer particles, that is easily disrupted by prolonged shearing, giving rise to the formation of densely packed flocs that become clearly oriented in the direction of the shearing. At high concentrations, these changes in the microstructure on homogenisation and subsequent shearing were better reflected by differences in ø than in G′. The rheological behaviour of the suspensions exhibits a power-law dependence on ø, over a large range of PSD and for 0.05 < ø < 0.55. Finally, an experimental equation, including ø and the size of the coarse particles in the surface-weighted PSD, is found to accurately estimate G′ (R² > 99.3%, p < 0.001).     

Surface Properties of Heat‐Induced Soluble Soy Protein Aggregates of Different Molecular Masses

Suspensions (2% and 5%, w/v) of soy protein isolate (SPI) were heated at 80, 90, or 100 °C for different time periods to produce soluble aggregates of different molecular sizes to investigate the relationship between particle size and surface properties (emulsions and foams). Soluble aggregates generated in these model systems were characterized by gel permeation chromatography and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Heat treatment increased surface hydrophobicity, induced SPI aggregation via hydrophobic interaction and disulfide bonds, and formed soluble aggregates of different sizes. Heating of 5% SPI always promoted large‐size aggregate (LA; >1000 kDa) formation irrespective of temperature, whereas the aggregate size distribution in 2% SPI was temperature dependent: the LA fraction progressively rose with temperature (80→90→100 °C), corresponding to the attenuation of medium‐size aggregates (MA; 670 to 1000 kDa) initially abundant at 80 °C. Heated SPI with abundant LA (>50%) promoted foam stability. LA also exhibited excellent emulsifying activity and stabilized emulsions by promoting the formation of small oil droplets covered with a thick interfacial protein layer. However, despite a similar influence on emulsion stability, MA enhanced foaming capacity but were less capable of stabilizing emulsions than LA. The functionality variation between heated SPI samples is clearly related to the distribution of aggregates that differ in molecular size and surface activity. The findings may encourage further research to develop functional SPI aggregates for various commercial applications.     

The effect of ethoxylated nonyl phenols on viscosity of crude oil

In this study, viscosities of different crude oils was determined in the temperature range of (298–373 K) in presence of ethoxylated nonyl phenols as nonionic surfactant with ethoxy group numbers 4 and 9 (nonyl phenol 4 and nonyl phenol 9). Viscosity was measured using Viscolab PVT viscometer. Viscosity of crude oil decreased with the increase of concentration in the range of 0–1.4 g l^?1). The most radical change was observed in the presence of nonyl phenol 9. For both surfactants, the viscosities of crude oil decreased with the increase of temperature, but the effect of temperature on the viscosity of crude oil decreased when surfactant concentration increased. Because of the formation of mixed micellar aggregates, the effect of mixed surfactants on the reduction of viscosity was more obvious than individual surfactant, but mixed surfactants had very little sensitivity to the temperature than individual surfactant. The best mixture of two surfactants system was observed in the mass ratio of 3 for nonyl phenol 9 and nonyl phenol 4.     

Environmental effects of coal gangue and its utilization

Coal gangue has accumulated huge coal gangue piles, occupying lots of land as well as having striking influence on the neighboring environmental effects. This paper seeks a new way of coal gangue treatment in which the coal gangue blended with shale and sludge was sintered in rotary kiln to form lightweight aggregates. The results show that the optimum mixture ratio of coal gangue, shale, and sludge is 50, 40, and 10 wt% and the corresponding indicators of aggregates obtained are: (a) bulk density of 658 kg/m³, (b) granule strength of 643N, (c) 1 h absorption water to be 13.8%.     

热处理影响牛乳蛋白凝胶特性的研究进展

热处理是各种乳制品生产过程中不可或缺的工艺手段,热处理过程中乳体系的蛋白质会发生变化,影响制品的凝胶特性.介绍了牛乳酸凝胶的模型和酶凝胶的形成阶段,分析了加热过程中蛋白质可能发生的变化,简要阐述了热处理对凝乳效果的影响,指出热诱乳蛋白聚合物与凝乳的机制密切相关,旨在为乳制品加工中热处理的潜在影响提供理论参考.     

Presence of indigestible peptide aggregates of soybean meal in pig ileal digesta residue

With the purpose of analysing the molecular size and composition, proteinaceous material was extracted from the insoluble components of a digesta sample obtained from pigs fed a feed consisting of only soybean meal. Gel permeation chromatography indicated that the alkali‐extractable fraction of the proteinaceous material from the residue was of relatively high apparent molecular weight. However, the combined results from gel electrophoresis, RPLC‐MS, and MALDI‐ToF MS showed that the extracted protein material was in fact, to a high extent, composed of aggregated peptides. To our knowledge this has not previously been described. Aggregates extracted by dilute alkali were fully degraded upon subsequent proteolytic treatment. N‐terminal sequencing of selected protein bands from SDS‐PAGE gels indicated the presence of partly degraded β‐conglycinin alpha subunits in the residue. Copyright © 2007 Society of Chemical Industry     

Behead and live long or the tale of cathepsin L

In recent decades Saccharomyces cerevisiae has proven to be one of the most valuable model organisms of aging research. Pathways such as autophagy or the effect of substances like resveratrol and spermidine that prolong the replicative as well as chronological lifespan of cells were described for the first time in S. cerevisiae. In this study we describe the establishment of an aging reporter that allows a reliable and relative quick screening of substances and genes that have an impact on the replicative lifespan. A cDNA library of the flatworm Dugesia tigrina that can be immortalized by beheading was screened using this aging reporter. Of all the flatworm genes, only one could be identified that significantly increased the replicative lifespan of S.cerevisiae. This gene is the cysteine protease cathepsin L that was sequenced for the first time in this study. We were able to show that this protease has the capability to degrade such proteins as the yeast Sup35 protein or the human α‐synuclein protein in yeast cells that are both capable of forming cytosolic toxic aggregates. The degradation of these proteins by cathepsin L prevents the formation of these unfolded protein aggregates and this seems to be responsible for the increase in replicative lifespan.     

Enhanced mechanical properties of lightweight Al2O3-C refractories reinforced by combined one-dimensional ceramic phases

We prepared a new lightweight Al₂O₃-C refractory material with a higher strength by using microporous corundum aggregates instead of dense tabular corundum aggregates, which was reinforced by in situ formed SiC whiskers, multi-walled carbon nanotubes (MWCNTs), and mullite rods. A comparative study of the microstructure, mechanical properties, and fracture behavior was carried out for dense and lightweight Al₂O₃-C refractories coked at 1200°C and 1400°C, respectively. By using the microporous corundum aggregates, a better aggregate/matrix interface bonding and an optimized distribution of SiC whiskers were obtained. The SiC whiskers formed inside the microporous corundum aggregates and simultaneously in the matrix by a vapor-solid reaction mechanism, resulting in an enhancement at the microporous aggregate/matrix interface. Furthermore, the in situ formed MWCNTs and well-developed mullite rods at 1200°C in the matrix also contributed to the better interface structure. Thus, due to the improved microporous aggregate/matrix interface, the crack propagation along the aggregate/matrix interface was suppressed, resulting in an increased crack propagation within the aggregates. Consequently, the synergy between microporous corundum aggregates and combined one-dimensional ceramic phases caused a lower bulk density but a markedly higher strength, a higher fracture energy, and a higher toughness of lightweight Al₂O₃-C refractories compared to the dense ones. Overall, our study allows to overcome the traditional concept that a higher strength of refractories is reached by a higher density.