Showing papers by "Sylwester J. Rzoska published in 2019"

Comparative effect of supercritical carbon dioxide and high pressure processing on structural changes and activity loss of oxidoreductive enzymes

Abstract: Due to the CO2 specific characteristics, it has been used as supercritical (Sc) fluid for several applications, including enzyme inactivation. The influence of Sc-CO2 (10–65 MPa/10–30 min/35–65 °C) on mushroom polyphenol oxidase (PPO) and horseradish peroxidase (POD) was evaluated and the results were compared with those found using high pressure processing (HPP) (200–900 MPa/5–45 °C/1–15 min). The free ion concentration was also studied to compare the enzymatic activity and changes in electrical conductivity. Additionally both enzymes, untreated or treated using either Sc-CO2 or HPP, were used as additives in the CuCl2 crystallization method. The resulting additive-specific CuCl2 patterns were characterized based on different structural features. Sc-CO2 was found to have a significant influence on PPO and POD activities, and an increased reduction in the residual activity of both enzymes was observed when the Sc-CO2 pressure was increased. However, PPO was more resistant to temperature and pressure than POD. The D-value calculated for POD was in the range of 38.3 and 592.0 min, and 60.6 and 291.5 min, for HPP and Sc-CO2 treatments, respectively; whereas for PPO varied from 103.1 to 284.3 min under HPP and from 83.4 to 303.0 min using the Sc-CO2 treatment. It can be concluded that the application of Sc-CO2 could be an effective tool for inactivating PPO and POD enzymes. Moreover, both enzymes and treatments could be differentiated significantly based on the resulting CuCl2 crystallization patterns.

Revisiting the Dependence of Poisson's Ratio on Liquid Fragility and Atomic Packing Density in Oxide Glasses.

Abstract: Poisson's ratio (ν) defines a material's propensity to laterally expand upon compression, or laterally shrink upon tension for non-auxetic materials. This fundamental metric has traditionally, in some fields, been assumed to be a material-independent constant, but it is clear that it varies with composition across glasses, ceramics, metals, and polymers. The intrinsically elastic metric has also been suggested to control a range of properties, even beyond the linear-elastic regime. Notably, metallic glasses show a striking brittle-to-ductile (BTD) transition for ν-values above ~0.32. The BTD transition has also been suggested to be valid for oxide glasses, but, unfortunately, direct prediction of Poisson's ratio from chemical composition remains challenging. With the long-term goal to discover such high-ν oxide glasses, we here revisit whether previously proposed relationships between Poisson's ratio and liquid fragility (m) and atomic packing density (Cg) hold for oxide glasses, since this would enable m and Cg to be used as surrogates for ν. To do so, we have performed an extensive literature review and synthesized new oxide glasses within the zinc borate and aluminoborate families that are found to exhibit high Poisson's ratio values up to ~0.34. We are not able to unequivocally confirm the universality of the Novikov-Sokolov correlation between ν and m and that between ν and Cg for oxide glass-formers, nor for the organic, ionic, chalcogenide, halogenide, or metallic glasses. Despite significant scatter, we do, however, observe an overall increase in ν with increasing m and Cg, but it is clear that additional structural details besides m or Cg are needed to predict and understand the composition dependence of Poisson's ratio. Finally, we also infer from literature data that, in addition to high ν, high Young's modulus is also needed to obtain glasses with high fracture toughness.

Enzyme inactivation and evaluation of physicochemical properties, sugar and phenolic profile changes in cloudy apple juices after high pressure processing, and subsequent refrigerated storage

Abstract: The effect of high pressure processing (HPP) (200–600 MPa/5–45°C/1–15 min) on the enzyme activity and some quality parameters of cloudy apple juice during subsequent storage (4°C for 12 weeks) was investigated. Statistical analysis showed that pressure, temperature, and time had a significant effect (p < 0.05) on tissue enzyme activity, decreasing the activity of polyphenol oxidases (PPO) and peroxidases (POD). No significant changes in physicochemical parameters (pH, total soluble solids, sugars, and vitamin C) were observed after HPP treatments. The main polyphenols detected in apple juice were dichydrochalcones, being phloridzin the predominant (48.8 mg/L), and flavanols, with the highest concentration of (−) epicatechin (20.6 mg/L) followed by (+) catechin (6.4 mg/L) and procyanidin B₁ (1.9 mg/L). Moreover, the application of HPP treatment significantly decreased gallic acid, all flavanols and dichydrochalcones. The storage time significantly affected total polyphenol content (TPC) and selected phenolic compounds, but the most stable were TPC. PRACTICAL APPLICATIONS: This study demonstrated that nutritional quality of cloudy not produced from concentrate apple juice after high pressure processing (HPP) and during subsequent cold storage. HPP significantly influenced on tissue oxidoreductive enzymes decreasing their residual activity below 1 and 33%, respectively, for polyphenol oxidases and peroxidases. The results showed that HPP might be a useful method for preservation apple products, resulting higher color stability due to the inhibition of enzymatic reactions during storage time.

Nanoparticle-controlled glassy dynamics in nematogen-based nanocolloids.

Abstract: Results of broad-band dielectric spectroscopy studies in liquid crystal (pentylcyanobiphenyl, 5CB)-based nanocolloids are presented. They reveal the strong impact of ${\mathrm{BaTiO}}_{3}$ nanoparticles on dynamics and uniaxial ordering. Studies were carried out in an extreme range of temperatures ($\ensuremath{\sim}150$ K), including the supercooled nematic phase. For the latter, the unique ``pretransitional'' effect for dielectric constant on approaching solid state is reported. The distortion-sensitive analysis revealed super-Arrhenius dynamics but associated with critical-like behavior. In the isotropic phase, translational-orientational decoupling, unusual for the high temperature dynamic domain, was detected. It can be directly link to heterogeneities---prenematic fluctuations. The model linking the classical Landau-de Gennes approach with Imry-Ma arguments has been developed to discuss experimental results.

Impact of Weak Nanoparticle Induced Disorder on Nematic Ordering

Abstract: Dilute mixtures of nanoparticles (NPs) and nematic liquid crystals (LCs) are considered. We focus on cases where NPs enforce a relatively weak disorder to the LC host. We use a Lebwohl-Lasher semi-microscopic-type modeling where we assume that NPs effectively act as a spatially-dependent external field on nematic spins. The orientational distribution of locally favoured “easy” orientations is described by a probabilistic distribution function P. By means of a mean field-type approach, we derive a self-consistent equation for the average degree of nematic uniaxial order parameter S as a function of the concentration p of NPs, NP-LC coupling strength and P. Using a simple step-like probability distribution shape, we obtain the S(p) dependence displaying a crossover behaviour between two different regimes which is in line with recent experimental observations. We also discuss a possible origin of commonly observed non-monotonous variations of the nematic-isotropic phase temperature coexistence width on varying p.

Permanent Densification of Calcium Aluminophosphate Glasses

Abstract: High temperature densification of oxide glasses influences their interatomic distances and bonding patterns, resulting in changes in the mechanical and chemical properties. Most of the high-pressure investigations have focused on aluminosilicate and aluminoborosilicate based glasses, due to their relevance for the glass industry as well as the geological sciences. Relatively few studies have explored the pressure-induced changes in structure and properties of phosphate based glasses, although P2O5 is an important component in various multicomponent oxide glasses of industrial interest. In this work, we investigate the influence of permanent densification on the structure, mechanical properties (Vickers’s hardness), and chemical durability (weight loss in water) of binary CaO-P2O5 and ternary CaO-Al2O3-P2O5 glasses. The densification of bulk glasses is obtained through isostatic compression (1-2 GPa) at the glass transition temperature. The binary CaO-P2O5 series is prepared with varying [CaO]/[P2O5] ratio to obtain glasses with different O/P ratios, while the ternary series CaO-Al2O3-P2O5 is prepared with constant O/P ratio of 3 (metaphosphate) but with varying [CaO]/([CaO]+[Al2O3]) ratio from 0~1. Using Raman and 31P NMR spectroscopy, we observed minor, yet systematic and composition-dependent changes in the phosphate network connectivity upon compression. On the other hand, 27Al NMR analysis of the compressed CaO-Al2O3-P2O5 glasses highlights an increase in the Al coordination number. We discuss these structural changes in relation to the pressure-induced increase in density, Vickers’s hardness, and chemical durability.

Multifold pressure-induced increase of electric conductivity in LiFe 0.75 V 0.10 PO 4 glass.

Abstract: We investigated the impact of high pressure and high-temperature annealing on lithium-vanadium-iron-phosphate (LiFe0.75V0.10PO4) glass materials, proposed for the use in cathodes for high-performance batteries. The treatment was carried out below the glass transition temperature (Tg ≈ 483 °C) at P = 1 GPa pressure, in an argon atmosphere. It led to the multifold electrical conductivity increase. Broadband dielectric spectroscopy (BDS) measurements before and after the process revealed the strong DC-conductivity increase across the whole studied frequency range by two orders of magnitude. The phenomenon is explained using Mott’s theory of polaron hopping in disordered solids containing transition metal oxides. The pressure evolution of the glass transition temperature and the crystallisation temperature above Tg is shown.

The usage of high hydrostatic pressure (HHP) to control food-borne pathogens in hummus

Abstract: With the increasing demand for fresher, higher quality, minimally processed and safer food, there is a strong necessity to develop non-thermal processing techniques. Also for hummus, which ...

Polymer matrix ferroelectric composites under pressure: Negative electric capacitance and glassy dynamics.

Abstract: This report presents the results of high-pressure and broadband dielectric spectroscopy studies in polyvinylidene difluoride (PVDF) and barium strontium titanate (BST) microparticles composites (BST/PVDF). It shows that the Arrhenius behaviour for the temperature-related dynamics under atmospheric pressure is coupled to Super-Arrhenius/Super-Barus isothermal pressure changes of the primary relaxation time. Following these results, an explanation of the unique behaviour of the BST/PVDF composite is proposed. Subsequently, it is shown that when approaching the GPa domain the negative electric capacitance phenomenon occurs.

The impact of pressure on the critical miscibility of nitro compounds and n-alkanes mixtures

Abstract: The impact of pressure on the critical consolute temperature in nitrobenzene, nitrotoluene, and nitropropane plus n-alkanes from pentane to eicosane is discussed.