RIOFH - Repository of Institute of General and Physical Chemistry
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Raw kaolinitic-illitic clays as high-mechanical-performance hydraulically pressed refractories
No full textThe usage possibility of 19 composites of raw refractory clays from Serbia containing approximately 53.29% of SiO2 and 26.73% of Al2O3 is presented. The sum of fluxing oxides was 57.74%, while these materials contained 32% of quartz, 29% of kaolinite and 26% of illite-mica. Dilatometry tests revealed a sudden shrinkage with the peak at approximately 1115 & DEG;C, owing to the formation of mullite. The refractoriness was in the range of 1581-1718 & DEG;C, which classifies the composites from low- to high-duty refractories. Based on correlation analysis, the refractoriness mostly depended on the content of alumina. The lightness of the fired test pieces was lower after firing when compared to the dry samples, and it decreased with the firing temperature from reddish to grayish. The study presents a novel attempt to define all the necessary properties of raw refractory clays and products fired at the 1100-1300 & DEG;C range on a laboratory level. Most of these clays can be used as natural refractory materials for ceramic and glass furnace lining. The organic matter in some of the samples influences negatively the fast-firing process
Antibacterial activity of donkey's milk against clinical isolate of Klebsiella pneumoniae
No full textThe purpose of this study was to investigate the antibacterial activity of raw donkey milk toward the clinical isolate of Klebsiella pneumoniae at 9, 15 and 38 degrees C as well as to clarify the role of lysozyme, lactoferrin and calcium content in the antibacterial activity of donkey's milk. The effects of contamination level and incubation period on this antibacterial activity were also examined. Antibacterial assays were performed by determing the bacterial count in intentionally contaminated (10(2), 10(3), 10(4) cfu/mL) donkey milk samples during 8 and 96 hours. Lab-on-a-chip electrophoresis and atomic absorption spectrometry were used for the determination of lysozyme, lactoferrin and calcium contents in donkey milk, respectively. The donkey milk samples showed varying degrees of antibacterial activity against the tested strain K. pneumoniae. The antibacterial synergism of lysozyme and lactoferrin was proven for this clinical strain as the samples with higher lactoferrin amount showed a stronger antibacterial activity. The correlation between calcium content and antibacterial activity of donkey milk samples was not established. Donkey milk showed stronger antibacterial potential at 15 degrees C compared to 9 degrees C, but this was limited by a higher growth rate of K. pneumoniae at 15 degrees C. The higher level of contamination resulted in a faster consumption of the antibacterial capacity of donkey milk. The artificial neural network model for prediction of K. pneumoniae count gave acurate fit to experimental data, showing a reasonably good (overall r(2) for donkey milk was 0.986, with training error 4.67.10(-4), while r(2) for nutrient broth was 0.982 and training error was 0.002)
Design and characterization of whey protein nanocarriers for thyme essential oil encapsulation obtained by freeze-drying
No full textInnovative coating powders, based on whey protein concentrate (10-15 wt%) as native (WPC) or denatured protein (D-WPC), solely or in combination with alginate (0.75 wt%, AL), containing thyme essential oil, were produced using the freeze-drying technique. The impact of individual components (protein, alginate and oil) as well as the effect of heat-induced protein denaturation, was resolved regarding physicochemical, thermal and morphological properties of powders. High product yield (~100%), particle size (223-257 nm), low moisture content (0.10-0.13%) and zeta potential (-19 to -25.6 mV) were determined for all samples. Strong antimicrobial activity of thyme oil nanocarriers against foodborne pathogens was demonstrated. Thermogravimetric analysis (TGA) indicated enhanced thermal stability of encapsulated oil. The most specific bands of structural compounds were identified in Raman spectra of the tested formulations, but principal component analysis (PCA) on recorded spectra was necessary to show the differences between carriers of different wall materials
Numerical study of the hydrodynamics and mass transfer in the external loop airlift reactor
No full textThe objective of this study was to investigate the hydrodynamics and the gas-liquid mass transfer coefficient of an external-loop airlift reactor (ELAR). The ELAR was operated in three cases: different inlet velocities of fluids, different alcohols solutions (water, 0.5% methanol, 0.5% ethanol, 0.5% propanol and 0.5% butanol) and different concentration of methanol in solutions (0%, 0.5%, 1%, 2% and 5%). The influence of superficial gas velocity and various diluted alcohol solutions on hydrodynamics and the gas-liquid mass transfer coefficient of the ELAR was studied. Experimentally, the gas hold-up, liquid velocities and volumetric mass transfer coefficient values in the riser and the downcomer were obtained from the literature source. A computational fluid dynamics (CFD) model was developed, based on two-phase flow, investigating different liquids regarding surface tension, assuming the ideal gas flow, applying the finite volume method and Eulerian-Eulerian model. The volumetric mass transfer coefficient was determined using the CFD and artificial neural network model. The effects of liquid parameters and gas velocity on the characteristics of the gas-liquid mass transfer were simulated. These models were compared with the appropriate experimental results. The CFD model successfully simulates the influence of different alcohols regarding the number of C-atoms on hydrodynamics and mass transfer
Biological activity and profiling of Salvia sclarea essential oil obtained by steam and hydrodistillation extraction methods via chemometrics tools
No full textSalvia sclarea L. or clary sage is cultivated worldwide in temperate and sub-tropical climates, as an ornamental and essential oil (EO) bearing plant. EO is obtained from fresh spikes in full flowering stage and is recognized as an important commercial product for food, beverage and cosmetic industries. This study investigated the EO composition of S. sclarea grown in Serbia (Southeast Europe) obtained by two different methods, steam (SD) and hydrodistillation (HD). GC-MS analysis identified oxygenated monoterpenes as the main class of compounds for all EOs (between 81.8% and 88.2% depending on the distillation process). The most abundant oxygenated monoterpenes were linalyl acetate and linalool. In addition, in vitro antimicrobial (modified resazurin microtitre-plate assay) and antioxidant activities (DPPH center dot assay) and total polyphenol content of obtained EOs were also evaluated. According to the assay used for the evaluation of the antibacterial activity, Gram-negative bacteria were more sensitive to S. sclarea EO in comparison to Gram-positive bacteria. EOs exhibited low antioxidant capacity, below 3% neutralized DPPH center dot radicals, reaching up to approximately 400 mu g AAE mL(-1). This study also investigated a possibility for predicting retention indices (RIs) of compounds isolated from EOs. In total, 78 experimentally obtained RIs were applied to construct the prediction model. The quantitative structure-chromatographic retention relationship (QSRR) model was used to anticipate the experimentally obtained RIs. Five molecular descriptors were selected by factor analysis and genetic algorithm to predict RIs. The obtained accuracy of the QSRR model reached r(2) = .912, which showed that these models might be applied for predicting retention indices
Textural, Color and Sensory Features of Spelt Wholegrain Snack Enriched with Betaine
No full textThe influence of different extrusion parameters, including screw speed (250-750 rpm), feed rate (15-25 kg/h) and feed moisture content (15-25%), on the textural and color properties of spelt wholegrain snack products produced on a co-rotating twin-screw extruder with added betaine was investigated. In order to determine the relative influence of input variables in the artificial neural network (ANN) model, Yoon's interpretation method was used, and it was concluded that feed moisture content has the greatest influence on L* values, while screw speed has the greatest influence on a* and b* values. The softest samples were obtained at the lowest moisture content. Sensory analysis was carried out on selected samples, and it showed that betaine addition did not intensify the bitter taste. The sample with the largest expansion exhibited the lowest hardness and chewiness before and after immersion in milk, and this sample is the most suitable for enrichment with betaine
The Effects of a Meldonium Pre-Treatment on the Course of the LPS-Induced Sepsis in Rats
No full textA dysregulated and overwhelming response to an infection accompanied by the exaggerated pro-inflammatory state and metabolism disturbance leads to the fatal outcome in sepsis. Previously we showed that meldonium, an anti-ischemic drug clinically used to treat myocardial and cerebral ischemia, strongly increases mortality in faecal-induced peritonitis (FIP) in rats. We postulated that the same mechanism that is responsible for the otherwise strong anti-inflammatory effects of meldonium could be the culprit of the increased mortality. In the present study, we applied the LPS-induced model of sepsis to explore the presence of any differences from and/or similarities to the FIP model. When it comes to energy production, despite some shared similarities, it is evident that LPS and FIP models of sepsis differ greatly. A different profile of sympathoadrenal activation may account for this observation, as it was lacking in the FIP model, whereas in the LPS model it was strong enough to overcome the effects of meldonium. Therefore, choosing the appropriate model of sepsis induction is of great importance, especially if energy homeostasis is the main focus of the study. Even when differences in the experimental design of the two models are acknowledged, the role of different patterns of energy production cannot be excluded. On that account, our results draw attention to the importance of uninterrupted energy production in sepsis but also call for much-needed revisions of the current recommendations for its treatment
Influence of arginine vasopressin on the ultradian dynamics of Hypothalamic-Pituitary-Adrenal axis
No full textNumerous studies on humans and animals have indicated that the corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) stimulate both individually and synergistically secretion of adrenocorticotropic hormone (ACTH) by corticotropic cells in anterior pituitary. With aim to characterize and better comprehend the mechanisms underlying the effects of AVP on Hypothalamic-Pituitary-Adrenal (HPA) axis ultradian dynamics, AVP is here incorporated into our previously proposed stoichiometric model of HPA axis in humans. This extended nonlinear network reaction model took into account AVP by: reaction steps associated with two separate inflows of AVP into pituitary portal system, that is synthesized and released from hypothalamic parvocellular and magnocellular neuronal populations, as well as summarized reaction steps related to its individual and synergistic action with CRH on corticotropic cells. To explore the properties of extended model and its capacity to emulate the effects of AVP, nonlinear dynamical systems theory and bifurcation analyses based on numerical simulations were utilized to determine the dependence of ultradian oscillations on rate constants of the inflows of CRH and AVP from parvocellular neuronal populations, the conditions under which dynamical transitions occur due to their synergistic action and, moreover, the types of these transitions. The results show that under certain conditions, HPA system could enter into oscillatory dynamic states from stable steady state and vice versa under the influence of synergy reaction rate constant. Transitions between these dynamical states were always through supercritical Andronov-Hopf bifurcation point. Also, results revealed the conditions under which amplitudes of ultradian oscillations could increase several-fold due to CRH and AVP synergistic stimulation of ACTH secretion in accordance with results reported in the literature. Moreover, results showed experimentally observed superiority of CRH as a stimulator of ACTH secretion compared to AVP in humans. The proposed model can be very useful in studies related to the role of AVP and its synergistic action with CRH in life-threatening circumstances such as acute homeostasis dynamic crisis, autoimmune inflammations or severe hypovolemia requiring instant or several-days sustained corticosteroid excess levels. Moreover, the model can be helpful for investigations of indirect AVP-induced HPA activity by exogenously administered AVP used in therapeutic treatment
Enhancement of nutritional, physical and structural characteristics of apple pomace flour by agglomeration with prebiotics using fluid-bed granulation
No full textDiversity of amino acids composition in cereals
No full textKvalitet proteina zasniva se na njihovom sastavu aminokiselina, posebno na sadržaju i dostupnosti esencijalnih aminokiselina. Žitarice su važni izvori proteina za ishranu ljudi, ali su limitirajuće u količinama esencijalnih aminokiselina, posebno lizina. Cilj ove studije bila je analiza hemijskog sastava i profila aminokiselina različitih žitarica koje su važne za ishranu ljudi. Sadržaj proteina, vlage i sirovih masti značajno je varirao od 7.83 do 13.22%, 11.45 do 13.80%, odnosno od 1.57 do 6.35%. Dobijeni rezultati su pokazali da ovas ima najveći sadržaj sirovih proteina (13.22%), sirove masti (6.35%) i sirove celuloze (9.42 %) u poređenju sa drugim žitaricama. Značajne (p LT 0.05) varijacije postojale su u sadržaju esencijalnih i neesencijalnih aminokiselina među uzorcima sa najvećim nivoom u ovsu i pšenici. Što se tiče udela esencijalnih aminokiselina u ukupnim aminokiselinama, moglo bi se zaključiti da je on iznosio jednu trećinu u testiranim žitaricama. Utvrđeno je da je glutaminska kiselina najzastupljenija aminokiselina. Moglo bi se zaključiti da je aminokiselinski sastav ovsa najpovoljniji među žitaricama zbog visokog sadržaja proteina i lizina koji se u ograničenim količinama nalazi u većini žitarica.The quality of protein is based on their amino acid composition, especially on the content and availability of essential amino acids. Cereals are important sources of protein for human nutrition, but are limited in the amounts of essential amino acids, notably lysine. The aim of this study was to analyze the chemical composition and amino acid profiles of different cereals that are important for nutritional purposes in human diet. The content of protein, moisture and crude fat in cereals varied significantly from 7.83 to 13.22%, 11.45 to 13.80%, and from 1.67 to 6.35%, respectively. The obtained results showed that oat had the highest contents of crude protein (13.22%), crude fat (6.35%) and crude cellulose (9.42%) compared to other cereals. Significant (p LT 0.05) variation existed in the content of essential and nonessential amino acids among samples with the highest level in oat and wheat. Essential amino acids accounted for one-third of the total amino acids in the tested cereals. Glutamic acid was found to be the most abundant amino acid. It could be concluded that the amino acid composition of oat is the most favorable among cereals due to its high protein content and the content of lysine which can be found in limited amounts in most of the cereals