•Ultrasound energy was used as mixing system in the esterification reaction of flavor esters.•Enzyme stability in butyric acid was improved under ultrasound-assisted reaction.•The use of molecular ...sieves improved the yield 1.5-times.•The combined use of molecular sieves and ultrasound increased the operational stability.
In this work, the combined use of ultrasound energy and molecular sieves was investigated for the synthesis of ethyl butyrate, ester with mango and banana notes, catalyzed by the immobilized lipase from Thermomyces lanuginosus (Lipozyme TL-IM). Initially, the best concentrations of biocatalysts (35%) and butyric acid (0.7M) were tested using ultrasound as an alternative to mechanical agitation. The amount of acid in the reaction could be increased by 2-fold when compared to previous works where mechanical agitation was used. In the next step, substrate molar ratio and reaction temperature were optimized and the best conditions were at their lowest levels: 1:1 (acid:alcohol), and 30°C, reaching 61% of conversion in 6h. Molecular sieves (3Å) were added to optimized reaction medium in order to remove the formed water and improve the maximum yield. The reaction yield increased 1.5 times, reaching 90% of conversion in 6h, when 60mg of molecular sieves per mmol of butyric acid was used. Finally, the reuse of Lipozyme TL-IM for the ultrasound-assisted synthesis of ethyl butyrate was verified for 10 batches, without any appreciable loss of activity, whereas in systems using mechanical agitation, the biocatalyst was completely inactivated after 5 batches. These results suggest that the combined use of ultrasound and molecular sieves greatly improve esterification reactions by stabilizing the enzyme and increasing yields.
► High thermal stability in presence of concentrated lactose. ► GOS synthesized with high productivities. ► Effective lactose conversion in a 15 days steady-state operation.
β-d-Galactosidase from ...Kluyveromyces lactis was immobilized on glutaraldehyde-activated chitosan and used in a packed-bed reactor for the continuous hydrolysis of lactose and the synthesis of galactooligosaccharides (GOS). The biocatalyst was tested for its optima pH and temperature, thermal stability in the presence of substrate and products, and operational stability. Immobilization increased the range of operational pH and temperature, and the enzyme thermal stability was sharply increased in the presence of lactose. Almost complete lactose hydrolysis was achieved for both milk whey and lactose solution at 37°C at flow rates up to 2.6mLmin−1. Maximal GOS concentration of 26gL−1 was obtained at a flow rate of 3.1mLmin−1, with a productivity of 186gL−1h−1. Steady-state operation for 15 days showed the reactor stability concerning lactose hydrolysis.
Pterin deaminase is an amidohydrolase enzyme hydrolyzing pteridines to form lumazine derivatives and ammonia. The enzyme captured the attention of scientists as early as 1959 and had been patented ...for its application as an anticancer agent. It is ubiquitously present in prokaryotes and has been reported in some eukaryotes such as honey bee, silkworm and rats. The enzyme has been observed to have a spectrum of substrates with the formation of respective lumazines. The role of the substrates of the enzyme in various metabolic pathways warrants a significant role in the biological activity of both prokaryotes and eukaryotes. Even though the functions of the enzyme have been explored in prokaryotes, their niche in the eukaryotic system is not clear. There is very few information on the structural and functional properties of the enzyme. This review has been congregated to emphasize the significance of pterin deaminase and analyzes the lacunae in understanding the biological characters of the enzyme.
► TLL was immobilized on styrene-divinylbenzene beads (MCI-TLL). ► MCI-TLL was compared to Lipozyme TL-IM in butyl butyrate synthesis. ► MCI-TLL presented two-times more protein than Lipozyme TL-IM. ...► The prepared biocatalyst was stable to higher concentration of butyric acid. ► MCI-TLL showed productivity 4-times higher than Lipozyme TL-IM.
Two immobilized preparations from Thermomyces lanuginosus lipase (TLL) were compared in the synthesis of butyl butyrate. The commercial Lipozyme TL-IM, and TLL immobilized on styrene–divinylbenzene beads (MCI-TLL) were tested in the esterification reaction using n-hexane as solvent. The variables temperature (30–60°C), substrate molar ratio (1:1 to 5:1), added water (0–1%), and biocatalyst content (3–40%) were evaluated in terms of initial reaction rate for each biocatalyst. SDS–PAGE analysis revealed that MCI-TLL had an immobilized enzymatic load twice as high as Lipozyme TL-IM, but with an activity 3-fold higher. MCI-TLL presented high initial reaction rates up to 1.0M butyric acid, while Lipozyme TL-IM showed a decrease in its activity above 0.5M. Moreover, MCI-TLL allowed a productivity of 14.5mmolg−1h−1, while Lipozyme TL-IM 3.2mmolg−1h−1, both by mass of biocatalyst.
► Ultrasound energy was used as mixing system in the esterification reaction of flavor esters. ► Synthesis of butyl butyrate catalyzed by Novozym 435 was optimized. ► Under the optimal conditions ...over 94% of conversion was obtained in 2.5h. ► Enzyme was reused for 14 reaction cycles, keeping 70% of its original activity. ► Enzyme stability in acetic acid was improved under ultrasound-assisted reaction.
The influence of low-frequency ultrasound (40kHz) in the esterification reaction between acetic acid and butanol for flavor ester synthesis catalyzed by the commercial immobilized lipase B from Candida antarctica (Novozym 435) was evaluated. A central composite design and the response surface methodology were used to analyze the effects of the reaction parameters (temperature, substrate molar ratio, enzyme content and added water) and their response (yields of conversion in 2.5h of reaction). The reaction was carried out using n-hexane as solvent. The optimal conditions for ultrasound-assisted butyl acetate synthesis were found to be: temperature of 46°C; substrate molar ratio of 3.6:1 butanol:acetic acid; enzyme content of 7%; added water of 0.25%, conditions that are slightly different from those found using mechanical mixing. Over 94% of conversion was obtained in 2.5h under these conditions. The optimal acid concentration for the reaction was determined to be 2.0M, compared to 0.3M without ultrasound treatment. Enzyme productivity was significantly improved to around 7.5-fold for each batch when comparing ultrasound and standard mechanical agitation. The biocatalyst could be directly reused for 14 reactions cycles keeping around 70% of its original activity, while activity was virtually zeroed in the third cycle using the standard mixing system. Thus, compared to the traditional mechanical agitation, ultrasound technology not only improves the process productivity, but also enhances enzyme recycling and stability in the presence of acetic acid, being a powerful tool to improve biocatalyst performance in this type of reaction.
The present paper explores the utilisation of dopants to increase the critical temperature of Carbon Dioxide (sCO2) as a solution towards maintaining the high thermal efficiencies of sCO2 cycles even ...when ambient temperatures compromise their feasibility. To this end, the impact of adopting CO2-based mixtures on the performance of power blocks representative of Concentrated Solar Power plants is explored, considering two possible dopants: hexafluorobenzene (C6F6) and titanium tetrachloride (TiCl4). The analysis is applied to a well-known cycle -Recuperated Rankine- and a less common layout -Precompression-. The latter is found capable of fully exploiting the interesting features of these non-conventional working fluids, enabling thermal efficiencies up to 2.3% higher than the simple recuperative configuration. Different scenarios for maximum cycle pressure (250–300 bar), turbine inlet temperature (550–700 °C) and working fluid composition (10–25% molar fraction of dopant) are considered. The results in this work show that CO2-blends with 15–25%(v) of the cited dopants enable efficiencies well in excess of 50% for minimum cycle temperatures as high as 50 °C. To verify this potential gain, the most representative pure sCO2 cycles have been optimised at two minimum cycle temperatures (32 °C and 50°C), proving the superiority of the proposed blended technology in high ambient temperature applications.
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•CO2 blends enable thermal efficiencies higher than 50% at high ambient temperatures.•For a given layout, sCO2 blends enable 4–5 pp higher efficiency than pure sCO2 cycles.•Precompression is the most interesting layout to better exploit CO2– C6F6 blends.•The composition of the best-performing blend depends on ambient temperature.•Cycle layout and dopant composition/fraction are independent optimisation variables.
Background: Human coronaviruses (hCoV) usually cause mild to moderate upper respiratory tract illnesses. The novel coronavirus (nCoV), or Middle East respiratory syndrome coronavirus (MERS-CoV), is a ...particular strain different from any other known hCoV with the possibility of human and also zoonotic transmissions. The aim of the study to assess primary health care (PHC) physicians' knowledge and adherence regarding Saudi Ministry of Health guidelines regarding MERS-CoV. Materials and Methods: A cross-sectional study design was followed to include 85 PHC physicians in Abha city. An interview questionnaire has been designed by the researcher that was used to assess knowledge and practices of PHC physicians regarding diagnosis and management of MERS-CoV. It includes personal characteristics, the MERS-CoV knowledge assessment questionnaire, and practices related to adherence toward guidelines regarding MERS-CoV. Results: PHC physicians' knowledge gaps regarding MERS-CoV included protected exposure (32.9%), highest seasonal incidence of MERS-CoV in Saudi Arabia (60%), relation between incidence of MERS-CoV and overcrowding (62.4%), case fatality of MERS-CoV cases (63.5%), and collecting specimens from MERS-CoV patients (64.7%). The knowledge of PHC physicians about MERS-CoV was poor among 5.9%, good among 63.5%, and excellent among 30.6%. Personal protective equipment to be used when seeing suspected cases of MERS-CoV infection were mainly the mask (94.1%), gloves (78.8%), the gown (60%), goggles (31.8%), and the cap (22.4%). All participants stated that the most important standard precaution that should be applied when seeing a case of MERS-CoV infection is hand washing, whereas 97.6% stated that the most important respiratory precaution to prevent transmission of respiratory infections in PHC setting when seeing a case of MERS-CoV infection is masking and separation of suspected MERS-CoV patients, and 81.2% stated that upon exit from the room of a MERS-CoV patient, the physician should remove and discard personal protective equipment. PHC physicians' knowledge about MERS-CoV differed significantly according to their nationality (P = 0.038), with non-Saudi physicians expressing higher percent of excellent knowledge than Saudi physicians (40% and 20%, respectively). Those who attended continuing medical education (CME) activities had significantly higher percent of excellent knowledge than those who did not attend a CME activity (55.6% and 23.9%, respectively, P = 0.011). PHC physicians' knowledge did not differ significantly according to their age, gender, qualification, experience in PHC, and practice-related adherence to guidelines. PHC physicians' practice-related adherence to guidelines about MERS-CoV differed significantly according to their position (P = 0.035), with specialists having the highest percent of excellent practice (13%). Conclusions: There are knowledge gaps among PHC physicians in Abha city, and their practice is suboptimal regarding MERS-CoV infection. Less than one-fourth of PHC physicians attend CME activities about MERS-CoV infection. However, significantly less practice-related adherence to guidelines are associated with Saudi PHC physicians, those who did not attend a related CME activity, and MBBS qualified physicians' general practitioners. To increase awareness, more CME activities related to MERS-CoV infection management needs to be organized.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Glycoside hydrolases (GH) are enzymes capable to hydrolyze the glycosidic bond between two carbohydrates or even between a carbohydrate and a non-carbohydrate moiety. Because of the increasing ...interest for industrial applications of these enzymes, the immobilization of GH has become an important development in order to improve its activity, stability, as well as the possibility of its reuse in batch reactions and in continuous processes. In this review, we focus on the broad aspects of immobilization of enzymes from the specific GH families. A brief introduction on methods of enzyme immobilization is presented, discussing some advantages and drawbacks of this technology. We then review the state of the art of enzyme immobilization of families GH1, GH13, and GH70, with special attention on the enzymes β-glucosidase, α-amylase, cyclodextrin glycosyltransferase, and dextransucrase. In each case, the immobilization protocols are evaluated considering their positive and negative aspects. Finally, the perspectives on new immobilization methods are briefly presented.
•A comprehensive procedure for innovative fluid identification is proposed.•Thermodynamic properties must be assessed through Equation of state.•Equation of State must be calibrated with VLE ...experiments for innovative fluids.•Maximum operating fluid temperature is identified through thermal stability tests.
In the last years, several fluids have been proposed to replace steam as working fluid in power cycle for converting thermal power into electricity. This paper describes the procedure to be adopted for the selection of any innovative fluid which can be even mixtures of fluids. The first step consists of the working fluid characterization in terms of thermodynamic properties through equations of state. The equations of state have to be calibrated on experimental Vapour-Liquid Equilibrium measurements while, in the second step, the maximum operating temperature is identified through thermal stability tests. Finally, the impact of the fluid thermodynamic properties on the performance of the power cycle in which it is implemented must be assessed through modelling tools. In this work, the procedure is discussed for the mixture of CO2 and C6F14 as a potential working fluid for gas thermodynamic cycles with liquid phase compression. Results of the application of this mixture in a closed cycle show the benefit of using a CO2/C6F14 mixture which provides 3% points efficiency increase at 400 °C with respect to the pure CO2 together with a preliminary design of the expander.
Undergraduate students' statistics engagement plays a vital role in their performance in introductory statistics courses. Self-efficacy and attitudes towards statistics were claimed to influence ...students' engagement. Accordingly, this study investigated the influence of self-efficacy and attitudes towards statistics on undergraduate students' statistics engagement in a Malaysian public university. This study was conducted on first year students from various fields of study enrolled in an introductory statistics course. A random sample of 293 students were selected to participate in the survey. Descriptive analysis revealed that both students' statistics engagement and self-efficacy were moderate, while their attitudes towards statistics were positive. Correlation analysis indicated that statistics engagement was significantly related to self-efficacy and attitudes towards statistics. Furthermore, multiple linear regression analysis showed that self-efficacy and attitudes towards statistics are significant predictors of statistics engagement and explained half of its' variation. Attitudes towards statistics had a greater influence on statistics engagement than self-efficacy for these students. These findings affirmed that self-efficacy and attitudes towards statistics influenced students' statistics engagement. In essence, having high self-efficacy and positive attitudes towards statistics will help stduents to be highly engaged in their learning to perform better in statistics course.
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