Remarkable change in the broadband electrical behavior of poly(vinylidene fluoride)–multiwalled carbon nanotube nanocomposites with the use of different processing routes

Poly(vinylidene fluoride) (PVDF) nanocomposites have plenty of applications in the electronic realm. In this study, we produced nanocomposites based on PVDF and multiwalled carbon nanotubes (MWCNTs), with various MWCNT loadings, using three different processing routes: solution mixing, melt mixing, and electrospinning. The broadband electrical behavior of these nanocomposites was studied and compared via impedance spectroscopy. The morphologies of the nanocomposites were characterized by transmission electron microscopy and scanning electron microscopy. The results reveal that the electrical behaviors of the samples were completely different according to the processing route used. Solution mixing was the most suitable method for producing nanocomposites with the highest conductivities, at low MWCNT loadings, whereas electrospinning was the most suitable method for producing nanocomposites with the lowest dielectric permittivity. These differences were attributed to the different arrangements of the MWCNTs caused by the different processes. Although the solution-mixed samples exhibited long and twisted MWCNTs, the melt-mixed samples had shorter MWCNTs, and the electrospun samples had MWCNTs embedded and aligned inside the insulating polymer nanofibers. Thus, these results project a vast horizon for tailoring the structure and thereby the broadband electrical behavior of PVDF–MWCNT nanocomposites for different types of applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47409.     

Critical water activity for the preservation of Lactobacillus bulgaricus by vacuum drying

Lactobacillus delbrueckii subsp. bulgaricus was dried under vacuum at different temperatures and its preservation evaluated analyzing the evolution of three parameters throughout the process: lag time, percentage of membrane damage and zeta potential. Microorganisms were dehydrated at 30, 45 and 70 degrees C in a vacuum centrifuge for different times. The aw achieved for each time of drying was correlated with the cell recovery at all the temperatures assayed. The recovery of microorganisms was evaluated by means of: a) kinetics of growth in milk after drying, as a measure of the global damage; b) quantification of the membrane damage using the fluorescent dyes SYTO 9 and PI; c) determination of changes in the superficial charges (zeta potential) as measured of the increase in the hydrophobic residues exposed in the bacterial surface after dehydration. These changes correlate well with the bacterial damage occurred during the dehydration process. The Page's equation allowed fitting of aw and time of drying, thus making possible the determination of the appropriate dehydration conditions (time-temperature ratios) for which no cell damage occurs. The evaluation of three parameters (lag time, percentage of membrane damage and zeta potential) allowed us to conclude that at the lowest temperature of dehydration, the first target of damage is the cell membrane. However, this damage is not decisive for the bacterial recovery after rehydration, as are the increase in the lag time and the changes in the zeta potential, as was observed for L. bulgaricus dehydrated at 45 and 70 degrees C for larger times.     

Characterization of tannase activity in cell-free extracts of Lactobacillus plantarum CECT 748T

In foods, tannins are considered nutritionally undesirable. Spectrophotometric methods have been used to detect tannin degradation by L. plantarum strains isolated from food substrates. Enzymatic degradation of tannic acid by L. plantarum CECT 748T was examined in liquid cultures and in cell-free extracts by HPLC. Significative reduction of tannic acid was not observed during incubation in the presence of L. plantarum cells after 7 days incubation. However, tannic acid was effectively degraded by cell-free extracts of L. plantarum during 16 h incubation. We have partially characterized L. plantarum tannase activity by measuring its esterase activity on methyl gallate. Tannase activity was optimal at pH 5.0 and 30 degrees C, and showed nearly 75% of the maximal activity at 50 degrees C. The biochemical characteristics showed by L. plantarum tannase are considered favourable for tannin biodegradation in the food-processing industry.     

Enhanced bactericidal effect of enterocin AS-48 in combination with high-intensity pulsed-electric field treatment against Salmonella enterica in apple juice

The effect of the broad spectrum cyclic antimicrobial peptide enterocin AS-48 combination with high-intensity pulsed-electric field (HIPEF) treatment (35 kV/cm, 150 Hz, 4 micros and bipolar mode) was tested on Salmonella enterica CECT 915 in apple juice. A response surface methodology was applied to study the bactericidal effects of the combined treatment. The process variables were AS-48 concentration, temperature, and HIPEF treatment time. While treatment with enterocin AS-48 alone up to 60 microg/ml had no effect on the viability of S. enterica in apple juice, an increased bactericidal activity was observed in combination with HIPEF treatments. Survival fraction was affected by treatment time, enterocin AS48 concentration and treatment temperature. The combination of 100 micros of HIPEF treatment, 30 microg/ml of AS-48, and temperature of 20 degrees C resulted in the lowest inactivation, with only a 1.2-log reduction. The maximum inactivation of 4.5-log cycles was achieved with HIPEF treatment for 1000 micros in combination with 60 microg/ml of AS-48 and a treatment temperature of 40 degrees C. Synergism between enterocin AS-48 and HIPEF treatment depended on the sequence order application, since it was observed only when HIPEF was applied in the presence of previously-added bacteriocin. The combined treatment could improve the safety of freshly-made apple juice against S. enterica transmission.     

Free radical-scavenging activity of nonenzymatically-browned phospholipids produced in the reaction between phosphatidylethanolamine and ribose in hydrophobic media

The reaction of phosphatidylethanolamine (PE) and ribose (RI) in olive oil was studied in an attempt to both explore the possibilities of producing Maillard reaction in hydrophobic media and analyse the antioxidant properties of the formed compounds. When oil samples containing PE/RI mixtures were heated at a temperature higher than 90 °C, the oil rapidly developed browning, fluorescence, and free radical-scavenging activity, which was higher than the developed by the oil in the absence of added compounds or in the presence of only either PE or RI. These changes were a consequence of the formation of Maillard reaction products in the oil by reaction between PE and RI. Among them, the N-alkylpyrrole derivatives produced in this reaction could be determined by GC–MS after transpyrrolisation. Differently to Maillard products formed between carbohydrates and amino acids, the products of the reaction with aminophospholipids are more hydrophobic and, therefore, better candidates to be employed as lipophilic antioxidants in food products. Because of the different polarity of Maillard products between carbohydrates and either amino acids or aminophospholipids, Maillard reaction can be a useful procedure to obtain a wide range of antioxidants with different polarities to be employed in different food systems.     

A Topical Formulation of Melatoninergic Compounds Exerts Strong Hypotensive and Neuroprotective Effects in a Rat Model of Hypertensive Glaucoma

Melatonin is of great importance for regulating several eye processes, including pressure homeostasis. Melatonin in combination with agomelatine has been recently reported to reduce intraocular pressure (IOP) with higher efficacy than each compound alone. Here, we used the methylcellulose (MCE) rat model of hypertensive glaucoma, an optic neuropathy characterized by the apoptotic death of retinal ganglion cells (RGCs), to evaluate the hypotensive and neuroprotective efficacy of an eye drop nanomicellar formulation containing melatonin/agomelatine. Eye tissue distribution of melatonin/agomelatine in healthy rats was evaluated by HPLC/MS/MS. In the MCE model, we assessed by tonometry the hypotensive efficacy of melatonin/agomelatine. Neuroprotection was revealed by electroretinography; by levels of inflammatory and apoptotic markers; and by RGC density. The effects of melatonin/agomelatine were compared with those of timolol (a beta blocker with prevalent hypotensive activity) or brimonidine (an alpha 2 adrenergic agonist with potential neuroprotective efficacy), two drugs commonly used to treat glaucoma. Both melatonin and agomelatine penetrate the posterior segment of the eye. In the MCE model, IOP elevation was drastically reduced by melatonin/agomelatine with higher efficacy than that of timolol or brimonidine. Concomitantly, gliosis-related inflammation and the Bax-associated apoptosis were partially prevented, thus leading to RGC survival and recovered retinal dysfunction. We suggest that topical melatoninergic compounds might be beneficial for ocular health.     

Optimal design of an integrated renewable-storage energy system in a mixed-use building

The rise of mixed-use buildings contributes to the sustainable development of cities but are still met with challenges in energy management due to the lack of energy efficiency and sustainability guidelines. The use of integrated renewable-storage energy systems is a more beneficial solution to this problem over individual solutions; however, most design studies only focused on single-type buildings. Thus, this study aims to optimally design an integrated energy system for mixed-use buildings using HOMER Grid. The objective is to minimize the net present costs, subject to capacity limits, energy balances, and operational constraints. Economic metrics were used to evaluate and compare the proposed system to the varying design cases such as business-as-usual, stand-alone renewable source, and stand-alone energy storage. The case study considered a mixed-use building in a tropical area, with a solar photovoltaic system as the renewable energy source and lithium-ion battery as the energy storage system technology. The results show that the integrated system is the most financially attractive design case. It has a levelized cost of electricity of 0.1384 US$ kWh⁻¹, which is significantly less than the 0.2580 US$ kWh⁻¹ baseline. The system also provides electricity cost savings of 294 698 US$ y⁻¹, excess electricity of 35 746 kWh, and carbon emission reduction of 550 tons annually for a mixed-use building with daily average consumption of 4557-kWh and 763-kW peak demand.