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Antioxidant products present a very high added value and are demanded in the market. The optimization of their extraction is a high-stakes matter for both economic and environmental points of view. Ultrasound extraction has been considered one of the most promising methods, so the relative importance of key parameters may have decisive economic significance. For this reason, different parameters that have influence on the extraction capacity such as ultrasound power, time, temperature, pH and % ethanol in water have been studied to know the relationships between the independent parameters and their influence on the extraction from Eucalyptus globulus leaves. An experimental Box-Behnken factorial design and subsequent analysis by neural networks have been used. The relative influence of each parameter varies according to the nature of the extracted compound. In this regard, the higher capacity of extraction of the selected antioxidant compounds by means of the variation of the operation conditions can be facilitated. For all the studied compounds, temperature has been the most important parameter for their extraction. The relative content (%) of bioactive compounds (terpenes) in the optimized Eucalyptus globulus extract has been performed by GC-MS analysis.

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The valorization of urban solid waste compost (MSW) in two different composting conditions (different aeration and humidity) has been studied (we work with the hypothesis that the composting process can have a significant influence on a subsequent pyrolysis process). The influence of composting on subsequent pyrolysis of the material was assessed by examining the kinetics of the process, maximizing hydrogen production and minimizing the activation energy. The thermogravimetric analysis carried out on the samples have shown that they have a greater loss of weight of 9-14% at 270-275 °C and 22-27% at 444-446 °C. Using the Kissinger-Akahira-Sunose method, the activation energy values are found to be in the range of 57.78-581.69 kJ mol-1, and the assumption that pyrolysis of compost could be modeled by a first-order reaction may be a suitable approximation. The analysis of the gases produced from the pyrolysis process revealed that hydrogen increases in concentration as composting time advances until intermediate time. In this form, the composting process could be a suitable previous treatment for improving the pyrolysis process. In fact, decreasing aeration and moisture in the MSW composting process led to the production of an increased amount of hydrogen (8.3%) by pyrolysis of the resulting compost and also to a decreased activation energy (102.8 kJ mol-1). These effects were also observed before the end of the composting process in the form of maximum hydrogen production and minimum activation energy after 20 days.

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The anodic oxidation of mercury in the presence of hydrogen peroxide in differential pulse voltammetry (DPV) was used to determine the antioxidant (AO) character of radical scavengers. Hydroperoxide radical is formed at the potentials of the oxidation peak on mercury electrodes, such radical reacting with the antioxidants in different extension. The parameter C10 (antioxidant concentration at which the peak area decreases by 10%) is used to measure the scavenging activity of the individual antioxidants. To establish the scavenging activity of antioxidant mixtures as a whole, the parameter, µ10 as the reverse of V10, V10 being the volume necessary to decrease the peak area in DPV by 10%, was selected. Higher µ10 values correspond to higher scavenging activity. The studies have been extended to aqueous extracts of some species. The results may be useful in explaining the effect of spices in vitro and in vivo studies.

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Antioxidant activity of a number of small (low molecular weight) natural compounds found in spices, condiments or drugs (gallic acid, sesamol, eugenol, thymol, carvacrol, vanillin, salicylaldehyde, limonene, geraniol, 4-hexylresorcinol, etc.) has been evaluated using electrochemical and DPPH• radical scavenging measurements. Structural analysis of the tested compound suggest a remarkable activity for phenol derivatives and the importance of the -R groups located on the phenolic ring in the molecule's ability to act as free radical scavenging as well as their influence in the electrochemical behavior. The voltammetric method can be used for the determination of the antioxidant capability in the same manner as the DPPH• radical scavenging because of the correlation found between oxidation potentials and anti-radical power (ARP = 1/EC50). Such electrochemical determination is fast and cheap and allows making measurements under a variety of experimental conditions. The accuracy of the electrochemical measurements is the same for all the compounds, irrespective of their scavenging activity, the opposite of what occurs in the DPPH• test.

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The influence of control parameters (aeration, moisture, and C/N ratio) during composting of a municipal solid waste (MSW)-legume-trimming residue (LTR) mixture was studied at a pilot plant scale. Factors measured included the composition of the main volatile organic carbons (VOCs) emitted including limonene, ß-pinene, 2-butanone, undecane, phenol, toluene, and dimethyl disulfide. Polynomial models were found to reproduce the experimental results with errors at less than 10%. The relative influence of the independent variables on temperature and selected VOCs followed the order: aeration > moisture > C/N. A high aeration rate results in higher (strong negative effect) values on selected VOCs emissions (41-71% on emitted VOCs variation). Moisture had a positive and negative effect depending on the selected VOCs. A high C/N ratio caused lower production of VOCs except for undecane and 2-butanone. Providing an aerobic environment (0.05 Lair kg(-1) min(-1)), high C/N ratios (>50), and medium moisture (55%) minimize emitted VOCs during MSW composting, ultimately resulting in less odors in the surrounding environment.

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