Search

A solid standard mixture (SSM) representing the annual composition of fresh fruits and vegetables residues generated at the Supply Center in Mexico City was used for bioethanol production. This type of residues allows bioethanol production with a single thermal pre-treatment instead of hard thermochemical or enzymatic treatments. The release of fermentable carbohydrates from the SSM by a mild thermal pretreatment was firstly optimized. After that, mixed and single cultures of Saccharomyces cerevisiae, Scheffersomyces stipitis, and Schwanniomyces occidentalis were evaluated for bioethanol production. The maximum ethanol production, 282.61 ± 13.09 L ethanol per ton of dry matter (DM), was reached using a severity factor (SF) of 2.35 and a mixed culture composed of Saccharomyces cerevisiae, Scheffersomyces stipitis, and Schwanniomyces occidentalis. The improved lab scale conditions were evaluated in a pilot scale (18 Kg) stirred bioreactor with an SF of 2.35 and the mixed culture, obtaining 245.72 ± 17.76 L ethanol per ton DM. The obtained results demonstrate for the first time the use of fresh fruits and vegetables residues for bioethanol production under solid-state culture conditions without any thermochemical or enzymatic pre-treatment.

In this work we studied two approaches for the revalorization of corn stover (CS): Feedstock for bioethanol generation and substrate for the production of biocatalysts. The practical application of two of these biocatalysts (laccases and cellulases) was also evaluated. The hydrolysis of CS was improved through a pretreatment with the thermotolerant fungus Fomes sp. EUM1; simultaneously, enzymatic extracts enriched with laccases or cellulases were obtained and applied for the pretreatment or hydrolysis of untreated CS. After 7 days, the fungal pretreatment promoted a significant increase in the release of reducing sugars (60%) and in the hydrolysis rate (50%). Lignin content decreased 61.2%, while holocellulose remained practically unchanged; a significant positive correlation (r = 0.948, p = 0.01) was found between laccase production and lignin degradation. Regarding biocatalysts application, the cellulases of Fomes sp. EUM1 showed catalytic properties similar to those of commercial enzymes; in addition, the pretreatment with laccases reduced 70% the processing-time (compared to the fungal treatment), and improved the release of reducing sugars and the hydrolysis rate by 26 and 29%, respectively. The pretreatment of CS with Fomes sp. EUM1 produces two valuable products: saccharificable biomass useful for bioethanol production and highly active enzymes applicable in bioconversion processes.

The goal of this study was to evaluate the effect of high Tween 80 concentrations on hydrocarbon contaminants and hydrocarbonoclastic microorganisms present in contaminated mining soil during a bioremediation process. The independent variables included Tween 80 concentration and process time. The elected response variables included concentration of total petroleum hydrocarbons (TPH), the chemical composition of contaminants, viable microbial count, and CO2 production. These were measured at various time points during the bioremediation process, which was conducted at room temperature. Higher removal of pollutants occurred at low Tween 80 concentrations. An analysis of the normalized variables shows that the rate of TPH degradation depended on microbial growth rate, which depended on Tween 80 concentration. The addition of Tween 80 changed the concentration and type of the residual hydrocarbon contaminants present, as well as the count and genus of the hydrocarbonoclastic microorganisms that grew during the bioremediation process. Higher concentrations of Tween 80 increased the levels of the chemical compounds present in the bioremediated soil while reducing the viable count and microbial diversity during the bioremediation process. Conversely, low Tween 80 concentrations produced only monoethylhexyl phthalate, which is not a petroleum hydrocarbon derivative. Overall, these results prove that the removal of TPH is dependent on the count and genus of active indigenous hydrocarbonoclastic microorganisms in soil, and these conditions may be controlled by modulating the concentration of Tween 80 that is applied.

Agave is a good source of polysaccharides for the production of fermentable sugars as sustainable bioenergy feedstock solutions for semi-arid and arid lands. This plant grows in arid areas, which correspond to a large territory in northern Mexico. Having lignocellulose as the polysaccharide of interest, the information for the enzymatic saccharification of this kind of material is limited. Agave cell walls have a unique recalcitrant nature, but having a high cellulose content, makes this plant material an interesting research subject. In this work, acidic, alkaline and aqueous pretreatments were evaluated to generate a biomass rich in cellulose. The saccharification of pretreated Agave leaves-residue was evaluated under experimental designs to identify the most suitable conditions for enzymatic hydrolysis. Maximum value obtained was 31% glucose, which further increased to 41.4% at extended hydrolysis time of 96 h. The highest cellulose-saccharification reached was up to 61.81%, making Agave atrovirens an alternative for bioethanol production in its geographical area of cultivation.

Imagining motor actions is enough to enhance cortical motor excitability. However, the fact that execution of the motor task has to be inhibited should have a correlate on the extent of cortical excitability enhancement. Therefore, we examined the possible differences between real and motor imagery of simple reaction time tasks (SRT) in the facilitation of the motor-evoked potential (MEP) to transcranial magnetic stimulation (TMS) and in the reduction of short-interval intracortical inhibition (SICI) taking place before the movement onset. Thirteen healthy volunteers were requested to perform visual real or imaginary SRT tasks (rSRT and iSRT) with their dominant hand. For rSRT, subjects had to perform a rapid isometric squeeze as soon as possible after the imperative signal. For iSRT they had to imagine the same movement without actually doing it. Electromyographic (EMG) signals were recorded from the first dorsal interosseus (FDI) muscle. The mean EMG onset was calculated for each subject in rSRT trials. Single-and paired-pulse TMS (at an interstimulus interval of 2.5 ms) were applied at rest and at time intervals of -25, -50, -75, -100 and -125 ms before the expected real (rSRT) mean EMG onset. In rSRT there was a significant increase of MEP to single-pulseTMS at the intervals of -50 and -25 ms, and in iSRT at -50 ms in comparison to the rest condition. % SICI changes were significantly reduced at the intervals of -75, -50 and -25 ms, before EMG the onset in rSRT and at -50 and -25 in iSRT (P < 0.05) in comparison to % SICI changes at rest. The differences between MEPs to spTMS and MEP to ppTMS were significantly larger at rest, -125 and -100 ms intervals in rSRT, and at all intervals in iSRT. Imagining to move causes an increase in corticospinal excitability and a decrease in intracortical inhibition that follow a temporal profile similar to those observed with real movements. However, complete removal of SICI happened only in rSRT at the shortest intervals before the EMG onset. Such action may delineate new tool in motor rehabilitation of patients who have limitation to move.