Time filter

Source Type

Toscano L.,Autonomous University of Baja California | Toscano L.,Technological Institute of Mexicali | Montero G.,Autonomous University of Baja California | Cervantes L.,Autonomous University of Baja California | And 3 more authors.
Biotechnology and Biotechnological Equipment | Year: 2013

The growing interest in lipase production is related to the potential biotechnological applications that these enzymes present. Current studies on lipase production by solid state fermentation involve the use of agro-industrial residues, aiming at increasing the economic attractiveness. Based on these aspects, the objective of this work was to investigate lipase production by a local strain Trichoderma harzianum in solid-state fermentation (SSF), using wheat bran as a solid substrate, and compare this lipase production with submerged fermentation (SmF) using a mineral culture medium. The maximum lipase activity, 1.82 U·mL-1 ± 0.01 U·mL-1, was obtained during submerged fermentation in a medium containing 2% sucrose and 2% olive oil. However, 71.3 U·g-1 ± 1.48 U·g-1 of dry solid substrate equivalent to 14.3 U·mL-1 of lipase activity was reached using a solid-state fermentation process with a medium containing 0.75 % ammonium sulphate and 0.34 % urea, 2 % olive oil and wheat bran as a solid substrate. The pH and temperature optima for lipase were 8.03 and 40 °C, respectively. The Michaelis constant (KM = 6.6 mmol·L-1) was obtained from two different plots, i.e. Lineweaver-Burk and Hanes-Woolf. Vmax of the enzyme reaction was found to be 7.5 U·mL-1.

Toscano L.,Autonomous University of Baja California | Toscano L.,Technological Institute of Mexicali | Montero G.,Autonomous University of Baja California | Stoytcheva M.,Autonomous University of Baja California | And 7 more authors.
Biotechnology and Biotechnological Equipment | Year: 2013

Extracellular lipase production by Penicillium chrysogenum, Trichoderma harzianum and Aspergillus flavus was carried out through solid state fermentation using agro-industrial residues as substrates. For all three strains, the growth temperature was 29±1 °C, and 65 % w (g/gds) moisture content. The effect of three factors on lipase production rate was investigated: initial pH (6.0 and 7.0), time of fermentation (72 h, 96 h and 120 h), and type of mixed substrate (wheat bran-olive oil, and wheat bran-castor oil cake). The process was optimized applying a mixed level factorial design. Fermentation time and pH were found to have positive effects on lipase production and secretion rates. However, the time effect was larger than initial pH. Type of substrate demonstrated minor effective importance than the other two factors, and Aspergillus flavus showed the larger lipase production among the three strains. Results indicated that the three fungal strains were able to grow and produce lipase in both culture mediums. The maximum lipase activity achieved was 121.35 U/gds by Aspergillus flavus, which was five and nine times the lipase produced by Trichoderma harzianum and P. chrysogenum respectively, at the same conditions. An initial neutral pH and 96 h of fermentation time were the optimum conditions for lipase production by Aspergillus flavus. © Biotechnol. & Biotechnol. Eq.

Stoytcheva M.,Autonomous University of Baja California | Zlatev R.,Autonomous University of Baja California | Gonzalez Navarro F.F.,Autonomous University of Baja California | Velkova Z.,Medical university-Plovdiv | And 5 more authors.
Analytical Methods | Year: 2016

The development of highly sensitive amperometric biosensors for dopamine determination using commercially available SPEs in combination with the PVA-AWP photopolymer as the enzyme immobilization matrix is described in this work. This research focuses on (i) the optimization of the conditions for SPE biofunctionalization by tyrosinase entrapment in PVA-AWP and of the working conditions for dopamine determination by mathematical model application, and (ii) the evaluation of the analytical performances of the PVA-AWP/tyrosinase functionalized SPEs. Dopamine determination under optimum conditions for electrode biofunctionalization (PVA-AWP 3%, 60 min UV light exposure) and under optimum working conditions (pH 6.5, 25 °C) was performed in the dynamic concentration range of 0.9-500 μmol L-1, 0.2-400 μmol L-1, and 0.03-150 μmol L-1, using respectively C SPE, MWCNT-GNP/C SPE, and graphene-GNP/C SPE. The LOD was found to be 300 nmol L-1, 60 nmol L-1, and as low as 10 nmol L-1, correspondingly. The excellent analytical performances of the graphene-GNP C SPE and MWCNT-GNP C SPE were associated with their large active area (19.72 mm2 and 15.3 mm2) and enhanced electrocatalytic properties (ko = 8.1 × 10-3 cm s-1 and 4.4 × 10-3 cm s-1) compared with the bare C SPE (12.47 mm2 and ko = 3.0 × 10-3 cm s-1). The developed biosensors were stable, reproducible, and more sensitive than most of the known biosensors for dopamine determination. They were successfully applied for dopamine determination in injections. Taking into consideration the fact that the selected enzyme immobilization approach using a water-soluble photopolymer opens the possibility of SPE biofunctionalization by photolithography, the developed biosensors are promising for fast, simple, sensitive, selective, and cost effective analysis of dopamine. © The Royal Society of Chemistry 2016.

Toscano L.,Autonomous University of Baja California | Toscano L.,Technological Institute of Mexicali | Montero G.,Autonomous University of Baja California | Stoytcheva M.,Autonomous University of Baja California | And 2 more authors.
Biotechnology and Biotechnological Equipment | Year: 2014

Four hydrophilic polymers in the form of beads - chitosan, alginate, alginate/polyvinyl alcohol (PVA), and chitosan-coated alginate - were used as supports for lipase immobilisation. Hydrogel beads were characterised by bead-size-distribution estimation, surface morphology studies, and polymer interactions assessment. Matrix performances - loading efficiency, immobilisation yield, enzyme activity, and stability retention - were evaluated and compared. Although the loading efficiency of the chitosan-coated Ca-alginate beads (79.8%) was inferior to that of the Ca-alginate (87%) and of the Caalginate/PVA beads (81.3%), their enzyme immobilisation yield (63.96%) was the most important. Moreover, lipase encapsulated in chitosan-coated Ca-alginate beads demonstrated better pH, thermal, and storage (89% residual activity after 30 days) stabilities. Immobilised lipase activity also increased in the order: alginate/PVA > chitosan > alginate > alginate/chitosan, and displayed a maximum at pH 8 and at temperatures of 45 °C (chitosan and Ca-alginate/PVA beads) and 50 °C (Ca-alginate and chitosan-coated Ca-alginate beads). Thus, chitosan-coated Ca-alginate beads could be considered as a suitable support for lipase immobilisation. © 2014 The Author(s).

Flores-Fuentes W.,Engineering Faculty | Rodriguez-Quinonez J.C.,Engineering Faculty | Hernandez-Balbuena D.,Engineering Faculty | Rivas-Lopez M.,Autonomous University of Baja California | And 5 more authors.
IEEE International Symposium on Industrial Electronics | Year: 2015

Machine vision methods to provide spatial coordinates measurement has developed in a wide range of technologies for multiples fields of applications such as robot navigation, medical scanning, and structural monitoring. Each technology with specified properties that could be categorized as advantage and disadvantage according its utility to the application purpose. This paper presents the photodiode and charge coupled device sensors fusion as the base for those systems with non-lineal behavior supported by artificial intelligence techniques, which require the use of information from various sensors for pattern recognition to produce an enhanced output. © 2015 IEEE.

Discover hidden collaborations