Papers by Alfonso Robles Medina
of structured triacylglycerols by acidolysis catalyzed by
Journal of Chemical Technology & Biotechnology, 1996
The effects of temperature (25-40°C), H,SO, concentration (31-70% (w/v)) and the acid/substrate r... more The effects of temperature (25-40°C), H,SO, concentration (31-70% (w/v)) and the acid/substrate relationship (1-5 cm3 of H,SO, per g-' of cellulose) on the solubilization rate of microcrystalline cellulose and on the glucose production rate have been analysed. The solubilization process was by determining reducing groups present in solution. For acid/substrate relationships of more than 1 cm3 g-' and H,SO, concentrations of greater than 62% (w/v), the acid promoted the total solubilization of the cellulose in the form of chains with a low degree of polymerization within 4 h. The solubilization demonstrated zero-order kinetics in which the specific rate and time of total solubilization are a function of the variables in operation. Glucose was produced according to a mechanism of two consecutive first-order pseudo-homogeneous reactions. The values of the kinetic constants k , and k, have been correlated with temperature, the H,SO, concentration and the acid/substrate relationship.
En esta memoria se da cuenta de los resultados obtenidos al estudiar la hidrolisis enzimatica y a... more En esta memoria se da cuenta de los resultados obtenidos al estudiar la hidrolisis enzimatica y acida de una celulosa microcristalina comercial. En una primera etapa se ha estudiado la hidrolisis enzimatica con celulosas de t. Viride ph = 4 9 y 40 grados c de carboximetilcelulosa y se ha puesto de manifiesto la existencia de un sinergismo entre los endo y exoglucanasas que componen el complejo celulolitico. Ademas se han reproducido los resultados experimentales en ausencia de sinergismo mediante un modelo de dos reacciones en serie y con inhibicion competitiva por producto. De los pretratamientos ensayados (fetna zincoxen naoh 1 5m y so4h2 del 70%) el mas eficaz con gran diferencia es el realizado con so4h2 del 70% ya que solubiliza a la celulosa debido a la existencia de una prehidrolisis acida. Debido a este hecho se ha estudiado la influencia de la concentracion del acido (31% a 70%) de la temperatura (25 a 40 grados c y de la relacion disolvente/ sustrato 1 0 a 5 ml/g (d/s) sob...
European Journal of Lipid Science and Technology, 2001
The free fatty acids eicosapentaenoic acid (C20:5ω3, EPA) and docosahexaenoic acid (C22:6ω3), obt... more The free fatty acids eicosapentaenoic acid (C20:5ω3, EPA) and docosahexaenoic acid (C22:6ω3), obtained from the microalgae Phaeodactylum tricornutum, and the EPA methyl ester were compared with regard to their extent of peroxidation using different storage conditions. Several series were stored according to selected variables: hexane addition versus no addition, 4 °C versus 25 °C, and antioxidant addition (octyl gallate) versus no antioxidant addition, always in the dark. Previously, the EPA and methyl EPA structures were confirmed by NMR spectra to discard the formation of conjugated dienes after the downstream process. The results showed that the stability was higher for methyl EPA than for the free fatty acid, and that peroxidation can be retarded by low temperature storage and mainly by hexane addition. The peroxidation process was evaluated by the peroxide value (spectrophotometric method by iodine absorption), although the conjugated diene absorbance and the loss in percentage of the fatty acid have been tested as good indicators of the peroxidation process. A simple kinetic model that explains the peroxidation process during the initiation and propagation steps is given.
Biomass Conversion and Biorefinery, 2022
Current research indicates that n-3 polyunsaturated fatty acids (PUFAs) bind to polar lipids (pho... more Current research indicates that n-3 polyunsaturated fatty acids (PUFAs) bind to polar lipids (phospholipids and glycolipids) seem to exert a greater bioavailability compared to their neutral forms. The aim of this work was to obtain eicosapentaenoic acid (EPA) rich polar lipids from the saponifiable lipids (SLs) extracted from the microalga Nannochloropsis sp. (33.4 ± 0.1% of EPA; 60 ± 0.6% polar lipids) by fractionation using silica-gel columns and importantly, non-polar and polar (ethanol) non-toxic solvents. Nowadays, few studies have been conducted towards the extraction and purification of polar lipids. Firstly, the solvent type for obtaining the neutral saponifiable lipid (NSL) fraction (ethyl acetate, EA, butyl acetate, BA) and the SL/silica-gel, SL/BA, and SL/ethanol ratios were optimized in a small silica-gel cartridge (0.69 g silica gel). The optimized conditions were an SL/silica-gel ratio of 22.6 mg/g, an SL/BA ratio of 1.56 mg/mL and an SL/ethanol ratio of 0.312 mg/mL. ...
Numero de publicacion: ES2292341 A1 (01.03.2008) Tambien publicado como: ES2292341 B1 (16.03.2009... more Numero de publicacion: ES2292341 A1 (01.03.2008) Tambien publicado como: ES2292341 B1 (16.03.2009) Numero de Solicitud: Consulta de Expedientes OEPM (C.E.O.)P200600777 (13.03.2006)
Numero de publicacion: ES2120898 A1 (01.11.1998) Tambien publicado como: ES2120898 B1 (16.05.1999... more Numero de publicacion: ES2120898 A1 (01.11.1998) Tambien publicado como: ES2120898 B1 (16.05.1999) Numero de Solicitud: Consulta de Expedientes OEPM (C.E.O.) P9602090 (04.10.1996)
Algal Research, 2020
Saponifiable lipids (SLs), rich in eicosapentaenoic acid (EPA), were extracted and purified from ... more Saponifiable lipids (SLs), rich in eicosapentaenoic acid (EPA), were extracted and purified from Nannochloropsis gaditana biomass. Firstly, the SLs were extracted using ethanol (96% v/v). The influence of the following operational variables was studied: water content of the wet biomass, solvent/biomass ratio, homogenization pressure and temperature. SL yields of 92-99 wt% and 80-90 wt% were achieved from dry and wet biomass, respectively, under various operational conditions from batches with different SL contents and lipid profiles. These SLs were extracted with only a 20-22 wt% purity, which was increased to 42% (100 wt% yield) by extracting the SLs with hexane. In this hexane extraction step, it was important to extract the SLs from a highly concentrated hydroethanolic solution. The SL purity was further increased to 95 wt% by acetone crystallization. Throughout this extraction-purification process, SLs were fractionated into neutral lipids, glycolipids and phospholipids-neutral lipids were recovered with higher yields than were glycolipids and phospholipids. The energy consumption per unit mass of extracted lipids was estimated, along with the solvent recovery, and compared for the dry and wet methods. When wet biomass was used, the presence of water significantly increased the energy required for ethanol. However, when cost and capacity of the main equipment (freeze-dryer, homogenizer and centrifuge) were considered, SL extraction from high pressure homogenized wet biomass resulted in a lower economic cost.
Biomass and Bioenergy, 2016
The aim of this work was to optimize the production of fatty acid methyl ester (FAME, biodiesel) ... more The aim of this work was to optimize the production of fatty acid methyl ester (FAME, biodiesel) from wet Nannchloropsis gaditana microalgal biomass by direct enzymatic transesterification. This was done in order to avoid the high cost associated with the prior steps of drying and oil extraction. Saponifiable lipids (SLs) from microalgal biomass were transformed to FAME using the lipase Novozyme 435 (N435) from Candida antarctica as the catalyst, and finally the FAME were extracted with hexane. t-Butanol was used as the reaction medium so as to decrease lipase deactivation and increase mass transfer velocity. A FAME conversion of 99.5% was achieved using wet microalgal biomass homogenized at 140 MPa to enhance cell disruption, a N435:oil mass ratio of 0.32, methanol added in 3 stages to achieve a total of 4.6 cm 3 g À1 of oil and 7.1 cm 3 g À1 oil of added t-butanol, with a reaction time of 56 h. The FAME conversion decreased to 57% after catalyzing three reactions with the same lipase batch. This work shows the influence of the polar lipids contained in the microalgal biomass both on the reaction velocity and on lipase activity.
Bioresource Technology, 2016
h i g h l i g h t s Saponifiable lipids (SLs) were extracted from wet biomass using ethanol and h... more h i g h l i g h t s Saponifiable lipids (SLs) were extracted from wet biomass using ethanol and hexane. Intracellular R. oryzae lipase catalyzed the methanolysis of microalgal SLs. Biodiesel yield and lipase reuse were higher using SLs poorer in polar lipid. Biodiesel yield and lipase reutilization were higher in tertbutanol than in hexane. 83% of microalgal SLs were transformed to biodiesel in the optimized conditions.
Bioresource Technology, 2016
In order to obtain microalgal saponifiable lipids (SLs) fractions containing different polar lipi... more In order to obtain microalgal saponifiable lipids (SLs) fractions containing different polar lipid (glycolipids and phospholipids) contents, SLs were extracted from wet Nannochloropsis gaditana microalgal biomass using seven extraction systems, and the polar lipid contents of some fractions were reduced by low temperature acetone crystallization. We observed that the polar lipid content in the extracted lipids depended on the polarity of the first solvent used in the extraction system. Lipid fractions with polar lipid contents between 75.1% and 15.3% were obtained. Some of these fractions were transformed into fatty acid methyl esters (FAMEs, biodiesel) by methanolysis, catalyzed by the lipases Novozym 435 and Rhizopus oryzae in tert-butanol medium. We observed that the reaction velocity was higher the lower the polar lipid content, and that the final FAME conversions achieved after using the same lipase batch to catalyze consecutive reactions decreased in relation to an increase in the polar lipid content.
The aim of this work was to produce structured triacylglycerols (STAGs), with caprylic acid locat... more The aim of this work was to produce structured triacylglycerols (STAGs), with caprylic acid located at positions 1 and 3 of the glycerol backbone and docosohexaenoic acid (DHA) at position 2, by acidolysis of tuna oil and caprylic acid (CA) catalyzed by lipases Rd, from Rhizopus delemar, and Palatase 20000L from Mucor miehei immobilized on Accurel MP1000 in a packed bed reactor (PBR), working in continuous and recirculation modes. First, different lipase/support ratios were tested for the immobilization of lipases and the best results were obtained with ratios of 0.67 (w/w) for lipase Rd and 6.67 (w/w) for Palatase. Both lipases were stable for at least 4 days in the operational conditions. In the storage conditions (5 °C) lipases Rd and Palatase maintained constant activity for 5 months and 1 month, respectively. These catalysts have been used to obtain STAGs by acidolysis of tuna oil and CA in a PBR operating with recirculation of the reaction mixture through the lipase bed. Thus,...
The aim of this work was to obtain biodiesel (methyl esters) from the saponifiable lipids (SLs) f... more The aim of this work was to obtain biodiesel (methyl esters) from the saponifiable lipids (SLs) fraction of the microalga Nannochloropsis gaditana, whose biomass dry weight contains 12.1 wt% of these lipids. SLs were extracted from the microalga as free fatty acids (FFAs) for subsequent transformation to methyl esters (biodiesel) by enzymatic esterification. Extraction as FFAs rather than as SLs allows them to be obtained with higher purity. Microalgal FFAs were obtained by direct saponification of lipids in the biomass and subsequent extraction-purification with hexane. Esterification of FFAs with methanol was catalysed by lipase Novozym 435 from Candida antarctica. Stability studies of this lipase in the operational conditions showed that the esterification degree (ED) attained with the same batch of lipase remained constant over six reaction cycles (36 h total reaction time). The optimal conditions attained for 4 g of FFAs were 25°C, 200 rpm, methanol/FFA molar ratio of 1.5:1, No...
Journal of Applied Phycology
Journal of Molecular Catalysis B: Enzymatic, 2015
Applied Phycology and Biotechnology, 2013
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Papers by Alfonso Robles Medina