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Biomedical subjects

R Guillén

Publications and source records attributed to R Guillén.

15 recordsLinked to original sources
PubMed2001

Steam-explosion of olive stones: hemicellulose solubilization and enhancement of enzymatic hydrolysis of cellulose.

Olive stones (whole stones and seed husks in fragments) were processed by steam-explosion under different experimental conditions of temperature and time, 200-236 degrees C for 2-4 min, with or without previous acid impregnation with 0.1%, H2SO4 (w/w). This paper examines the solubilization of hemicelluloses and their molecular weight distribution. The subsequent enzymatic hydrolysis of the solid residue, using a preparation of cellulase, was also studied. The maximum yield of the pentosan recovered in the water solution was 63% pentose in the starting material for seed husk treated at 200 degrees C for 2 min (log R0 3.24) prior to acid-impregnation, or at 215 degrees C for 2 min (log R0 3.69) without acid, compared to 39% of the potential yield for whole stones pre-impregnated with acid under more severe conditions (at log R0 = 4.07). This indicates that the autohydrolysis of hemicellulose in seed husks when compared to whole stones is enhanced. The molecular weight distribution of profile sugars showed that the depolymerization of hemicelluloses is a function of the severity of the treatment. Steam-explosion improved the accessibility of the cellulose and increased the enzymatic hydrolysis yield after steam-explosion with respect to material without steam explosion (ball-milled material), although little increase in the extent of saccharification occurred when the alkali-soluble lignin was removed. Only when the substrate was post-treated with Na-chlorite was the enzymatic hydrolysis improved, the water-insoluble residue being almost completely hydrolyzed in 8 h of incubation.

Atmospheric Pressure↗
PubMed2001

Olive fruit cell wall: degradation of pectic polysaccharides during ripening.

Olive fruits at three stages of ripening (green, cherry, and black) have been studied. After cell wall isolation, the compositions of the cell wall and that of the phosphate-soluble polysaccharides were determined. In cell walls, decreases in arabinose, xylose, glucose, and uronic acid levels were observed, together with a slight increase in mannose on ripening. At the beginning of ripening, fragments of pectic polymers were the major constituents of the phosphate-soluble fraction, with the hemicellulosic ones increasing toward the end of the process. The molecular weight of the fragments solubilized was approximately 6 kDa. After cell wall fractionation, the pectic polysaccharides soluble in imidazole and sodium carbonate were also studied. In both fractions, between the green and cherry stages of ripening, a significant loss of homogalacturonans took place. Between the cherry and black stages of ripening, rhamnogalacturonan side chains were also released in addition to homogalacturonans. In any of the pectic fractions, changes in apparent molecular weight were quantified.

Arabinose↗
PubMed2001

Olive fruit cell wall: degradation of cellulosic and hemicellulosic polysaccharides during ripening.

Cellulose and hemicelluloses obtained from the cell walls of partially depectinated olives have been studied at three stages of ripening (green, cherry, and black). Hemicelluloses were fractionated into two groups, the amounts of which diminished during ripening: those soluble in 4% KOH diminished between the cherry and black stages, whereas those soluble in 24% KOH did so between the green and cherry stages. Arabinoxylans, xyloglucans, and homo- and/or rhamnogalacturonans to a lesser extent were present in these fractions. After ion exchange and size exclusion chromatographies, decreases in the molecular weights of hemicelluloses, mainly in the neutral fractions, were observed. The amount of cellulose also decreased, but at the second stage of the ripening process. Approximately 2 mg/fruit of glucose was lost from cellulose, and the amount of uronic acids increased (0.23 mg/fruit).

Cell Wall↗
PubMed2000

Microwave processing for scanning electron microscopy.

The normal processing of biological samples for Scanning Electron Microscopy, includes treatment with aldehyde (1 to 2 hours), postfixation with Osmium (1 hour), followed by dehydration in a ascending grade of ethanol (30 a 100%), 10 to 15 minutes in each step, and finally drying. This procedure takes at least 8 hours. In this work, samples of mosquitoes (Aedes), protozoa (Tritrichomonas muris), bacteria (Clostridium oceanicum), murine liver, and small intestine were processed in the same manner in a domestic microwave oven for two minutes at 20% of its maximum power. The complete procedure from the initial fixation to dehydration in 100% ethanol was reduced to one hour with good preservation of the ultrastructural details of the specimens.

Aedes↗
PubMed1999

Postharvest changes in white asparagus cell wall during refrigerated storage.

The postharvest changes of the white asparagus cell wall have been studied in relation to the toughening process along the length of a spear that was divided into three sections: apical, middle, and basal. Polysaccharides underwent significant turnover during storage. Uronic acid concentration decreased in all sections and in almost all polysaccharide fractions, while neutral sugars increased very slightly in the apical section, decreased in the middle, and increased in the basal one. Xylose, glucose, and galactose are the main neutral sugars implicated in the turnover; xylose accumulated in the hemicellulose fractions of the middle and basal sections, glucose decreased in the hemicellulose and cellulose fractions of the middle section and increased in the cellulose fraction of the basal one, and galactose disappeared mostly from the cellulose fractions of the three sections. Lignin increased most in the middle section and least in the basal one. No increase was detected in the apical one. No important increases of wall phenolics were detected in any part of the spear. The hardening process was limited only to the basal section.

Cell Wall↗
PubMed1999

Turnover of white asparagus cell wall polysaccharides during postharvest storage.

The main polysaccharides involved in asparagus cell wall turnover have been identified. Homogalacturonans are lost from both the apical and basal sections of the spear. Galactans are mobilized from the cellulose residue of the apical section and recovered in the KOH-soluble fractions while they are lost from the cellulose residue of the basal section. Xyloglucans are incorporated in the apical region and degraded from the basal one. Cellulose is incorporated in the basal region and lost from the apical one, and acidic xylans are incorporated in high amounts in the basal section of the spear.

Agriculture↗
PubMed1998

Degradation of pectic polysaccharides in pickled green olives.

The changes that occur in the pectic fractions in the cell wall of olives of the Manzanilla variety (Olea europaea pomiformis) during processing (initial treatment at high pH and subsequent lactic fermentation) have been researched. After studying various conditions for fractionating the pectic polysaccharides, the most adequate were chosen, involving sequential extraction with water, imidazole-hydrochloric acid buffer, sodium carbonate, 1 M potassium hydroxide, and 4 M potassium hydroxide. In the unprocessed fruit, the fractions studied consist mainly of high-molecular-weight acidic polysaccharides (70 to 250 kDa): homogalacturonans, rhamnogalacturonans, and branched arabinans. These were found in different proportions depending on the extraction agent used. At the same time, significant amounts of relatively low-molecular-weight (10 to 10.5 kDa) neutral branched arabinans were found in the water-soluble fraction. As a result of the processing, changes occurred in the proportions of the different groups of polysaccharides in accordance with changes in their solubility characteristics. These changes were reflected in the processed fruit by (i) and increase in the neutral branched arabinans in the water-soluble fraction due to the increased presence of such polysaccharides originally found in the carbonate and 4 M KOH-soluble fractions; (ii) an increase in homogalacturonans and rhamnogalacturonans, without significant changes in molecular weights, in the imidazole-soluble fraction as a result of the increased presence of corresponding polysaccharides originally found in the carbonate-soluble and water-soluble fractions; (iii) a substantial increase in uronic acids in the 1 M potassium hydroxide-soluble fraction, preferentially as low-molecular-weight polysaccharides; and (iv) a solubilization of arabinans in the 4 M potassium hydroxide-soluble fraction.

Cell Wall↗
PubMed1998

Degradation of hemicellulosic and cellulosic polysaccharides in pickled green olives.

Changes that take place in the hemicellulosic and cellulosic polysaccharide fractions of the cell wall of olives (Olea europaea pomiformis, Manzanilla variety) during "Spanish style" processing have been studied. A comparative study of the extraction of hemicellulosic polysaccharides with and without prior delignification showed that these compounds could be extracted without previous delignification of the cell wall material. The depectinated material was sequentially extracted with 1 M and 4 M potassium hydroxide. In the unprocessed fruit, the neutral polysaccharides of the 1 M potassium hydroxide-soluble fraction contained mainly xyloglucans with significant amounts of arabinans. In the 4 M potassium hydroxide-soluble fraction, xyloglucans were the most important polysaccharide. The apparent molecular weight of these polysaccharides was 40 to 250 kDa. In addition, hemicelluloses (xylans and xyloglucans), which it was not possible to isolate in the previous stages of fractionation, were also found to be closely linked to the cellulose fraction. The most important changes during processing were the decrease in the molecular weight of xyloglucans in the 4 M potassium hydroxide-soluble fraction and the substantial decrease in the cellulose fraction, which in quantitative terms was one of the largest decreases that took place in the components of the total cell wall polysaccharides.

Cellulose↗
PubMed1995

Metabolism of xyloglucan generates xylose-deficient oligosaccharide subunits of this polysaccharide in etiolated peas.

Oligosaccharide subunits of xyloglucan were isolated from the stems and roots of etiolated pea plants and structurally characterized. The two most abundant subunits of pea xyloglucan are the well-known nonasaccharide, XXFG, and heptasaccharide, XXXG. In addition, significant amounts of oligosaccharides that have not previously been reported to be subunits of pea xyloglucan were detected, including a decasaccharide, XLFG, two octasaccharides, XLXG and XXLG, a pentasaccharide, XXG, and a trisaccharide, XG. Several novel oligosaccharide subunits, including the octasaccharide, GXFG, and the hexasaccharide, GXXG, were also found. Xyloglucan oligosaccharides generated by treatment of intact pea stem cell walls were compared to oligosaccharides generated by endoglucanase treatment of xyloglucan polysaccharides obtained by subsequent alkali extraction of the same cell walls. The results suggest that the xyloglucan in etiolated pea stems is distributed between at least two domains, one of which is distinguished by its enzyme accessibility. We further hypothesize that the chemical modification of a xyloglucan during cell-wall maturation depends on its physical environment (i.e., the domain in which it resides). For example, only the endoglucanase-released material, representing the enzyme-accessible xyloglucan domain, contains significant amounts of the two unusual oligosaccharide subunits, GXXG and GXFG, both of which have a nonreducing terminal glucosyl residue. This structure may be generated during cell-wall maturation by the sequential action of an endolytic enzyme (such as xyloglucan endotransglycosylase or endoglucanase) and an alpha-xylosidase.

Carbohydrate Sequence↗
PubMed1995

Dietary fibre in white asparagus before and after processing.

The changes that occur, especially in the dietary fibre, during processing of white asparagus have been studied. Processing consists of submitting the vegetable to a treatment with hot water (96 degrees C), for 4 min (blanching) and subsequently immersing it in a sodium chloride solution (brining). Finally, the asparagus is sealed and sterilised at 115-116 degrees C. The study was performed on the whole asparagus and also, separately, on the apex and stem. As a result of processing there was an increase in the moisture and protein contents and a decrease in those of uronic acids and free sugars, saccharose disappearing entirely. It is concluded that the most important changes taking place in the asparagus fibre fraction during thermal treatments are the slight decrease of lignin and uronic acids, the slight increase in proteins and an important decrease in hemicelluloses.

Cold Temperature↗
PubMed1995

Composition of plant cell walls.

The present study reviews the most recent research published (starting approximately in the 1980s) on the composition of plant cell walls, with a description of the polysaccharides contained in the microfibrillar and amorphous phases: cellulose, hemicellulose and pectic substances, as well as the other components: lignin, proteins and enzymes. Cellulose is a linear homopolymer made up of microfibrils that form a para-crystalline structure stabilised by hydrogen bridges. The hemicelluloses constitute an important group of polysaccharides, which are inter-linked and also linked to microfibrils of cellulose and/or pectins, the most important being: xylans, arabinoxylans, mannans, galactomannans, glucomannans, arabinogalactan II, beta-1,3-glucan and beta-1,3-beta-1,4-glucans. The pectic substances are a complex mixture of colloidal polysaccharides that can be extracted from the cell wall with water or chelating agents, the most significant being: rhamnogalacturonan I, rhamnogalacturonan II, arabinan, galactan, arabinogalactan I and D-galacturonan.

Carbohydrate Conformation↗
PubMed1993

Apparent digestibility of dietary fibre and other components in table olives.

The apparent digestibility of the main components of the olive (Olea europaea arolensis) has been studied using young Wistar rats. An appreciable digestibility of fibre was found (of the order of 31% Neutral Detergent Fibre) and a high digestibility of fats (higher than 60%) and sugars (100% of glucose and 76% of fructose). Some 41% of the protein was digested, a relatively low value when compared with other products. If the diet is previously desalted, the digestibility of the components diminishes. There are significant differences in the digestibility of dry matter, fibre, cellulose and lignin, but not in proteins and fat.

Animals↗