Rafael Guillén

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.

Characterization of the lignin obtained by alkaline delignification and of the cellulose residue from steam-exploded olive stones

The lignocellulosic by-products (whole stones and seed husks) obtained from pitted table olive and olive oil processing (respectively) were pretreated under various conditions of steam-explosion, with respect to pressure and time and with a dilute solution of sulfuric acid and without previous acid impregnation. The two materials exhibited considerable difference in behavior. The pre-impregnation of whole stones with low level of acid prior to steam treatment was necessary to improve the fractionation and the autohydrolysis of hemicellulose, while the results with seed husks were similar both with and without an acid catalyst. The lignins recovered from water-washed solid residue by alkaline-extraction followed by acidification were characterized. These lignin preparations from whole stones contained a very high amount of fat and almost no neutral sugars. The results also showed that these lignin preparations were guaiacyl-syringyl lignin, similar to exploded hardwood lignin, with an extensive cleavage of the β-aryl-ether linkage. The effect of treatment severity on the major physical properties of cellulose was also investigated. The cellulose fraction derived from steam-exploded whole stones was rapidly depolymerized as severity increased, leading to a degree of polymerization of 180, at a severity of log R0 = 4.07. In seed husks, under similar severity conditions, depolymerization of cellulose was much slower, and only reached a value of 821 (at log R0 = 4.07) or a value of 600 at log R0 = 4.34 without acid impregnation. The cellulose derived from both steam-exploded materials was moderately crystalline, the relative crystallinity index values of seed husks being higher than those of whole stones. The results indicated that the cellulose from seed husks was more protected than that of the whole stones in the steam-explosion process, and could be used to produce a cellulose with different properties and applications depending on severity and on the different treated material.

Composition of plant cell walls.

ZusammenfassungDer Artikel faßt jüngere Forschungsergebnisse (ungefähr ab Beginn der achtziger Jahre) über die Zusammensetzung der Zellwände von Pflanzen zusammen mit einer Beschreibung der in den mikrofibrillären und amorphen Phasen enthaltenen Polysaccharide: Cellulose, Hemicellulosen und Pektinsubstanzen sowie der übrigen Komponenten: Lignin, Proteine und Enzyme. - Cellulose ist ein lineares Homopolymer aus Mikrofasern, deren parakristalline Struktur durch Wasserstoffbrückenbindungen stabilisiert wird. Die Hemicellulosen stellen eine wichtige Gruppe unter den Polysacchariden dar, die untereinander und mit den Cellulose- und/oder Pektin-Mikro-fibrillen verbunden sind. Als wichtigste Scien genannt: Xylane, Arabinoxylane, Mannane, Galactomannane, Glucomannane, Xyloglucane, Glucuronomannane, Arabinoga-lactan II, β-1,3- und β-l,4-Glucane. Die Pektinsubstanzen sind eine komplexe Mischung von kolloidalen Polysacchariden, die der Zellwand mit Wasser oder löslichen organischen Komponenten (chelating agents) entzogen werden können, wobei die bedeutendsten folgende sind: Rhamno-galacturonan I, Rhamnogalacturonan II, Arabinan, Galactan, Arabinogalactan I und D-Galacturonan.AbstractThe 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, β-l,3-glucan and β-l,3-β-l,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.

Dietary fibre content of table olives processed under different European styles: study of physico-chemical characteristics

Some European varieties of olive fruit (Douro, Hojiblanca, Cassanese, Conservolia, Taggiasca, and Thasos), processed under different conditions (black oxidised, fermented in brine or dried by different methods) were analysed, their contents of moisture, fat and dietary fibre being quantified. The percentages of moisture and fat were very different between varieties due to the different processing conditions, although differences between samples of the same variety were much less. The content of dietary fibre was around 12% of the fresh weight, although in dried samples this percentage increased to around 20%. Some physico-chemical characteristics (water holding capacity, cation exchange capacity, and ion retention capacity) were measured. The water holding capacities were related to moisture content, dry samples having the lowest values. Processed olives had very low cation exchange capacity in comparison to other vegetables, exhibiting the same relationship between this characteristic and moisture content. Olive fibre retained more iron than calcium under the assay conditions. © 2000 Society of Chemical Industry

Fibre fraction carbohydrates in Olea europaea (Gordal and Manzanilla var.)

Abstract Olive dietary fibre, Gordal and Manzanilla varieties, has been isolated by chemical (acid and neutral detergent fibre of Van Soest) and enzymatic (soluble and insoluble fibre of Asp) methods. NDF and ADF values were lower than IF. All of the fractions were hydrolysed and the resultant neutral sugars quantified. Glucose was the main component in NDF, ADF and IF, and arabinose was the major one in SF. The content of protein was significantly different between fractions but not between varieties, and the content of cellulose was significantly different between fractions and varieties. The determination of hemicelluloses by the Van Soest method showed a very low precision (cv. > 40%); determined by acid hydrolysis there were significant differences between fractions and varieties.

Activity of glycosidases during development and ripening of olive fruit

ZusammenfassungEs wurde die Aktivität von verschiedenenp-Nitrophenyl-d-glycosidasen während der Entwicklung und Reifung der Oliven in drei Jahren (1987–88; 1988–89, 1989–90) untersucht. Es wurde keine Aktivität in der voll entwickelten Frucht festgestellt. Es wurden die Aktivitätenα-Galactosidase,β-Galactosidase,α-Mannosidase,α-Arabinosidase undα-Xylosidase entdeckt und ihre Molekularmassen durch Gelfiltration-Chromatographie mit Sephadex G-100 bestimmt. Es gibt eine zeitliche Wechselwirkung zwischen der enzymatischen Aktivität und der Abnahme in der Zuckerzusammensetzung in dem Nichtcellulose-Anteil der Zellwand.SummaryWe have studied the activity of variousp-nitrophenyl-d-glycosidases during development and ripening of olive fruit in three seasons (1987–88, 1988–89, 1989–90). Activity was absent in the first phases of ripening but appeared in the completely developed fruit,α-Galactosidase,β-galactosidase,α-mannosidase,α-arabinosidase, andα-xylosidase activities were detected and their relative molecular mass determined by gel filtration chromatography using Sephadex G-100. There is a temporal correlation between enzymatic activity and decrease in non-cellulosic cell-wall neutral sugar composition.

3,4-Dihydroxyphenylglycol (DHPG): an important phenolic compound present in natural table olives.

The presence of 3,4-dihydroxyphenylglycol (DHPG) was studied in 32 samples and 10 different cultivars of natural table olives, using an accurate method to avoid wrong quantification. Hydroxytyrosol (HT), tyrosol, and verbascoside were also quantified, as these four compounds comprise the majority of the chromatographic profile. Analyses were carried out by HPLC-DAD-UV after extraction of all phenolics, and hydroxytyrosol was the major component in nearly all samples. High levels of DHPG (up to 368 mg/kg of dry weight) were found in the pulp of natural black olives independent of cultivar and processing method, similar to its concentration in the brine in almost all of the samples. The presented data for this antioxidant indicate that natural table olives are a rich source of DHPG and hydroxytyrosol, compounds with interesting nutritional and antioxidant properties.

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.

Cellulase inhibition by polyphenols in olive fruits.

Abstract The inhibition of cellulolytic enzymes by polyphenolic compounds present in the olive fruit (Hojiblanca variety) and by those which remain in the acetone powder is described. Basidiomycetes cellulase and cellulolytic enzyme extracts from the fruit itself were tested. An inhibition of 80% was reached. Polyphenols were determined by derivative spectroscopy.

Changes in pectic polysaccharides during elaboration of table olives

Abstract A traditional system for the preparation of table olives, involves a treatment of the fresh fruit with a solution of NaOH to hydrolised the bitter glycoside oleuropein, followed by a lactic fermentation in brine. The modifications that take place on pectic polysaccharides of olives (Manzanilla variety) during this process was studied. Processing induced a net loss of polysaccharides soluble in sodium carbonate and a paralel accumulation of water and Imidazole/HCl soluble polysaccharides. A general decrease of the apparent molecular weight of water and carbonate soluble polysaccharides was also detected.