J.-F. Thibault

University of Yaounde I, Yaoundé, Centre Province, Cameroon

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Publications (150)118.64 Total impact

  • E. Bonnin, M.C. Ralet, J.F. Thibault, H.A. Schols
    01/2009: pages 257-285; , ISBN: 978-1-84569-391-6
  • Marie-Christine Ralet, J.F. Thibault
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    ABSTRACT: Pectins are extremely complex polysaccharides that can be viewed as multiblock co-biopolymers. Although the fine structure of the different pectic blocks is now quite well known, the way in which they are combined into a macromolecular structure is still a matter of debate. Large differences in pectins quality and quantity exist between different cell types, at different stages of cellular development and even within the thickness of a given wall. A way to understand how the different structural elements are connected to one another to form variable macromolecular structures is to isolate and identify the different connection points. Another, and complementary, way is to specifically isolate the different pectic domains in order to study their hydrodynamic properties. Six monocotyledonous and dicotyledonous species were selected and pectins were extracted from cell wall materials using a four-step sequential extraction scheme. The isolation and characterization of pectin structural elements showed that structural discrepancies of pectins differing in HG/RG-I balance could be due to a variable amount of HG domains decorating an RG-I backbone. Our results also support the hypothesis of a hyper-variability of RG-I backbone length. However, the structural complexity and heterogeneity of pectins make it very difficult to appraise the relationship between pectin fine structure and hydrodynamic properties, especially when the compared pectins are derived from different plant species and obtained with different extractants. The Arabidopsis pectin mutant quasimodo2 was thereby studied. By specifically isolating HG blocks, qua2 appeared to be specifically deficient in HG, with no change in the amount of RG-I blocks. Moreover, the remaining HGs had maintained the same size as those in the wild type. The possible macromolecular build up of pectins is discussed in the light of the presented results.
    01/2009: pages 35-48; , ISBN: 978-90-8686-108-8
  • Jean‐François Thibault, Marie‐Christine Ralet
    04/2008: pages 367 - 378; , ISBN: 9780470999615
  • Source
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    ABSTRACT: The extraction of pectins from mango peels can offer a way to upgrade byproducts arising from the processing of these tropical fruits. In this work, several extraction conditions (HCl, or deionised water, or ammonium oxalate) were tested in order to isolate pectins from the peels of two mango varieties (Améliorée and Mango) harvested in Cameroon. After determining uronic acid and neutral sugar contents of mango peels and their alcohol insoluble residues (AIR), extracted pectins were analysed for their uronic acid and neutral sugar contents, their degree of methylation and acetylation, and their average molar mass and intrinsic viscosity. The extraction method was shown to significantly act upon yield (9–32% dry AIR), uronic acid (262–709 mg/g dry weight) and neutral sugar (160–480 mg/g) contents of pectin, their degree of methylation (52–86%) and acetylation (1–8%), their molar mass (245,000–432,000 g/mol), and their intrinsic viscosity (320–1346 mL/g). The physicochemical behaviour of pectins could be influenced thereof. With a good recovery yield, a high average molar mass and intrinsic viscosity and a high degree of methylation, ammonium oxalate-extracted mango pectins present good characteristics to be exploited industrially for their gelling properties.
    Food Hydrocolloids. 01/2008;
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    ABSTRACT: Extraction and use of pectins from ambarella peels could add value to the waste products arising from processing of the fruit. Dried alcohol-insoluble residues (AIR) of ambarella peels were treated separately with HCl, deionised water and oxalic acid/ammonium oxalate solutions, and the resulting pectin extracts analysed for some biochemical and physicochemical parameters. The results show that pectin yield (9–30% dry AIR), uronic acid (557–727 mg/g dry weight), neutral sugars (125–158 mg/g), degree of methylation (50–58%) and acetylation (4–6%), molar mass (263,000–303,000 g/mol) and intrinsic viscosity (179–480 ml/g) varied significantly (p < 0.05) with the various extraction methods used. Extraction with oxalic acid/ammonium oxalate solution gave the highest pectin yield, with high molar mass and degree of methylation, making the extracts suitable for use as additives in the food industry. The results compared well to lime pectin extracted under the same conditions, indicating their commercial significance.
    Food Chemistry. 01/2008; 106(3):1202-1207.
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    ABSTRACT: An acetylesterase was purified from Aspergillus aculeatus on the basis of its ability to deacetylate homogalacturonan. A series of well-characterized substrates was prepared and used to investigate its specificity, including pectin with various degrees of methylation and acetylation, pectic domains with various structures, and oligomers. It was then compared to a rhamnogalacturonan acetylesterase previously isolated from the same fungus. Both enzymes were active towards various acetylated pectins, and were able to release acetyl groups from acetylated homogalacturonan, oligogalacturonates as well as rhamnogalacturonan at different extent. It was thus concluded that while the two enzymes differed in their efficiency, they are both pectin acetylesterases, able to act in the “smooth” as well as in the “hairy” regions of pectin.
    Carbohydrate Polymers. 01/2008;
  • 01/2008: pages 60-70; , ISBN: 978-4-903313-17-7
  • M. Panouille, M.C. Ralet, E. Bonnin, J.F. Thibault
    01/2007: pages 417-447; , ISBN: 978-1-84569-025-0
  • Patrice Massiot, Jean‐François Thibault, Xavier Rouau
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    ABSTRACT: Carrot Daucus carota L fibres were degraded with two enzyme preparations, SP249 from Aspergillus aculeatus and Celluclast from Trichoderma reesei. The enzymic activities of these complexes indicate that SP249 was particularly active on pectic polymers, and Celluclast could degrade amorphous and crystalline cellulose. A combination of both preparations degraded carrot fibres with a synergistic effect and led to the solubilisation of 95% of the cell-wall polysaccharides. The kinetics of solubilisation of sugars and gel-permeation chromatography of the soluble products show that pectic polymers were rapidly solubilised and then, in a second stage, degraded mainly to monomers, whereas cellulose was more slowly hydrolysed to cellobiose and glucose. Part (67%) of the polysaccharides were saccharified, the residual soluble material being rhamnogalacturonans containing arabinose residues. Residual insoluble fibres (10% of initial weight) were not liquefied and were composed mainly of lignin, proteins and polymers of glucose, xylose and galacturonic acid.
    Journal of the Science of Food and Agriculture 09/2006; 49(1):45 - 58. · 1.76 Impact Factor
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    ABSTRACT: Two dietary fibres with distinct structural features (pea hull and apple fibre) were fermented in vitro with human faecal bacteria. The composition and physicochemical properties (cation exchange, hydration properties) of the residues were examined. Gas and short-chain fatty acid (SFCA) productions attested of the highest fermentability of apple fibre. After 24 h, 75% of the pea fibre and 42% of the apple fibre could be recovered. Production of the major SCFA, acetate, propionate and butyrate occured in the molar ratio 68:17:9 for both fibres. Uronic acid and arabinose were the most extensively fermented sugars while xylose and glucose were the least fermented. Cation exchange capacity of the two fibres did not decrease much during fermentation, which implies that the amount of bound mineral is proportional to the amount of residual fibres. The values of the hydration properties of the residual fibres were at least equal to or higher than those of initial fibres. In spite of the degradation of the fibres during fermentation, a physical structure able to retain water remained.
    Journal of the Science of Food and Agriculture 09/2006; 68(4):521 - 529. · 1.76 Impact Factor
  • Chantal Bertin, Xavier Rouau, Jean‐François Thibault
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    ABSTRACT: Fibrous fractions were prepared from sugar beet pulp (RF) by sequential extractions with potassium oxalate, 0.05 M hydrochloric acid at 85°C and 0.05 m sodium hydroxide at 4°C. The overall composition, polysaccharide structure and some physico-chemical properties (cation exchange capacity, CEC; water holding capacity, WHC; swelling) of each fraction were determined.RF was mostly composed of carbohydrates (66.3 %) with minor amounts of ash, proteins and lignin. The main polysaccharides were highly methylated and acetylated pectins, cellulose and arabinans. The oxalate residue (82.1 % of RF) exhibited only minute differences from RF whereas the acidic and alkaline residues, accounting for 42.8 % and 35.5 % of RF, respectively, were enriched in cellulose and hemicelluloses (xylans, xyloglucans, mannans) and mostly devoid of pectins and arabinans.CEC and WHC of fractions were closely related to the content of unmethylated galacturonic acid residues. The influence of the ionic form of ionisable groups was demonstrated, the Na+ form giving the highest WHC. The ionic strength of the medium can reduce the WHC, especially in the case of the acid and alkali-extracted fibres.
    Journal of the Science of Food and Agriculture 09/2006; 44(1):15 - 29. · 1.76 Impact Factor
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    ABSTRACT: Conditions (pH, temperature, time) for the extraction of sugar beet pulp pectins were studied on a laboratory scale and transposed into a pilot plant. Good yields (∼ 14%) of pectins are obtained if the pulp is treated at pH 1.0, 85°C for 1 hr. The characteristics of the pilot extracted pectins are very close to those of the laboratory ones, except for a lower molecular weight (∼30,000 daltons). Their physicochemical properties confirm their poor gelling ability.
    Journal of Food Science 08/2006; 50(5):1499 - 1500. · 1.78 Impact Factor
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    ABSTRACT: The objective of the present work was to relate the physical evolution quantified by image analysis to the chemical transformation of beet pulp particles during enzymatic degradation. Beet pulps were degraded into a torus reactor equipped for visualisation. Pectinolytic and cellulolytic enzymes were used separately or in combination. Two global image analysis techniques were tested to characterise the size distribution of overlapping particles. Granulometric curves were extracted by mathematical morphology and a regularisation dimension was assessed by fractal analysis. Both techniques proved efficient to follow particle size evolution during degradation. When using cellulolytic enzymes alone, no chemical or physical evolution was observed. When using pectinolytic enzymes, a chemical modification occurred without any physical evolution. Particles physically disappeared when both enzymes were used. The chemical and physical evolutions of particles during degradation were interpreted taking into account the current model of molecular arrangement of primary cell walls.
    Journal of Food Engineering. 01/2006;
  • Chapter: Pectins
    01/2005: pages 351-387; , ISBN: 3527313451
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    J. F. Thibault, M. Rinaudo
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    ABSTRACT: The chain association of pectic molecules with different levels and patterns of esterification during calcium-induced gelation was studied by methods such as light scattering, viscometry, and determination of calcium activity coefficient and of calcium transport parameter. A gel point can be determined, assuming a power law including a critical ratio (equivalent concentration of calcium ions/pectin carboxylic groups) and quasi-critical exponents varying in the range 0.50–1.26. The values of these critical parameters were discussed as a function of polymer concentration, of level and pattern of esterification, and of the nature of the divalent counterion. The lower these values are, the better, apparently, the gel-forming ability of the pectins is.
    Biopolymers 01/2004; 25(3):455 - 468. · 2.88 Impact Factor
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    ABSTRACT: The intrinsic pK values, as well as the free fractions of sodium and calcium counterions, were determined on salt-free solutions of amidated pectinates and amidated pectates. The apparent pK values were non dependent of the degree of amidation but only to the effective charge density of the pectic polymers and an unique value of 2.9 ± 0.1 was found for the intrinsic pK value. The results obtained by conductimetry and with (sodium and calcium) specific electrodes showed a blockwise distribution of amide and acid groups in amidated pectates and a blockwise distribution of amide groups and a rather statistical distribution of acid groups in amidated pectinates.
    Biopolymers 01/2004; 28(8):1435 - 1448. · 2.88 Impact Factor
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    J. F. Thibault, M. Rinaudo
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    ABSTRACT: The free fractions of monovalent and divalent counterions were determined on salt-free solutions of pectins. The effects of charge density, distribution of the carboxyl groups, polymer concentration, and the nature of the counterion were investigated by determinating the calcium and sodium activity coefficients (with specific electrodes) and by measuring the transport parameters (by conductimetry). Poor agreement for calcium ions was found with the Manning theory. The strong binding of these ions to highly charged polymers, which is ascribed to a dimerization process was demonstrated in very dilute solutions.
    Biopolymers 01/2004; 24(11):2131 - 2143. · 2.88 Impact Factor
  • 01/2003: pages 419-430; , ISBN: 1-4020-1144-X
  • M Thomas, F Guillemin, F Guillon, J.-F Thibault
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    ABSTRACT: The pectin content, composition and physico-chemical properties were studied in the fruits of two genotypes of Japanese quince. On average, the fruits contained 11 g pectins/100 g dry fruit and 1.4 g pectins/100 g fresh fruit. A sequential extraction was used to isolate the pectins from the fruits. The cells from the flesh were examined using a confocal laser scan microscope, fresh and after each extraction step of the sequence. The dilute acid conditions were the most efficient for pectin extraction. Pectins extracted by water or potassium oxalate had higher (>600 ml/g) intrinsic viscosities than the pectins extracted by dilute acid (
    Carbohydrate Polymers - CARBOHYD POLYM. 01/2003; 53(4):361-372.
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    ABSTRACT: Endopolygalacturonase from Fusarium moniliforme was used to degrade acetylated homogalacturonan previously prepared from sugar beet pulp. The initial velocity and the final percentage of hydrolysis decreased very rapidly with increasing degree of acetylation, showing that acetyl substitution markedly affected the enzymatic activity. MALDI-TOF mass spectrometry was used to analyse the reaction products and to show acetyl groups on the oligogalacturonates. The results demonstrated that the enzyme was able to accommodate acetyl groups in its active site cleft. The influence of acetyl groups on the mode of action of the enzyme was discussed and compared to the influence of methyl groups.
    Carbohydrate Polymers. 01/2003;

Publication Stats

2k Citations
118.64 Total Impact Points

Institutions

  • 2008
    • University of Yaounde I
      • Department of Biochemistry
      Yaoundé, Centre Province, Cameroon
  • 2006
    • Ecole Centrale de Nantes
      Naoned, Pays de la Loire, France
  • 1993–2003
    • French National Institute for Agricultural Research
      • Biopolymères, Interactions, Assemblages (BIA)
      Lutetia Parisorum, Île-de-France, France
  • 1986–2003
    • Wageningen University
      • Laboratory of Food Chemistry
      Wageningen, Provincie Gelderland, Netherlands
  • 2002
    • Swedish University of Agricultural Sciences
      Uppsala, Uppsala, Sweden
  • 2000
    • Biotechnology and Biological Sciences Research Council
      Swindon, England, United Kingdom
  • 1995–1998
    • New York State
      New York City, New York, United States