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B Bouchet

Publications and source records attributed to B Bouchet.

At least 19 recordsLinked to original sources
PubMed2005

Non-covalent interaction between procyanidins and apple cell wall material. Part III: Study on model polysaccharides.

The adsorption of condensed tannins (procyanidins) of varying degrees of polymerisation and percentage of galloylation on solid polysaccharides substrates was quantified using the Langmuir isotherms formulation. Pectins and xyloglucans, which are soluble polysaccharides, were first cross-linked by, respectively, dibromopropane and epichlorohydrin to obtain insoluble covalent gels. Cellulose and starch, being insoluble in the buffer solution at room temperature, were used as bought. Apparent affinity constants obtained for the pure polysaccharides were as follows: pectin>>xyloglucan>starch>cellulose. The apparent affinity constants increased with the molecular weight of the procyanidins, except with cellulose. Higher affinities were obtained with pectin, a polysaccharide having the ability to develop a gel-like network, forming hydrophobic pockets able to encapsulate procyanidins. Filamentous and globular polysaccharides, like cellulose and xyloglucan, bound procyanidins weakly. Higher apparent saturation levels were obtained for cellulose and xyloglucans, the arrangement of which would favour cooperativity and stacking. Pectin had lower saturation levels probably due to a steric hindrance effect.

Absorption↗
PubMed2001

Two loci control phytoglycogen production in the monocellular green alga Chlamydomonas reinhardtii.

The STA8 locus of Chlamydomonas reinhardtii was identified in a genetic screen as a factor that controls starch biosynthesis. Mutations of STA8 cause a significant reduction in the amount of granular starch produced during nutrient limitation and accumulate phytoglycogen. The granules remaining in sta8 mutants are misshapen, and the abundance of amylose and long chains in amylopectin is altered. Mutations of the STA7 locus, which completely lack isoamylase activity, also cause accumulation of phytoglycogen, although sta8 and sta7 mutants differ in that there is a complete loss of granular starch in the latter. This is the first instance in which mutations of two different genetic elements in one plant species have been shown to cause phytoglycogen accumulation. An analytical procedure that allows assay of isoamylase in total extracts was developed and used to show that sta8 mutations cause a 65% reduction in the level of this activity. All other enzymes known to be involved in starch biosynthesis were shown to be unaffected in sta8 mutants. The same amount of total isoamylase activity (approximately) as that present in sta8 mutants was observed in heterozygous triploids containing two sta7 mutant alleles and one wild-type allele. This strain, however, accumulates normal levels of starch granules and lacks phytoglycogen. The total level of isoamylase activity, therefore, is not the major determinant of whether granule production is reduced and phytoglycogen accumulates. Instead, a qualitative property of the isoamylase that is affected by the sta8 mutation is likely to be the critical factor in phytoglycogen production.

Amylopectin↗
PubMed1999

Novel, starch-like polysaccharides are synthesized by an unbound form of granule-bound starch synthase in glycogen-accumulating mutants of Chlamydomonas reinhardtii.

In vascular plants, mutations leading to a defect in debranching enzyme lead to the simultaneous synthesis of glycogen-like material and normal starch. In Chlamydomonas reinhardtii comparable defects lead to the replacement of starch by phytoglycogen. Therefore, debranching was proposed to define a mandatory step for starch biosynthesis. We now report the characterization of small amounts of an insoluble, amylose-like material found in the mutant algae. This novel, starch-like material was shown to be entirely dependent on the presence of granule-bound starch synthase (GBSSI), the enzyme responsible for amylose synthesis in plants. However, enzyme activity assays, solubilization of proteins from the granule, and western blots all failed to detect GBSSI within the insoluble polysaccharide matrix. The glycogen-like polysaccharides produced in the absence of GBSSI were proved to be qualitatively and quantitatively identical to those produced in its presence. Therefore, we propose that GBSSI requires the presence of crystalline amylopectin for granule binding and that the synthesis of amylose-like material can proceed at low levels without the binding of GBSSI to the polysaccharide matrix. Our results confirm that amylopectin synthesis is completely blocked in debranching-enzyme-defective mutants of C. reinhardtii.

Amylopectin↗
PubMed1999

Genetic and biochemical evidence for the involvement of alpha-1,4 glucanotransferases in amylopectin synthesis

We describe a novel mutation in the Chlamydomonas reinhardtii STA11 gene, which results in significantly reduced granular starch deposition and major modifications in amylopectin structure and granule shape. This defect simultaneously leads to the accumulation of linear malto-oligosaccharides. The sta11-1 mutation causes the absence of an alpha-1,4 glucanotransferase known as disproportionating enzyme (D-enzyme). D-enzyme activity was found to be correlated with the amount of wild-type allele doses in gene dosage experiments. All other enzymes involved in starch biosynthesis, including ADP-glucose pyrophosphorylase, debranching enzymes, soluble and granule-bound starch synthases, branching enzymes, phosphorylases, alpha-glucosidases (maltases), and amylases, were unaffected by the mutation. These data indicate that the D-enzyme is required for normal starch granule biogenesis in the monocellular alga C. reinhardtii.

Journal Article↗
PubMed1998

Physical and chemical transformations of cereal food during oral digestion in human subjects.

Chemical and physical transformations of solid food begin in the mouth, but the oral phase of digestion has rarely been studied. In the present study, twelve healthy volunteers masticated mouthfuls of either bread or spaghetti for a physiologically-determined time, and the levels of particle degradation and starch digestion before swallowing were compared for each food. The amounts of saliva moistening bread and spaghetti before swallowing were, respectively, 220 (SEM 12) v. 39 (SEM 6) g/kg fresh matter. Particle size reduction also differed since bread particles were highly degraded, showing a loss of structure, whereas spaghetti retained its physical structure, with rough and incomplete reduction of particle size. Starch hydrolysis was twice as high for bread as for spaghetti, mainly because of the release of high-molecular-mass alpha-glucans. The production of oligosaccharides was similar after mastication of the two foods, respectively 125 (SEM 8) and 92 (SEM 7) g/kg total starch. Starch hydrolysis, which clearly began in the mouth, depended on the initial structure of the food, as in the breakdown of solid food. These significant physical and chemical degradations of solid foods during oral digestion may influence the entire digestive process.

Adult↗
PubMed1998

Key indicators for the monitoring and evaluation of control programmes of human African trypanosomiasis due to Trypanosoma brucei gambiense.

Very little research has been devoted to the design of epidemiological tools for the monitoring and evaluation of National Human African Trypanosomiasis (HAT) Control Programmes and daily management decisions are made in the absence of accurate knowledge of the situation. This paper identifies key indicators necessary to make decisions in the field and constantly adjust control activities to changing situations. Examples are derived from the Médecins Sans Frontières (MSF) HAT Control Programme in Adjumani, Uganda. Based on the principles of quality assurance, the focus is placed on process indicators. A conceptual framework derived from a system view/planning cycle perspective is also described for the construction of indicators. Finally, some specific challenging aspects of the epidemiology of HAT are presented and the limitations of the interpretation of the indicators discussed.

Animals↗
PubMed1998

Digestion of carbohydrate from white beans (Phaseolus vulgaris L.) in healthy humans.

Resistant starch (RS) is thought to be present in large amounts in legume seeds; however, it has never been quantified in healthy humans. RS from cooked (atmospheric pressure) white beans was quantified in humans and pigs, and characterized to explain its low digestibility. Six human volunteers were intubated to collect ileal digesta after an experimental meal composed of orange juice, butter and 167 g beans (dry matter basis). The reliability of the intubation method was examined in a pig study in which it was compared with another collection method, ileal cannulation. Chemical analyses, microscopy and size exclusion chromatography were performed on human and pig digesta. The pig study showed that the intubation method may underestimate the quantity of RS. However, no chemical/physical difference was observed between the RS collected by the two techniques. In the human study, 16.5 +/- 1.3% (11.3 g) of the ingested starch was recovered as RS. The microscopy of the digesta showed that part of the RS was enclosed in the cell walls. Although the RS was composed mainly of alpha-glucan molecules with a degree of polymerization (DP) 40 to 60, oligosaccharides and large molecules of DP > 400 were also present. Retrogradation was not found to be the main factor responsible for starch malabsorption. We conclude that white beans may contain a large amount of RS formed mainly by partially degraded molecules protected by the cell walls during their transit through the gut.

Adult↗
PubMed1997

Starches from A to C. Chlamydomonas reinhardtii as a model microbial system to investigate the biosynthesis of the plant amylopectin crystal.

Wide-angle powder x-ray diffraction analysis was carried out on starch extracted from wild-type and mutant Chlamydomonas reinhardtii cells. Strains containing no defective starch synthases as well as mutants carrying a disrupted granule-bound starch synthase structural gene displayed the A type of diffraction pattern with a high degree of crystallinity. Mutants carrying a defect for the major soluble starch synthase (SSS), SSS II, were characterized by a switch to the B type of diffraction pattern with very low crystallinity. Mutant strains carrying SSS I as the only glucan elongation enzyme regained some of their crystallinity but switched to the C type of diffraction pattern. Differential scanning calorimetry analysis correlated tightly with the x-ray diffraction results. Together with the electron microscopy analyses, these results establish C. reinhardtii as a microbial model system displaying all aspects of cereal starch synthesis and structure. We further show that SSS II is the major enzyme involved in the synthesis of crystalline structures in starch and demonstrate that SSS I alone builds a new type of amylopectin structure.

Amylopectin↗
PubMed1995

Banana starch breakdown in the human small intestine studied by electron microscopy.

OBJECTIVE: To determine the origin of the poor digestibility of banana starch granules in the human small intestine. DESIGN: The subjects received the same experimental meal. SETTING: Nutrition Research Unit, Laënnec Hospital, CHU, Nantes. SUBJECTS: Six healthy young subjects. INTERVENTIONS: The digestion of raw green banana flour in the upper part of the gut was studied by the intubation technique. After ingestion of 30 g banana flour mixed with a complex meal, ileal samples were continuously collected during 14 h. In order to determine the structural nature of this resistant starch, the dried ileal samples were observed with scanning and transmission electron microscopy. Transmission electron microscopy was performed after treatment with periodic acid-thiosemicarbazide-silver nitrate. RESULTS: Banana starch proved very resistant to in vivo amylase hydrolysis since 84% of the starch ingested reached the terminal ileum. The microscopic observations showed that raw banana flour contained irregularly shaped dense starch granules with smooth surfaces. After their passage through the small intestine, starch granules appeared exocorroded, with porous surfaces, and some exhibited several irregular pits, crevices or holes by which the enzymes had penetrated and hydrolysed the inner part. Cell walls closely associated with starch granules could have hindered enzyme access to starch. CONCLUSIONS: Encapsulation could be partly responsible for the low digestibility of starch in banana flour, together with the intrinsic resistance of banana starch granules.

Digestion↗
PubMed1992

Contribution of the digestive tract microflora to amylomaize starch degradation in the rat.

To study in vivo the contribution of the bacterial flora to amylomaize starch degradation in the rat, germ-free and conventional rats were fed on a diet containing either a normal maize starch or an amylomaize starch. In germ-free rats maize starch was almost totally digested in the small intestine, whereas 40% of the ingested amylomaize starch reached the caecum and 30% was excreted, despite the very high endogenous amylase activity. Study by transmission electron microscopy of germ-free caecal contents showed an endocorrosion of the starch granule. In conventional rats, as in germ-free rats, digestibility of maize starch reached 98% in the small intestine, whereas that of amylomaize starch was only 60%. In the caecum of these rats amylomaize starch was fermented, and this led to a decrease in caecal pH and to formation of short-chain fatty acids (SCFA), especially propionate. Comparison between conventional rats fed on maize starch or amylomaize starch showed that caecal SCFA concentrations during a circadian cycle varied in the same way whereas total SCFA and lactic acid concentrations were much higher in rats fed on amylomaize starch. Amylase (EC 3.2.1.1) activity was similar in the caecal contents of conventional rats whatever the ingested starch. It was lower in conventional than in germ-free rats, but no starch granule remained in the caecum of conventional rats. These results showed that bacterial amylase was more efficient at degrading resistant amylomaize starch than endogenous amylase.

Amylases↗
PubMed1992

Physical characteristics of starch granules and susceptibility to enzymatic degradation.

Starch, the most abundant component of the diet, is characterized by its variety as well as the versatility of its derivatives in foods. This paper is an overview of the main physical characteristics of the native starch granule. Three different levels of organization are presented: macromolecular structure, crystalline organization and ultrastructure. Starch consists of amylose and amylopectin. Amylose is an essentially linear polymer composed of alpha-1,4-linked D-anhydroglucose units (AGU); amylopectin is a branched polymer clustering a large amount of short linear chains by the linkage of alpha-1,6-bonds, constituting about 5% of the total glycosidic bonds. In the native starch granules, a large number of the macromolecular chains are organized in crystalline structures. Three forms have been found, the A, B and C patterns. So far only A and B starch crystals have been modelled. There is a variation in the susceptibility of the starch granules to enzymatic digestion. This is explained by variation in the morphology of the granules and their crystalline organization.

Chemical Phenomena↗
PubMed1990

[Prevalence of HIV-1 and HIV-2 antibodies in rural areas of Benin].

A transversal survey has been performed in the Zou Province in the central part of Benin located in West Africa close to the western border of Nigeria. The Zou Province is an agricultural region which population is about 900,000. A randomised sample of 1936 people had been chosen according 1,984 census data. All the samples have been examined by ELISA Rapid Elavia Mixt (Pasteur Vaccin). All positive samples have been tested with both Elavia I and Elavia II (Pasteur Vaccin). 6.6% of sampled population show positive result for HIV1 in ELISA and 0.9% are positive in ELISA for HIV2. Age, sex and geographical distribution of ELISA positive samples is quite uniform. None of positive plasma in ELISA can be interpreted as positive in Western-Blot. The first hypothesis discussed by authors is possibility of serological conversion occurring at the time of the survey. If this unlikely hypothesis is confirmed it means that both viruses have recently and suddenly infected the Zou Province at various level of population and in all villages of the Province. A second hypothesis is that all plasma have antibodies for unidentified related virus which cross reacts with HIV1 or HIV2. A third hypothesis is that dysproteinaemia due to parasite or nutrition factors produce false positive reactions. This could explain such a positive reaction distribution among the whole population. So the last hypothesis must be considered with attention.

Adolescent↗
PubMed1978

[Anetodermic cutaneous changes above Malherbe's tumors (author's transl)].

Clinical and histological anetoderma-like changes of the skin above Malherbe's tumor (pilomatricoma) may be of diagnostic value since they have been observed 5 times in a series of 22 consecutive cases. The histological study of 46 cases of Malherbe's tumor shows a high incidence of dermal atrophy and decrease of elastic fibers in reticular dermis above the tumor, a possible consequence of cellular infiltrates surrounding the tumor and seen in half our cases.

Adolescent↗
PubMed1977

[Reticulate erythema with mucinosis (R. E. M. Steigleder syndrome) (author's transl)].

We described a case similar to the four cases reported by Steigleder, Gartman and Linker in 1974 and entitled: "R.E.M. syndrome reticular erythematous mucinosis, a new entity?". In our case, clinical and histological findings were strictly identical to those previously reported. Furthermore, we detected no antibodies in the cutaneous lesions.

Adrenal Cortex Hormones↗