Fate of yeast and grape pectic polysaccharides of a young red wine in the cross-flow microfiltration process

Cross-flow microfiltration of a young red wine through a mineral membrane of zirconium oxide (average pore size 0.2 μm) laid over a support of agglomerated microporous carbon reduced by 44 % the concentration of the starting wine in soluble polysaccharides. These carbohydrate polymers were mainly constituted of mannose, arabinose, galactose and galacturonic acid associated with minor amounts of rhamnose, glucose, xylose and fucose. The polysaccharides from starting wine and final permeate were separated by gel filtration on Ultrogel AcA 34 (exclusion limit for globular proteins 750,000) in at least four fractions (I-IV) of respective Kav 0.22, 0.50, 0.75 and 0.90. Each polysaccharidic population contained various proportions of yeast mannans, while grape polysaccharides were unequally distributed, fraction I containing neutral type II arabinogalactans and fractions II to IV being complex mixtures of type II arabinogalactans, arabinans and degraded forms of acidic rhamnogalactumnans (pectins). Losses due to microfiltration were positively correlated to hydrodynamic volume (molecular weight) of molecules: (I) "" 79 %, (II) "" 58 %, (III) "" 38 % and (IV) no loss. Yeast and grape polysaccharides coexisting in a given fraction (having the same Kav) were not equally affected by the microfiltration process, yeast mannans passing preferentially the membrane, while grape polymers were more retained. This differential retention was only observed in fractions of high molecular weights (I and II) and was discussed in relation with possible modifications at the molecular level (size and shape of polysaccharides) occurring in the concentration polarisation layer. Application of a back-flush pulse destined to unplug the membrane resulted in a reenrichment of the permeate in the polysaccharides present in the starting wine at a 82 % level

Ultrastructural Study of Yam Tuber as Related to Postharvest Hardness

Usually, parenchyma cell walls of monocotyledons do not develop secondary walls; however a few days after harvesting, the yam tuber of Dioscorea dumetorum starts to harden. Two or three weeks Iater, hardness is so pronounced that the tubers cannot be eaten, even after a long cooking time. Cytochemical studies using autofluorescence or some fluorescent dyes, such as phloroglucinol hydrochloride showed that the thin, and flexible cell walls of parenchyma tubers very quickly became fully lignified after harvesting. Ultrastructura 1 stud ies of the hardened ce 11 wa 11 s showed very thick secondary wa 11 s and very deep pit apertures. These secondary walls reacted strong ly with li gn in reactants such as potassium permanganate. The use of a radioactive (l \u27• C) ce llulose precursor, uri dine- 5\u27-d ipho sphateglucose, confirmed the formation of such secondary walls. The lignification started from the corners of the cells around intercellular spaces and proceeded along the walls

Leaf Volatile Compounds of Seven Citrus Somatic Tetraploid Hybrids Sharing Willow Leaf Mandarine (Citrus deliciosa Ten) as Their Common Parent

International audienc

Enzyme collagen membrane for electrochemical determination of glucose

International audienceA new trace glucose analyzer has been designed using electrochemical sensors. The differential device includes (a) a glucose sensor consisting of a modified gas electrode in which ihe pH detector was replaced by a platinum disk and the porous film by a collagen membrane on which beta-D-glucose oxidase has been covalently bound after an acyl-azide activation process; (b) a compensating electrode mounted with a nonenzymatic collagen membrane. After injection of a glucose containing sample into the reaction vessel, where the probes are immersed, an anodic current is detected at the enzyme working electrode. Current outputs of both electrodes are subtracted and twice differentiated; a steady state is reached and the stationary and dynamic responses are recorded. Both responses are proportional to glucose concentration in the 0.1 µM-2 mM range, and the reproducibility was found to be better than 2% using these conditions. The extreme sensitivity exhibited by our system, i.e., 10 nM, is better than previously reported data by 3 orders of magnitude, and is very favorable for trace glucose assays in food and biological samples