Judy D. Timpa

Influence of avocado (Persea americana) Cx-cellulase on the structural features of avocado cellulose

Avocado (Persea americana Mill.) fruit produce copious quantities of the enzyme Cx-cellulase (EC 3.2.1.4) during ripening. The possibility that Cx-cellulase is able to disrupt cellulose microfibril oranization was investigated using molecular weight (Mr), x-ray diffraction, and ultrastructural analyses of cell walls from unripe avocado fruit incubated with the purified enzyme. Results indicate that Cx-cellulase causes a downshift in the Mr of unbranched cell-wall polymers in the Mr range of 106–107 Da. There is an increase in the proportion of crystalline cellulose, and cellulose fibrils appear to lose cohesiveness in response to enzyme activity. We propose that Cx-cellulase attacks avocado cellulose at accessible sites in the peripheral and integral noncrystalline regions of the microfibril, resulting in a loss of cohesiveness within the fibril structure and an alteration in the binding of associated cell-wall matrix polysaccharides. The initial loss of avocado mesocarp firmness during fruit ripening may be linked to the onset of Cx-cellulase activity.

Analysis of cell-wall polymers during cotton fiber development

Although the fibers of cotton (Gossypium hirsutum L.) are single cells with a secondary wall composed primarily of cellulose, the cell-wall polymers of the fibers are technically difficult to characterize with respect to molecular weights. This limitation hinders understanding how the fiber wall composition changes during development, particularly with respect to genotypic variations, and how the molecular composition is related to physical properties. We analyzed cell-wall polymers from cotton fibers (cultivar, Texas Marker-1) at several developmental stages (8–60 days post-anthesis; DPA) by gel-permeation chromatography of components soluble in dimethyl acetamide and lithium chloride. This procedure solubilizes fiber cell-wall components directly without prior extraction or derivatization, processes that could lead to degradation of high-molecular-weight components. Cellwall polymers from fibers at primary cell-wall stages had lower molecular weights than the cellulose from fibers at the secondary wall stages; however, the high-molecularweight cellulose characteristic of mature cotton was detected as early as 8 DPA. High-molecular-weight material decreased during the period of 10–18 DPA with concomitant increase in lower-molecular-weight wall components, possibly indicating hydrolysis during the later stages of elongation.

Non-aqueous gel permeation chromatography of wheat starch in dimethylacetamide (DMAC) and LiCl: extrusion-induced fragmentation

Abstract Automated gel permeation chromatography (GPC) with application of the universal calibration concept was used to investigate the mechanism of extrusion-induced starch fragmentation in wheat. High and low protein flours were subjected to twin-screw extrusion and the effects of moisture, die temperature, screw speed, mass flow rate and protein content on starch structure and textural properties were investigated by non-aqueous GPC in dimethylacetamide (DMAC) and LiCl. This solvent system allowed for complete dissolution of the native and extruded starches. The use of refractive index and viscosity detectors enabled application of Mark-Houwink calculations to obtain quantitative size profiles of unprocessed and processed starch, and information describing branching patterns of the starch. Fragmentation was most pronounced in amylopectins of MW 10 7 –10 8 , which yielded fragments of MW 10 5 –10 7 . Of the operating parameters investigated, low die temperature and low moisture content led to extensive fragmentation. Methylation analysis showed only modest changes in linkage distributions, with little or no increase in terminal glucose indicating few fragmentation points relative to the total number of glycosidic linkages present. The lack of dextrins or oligosaccharides suggests that fragmentation occurs primarily in the B chains of amylopectin. Interactions between die temperature and moisture content were shown to significantly effect the hardness, cohesiveness, springiness, gumminess and chewiness of the extruded flours.

Multiple neutral alkali halide attachments onto oligosaccharides in electrospray ionization mass spectrometry

Abstract Oligosaccharides perform essential functions in a variety of biological and agricultural processes. Recent approaches to characterization of these molecules by mass spectrometry have utilized mainly soft-ionization methods such as electrospray ionization (ESI) and thermospray (TS), as well as fast atom bombardment (FAB). The behavior of a series of maltooligosaccharides with α-(1 → 4) linkages, maltose (G 2 ) through maltoheptaose (G 7 ), under ESI conditions, has been investigated here. The oligosaccharides were dissolved in N,N -dimethylacetamide containing lithium chloride (DMAc/LiCl) prior to analysis by ESI-MS. A highly unusual feature, evident in all mass spectra obtained using this solvent system, was the presence of multiple ‘neutral’ salt attachments onto lithium adducts of the sugars. Resultant ions took the form of [G x + Li + n LiCl + , where n may reach a value as high as eight. Compared to LiCl, the propensity for alkali halide attachment using other alkali chlorides or lithium halides was greatly reduced. An investigation of this phenomenon is presented in which the organic and inorganic portions of the employed solvent were systematically varied, and semi-empirical computer modeling was performed to better understand lithium coordination by the sugars.

Characterization of cell-wall polymers from cotton ovule culture fiber cells by gel permeation chromatography

SummaryCotton (Gossypium hirsutum, Texas Marker-1) fiber cells originating from ovule culture have been analyzed by gel permeation chromatography of dimethyl acetamide/lithium chloride-soluble components and compared within planta-grown fibers. The profile of cell-wall polymer molecular weights indicated that fibers grown for 21 d in culture more closely resembled fibers growingin planta for 30 d post-anthesis than fully mature fibers. The weight average molecular weight was 3 400 000 and number average molecular weight of polymers from ovule culture fibers was 109 000. Analysis of the polymer weight fraction distribution revealed that ovule culture fibers were similar to 30 d post-anthesis immature fibers but lacked a low molecular weight (log M 3–4) polymer fraction. Assessment of the polymer branching frequency showed that ovule culture fibers were intermediate in branching between 30 d post-anthesis fiber and maturein planta fiber. In summary, polymers deposited in cell walls of ovule culture fibers appear to grossly mimic the polymers accumulated during normal fiber biogenesisin planta, yet subtle differences may explain why ovule culture fibers rarely reach their full genetic potential in length.

Strength Losses and Structural Changes in Cotton Fabric Crosslinked with Dimethylolethyleneurea 1

Losses in tensile and tearing strengths and other physical properties of cotton fabric given durable-press finishes have been attributed to factors arising mainly from the crosslinking of the cellulose molecule. This conclusion was deduced from the results of textile testing of the treated fabrics. In order to define the sources of these strength losses, a study was made of cotton fabric treated with dimethylolethylene urea and a zinc nitrate catalyst in a commercial manner, but with varying times of cure. Heretofore unobtainable molecular parameters of durahle-press cotton fabric were estab lished from solubilized samples. Correlations made between physical properties of the fabric and the fine-structural features of the fiber, both of which were measured, estahlished the fractions of losses arising from molecular degradation and from crosslink embrittlement as a function of the extent of cure. In the shorter cure times, the predominant strength loss came from crosslink embritttement, but this proportion dropped rapidty and molecular degradation became the major source. Changes in degree of polymerization suggest that the catalyzed crosslinking reaction produces a limited chain extension of the cellulose molecule which becomes evident after removal of the crosslinks.

Molecular Characterization of Three Cotton Varieties

Cotton fiber cellulose was dissolved in the solvent dimethyl acetamide with lithium chloride without cleanup or formation of derivatives. Molecular weight distributions of cotton fiber samples were obtained by gel permeation chromatography using com mercially available instrumentation. Upland cotton fiber samples from three varieties (Deltapine Acala 90, Deltapine 41, and DES 422) possessed similar physical properties, indicated by measurements of fiber length, Micronaire, and strength by Stelometer, except for inconsistencies in the HVI strength values compared to those determined by Stelometer. An evaluation of the samples demonstrated different molecular weight distributions, different peak locations of the secondary wall, and different weight average molecular weights.

Gel Permeation Chromatography of Polysaccharides Using Universal Calibration

Abstract Gel permeation chromatography (GPC) has been utilized to characterize a number of representative polysaccharides (i.e., dextrans, pullulans, celluloses, arabinogalactans, amyloses, and amylopectins). N.N-dimethylacetamide with lithium chloride, the solvent of choice for high-molecular weight cellulose analysis, readily dissolved all samples and was also used as the mobile phase. GPC allows calculation and comparison of molecular weight averages and distribution, branching and intrinsic viscosity. The concept of universal calibration, which takes into account the hydrodynamic volume of the molecule, was successfully applied to this set of analyses.

Relationship Between Cotton Fiber Strength and Cellulose Molecular Weight Distribution: HVI Calibration Standards

High volume instrument (HVI) classing of the U.S. cotton crop has focused attention on fiber quality, particularly strength. Characteristic of polymers is the relationship between molecular weight and physical properties. Cotton fibers composed mostly of the polymer cellulose were dissolved in the solvent N,N-dimethylacetamide with lith ium chloride without cleanup or derivatization. Molecular weight distributions were determined by automated, nonaqueous gel permeation chromatography; HVI calibra tion standard cottons possessing a range of fiber lengths and strengths were sampled. Molecular compositional profiles indicate correlation of higher average molecular weight with greater strength of cotton fibers.

Photoinduced electron-transfer reactions of aryl glycosides☆

Abstract The photolytic effects of ultraviolet, as well as other electromagnetic, radiation on carbohydrates are of interest in connection with photodegradation of cellulose and potential application in the photolytic cleavage of lignocellulosic bonds. Aryl glycosides, model compounds for lignocellulosic systems, were irradiated under conditions selected to achieve photoinduced electron-transfer. Various anomeric phenyl d -gluco- and d -galacto-pyranoside solutions in acetonitrile saturated with oxygen, air, or nitrogen and containing 1,4-dicyanonaphthalene (DCN) were irradiated at 350 nm for extended periods, and cleavage of the radical cation formed upon electron transfer to give the simple monosaccharide and phenol was observed. In the presence of methanol, it is possible to intercept the cationic intermediate, with formation of the correspondingmethyl glycosides. Control experiments conducted in the presence of oxygen, air, or nitrogen in the absence of DCN showed little or no conversion. Comparison of the modes of fragmentation in solution with those observed in the gas phase upon electron impact in the mass spectrometer was made, and mechanisms for the reactions induced by electron transfer under these conditions are proposed.