High Acetyl Content Research Articles

Effects of monosaccharide composition and acetyl content on the rheological properties of sphingan WL

The novel sphingan WL produced by Sphingomonas sp. WG shows commercial potentials in the fields of medical, food, and petroleum. To elucidate the relationship between the molecular structure and rheological performance, the sphingan WL with different monosaccharide compositions, molecular weight and functional groups were obtained through welJ and pgmW overexpressed strains and partial hydrolysis. Rheological property was characterized at different temperatures and with different cations. Compared with the native WL, the WL-welJ sample produced by the welJ-overexpressed strain had low viscosity and viscoelasticity due to the low molecular weight, high acyl contents and loss of galactose. While, the WL-pgmW produced by the pgmW-overexpressed strain showed a better rheological property. The rheological property of WL samples with different acetyl contents demonstrated that WL with high acetyl content presented high G' and G′' values, but their viscosity decreased with high acetylation degree. Moreover, the gel structure of low acetyl content samples was less sensitive to salt due to the increasing salt bridge effect of the exposing carboxylic groups with Ca2+. We hope that this study would provide valuable information on the structure-function relationship of sphingan WL, and guide the application of sphingan WL.

Short communication: Stabilization of milk proteins at pH 5.5 using pectic polysaccharides derived from potato tubers

Potato pectin has unique molecular characteristics that differentiate it from commercially available pectins sourced from citrus peels or apple pomace, including a higher degree of branching and a higher acetyl content. The objective of this study was to evaluate the ability of potato pectin to stabilize milk proteins at an acidic pH above their isoelectric point, pH 5.5, at which no citrus- or apple-derived pectins are functional. Potato pectin was extracted from raw potato tubers by heating at pH 4.5 and 120°C for 30 min after removing starch solubilized using a dilute HCl solution adjusted to pH 2. The potato pectin was found to have a galacturonic acid content of 17.31 ± 3.29% (wt/wt) and a degree of acetylation of 20.20 ± 0.12%. A portion of the potato pectin was deacetylated by heating it in an alkaline condition. The deacetylation resulted in a galacturonic acid content of 19.12 ± 4.64% (wt/wt) and a degree of acetylation of 3.03 ± 0.03%. Particle size distributions in acidified milk drink (AMD) samples adjusted to pH 5.5 demonstrated that the acetylated and deacetylated potato pectins were capable of inhibiting the aggregation of milk proteins to the largest degree at a pectin concentration of 1.0 and 0.25% (wt/wt), respectively. Pectin molecules that were not bound to milk proteins in these AMD samples were quantified after centrifugally separating milk proteins and pectin bound to them from the serum. We found that, for the acetylated and deacetylated potato pectins, all or approximately half of the pectin molecules were bound to milk proteins at a pectin concentration of 0.25 or 1.0% (wt/wt), respectively. These results suggest that the presence of acetyl groups is a critical factor that determines how potato pectin molecules bind electrostatically to milk protein surfaces, form 3-dimensional structures there, and function as a stabilizer. The present results demonstrate that potato pectin can stabilize milk proteins at pH 5.5 and potentially enable the development of novel AMD products with improved functionality for casein-containing products with moderately acidic pH profiles.

Acetyl Groups in Typha capensis: Fate of Acetates during Organosolv and Ionosolv Pulping.

During biomass fractionation, any native acetylation of lignin and heteropolysaccharide may affect the process and the resulting lignin structure. In this study, Typha capensis (TC) and its lignin isolated by milling (MWL), ionosolv (ILL) and organosolv (EOL) methods were investigated for acetyl group content using FT-Raman, 1H NMR, 2D-NMR, back-titration, and Zemplén transesterification analytical methods. The study revealed that TC is a highly acetylated grass; extractive free TC (TCextr) and TC MWL exhibited similar values of acetyl content: 6 wt % and 8 wt % by Zemplén transesterification, respectively, and 11 wt % by back-titration. In contrast, lignin extracted from organosolv and [EMIm][OAc] pulping lost 80% of the original acetyl groups. With a high acetyl content in the natural state, TC could be an interesting raw material in biorefinery in which acetic acid could become an important by-product.

Cacao pod husks as a source of low-methoxyl, highly acetylated pectins able to gel in acidic media

Cacao pod husks, the main by-product from cocoa production, have been investigated for pectin isolation. In the present study, the rheological properties of two low-methoxyl (LM) pectins isolated from cacao pod husks using different extraction conditions were evaluated. One pectin was obtained from optimized conditions employing aqueous nitric acid as an extractant, and the other one was extracted with boiling water. Pectin gels (0.99% galacturonic acid equivalent, w/w) were prepared at pH 2.5–3.0 in the presence of 60% sucrose (w/w) and subjected to rheological analysis. Dynamic oscillatory experiments at 25°C indicated that better gels were obtained at the lowest pH (2.5). Steady shear measurements revealed a shear-thinning behavior. The apparent viscosities of the samples increased as pH decreased. Gelation with calcium ions was not observed for either of the highly acetylated LM pectins analyzed. The rheological analysis results showed that despite their high acetyl content, LM pectins extracted by different methods from cacao pod husks were able to form gels at low pH under reduced water activity, suggesting a possible application in acidic products.

Mode of action of Bacillus licheniformis pectin methylesterase on highly methylesterified and acetylated pectins

A gene encoding a putative pectinesterase from Bacillus licheniformis DSM13 was cloned and expressed in Escherichia coli. The resulting recombinant enzyme (BliPME) was purified and characterized as a pectin methylesterase. The enzyme showed maximum activity at pH 8.0 and 50°C. BliPME is able to release up to 100% of the methylesters from lime pectin (DM 34–76→DM 0) and up to 73% of all methylesters from SBPs (DM 30–73→DM 14). BliPME efficiently de-methylesterifies lemon pectins and SBPs in a blockwise manner and is quite tolerant towards the acetyl groups present within the SBPs. Detailed analysis of the BliPME-modified pectins using HILIC–MSn and the classical calcium reactivity measurement showed that the enzyme generates pectins with low methylesterification (lime and SBP) and high acetyl content (SBP) while creating blocks of nonmethylesterified galacturonic acid residues. The high activity of BliPME towards highly methylesterified and acetylated pectins makes this novel esterase more efficient in removing methylesters from highly esterified beet pectin compared to other PMEs, e.g. Aspergillus niger PME.

Highly acetylated pectin from cacao pod husks (Theobroma cacao L.) forms gel

A pectin (OP) obtained from cacao pod husk with a high acetyl content, which is a structural feature that could disturb the pectins' gel formation, was able to form gels at low pH and a high sucrose content. Pectin gels (1.32% GalA equivalent, w/w) were prepared at pH 2.5–3.3 in the presence of 60% sucrose (w/w). Rheological analyses were performed to determine the optimal pH for further studies. Next, the OP samples were prepared at pH 2.7 in concentrations ranging from 0.33 to 1.98% GalA (w/w) with 60% sucrose (w/w) and subjected to rheological analysis. Dynamic oscillatory experiments at 25 °C indicated the presence of gels for all of the analysed concentrations. Measurements of the elastic (G′) and viscous (G″) moduli at 25 °C also indicated that increasing the pectin concentration resulted in stronger gels. Rotational experiments revealed a shear-thinning behaviour in which the apparent viscosities of the samples increased as the concentration increased. Although the OP had a high degree of acetylation, this pectin was able to form gels, which suggests its potential for use as a gelling and thickening additive.

Extraction and characterization of sunflower pectin

Chemical composition and rheological properties of sunflower pectin, including gel-point temperature ( T g) were determined. Pectin from sunflower head residues was characterized and compared with low methoxyl commercial pectins. Pectin was isolated using sodium hexametaphosphate extraction followed by either acidified alcohol (KIM) or HCl solution (LIN) precipitation. LIN pectin resulted with a higher ash content (≈30%).The low methoxyl pectin extracted from sunflower heads had 11% degree of esterification, high anhydrogalacturonic acid content (77–85%) and low acetyl content (2.3–2.6%) on an ash-free basis. Viscosity average molecular weight ranged from 39,500 to 52,000. Sunflower pectin formed gels at high temperatures almost instantly in the presence of calcium ions.

Acetylation of solid wood using microwave heating

× t × l) of the same origin were acetylated separately, but under the same conditions in the microwave reactor. The variation in acetyl content both within and between the samples was less than 2% units. In general, a somewhat higher acetyl content was obtained in the middle of the acetylated wood than in the outer part of it. Microwave energy was also shown to be efficient in the removal of excess acetic anhydride and by-product acetic acid by evaporation under vacuum. During the vacuum step, about 70% of the chemicals could be removed within the first 30 minutes. Pine and spruce wood samples acetylated for 2 hours at 130 °C followed by a vacuum step for two hours at 120 °C, obtained an acetyl content of about 17% and the content of residual chemicals was about 3% calculated on a basis of dry acetylated wood. The temperature in the wood samples could be maintained at about 130 °C even at very low contents of residual excess chemicals without any formation of hot spots.

13C CP/MAS NMR Spectroscopy in the Analysis of Pectins

13C CP/MAS NMR spectra of powder commercial pectins were recorded and interpreted. NMR spectral results were applied for the calculation of galacturonic acid content (GalA), degrees of methylation (DM) and acetylation (DA). In most cases NMR values from GalA and DM agreed with values obtained by conventional methods (photometry and HPLC). The determination of DA using NMR data was successful only in the case of sugar beet pectin with high acetyl content. The C-6 carbon region was studied in detail and the chemical shift and the shape of peaks in this region were strongly influenced by the ratio of uronic carboxyl forms. Correlation between C-6 carbon chemical shift and DM values for pectins in their protonated form was evaluated.

Extraction, characterisation, and enzymatic degradation of lemon peel pectins

The albedo of Spanish lemons (16.0% w/w oof lemon fresh weight) was extracted to obtain a chelating agent soluble pectin fraction, a diluted sodium hydroxide soluble pectin fraction and a residue (4.2, 1.8, and 5.0% w/w of fresh albedo, respectively). These fractions represented 61.3, 12.4, and 10.4% of the galacturonic acid present in the albedo, respectively. Fractions were (MHR) (1.4% w/w of fresh albedo), solubilised from the albedo after treatment by a technical enzyme preparation. All extracted pectins were rich in galacturonic acid, next to varying amounts of arabinose, galactose, and glucose residues. Based on molecular size, albedo-MHR consisted of at least five populations. From the rhamnose:galacturonic acid ratio (0.2–0.28), the high acetyl content and the degradability by rhamnogalacturonase, it was concluded that the four major fractions represent rhamnogalacturonans having only small differences within their fine structure. The fifth fraction contained more galacturonic acid and was only degraded by polygalacturonase.

A preliminary characterization of some pectins from quince fruit ( Cydonia oblonga Mill.) and prickly pear ( Opuntia ficus indica) peel

The preliminary characterization of a hot acid extracted pectin from quince ( Cydonia oblonga Mill.) and from prickly pear ( Opuntia ficus indica) peel was carried out. The yield of the extraction, the galacturonic acid content and the neutral sugar composition were determined and compared with published data on apple and lemon pectins The pectin yield from quince was on average 0·53% on fresh weight, which is of a similar order to apple. The quince pectin had a high galacturonic content (about 78%), and a degree of methoxylation of about 59% corresponding to a medium-high methoxyl pectin. The prickly pear pectin yield was 0·12% on fresh weight. This pectin had a galacturonic acid content of 64%, a low degree of methoxylation (10%), a high acetyl (10%) and neutral sugar content (51% galacturonic). It might be related to similar polygalacturonides present in the mucilages of other Cactaceae.

Location of a second O-acetyl group in xanthan gum by the reductive-cleavage method

Xanthan gum is the extracellular polysaccharide produced by the bacterium Xanthomonas campestris. Its structure has been shown’,’ to consist of a (1 -+ 4) linked /3-D-glucan backbone with P-D-Manp-(I + 4)-P-D-GlcpA-(1 -+ 2)(U-DManp-(1 + side chains substituted at O-3 of alternating glucose residues. In addition, the side chains may contain 0-acetyl and pyruvic acid acetal groups, which are located at the 6-position of the internal mannose residue and at the 4,6-position of the terminal mannose group, respectively. The amount of noncarbohydrate substituents vary depending on the strain of bacteria, the fermentation conditions and the recovery procedure3-5. Samples of xanthan gum with high acetyl content have been observed6. The proportion of acetyl groups was shown to exceed the theoretical value of one residue per pentasaccharide repeat unit. Although the location of additional acetyl groups is uncertain, it has been speculated that multiple acetylation of the internal mannosyl residue is possible in some xanthan gum samples, as is acetylation of the terminal mannosyl group’. In X. campestris, three genes have been identified8,9 that encode enzymes which catalyze modifications of mannose residues. It was later shown” that one of these genes encodes an acetylase activity, termed acetylase II, directing acetylation of the terminal mannose group; however, the position of substitution was not determined. We now report the location of a second 0-acetyl group in xanthan gum using the reductive-cleavage technique”. A sample of xanthan gum was hydrolyzed using trifluoracetic acid and analyzed for the presence of organic acids by high-performance liquid chromatography (HPLC). The results of this analysis indicated the presence of acetic acid (6.8%) and pyruvic acid (2.7%). Assuming a sodium form of xanthan gum containing an average of 1.0 acetyl groups and 0.5 pyruvic acid acetal substituents per repeat unit, the theoretical content for acetic acid and pyruvic acid is 6.3 and 4.4%,

アセチル化によるＴＭＰの改質とアセチル化がシート強度に及ぼす影響

In order to modify the mechanical properties of high-yield pulps, thermomechanical pulp (TMP) and the other pulps were acetylated by a acetic acid/acetic anhydride/sulfuric acid mixture under the swelling condition (method A) or by a toluene/acetic anhydride/perchloric acid mixture (method B), and then the physical properties and sheet strengths of acetylated pulps were measured.The water retention value (WRV) of acetylated TMP did not depend solely on the degree of acetyl substitution. TMP acetylated by method A produced sample having high WRV up to 402%, while acetylation of TMP by method B gave pulp with less WRV than the value of the original pulp (108%).The total heat of wetting (THW) of acetylated TMP also was determined calorimetrically. The change in THW was markedly affected by the methods of acetylation. The THW of acetylated TMP having lower acetyl contents up to 20%, which was prepared by method A, was almost same with the value of original TMP. But, the THW of acetylated TMP with higher acetyl content and all acetylated TMP prepared by method B decreased sharply with an increase in acetyl content.The sheet strengths, such as, tensile strength, tear factor and burst factor of sheet from TMP acetylated by method A showed maxima at 20% of acetyl content, while these strengths of the pulp sheets acetylated by method B decreased gradually with an increase in acetyl content.From the change in morphological structure of acetylated TMP, it is indicated that swelling occurs only in TMP acetylated by method A and that interfiber contact area increases in the sheets from the TMP.

Analysis of bacterial exopolysaccharides.

Extracellular polysaccharides have been isolated from cultures of freshwater and marine bacteria originally isolated from material adhering to surfaces and underivatized hydrolysates have been analyzed by high-performance liquid chromatography methods. A scheme has been developed whereby the uronic acids can be identified on strong anion-exchange columns, while neutral monosaccharides can be separated and identified using aminobonded columns or cation-exchange adsorbent loaded with a heavy metal ion. The methods permit rapid and accurate comparison of polysaccharides with differing chemotype. The strains studied show a range of different chemotypes, all containing a uronic acid and several neutral monosaccharides. Some of the polysaccharides isolated from marine bacteria possessed a very high acetyl content.

Effect of Growth Conditions on the Production, Composition and Viscosity of Xanthomonas campestris Exopolysaccharide

Summary: A streptomycin-resistant variant of Xanthomonas campestris was grown in defined nutrient-deficient media in both batch and continuous culture. The production, composition and viscosity of the extracellular polysaccharide (xanthan) synthesized by this strain were influenced by the fermentation time and nutrient exhaustion in batch culture and by the dilution rate in continuous culture. The specific rate of exopolysaccharide synthesis was maximal during exponential growth in all of the nutrient-deficient media studied although some xanthan was formed during stationary phase. The concentration of exopolysaccharide decreased at later stages of stationary phase in some cultures. Both the extent of acylation and the consistency index of xanthan isolates were low or minimal during exponential growth, maximal in polysaccharide isolated as the growth rate fell and usually lower after this time. Between dilution rates of 0·03 and 0·06 h−1 in chemostat culture, the cell and exopolysaccharide dry weights were independent of dilution rate, the specific rate of xanthan synthesis decreasing at lower growth rates. Although the variation in the acyl content and consistency index was less than that observed in batch culture, exopolysaccharide isolated at higher dilution rates tended to have a higher acetyl content, lower pyruvyl content and lower consistency index.

Characterization of dermatan sulfate and heparan sulfate in the urine of a patient with the hunter syndrome.

Glycosaminoglycan isolated from the urine of a patient with the Hunter syndrome was composed of heparan sulfate (59.9%), dermatan sulfate (30.6%) and chondroitin sulfate (9.5%), and was heterogeneous in molecular weight (1,500-10,000) and in sulfate content (0.35-2.05 moles/mole of hexosamine). About 60% of dermatan sulfate and 10% of heparan sulfate had molecular weight of 7,000 to 10,000, while about 10% of the former and 60% of the latter had those of 1,500 to 3,500. Sulfate contents of dermatan sulfate and heparan sulfate were inversely related to their molecular weights. Higher total- and N-sulfate contents were measured in smaller molecular-weight heparan sulfate, and higher acetyl content was in larger molecular-weight heparan sulfate. On the basis of the chemical properties of dermatan sulfate and heparan sulfate isolated in this experiment, their catabolic processes in the Hunter syndrome were discussed.

DISSOLVED STATE OF CELLULOSE DIACETATE IN ACETONE

Dissolved state of cellulose diacetate in acetone was studied by means of gel-permeation chromatography (GPC), thin-layer chromatography and infra-red spectroscopy. Four peaks were detected in general in GPC elution curves named from lower count region prehump I, prehump II, mainhump, and posthump, respectively. Prehump I is attributed to the molecular aggregates of cellulose acetate with relatively high acetyl content (57-58%). This is principally equivalent to prehump in tetrahydrofuran found in the previous paper and is largely extractable with good solvents for cellulose triacetate. Prehump II is the molecular aggregates of cellulose diacetate having large molecular weight, which is closely connected with the contents of sodium, calcium and sulfuric acid. Prehump II can be removed by treating the sample with dilute acid solutions. Mainhump is due to the moleculary dispersed particles. The complicated dissolved state of cellulose diacetate in acetone, thus found, is ascribed partly to the distribution of degree of substitution (acetyl content) as well as molecular weight distribution and it is also due in part to the contamination of sodium and calcium as impurity and of sulfuric acid as combined ester in the original polymer.

DISSOLVED STATE OF CELLULOSE DIACETATE IN TETRAHYDROFURAN

Dissolved state of cellulose diacetate in tetrahydrofuran (THF) was studied by means of gel-permeation chromatography (GPC), thin-layer chromatography (TLC) and infra-red spectroscopy (IR). Two peaks were detected in GPC elution curves; the main peak at a higher count region is attributed to molecularly-dispersed cellulose diacetate. In the region of the main peak, the GPC curve reflects mainly the fractionation with respect to molecular size. The smaller peak at the lower count region (i.e., prehump) is attributed to the aggregates of 0.3-0.8)μ in diameter, which are composed of hemicellulose acetate and cellulose acetate with relatively high acetyl content. The components of prehump were predominantly precipitated together with cellulose acetate with high acetyl content into the first fraction when cellulose diacetate was fractionally precipitated with acetone/water system. The prehump content decreased remarkably with increased duration of hydrolysis or by extracting with good solvents for cellulose triacetate.

Alginic Acid Diacetate

BELIEVING that the usual methods of acetylation give degraded products, Wassermann1 has attempted to acetylate alginic acid with ketene. By this means he succeeded in introducing approximately one acetyl group into each repeating unit of the polymer. Some years ago we studied the action of ketene on alginic acid under various conditions, and although products with a higher acetyl content (20.9 per cent) than Wassermann's were obtained, the method was abandoned in favour of a simpler and more effective procedure2.

Citrus pectin

The albedo of Spanish lemons (16.0% w/w oof lemon fresh weight) was extracted to obtain a chelating agent soluble pectin fraction, a diluted sodium hydroxide soluble pectin fraction and a residue (4.2, 1.8, and 5.0% w/w of fresh albedo, respectively). These fractions represented 61.3, 12.4, and 10.4% of the galacturonic acid present in the albedo, respectively. Fractions were (MHR) (1.4% w/w of fresh albedo), solubilised from the albedo after treatment by a technical enzyme preparation. All extracted pectins were rich in galacturonic acid, next to varying amounts of arabinose, galactose, and glucose residues. Based on molecular size, albedo-MHR consisted of at least five populations. From the rhamnose:galacturonic acid ratio (0.2–0.28), the high acetyl content and the degradability by rhamnogalacturonase, it was concluded that the four major fractions represent rhamnogalacturonans having only small differences within their fine structure. The fifth fraction contained more galacturonic acid and was only degraded by polygalacturonase.