The comparison of chemical and structural differences of Caribean pine (Pinus caribea L.) wood and bark lignin

The presented paper deals with some chemical properties of Caribean pine wood and bark lignin. In order to obtain necessary data, the following operations and analyses were performed: dioxane lignin isolations, determination of Klason lignin, determination of methoxyl, carboxyl and phenolic hydroxyl groups in dioxane lignins and the nitrobenzene oxidation of both compared lignins and of the risidues remaining after dioxane lignins extraction. The oxidation products were analysed by GLC. The experimental data show that there are moderate differences between compared lignins.     

A comparison of methods of measuring "fibre" in vegetable material

A comparison has been made of four methods of estimating “fibre” in apple, cabbage, celery, turnip and four types of wheat bran. The method of van Soest appeared to be the quickest and applicable to present knowledge. The Southgate method is comprehensive but very time consuming. Lignin estimations by u.v. spectrum were not applicable to vegetables and fruits. In this study the results obtained by the van Soest and Southgate methods are similar. A larger number of samples are necessary to gain data for valid statistical comparisons of methods applicable to vegetable and fruits.     

Variations in anatomy and ultraviolet microspectrometry between normal and brown midrib mutant maizes possessing different rumen degradabilities

Normal and brown midrib mutant (bmr) maize (Zea mays L) were examined for variations in their morphological composition. The degradability of the leaf blade, leaf sheath and stem, proportional area of specific tissues in leaf blade, and the ultraviolet (UV) absorption spectra of cell walls were measured and related to variations in cell wall degradability by rumen microorganisms. The UV and infrared (IR) absorption spectra of the lignins isolated from leaf blades of both types, before and after reduction with sodium borohydride, were recorded. The bmr3 maize had higher dry matter (DM) and neutral detergent fibre (NDF) degradabilities for leaf blade, leaf sheath, and stem than the normal counterpart. Approximately 35% and 26% of the observed difference in DM degradability was attributed to the difference in DM degradability of stem and leaf blade, respectively, and 39% to the difference in DM composition of stem. Distinct differences in tissue degradation of the leaf blades were observed for mesophyll cell walls in the midrib portion, which were thinner and of greater number in the bmr3 maize. Sclerenchyma cells were present only in the vascular bundles in the bmr3 leaf blade, while in the normal type those cells were underneath the epidermis tissue. The bmr3 plant also had large epidermal cells. UV microspectrometry of mesophyll cell walls of the bmr3 maize showed their lower UV absorbance around 320 nm compared to that of the normal, but not at 280 nm. Considerable increase in the UV absorbance at 280 nm was observed for the isolated lignins after reduction, suggesting a lesser degree of lignification in the bmr3 maize tissues. Lowered UV absorbance of the isolated lignin around 320 nm after reduction was associated with the removal of the IR bands at 1730, 1660, 1600, and 1250 cm^?1.     

Characterization of asparagus lignin by HPLC

Lignin is the cell wall component most frequently associated with hardening. Its characterization and quantification are very important to understand the biochemical modifications related to the changes in texture of vegetables such as asparagus (Asparagus officinalis), in which this organoleptic attribute is a very important quality factor. In this study, asparagus lignin from the basal sections of fresh and stored spears was analyzed using 2 methods, the traditional (Klason lignin) and the recently developed derivatization, followed by reductive cleavage (DFRC) method. The latter is a simple and reproducible technique for lignin characterization based on a degradation procedure that produces analyzable monomers and dimers by cleaving alpha- and beta-aryl ethers in lignins. The primary monomers derived from DFRC degradation of lignins are essentially p-coumaryl peracetate, coniferyl peracetate, and sinapyl peracetate. To evaluate the efficiency of the DFRC method, our investigations have been carried on distinct sample types, including wood (data not shown), straw, and asparagus samples. The results have confirmed that lignin composition is affected by plant nature. It has been found that whereas wood samples mostly contain coniferyl units, plant foods, such as straw and asparagus, contain both coniferyl and guaiacyl units.     

造纸黑液中碱木素的提取及其在石化工业中的应用

主要介绍了碱木素的提取,碱木素的结构特性和反应性能。详细阐述了碱木素在石化工业中的应用及其它应用前景。     

Microwave-assisted organic acid extraction of lignin from bamboo: Structure and antioxidant activity investigation

Microwave-assisted extraction in organic acid aqueous solution (formic acid/acetic acid/water, 3/5/2, v/v/v) was applied to isolate lignin from bamboo. Additionally, the structural features of the extracted lignins were thoroughly investigated in terms of C₉ formula, molecular weight distribution, FT-IR, ¹H NMR and HSQC spectroscopy. It was found that with an increase in the severity of microwave-assisted extraction, there was an increase of phenolic hydroxyl content in the lignin. In addition, an increase of the severity resulted in a decrease of the bound carbohydrate content as well as molecular weight of the lignin. Antioxidant activity investigation indicated that the radical scavenging index of the extracted lignins (0.35–1.15) was higher than that of BHT (0.29) but lower than that of BHA (3.85). The results suggested that microwave-assisted organic acid extraction provides a promising way to prepare lignin from bamboo with good antioxidant activity for potential application in the food industry.     

The analysis of dietary fibre—the choices for the analyst

The analysis of dietary fibre (which is defined as the sum of lignin and the polysaccharides not digested by the endogenous secretions of the human digestive tract) presents several problems to the analyst. Dietary fibre is a mixture of substances derived from the structural materials of the plant cell wall and a range of polysaccharides of a non-structural nature either present naturally in foods or derived from food additives. The complete analysis of such a complex mixture would be difficult and time consuming and a number of practical alternatives have been used. These include methods based on the enzymatic removal of protein and starch to give an ?indigestible residue’? and procedures based on extraction with neutral detergent solutions. These procedures in their present form do not measure water-soluble components and therefore underestimate dietary fibre. More detailed methods in which the water-soluble and water-insoluble non-cellulosic polysaccharides, cellulose and lignin were measured separately are described. In these the non-cellulosic fraction was characterised in terms of its component sugars. It is suggested that methods of this type are necessary to characterise dietary fibre analytically in order to account for the properties of dietary fibre.     

Chemical and in vivo evaluation of a brown midrib mutant of Zea mays. II. Nuclear magnetic resonance spectra of digested and undigested alkali lignins and undigested dimethyformamide lignins

Nuclear magnetic resonance (n.m.r.) spectra were obtained on the alkali lignins extracted from Tr and bm₁ cornstalks, before and after digestion by sheep, and on the dimethylformamide lignins (DMFL) from undigested cornstalks. Differences due to solvent extraction, plant genotype and digestion were apparent. The bm¹ corn lignin has a higher degree of cross linking of the propane side chain of the lignin molecule than Tr corn lignin, a factor which may be significant in determining the effect of lignin on digestibility. The main effect of digestion was to increase the degree of cross-linking of the propane side chain, especially with the Tr lignin. Alkali lignin n.m.r. spectra were considerably different from DMFL n.m.r. spectra. For example over 40% of the total bm DMFL protons were highly shielded protons but these were virtually absent in the alkali lignins. These highly shielded protons cannot be explained by the presence of ferulic and p-coumaric acids in DMFL.     

Studies on dietary fibre. A method for the analysis and chemical characterisation of total dietary fibre

A procedure for the analysis of total dietary fibre (including non-starchy polysaccharides and Klason lignin) is described. The method consists of extraction of homogenised and/or milled foodstuffs with 80% ethanol and chloroform, and analysis of acidic and neutral polysaccharide constituents, starch and Klason lignin in the residue. Uronic acid constituents were determined by a decarboxylation method, neutral sugar constituents as alditol acetates by a gas-liquid chromatographic method, starch by an enzymic method, and Klason lignin gravimetrically. The sum of anhydrosugars, anhydrouronic acids and Klason lignin from which the starch content is subtracted provides a measure of the total dietary fibre. The method described is reproducible, fairly rapid and gives informative quantitative characterisation of the fibre constituents.     

Comparative study of Caribbean pine (Pinus caribaea L.) wood and bark dioxane lignin

The objective of this paper was to depict some differences between Caribbean pine bark and wood lignin. Gas chromotography (GC) of nitrobenzene oxidation products of extracted wood and bark meals and of corresponding dioxane lignins was performed. The isolated lignins were submitted to IR and UV spectrometry, gel permeation chromatography and differential thermo-gravimetry. The data obtained indicate differences in the contents of condensed bis-guaiacyl structures in the lignins. Contents of phenolic hydroxyl and α-carbonyl groups in both lignins do not markedly differ. There are also certain differences in the thermostability and the molecular weights of compared dioxane lignin preparations.     

Chemical and in vivo evaluation of a brown midrib mutant of Zea mays. I. Fibre, lignin and amino acid composition and digestibility for sheep

Two types of corn (maize) were used which were genetically identical except for a mutant gene (bm₁) in one which reduced the type and amount of lignin produced compared with the normal plant (Tr). The Tr plant appeared to have only slightly lower digestibilities of dry matter and fibre for sheep even though the protein contents of the cornstalks, normally less in the Tr, were equalised by supplementation with soya bean protein. Comparing the acid-detergent method of fibre and lignin determination with an acid-pepsin method revealed that the former method gave values considerably lower than the latter. The alkali—lignin contents of the bm₁ were higher than the acid—detergent lignins which must under-estimate the true lignin content. The acid—pepsin method gave fibre and lignin concentrations which were more closely correlated with rumen digestion of the diets as shown by dry matter loss of the diets suspended into the rumen in nylon bags. This technique also revealed there was a significant increase in the rate of rumen digestion after 69 to 74 h of incubation. Digestion of lignin on the Tr diet could be explained by loss of ferulic and p-coumaric acids. The reduced lignin and p-coumaric acid content of the bm corn was associated in young plants with a low phenylalanine content but normal tyrosine content suggesting that the genetic block in lignin synthesis in this plant may occur between prephenic acid and phenylalanine.     

Dietary fibre in some Norwegian plant foods during storage

The dietary fibre (DF) content of some storage-strong vegetables, grown in Norway, has been determined. The vegetables were collected at harvest time and at intervals during storage, to monitor the DF content during the storage season.Nantes, a variety of carrot, and Hygro, an onion variety, were available throughout the entire period of investigation. A slight decrease in the DF content with length of storage was observed for carrots, but not for onions.With cabbage (Golden Acre, Toten Amager and Blue Top varieties) and rutabaga (Gry and Bangholm varieties) any particular variety was available only for a shorter period (1–4 months), with little overlap between varieties. No systematic change in DF content was observed within any variety during this period. However, differences in DF content from variety to variety within the same vegetable were found.The observed DF variations within each vegetable, whether due to storage or to variety, were relatively slight and need not normally be taken into account when estimating the DF contents of diets containing these vegetables. Some methodological problems are discussed.     

Biological variability in lignification of maize: Expression of the brown midrib bm2 mutation

The cell wall phenolic components in the internodes of three maize genotypes, namely normal, bm2 and bm3 maize, were determined. The bm2 and bm3 brown midrib mutations lowered the lignin content of the bottom, middle and top internodes to a similar extent. However, unlike bm3, the bm2 trait did not induce a sharp reduction of the level of ester-bound p-coumaric acid in maize internodes. The other main alkali labile phenolic acid, ferulic acid, reached similar levels in the three genotypes. The main difference between bm2 and bm3 mutations occurred in the alkyl aryl ether linked structures of the lignin component. In contrast to bm3 lignins, which are characterised by a low syringyl content, the bm2 lignin had a lower content of guaiacyl units than lignin of normal maize internode. Consequently, the syringyl/guaiacyl molar ratio of bm2 lignin gave higher values (2.7–3.2) than those from either normal (0.9–1.5) or bm3 lignins (0.3). The alkali solubility of lignin was also compared between the three genotypes. Incorporation of the bm3 trait in maize led to a high recovery of alkali soluble lignin whereas the bm2 lignin had a similar solubility to the normal one in 2 M NaOH. The monomeric composition of the alkali soluble lignins was consistent with the non-condensed structures of the in-situ polymer. Although the bm3 and bm2 mutations had different effects on lignification, the modification of the cell wall phenolic level was also found in the bm2 maize stem as previously studied.     

Chemical and Structural Analysis of Fibre and Core Tissues from Flax

Samples of flax ( Linum usitatissimum ) stems from the cultivars ‘Natasja’ and ‘Ariane’ were separated into fibre and core fractions and analysed by gas–liquid chromatographic methods, ¹³C CPMAS NMR spectrometry, histochemistry, electron microscopy and UV absorption microspectrophotometry to assist in determining the structure and composition of these cell walls in relation to quality and utilisation. Analyses from chromatography and NMR gave similar results for carbohydrate and phenolic constituents in various samples and in the lower, more mature regions of the stem. Amounts of uronic acids and xylose were lower while amounts of mannose, galactose and glucose were higher in fibre vs core fractions. Quantities of phenolic constituents were significantly higher in the core than the fibre, with groups representative of both guaiacyl and syringyl lignins; amounts of phenolic acids were low. NMR showed a low intensity signal for aromatics in fibre, and it is possible that such signals arise from compounds in the cuticle rather than the fibre. Microscopic studies indicated that aromatic constituents were present in core cell walls, cuticle of the epidermis, and cell corners and middle lamellae of some regions within the fibre tissues. The lignin in fibre appeared to be of the guaiacyl type and may be too low in concentration to be unambiguously detected by NMR. Aromatic compounds were not observed in the epidermis or parenchyma cell walls. Similar analyses of dew-retted (unscutched) samples indicated that core tissues were mostly unchanged from unretted samples. Retted fibre tissues still contained lignified cell corners and middle lamellae in some regions. The cuticle, which was associated with retted fibres, was not degraded by dew-retting fungi. Fungi removed interfibre materials in some places and at times degraded the secondary wall near the cell lumen of fibre cells. Results indicate that microspectrophotometry and histochemistry are useful to identify the location and type of aromatics in fibre cell walls.     

竹材及其磺化化机浆木素结构与发色基团特性研究

研究了白夹竹及其磺化化机浆ＭＷＬ的结构与发色基团的特性，并把两者进行了对比。从而了解了木素特性及其磺化预处理后的变化。由１３Ｃ－ＮＭＲ谱和硝基苯氧化证明，竹料木素是ＧＳＨ型木素。竹料制成浆后，木素的分子量有很大降低，对香豆酸酯含量下降。醌式结构是木素中最主要的发色基团，制成浆后醌式结构有很大的增加。     

Bestimmung der phenolischen Hydroxylgruppen in Ligninen und Ligninfraktionen durch Aminolyse und FTIR-Spektroskopie

The quantitative analysis of phenolic OH groups is of interest for the characterization of isolated lignins when evaluating the extent to which lignin has been changed. While aminolysis is a very accurate if elaborate chemical method, the evaluation of the aliphatic and aromatic IR ester bands of acetylated lignins at 1745 and 1765 cm^?1 permits a quick, easy and reliable determination of the phenolic hydroxyl groups. The excellent correlation between the two methods was proved for 35 different lignins and lignin fractions of different molecular weights.     

A comparison of some chemical and physical properties of alkali lignins from grass and lucerne hays before and after digestion by sheep

The chemical and physical properties of alkali lignins from a grass hay and a lucerne hay were studied, before and after digestion by sheep. A greater proportion of the total grass lignins was dissolved by alkali than with the lucerne lignins but digestion increased this proportion with both species. Of the lignin dissolved by alkali, less of it was precipitated on acidification when faeces (50–70%) were compared with the undigested hays (86–92%). Extraction of lignins with boiling alkali produced a lignin with the smallest amount of amino acids but considerably altered the chemical structure as revealed by nuclear magnetic resonance (n.m.r.). Trypsin treatment of a cooler alkali extract was less effective in reducing amino acid contamination but did not alter the structure. Compared with the grass alkali lignins, the lucerne lignins had more total but fewer aromatic protons, fewer groups reacting with N-2,6-trichloro-p-benzoquinone imine, ionisable hydroxyl groups and fewer methoxyl groups. On Sephadex G-200 gel chromatography, three peaks were apparent with the lucerne, but only two with grass lignins. Both plant lignins showed large amounts of highly shielded n.m.r. protons but there were more with lucerne. Infrared spectra suggested that they were probably due to methyl groups. Digestion had very little effect on the n.m.r., ultraviolet or infrared spectra or the molecular weight distribution of the isolated lignins. It may have reduced the numbers of groups, reacting with N-2,6-trichloro-p-benzoquinone imine with the grass and two maize samples examined, but appeared to have the opposite effect with the lucerne.     

Functional and textural properties of vegetable‐fibre enriched yoghurt

In this study, different vegetable‐fibre enriched yoghurts namely control (C), pumpkin (PY), carrot (CY), green pea (GY) and zucchini (ZY), were produced. It was observed that Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus counts were higher in yoghurts supplemented with vegetable purees, in accordance with the enhanced growth of lactic acid bacteria due to the fibres, phenolic compounds and organic acids present in the vegetables. Furthermore, vegetable puree supplementation affected the pH, titratable acidity, syneresis, colour (L*, a*, b*, ΔE values), texture (firmness, cohesiveness, consistency and viscosity index) and sensorial properties of the yoghurts. Firmness, consistency and viscosity indices were higher in the yoghurt produced with carrot puree, whereas the highest antioxidant capacity was detected in the pumpkin yoghurt, which corresponded to the highest total phenolic, ascorbic acid and total carotenoid contents. The results of the present study could lead to an innovative approach in the functional dairy product market for the development of dairy products enriched with vegetables that have nutritional and potential therapeutic characteristics.     

A comparative study of hard and softwood lignins alterations during treatment in dioxane-water-HCl agent

The objective of the presented contribution was a study of the lignin alterations occurring in the process of the acidolytic delignification of chosen representatives of soft and hard wood species (maple and spruce) in dioxane-water-HCl mixture. All lignin samples were characterised by yield or recovery, molecular weights, as well as by GLC data of corresponding nitrobenzene oxidation products. In order to obtain more information about condensation and degradative reactions of lignin under conditions of acidolytic treatment a simulation of the process of lignin isolation was performed, too. Samples of dioxane lignins obtained after 90 min. of isolation at 82.5 and 98 °C were therefore recooked during 360 min. under identical conditions as applied in the lignin isolations. Concentrations of lignin in the reaction mixture were 1 and 10% thus approximately corresponding the lignin concentration inside and outside of the wood meal during the lignin isolation. The obtained experimental data point out the course of both degradative and condensation reactions. Maple wood lignin undergo deeper degradation than those of spruce under the same reaction conditions. The decreased yields of lignin oxidation products with the time of acidolytic treatment and after recooking hint at the formation of new linkages among building units of lignin thus modifying its macromolecules. The intensity of occurring alterations of examined lignins is not only dependent of time and temperature, but also of the concentration of lignin.     

Fractionation and characterization of ball‐milled and enzyme lignins from abaca fibre

An Erratum has been published for this article in Journal of the Science of Food and Agriculture 79(15) 1999, 2122. Ball‐milled and enzyme lignins were produced from abaca fibre via ball milling for 6 days followed by cellulase treatment for 3 days. The crude lignin preparations were fractionated into milled lignin (ML), enzyme lignin (EL), hemicellulose‐rich milled lignin (HRML), and lignin‐rich enzyme lignin (LREL) fractions using a two‐step precipitation method instead of a traditional ether precipitation procedure. The yield and chemical composition of the resulting lignin samples are reported. The ML and EL fractions contained low amounts of associated neutral sugars (2.0–3.3%) and uronic acids (1.4–1.5%), and showed relatively low average molecular weights (2500–2660), while the LREL and HRML fractions contained large amounts of bound polysaccharides (35.6–38.3%), and showed high molecular weights (8800–25000). The four lignin fractions are composed of a large proportion of syringyl units with fewer guaiacyl and p‐hydroxyphenyl units. The ML is mainly composed of β–O–4 ether bonds between the lignin structural units. The less common β–β, β–5 and 5–5′ carbon–carbon linkages are also present in the lignin molecules. It was found that uronic acids and 41–63% of p‐coumaric acids are esterified to lignin in the three lignin‐rich fractions of ML, EL and LREL. This level increased to over 90% in the hemicellulose‐rich fraction of HRML. For ferulic acids, 92–97% were found to be etherified to lignin in the three lignin‐rich fractions of ML, EL and LREL, while in the hemicellulose‐rich fraction of HRML this reduced to only 13%, suggesting that a majority of the ferulic acids are esterified to hemicelluloses or lignin in this fraction. © 1999 Society of Chemical Industry