Sequential Alkaline Extraction Research Articles

Improving the anti-mould capacity of bamboo through sequential alkaline extraction and laccase-mediated thymol modification

• An integrated anti-mould treatment of bamboo was effectively established. • Nearly no mould could grow on the modified bamboo with high hydrophobicity under investigation. • Relationships between anti-mould capacity and bamboo properties were summarized. The poor solubility of thymol restricts laccase catalytic efficiency for enhancing bamboo durability against exogenous mould. Herein, an integrated process of bamboo modification was established to improve the anti-mould capacity of bamboo through alkaline extraction and laccase-mediated thymol modification. The results showed that increased thymol dosages from 0 to 10.0% could significantly extend mould resistance activity persistence under laccase catalysis. Nearly no moulds could be found on the L-0.25Thy surface through the integrated strategy under a 30-day mould resistance test. The surface hydrophobicity of the modified bamboo increased from 52.5° to 123.5° due to various extents of thymol fixation. Multiple characterisation methods were employed to better grapple with the modified bamboo's chemical changes. This work demonstrates the complex dependence of improving the anti-mould capacity of bamboo through sequential alkaline extraction and laccase-mediated thymol modification to unlock the potential avenue to bamboo preservation.

Fractionation of carbohydrate polymers from Indonesian sorghum by-products

Extraction of cellulose and hemicellulose from natural resources has attracted considerable interest. In comparison to other cereals, there is relatively little knowledge on the cellulose, hemicellulose and lignin content of sorghum by-products. As such, the aims of this study were to develop a multi-step process for sorghum by-products (bran, stalk and panicles) fractionation and characterise them with regards to their physicochemical properties. In terms of chemical composition, sorghum panicles were found similar to bran, featuring a significant presence of arabinoxylans as well. A sequential alkaline extraction with varying concentrations of NaOH was applied, resulting in the generation of three fractions (residue, hemicellulose and alkali soluble lignin). Fractionation of sorghum stalks with 1.0 M NaOH at 50 °C for 3 h obtained ~64 % (w/w) cellulose rich fraction and 52 % (w/w) of xylose, predominant in the hemicellulose fraction. In the bran, the fractionation with 0.75 M NaOH at 50 °C for 3 h obtained ~40 % (w/w) cellulose rich fraction. Approximately 76 % of the glucose was in hemicellulose fraction reflecting starch solubilisation in the case of bran, while nearly 2 % (w/w) alkaline-soluble lignin was extracted. Overall, this study demonstrated an effective approach for the fractionation and the recovery of key components in sorghum by-products.

Enzymatic response of ryegrass cellulose and hemicellulose valorization introduced by sequential alkaline extractions

BackgroundIn view of the natural resistance of hemicelluloses in lignocellulosic biomass on bioconversion of cellulose into fermentable sugars, alkali extraction is considered as an effective method for gradually fractionating hemicelluloses and increasing the bioconversion efficiency of cellulose. In the present study, sequential alkaline extractions were performed on the delignified ryegrass material to achieve high bioconversion efficiency of cellulose and comprehensively investigated the structural features of hemicellulosic fractions for further applications.ResultsSequential alkaline extractions removed hemicelluloses from cellulose-rich substrates and degraded part of amorphous cellulose, reducing yields of cellulose-rich substrates from 73.0 to 27.7% and increasing crystallinity indexes from 31.7 to 41.0%. Alkaline extraction enhanced bioconversion of cellulose by removal of hemicelluloses and swelling of cellulose, increasing of enzymatic hydrolysis from 72.3 to 95.3%. In addition, alkaline extraction gradually fractionated hemicelluloses into six fractions, containing arabinoxylans as the main polysaccharides and part of β-glucans. Simultaneously, increasing of alkaline concentration degraded hemicellulosic polysaccharides, which resulted in a decreasing their molecular weights from 67,510 to 50,720 g/mol.ConclusionsThe present study demonstrated that the sequential alkaline extraction conditions had significant effects on the enzymatic hydrolysis efficiency of cellulose and the investigation of the physicochemical properties of hemicellulose. Overall, the investigation the enzymatic hydrolysis efficiency of cellulose-rich substrates and the structural features of hemicelluloses from ryegrass will provide useful information for the efficient utilization of cellulose and hemicelluloses in biorefineries.

COMPARATIVE CHARACTERISTICS OF THE CHEMICAL COMPOSITION OF SOME REPRESENTATIVES OF BROWN ALGAE OF THE WHITE AND YELLOW SEAS

Brown algae are a valuable source of a variety of biologically active compounds. Their accumulation is influenced by many environmental factors in which macrophytes grow. The purpose of this study is to carry out comparative studies of the general chemical composition of brown algae in the White and Yellow Seas to substantiate the possibility of their use as raw materials for obtaining new pharmaceutical substances. Using the proposed scheme, which involves sequential supercritical fluid, acid, alkaline and water extraction, it was possible to isolate various components of brown algae, including a protein-polysaccharide complex, which in the case of the species Laminaria digitata and Laminaria saccharina is more than 80% cellulose and squirrel. The data obtained by FTIR spectroscopy confirm the qualitative composition of the complexes and also indicate its purity. Significant differences were revealed in the chemical elemental and component composition, which are affected by the growing conditions of macrophytes. The resulting chemical compounds from brown algae biomass, in particular the protein-polysaccharide complex, have a high potential for obtaining new pharmacological preparations based on them for health protection purposes. Based on the previously obtained data, it can be assumed that this complex has a double activity – enterosorption and immunomodulatory.

Characterisation of allelochemical compounds signature in two mangrove forest species of Rhizophora apiculata and Acrostichum aureum and potential in suppressing weed growth

Rhizophora apiculata and Acrostichum aureum are a common mangrove species in Malaysia. Allelochemical interaction of the mangrove species was speculated to play an important role in dominance in the harsh mangrove environment. This study assessed the quantitative and qualitative determination for total phenolic content and individual phenolic compounds as allelochemical content for R. apiculata and A. aureum leaves as a potential allelopathic substance. The second objective is to investigate the allelopathic effect towards weed germination and growth through in vitro model system. Two types of maceration extraction comprising water extraction and sequential alkaline extract were used for allelochemical screening analysis. Both extractions were separated by ethyl acetate. Acrostichum aureum had the highest total phenolic content (1129.52 µg GAE/g DW) in comparison with R. apiculata. Meanwhile, the quantitative analysis by HPLC, revealed that different extraction detected different individual phenolic acid, Caffeic acid detected in both mangrove species in sequential alkaline extraction by A. aureum. The allelopathic effect of Chloris barbata for A. aureum extract indicated that during pre-emergent development, the suppression of weed growth was higher compared to post-emergent. Therefore, A. aureum may work as an allelochemical producer and can contribute to the establishment of pure colonies of A. aureum in the mangrove ecosystem.

Acid hydrolysis of xylan polysaccharides fractions isolated from argan (Argania spinosa) leaves

Xylan polysaccharides previously obtained from argan (Argania spinosa) leaves by sequential alkaline extractions and purified by chromatography on Sepharose CL-4B were fragmented by acid hydrolysis in 2 M HCl. The resulting fragments were separated by gel filtration on Biogel P2. The oligosaccharide fractions obtained were then characterized by gas–liquid chromatography (GLC) and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The results show the presence of acidic oligosaccharide motifs, some of which composed of xylose and 4-O-methylglucuronic acid and other ones comprising rhamnose and galacturonic acid.

Structural Investigation of Cell Wall Xylan Polysaccharides from the Leaves of Algerian Argania spinosa.

Xylan-type polysaccharides were isolated from the leaves of Argania spinosa (L.) Skeels collected in the Tindouf area (southwestern Algeria). Xylan fractions were obtained by sequential alkaline extractions and purified on Sepharose CL-4B. The xylan structure was investigated by enzymatic hydrolysis with an endo-β(1→4)-xylanase followed by chromatography of the resulting fragments on Biogel P2, characterization by sugar analysis and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS ). The results show that the A. spinosa xylan is composed of a β-(1→4)-d-xylopyranose backbone substituted with 4-O-methyl-d-glucuronic acid and L-arabinose residues.

Preparative yield and properties of humic acids obtained by sequential alkaline extractions

The preparative yield, composition, and structure of humic acids obtained by sequential alkaline extractions from two soils (a soddy-podzolic soil under forest and a typical chernozem in treatment with permanent black fallow of a long-term experiment since 1964) have been studied. The preparative yield of humic acids from the first extraction is 0.40 and 0.94% for the soddy-podzolic soil (Retisols) and the chernozem, respectively. The preparative yield from the second extraction is lower by several times, and the yield from the third extraction is lower by an order of magnitude. The study of the obtained preparations by elemental analysis, gel-permeation chromatography, and 13C NMR spectroscopy has shown insignificant changes in the elemental, molecular-weight, and structural-group composition of humic acids among the extractions. It has been supposed that this is related to the soil features: typical climatic factors for the formation of soil subtype in the case of soddy-podzolic soil and the land use in the long-term experiment in the case of typical chernozem. It has been concluded that that a single extraction is sufficient for the separation of humic acids and the preparation of a representative sample.

Isolation of structurally distinct lignin–carbohydrate fractions from maize stem by sequential alkaline extractions and endoglucanase treatment

Sequential fractionation of extractive-free maize stems was carried out using two mild alkaline extractions (0.5 and 2M NaOH, 20°C, 24h) before and after endoglucanase treatment. This procedure provided two lignin–carbohydrate fractions (LC1 and LC2) recovered after each alkali treatment. LC1 and LC2 contained 39% and 8% of the total lignin amount, respectively. These two fractions contained structurally distinct lignin molecules. While the content of resistant interunit bonds in lignin was 77% in LC1, it was increased up to 98% in LC2. Not unexpectedly, both alkali-soluble fractions contained substantial amount of p-coumaric and ferulic acids ether-linked to lignins. These results outline heterogeneity of maize stem lignins related to fractionation of grass materials.

The carbon distribution among the functional groups of humic acids isolated by sequential alkaline extraction from gray forest soil

Preparations of humic acids (HAs) were isolated from a gray forest soil by sequential alkaline extraction. From a sample of 500 g, HA preparations of 2.24, 0.23, and 0.20 g were obtained from the first, second, and third alkaline extracts, respectively. The structure of the preparations was determined by 13 C NMR spectroscopy. At each next extraction step, the portion of aliphatic fragments in the HA preparations increased and the content of aromatic structures decreased. The conclusion was drawn that a single extraction is sufficient for obtaining a representative HA sample.

Structure of humic acids isolated by sequential alkaline extraction from a typical chernozem

It was shown with the isolation of a humic acid (HA) preparation from a typical chernozem by sequential alkaline extraction as an example that the preparative yield of HAs decreased at each sequential extraction stage by 3–4 times. On the basis of studying the obtained preparations using elemental analysis, gel-penetration chromatography, and 13C NMR spectroscopy, the tendencies of the changes in the structural-group and molecular-weight compositions of the HAs from one extraction stage to the next one were revealed. The conclusion was drawn that a single extraction is sufficient for obtaining a representative HA sample.

Molecular Characteristics of Corn Fiber Gum and Their Influence on CFG Emulsifying Properties

ABSTRACTThe molecular characteristics of two purified arabinoxylan fractions derived from corn kernels, corn fiber gum‐1 and ‐2 (CFG‐1 and ‐2), have been studied and correlated with emulsifying properties. CFG‐1 and ‐2 fractions were isolated from different corn fiber sources by 1) a sequential alkaline extraction and H2O2 bleaching to produce CFG‐1; and 2) additional H2O2 treatment of the alkali‐extracted residue at pH 11.5, yielding CFG‐2. Multiangle laser light‐scattering and online viscosity were used to measure the molar mass, polydispersity, structure compactness, and intrinsic viscosity of the generated CFG fractions. Emulsification properties in an oil‐in‐water emulsion system with 10:1 oil‐to‐gum ratio was investigated by measuring turbidity of an aliquot from the bottom of the diluted emulsion over 10 days. The isolated CFG‐2 from each fiber source was higher in weight‐average molar mass (Mw) polydispersity) (Mw/Mn) and structure compactness, and also lower in solution weight‐average intrinsic viscosity (ηw) than the corresponding CFG‐1. Average Mw and ηw values were 244–491 kDa and 1.35–1.84 dL/g, respectively. The emulsion stabilizing capacity of CFG‐2 from each fiber source was superior to the corresponding CFG‐1.

Fractional isolation and structural characterisation of hemicellulosic polymers from delignified and ultrasonic irradiated sugarcane bagasse

AbstractHemicellulose-type polysaccharides were isolated from the delignified and ultrasonic irradiated sugarcane bagasse by a sequential two-step alkaline extraction. It was found that the successive extractions with 15% and 18% KOH for 2 h, 15% and 18% NaOH for 2 h, 8% and 10% KOH for 15 h, and with 8% and 10% NaOH for 15 h resulted in a total dissolution of 89.6%, 92.8%, 94.9%, and 97.3% of the original hemicelluloses, respectively. Sugar analysis revealed that xylose was the predominant sugar composition of all the hemicelluloses, comprising 57.4- 68.6% of the total sugars. Arabinose (12.3-18.4%) and glucose (10.8- 14.6%) appeared as the second and third major sugar constituents. Galactose (3.9-8.7%), uronic acids, mainly 4-O-methyl-glucuronic acid (2.7-5.8%), rhamnose (1.2-2.6%), and mannose (0.2-1.3%) were observed as minor constituents. The structural studies by 13C-NMR spectroscopy showed that L-arabino (4-O-methyl-D-glucurono) xylans were the major constituents of the hemicellulosic polymers. Furthermore, the current results also showed that the four alkali-soluble hemicellulosic fractions, isolated during the first step treatment with relatively lower concentrations of alkalis, were more branched and acidic, and had larger molecular weights (Mw, 23100-34500), but lower thermal stability than the other four alkali-soluble hemicellulosic preparations (Mw, 21700-28700), extracted during the second stage treatment with relatively higher concentrations of alkalis.

Corn fiber gum: A potential gum arabic replacer for beverage flavor emulsification

The US food industry would benefit from a domestically produced gum with a dependable supply and consistent quality that can be used for preparing oil-in-water (O-in-W) emulsions, such as citrus oil emulsions for beverages. Corn fiber gum (CFG) is an arabinoxylan (hemicellulose) extracted from the corn kernel pericarp and/or endosperm fiber fractions that can possibly fulfill this need. In this study two different types of CFG, CFG-1 and 2, were prepared from corn fiber collected from different wet or dry corn milling facilities by (a) sequential alkaline extraction and alkaline hydrogen peroxide bleaching and (b) an additional alkaline hydrogen peroxide treatment of the alkali treated residue, respectively. CFG-1 might be linked to the cell wall matrix through ester linkages and CFG-2 by non-ester linkages and/or other strong interactions. The stabilization of O-in-W emulsions by corn fiber and acacia gums was investigated by preparing emulsions with a high pressure homogenizer and monitoring the emulsion breakage by turbidity measurements. All CFG samples were effective emulsifiers but CFG-2 extracted separately from three different corn fiber sources was determined to be a better emulsifier than the corresponding CFG-1. CFGs isolated from wet milled pericarp and endosperm fiber and wet milled pericarp fiber have a higher protein content than CFGs isolated from dry milled pericarp fiber and were determined to be better emulsifiers for the O-in-W emulsion system. The emulsifying properties of all CFGs including an industrial grade commercial CFG were determined to be better than native and modified acacia gums.

Isolation and characterization of xylans from seed pericarp of Argania spinosa fruit

Hemicellulose-type polysaccharides were isolated from the pericarp of seeds of Argania spinosa (L.) Skeels fruit by sequential alkaline extractions and fractionated by precipitation. Water soluble and water insoluble fractions were obtained, purified and characterized by sugar analysis and 1H and 13C NMR spectroscopy. The water soluble fractions were assumed to be (4- O-methyl- d-glucurono)- d-xylans, with 4- O-methyl- d-glucopyranosyluronic acid groups linked to C-2 of a (1→4)-β- d-xylan. The 1H NMR spectrum showed that the water soluble xylans have, on average, one non-reducing terminal residue of 4- O-methyl- d-glucuronic acid for every seven xylose units. The water insoluble fractions consisted of a neutral xylan with linear (1→4)-β- d-xylopyranosyl units.

Effect of pH on the measurement of biogenic silica

For investigations of the biogenic silica content of plankton, sediment trap, and sediment samples, alkaline extraction is the most common procedure. Different extraction techniques, with respect to the pH of the leaching agent and the method applied to correct for the release of SiO2 by non-biogenic silica phases as clays or feldspars, are applied. By sequential extraction of marine sediment samples and clay standards with solutions of pH 8 to 14, we investigated the sensitivity of these leaching techniques to the pH of the leaching solution. In addition to the dissolved silica concentration, the temporal increase of the dissolved aluminum concentration of the leaching agent was measured. For sediments of low biogenic silica content, the results are considerably affected by the pH of the leaching agent and relative deviations of more than 300% were observed. Correction by the calculated SiO2/Al2O3 ratios of non-biogenic silica phases had no significant effect on the observed pH dependence. Measurements of samples which exceed ∼10% biogenic silica are only negligibly affected by the pH of the leaching solution. Based on the pH dependence and investigations of a pure Miocene diatom sample, sequential alkaline extraction with a pH of 12.5 is recommended for the determination of biogenic silica.

Non‐starch polysaccharides from sunflower (Helianthus annuus) meal and palm‐kernel (Elaeis guineensis) meal—investigation of the structure of major polysaccharides

AbstractFor the identification and characterisation of major non‐starch polysaccharides from sunflower (Helianthus annuus L) meal and palm‐kernel (Elaeis guineensis Jacq) meal, extracts obtained by sequential alkaline extraction and delignification of the corresponding cell wall materials were subfractionated by graded ethanol precipitation and size‐exclusion and adsorption chromatography. Determination of the sugar and glycosidic linkage composition of extracts and subfractions and intact cell wall materials allowed the identification and quantification of a variety of polysaccharides. In sunflower meal, cellulose (42% of total non‐starch polysaccharides), pectic polysaccharides (24%), (4‐O‐methyl)‐glucuronoxylans with 8‐11% uronic acid substitution (24%), (gluco)mannans (5%) and fucoxyloglucans (4.5%) were encountered. Major polysaccharides in palm‐kernel meal were linear mannans with very low galactose substitution (78% of total non‐starch polysaccharides), followed by cellulose (12%) and small amounts of (4‐O‐methyl)‐glucuronoxylans and arabinoxylans (3% each).