RU2454429C2 - Method of producing arabinogalactan - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of producing arabinogalactan. The method involves aqueous extraction of arabinogalactan from resin-free larchwood while heating. The obtained arabinogalactan extract is purified from high-molecular weight impurities by ultra filtration on hydrophobic membranes with pore size 0.03; 0.05; 0.08 mcm. Further, the extract is concentrated and purified from low-molecular weight impurities on a hydrophilic ultra filtration membrane. The extract then undergoes diafiltration with demineralised water on the same membrane. The end product is extracted via spray drying.

EFFECT: invention enables to obtain arabinogalactan with high degree of purity of up to 96,5-98,0%, cut duration of the purification process and reduce power consumption.

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Description

The invention relates to the chemical industry and for the allocation of larch arabinogalactan (AH) from wood.

Arabinogalactan is a water-soluble polysaccharide of plant origin, which has high biological activity (immunostimulating, prebiotic, antimutagenic, mitogenic, hypolipidemic, etc.) and low toxicity (does not exhibit acute toxicity at a dose of 5 g / kg and chronic toxicity at a dose of 500 mg / kg in day). In addition, AG is characterized by high membranotropy, dispersing ability, good solubility in water, low viscosity of concentrated aqueous solutions. AG is stable in an acidic environment and during heat treatment, it binds fat well and retains moisture, has no taste and smell.

The combination of these valuable properties determines the practical importance of hypertension for use in medicine, pharmaceutical, cosmetic industry, livestock, as well as in the food industry for the creation of therapeutic and prophylactic foods and drinks (bakery, confectionery, dairy, sausages, mayonnaise, desserts, ice cream , drinks, etc.) [1-4].

Known methods for the extraction of arabinogalactan from crushed larch wood by aqueous extraction without first removing phenolic compounds from it [5-9]. A significant drawback of these methods is that the extremely valuable biologically active components of larch wood — flavonoids and resinous substances — are not used, so the profitability of processing wood raw materials is significantly reduced. In addition, the implementation of these methods requires expensive equipment (continuous centrifuges, shock acoustic and microwave installations). Isolation of AG by the method [5] additionally provides for the use of an expensive imported polyamide sorbent and large quantities of methyl ethyl ketone — a toxic, flammable and expensive organic solvent. Using the method of [8] microwave exposure will require significant labor protection costs, because It is known that microwave radiation is harmful to the human body. In addition, the significant drawbacks of the methods [6-8] include the use of the method of planting large amounts of toxic flammable organic solvents (acetone, ethanol, dioxane) to isolate dry AG from aqueous extracts, which increases the fire hazard of production, worsens working conditions, and requires significant material costs for the regeneration of solvents.

A more rational method is the separation of arabinogalactan from an aqueous extract by concentrating the extract by ultrafiltration followed by spray drying [5], while the obtained AG contains up to 10% of impurities (monomers and oligomers of AG, minerals, uronic acids), in addition to the disadvantages of this method should include:

- to obtain AG, non-tarred larch wood is used, which leads to the loss of an extremely valuable product - dihydroquercetin, and does not provide sufficient purity of the AG extract;

- multi-stage process and the use of expensive equipment (continuous centrifuges);

- the use of powdered polyamide sorbent, which requires frequent regeneration and does not have industrial production in the Russian Federation.

Due to the noted drawbacks, these methods are low-tech and do not have a real prospect of industrial implementation.

A number of patents are devoted to methods of isolating AH from crushed larch wood after extraction of phenolic components (flavonoids, resinous substances) from it [10-12]. According to the method of [10], arabinogalactan is extracted from the crushed larch wood chips by aqueous extraction at a temperature of 80-90 ° C in a continuous circulation mode for 2 hours after removing dihydroquercetin (DHQ) from it with an organic solvent and drying the chips in a gentle mode. The aqueous extract of AG is concentrated under reduced pressure, treated with aqueous solutions of the coagulant — aluminum sulfate and the Sunfloc flocculant, followed by filtration and precipitation of the AG with four times the volume of ethyl alcohol, decantation of the supernatant, washing the precipitate with alcohol and drying.

The disadvantages of this method are:

- high energy consumption for the concentration of the aqueous extract of AG by evaporation under reduced pressure;

- use for the deposition of AG large quantities of ethyl alcohol, requiring special storage conditions and a special mode of operation with it;

- use together with a flocculant coagulant, which increases the cost of the process and leads to contamination of the product.

A known method of producing arabinogalactan in the complex processing of wood and larch needles [13], according to which arabinogalactan is extracted together with other extractive substances by extraction from wood raw materials with a mixture of an organic solvent with water in an inert gas. The aqueous phase is purified from colloidal impurities by baromembrane filtration using ceramic filters with a hole diameter of at least 10 μm (preferably up to 1000 μm). This process, according to the classification [14, 15], is not ultrafiltration, because with pore sizes greater than 10 microns, conventional classical filtration is carried out. The authors of [13] carry out the concentration of the aqueous phase by evaporation in an evaporator, rather than ultrafiltration. The aqueous concentrate is passed through a membrane filter with capillary holes of at least 0.005 μm. The target product is salted out with ethyl alcohol in the presence of a coagulant.

The disadvantages of this method are:

- carrying out extraction in an inert gas medium, which significantly increases the cost of the process;

- the use of additional equipment - an evaporator, as well as high energy consumption for the concentration of the aqueous phase by evaporation;

- the use for the precipitation of arabinogalactan of large quantities of ethyl alcohol (10 l per 1.05 kg of concentrate), requiring special storage conditions and a special mode of operation with it, as well as additional costs for its regeneration;

- the use of inorganic coagulant at the final stage of obtaining arabinogalactan, which may lead to contamination of the product.

It should be noted that when using a filter with a pore size of 0.005 μm, which is smaller than the size of arabinogalactan macromolecules, it is impossible to pass through it a concentrate, as described in the patent in the example. Using hydrophobic membranes with a pore size of 0.005 μm, it is possible to concentrate the solution of arabinogalactan and purify it only of low molecular weight impurities.

Closest to the proposed is a method for producing arabinogalactan [11], which consists in the extraction of larch wood in the form of crushed technological wood chips after removing from it DKV and other monomeric extractive substances with an organic solvent (ethyl acetate). The extraction of AG is carried out with water (a hydraulic module from 1: 1.5 to 1: 3.6 to the mass of absolutely dry raw materials) at a temperature of 80-90 ° C in continuous circulation for 2 hours. The aqueous extract, without cooling, is treated with stirring with water a solution of a cationic flocculant, it is filtered, then the concentration and additional purification of the extract by ultrafiltration are carried out using industrial cellulose acetate or polysulfonamide membranes, and the powdery target product is isolated from the concentrate by spray drying.

The filtrate passing through the ultrafiltration membrane is mixed with fresh water without additional treatment and reused for extraction.

This method eliminates the need for expensive sorbents and equipment, reduces energy costs, eliminates the use of toxic flammable solvents, provides closed water circulation, which reduces water consumption and significantly reduces the amount of wastewater.

Membrane separation and concentration methods, in particular ultrafiltration, are one of the promising areas of scientific and technological progress, as they open the way to the creation of resource-saving and waste-free production, allowing to solve a number of environmental problems. The rapid spread in recent years of ultrafiltration among membrane processes is associated not only with its versatility, but also with the simplicity of its design, low energy consumption, and the possibility of carrying out processes at ambient temperature.

AH aqueous extract contains finely divided high molecular weight impurities (lignin substances, tannins) that cannot be removed by conventional filtration. Therefore, ultrafiltration of the crude extract proceeds at a low speed, the membrane is rapidly blocked and requires frequent regeneration. Effective use of the ultrafiltration method requires preliminary purification of the extract. In the prototype method for removing high molecular weight impurities before ultrafiltration, the extract is treated with solutions of industrial synthetic cationic flocculants. As cationic flocculants, the use of such well-known flocculants as Praestol, Zetag, Fennopol, Entec and others is proposed.

The disadvantage of this method is the duration of the flocculation process, as well as the significant cost of removing from the clarified extract of the flocculated cake, which is a viscous mass, and its disposal. In addition, the flocculation process is difficult to mechanize and automate.

Despite the existence of a technologically advanced and environmentally friendly method, there is currently no industrial production of arabinogalactan in Russia. In connection with the introduction of technology for the production of dihydroquercetin from larch wood, AG extract became a waste product and goes into wastewater.

A quantitative analysis of the component composition of the crude extract obtained by the claimed method showed that, depending on the composition of the raw material, it contains 3.8-9.5% AG (solids content 4-10%) and 0.05-0.36% phenolic impurities.

The objective of the invention is to improve the process of obtaining arabinogalactan when used as a raw material for production of DHQ due to the intensification of the process, reducing material costs and increasing the level of mechanization and automation of the technological scheme by refusing to use reagents - flocculants, while ensuring high purity of the resulting product by replacing the flocculation stage to the more technologically advanced stage of ultrafiltration using hydrophobic, such as ceramic, membranes, and for centering solution and AH release it from low molecular weight impurities - using the method of ultrafiltration followed by diafiltration on hydrophilic membranes.

The problem is solved as follows: a hot extract obtained by extraction of crushed technological chips of larch wood with water after removal of DQF and other monomeric extractives from it with an organic solvent (ethyl acetate), filtered from mechanical impurities without cooling and fed to an ultrafiltration unit with an industrial hydrophobic membrane where it is freed from high molecular weight impurities and becomes transparent. Concentration and additional purification of the clarified extract from low molecular weight phenolic impurities and inorganic salts is carried out by diafiltration on an ultrafiltration unit using a hydrophilic membrane, for example cellulose acetate or polysulfonamide.

After diafiltration without additional treatment, the filtrate is reused for the extraction of DHQ and AG.

The inventive method retains all the advantages of the prototype and is characterized by the following advantages:

- the use of imported reagents - flocculants is excluded, in connection with which the costs of separating cake from the clarified extract of cake and its disposal are excluded;

- many times the permeability (filtration rate) and the life of the membrane during concentration and diafiltration;

- replacing flocculation by ultrafiltration through a hydrophobic membrane allows you to automate the technological scheme for obtaining AG and implement it in a continuous mode, which increases the processability and economic efficiency of the process;

- the use of diafiltration method allows to obtain arabinogalactan of high purity;

- reduced cleaning time of the extract;

- reduced energy costs.

The following examples illustrate the invention.

Example 1. The extraction was carried out on a pilot plant for the production of DHQ. After extracting DHQ by extraction with ethyl acetate, 850 kg of demineralized water continuously circulating at a temperature of 80-90 ° C were fed into an extractor containing 1390 kg of larch wood chips (solids content of 45%) for simultaneous extraction of AH and removal of the remaining ethyl acetate from the chips. The treatment was carried out for 2 hours. Received 650 l of an aqueous extract of AG, which is a turbid liquid of light brown color, with a solids content of 6.93%. The AH content in the dry residue is 94.2%, phenolic impurities (in terms of DHQ) is 1.70%, and the ash content is 3.44%. 500 ml of the obtained extract was passed through a ceramic membrane with a pore size of 0.08 μm. The extract passing through the membrane, which is a clear liquid of light brown color with a solids content of 6.94% and a phenolic content of solids of 1.65% solids, was concentrated on an ultrafiltration unit using a UAM-500P cellulose acetate membrane to a solids content of 15, 9% (concentrate volume 165 ml), then diafiltration was carried out on the same ultrafiltration unit, for which 175 ml of demineralized water was continuously fed while maintaining a constant volume of concentrate. The concentrate obtained after diafiltration (175 g) contained 15.25% arabinogalactan. After spray drying at 70 ° C, 28 g of arabinogalactan with a moisture content of 4% were obtained (yield 81.8% of AG in the initial extract). The content of phenolic impurities in the dry product is 0.45%, no ash content.

Example 2. In the conditions of example 1 received 650 kg of AG extract having a temperature of 60 ° C, with a solids content of 8.20%. The AH content in the dry residue of the extract is 94.3%, phenolic impurities - 2.00%, ash content 1.93%. 500 ml of the obtained extract was passed through a ceramic membrane with a pore size of 0.05 μm. The extract passing through the membrane, which is a clear liquid of light brown color with a solids content of 8.25% and a phenolic content of solids of 1.92% solids, was concentrated on an ultrafiltration unit using a UAM-500P cellulose acetate membrane to a solids content of 19, 5% (concentrate volume 170 ml), then diafiltration was carried out on the same ultrafiltration unit, for which 180 ml of demineralized water was continuously fed while maintaining a constant volume of concentrate. The concentrate obtained after diafiltration (180 g) contained 19.27% arabinogalactan. After spray drying at 70 ° C, 36 g of arabinogalactan with a moisture content of 5% were obtained (yield 87.0% of AG in the initial extract). The content of phenolic impurities in the dry product is 0.50%, no ash content.

Example 3. In the conditions of examples 1 and 2 received 650 kg of AG extract having a temperature of 50 ° C, with a solids content of 5.46%. The AH content in the dry residue is 94.8%, phenolic impurities 1.76%. 500 ml of the obtained extract was passed through a ceramic membrane with a pore size of 0.03 μm. The extract passing through the membrane, which is a clear liquid of light brown color with a solids content of 5.49% and a phenolic content of solids of 1.65% solids, was concentrated on an ultrafiltration unit using a UAM-500P cellulose acetate membrane to a solids content of 14, 3%, then subjected to diafiltration, as described in examples 1 and 2, with the addition of water in an amount of 140 ml. Received 140 g of concentrate with a solids content of 14.3%. After spray drying, 19.8 g of arabinogalactan with a moisture content of 4% were obtained (yield 73% of AG in the initial extract). The content of phenolic impurities in the finished product is 0.42%; no ash.

Example 4. In the conditions of examples 1-3 received 650 kg of AG extract having a temperature of 40 ° C, with a solids content of 9.56%. The AH content in the dry residue is 94.0%, phenolic impurities 2.8%. 500 ml of the obtained extract was passed through a ceramic membrane with a pore size of 0.08 μm. The extract passing through the membrane, which is a clear liquid of light brown color with a solids content of 9.51% and a phenolic content of solids of 1.7%, was concentrated on an ultrafiltration unit using a UAM-500P cellulose acetate membrane to a solids content of 23, 0%, then subjected to diafiltration, as described in examples 1-3, with the addition of water in an amount of 175 ml. Received 175 g of concentrate with a solids content of 22.6%. After spray drying, 41.3 g of arabinogalactan with a moisture content of 4% were obtained (yield 86.7% of AG in the initial extract). The content of phenolic impurities in the finished product is 0.44%; no ash.

Obtained by the proposed method, arabinogalactan is characterized by physicochemical methods (UV, IR, ¹³ C NMR spectroscopy) as a high-purity product (the content of the main substance is 96.5-98.0%), which meets the requirements of the food and pharmaceutical industries for use as a biologically active additive to food.

LITERATURE

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Claims (1)

A method of producing arabinogalactan, which includes sequentially performing aqueous extraction of arabinogalactan by heating from pre-tarred larch wood, purification of the extract from mechanical, colloidal and high molecular weight impurities, concentration of the extract by ultrafiltration and isolation of the target product by spray drying, characterized in that for cleaning the arabinogalactalan extract impurities instead of filtration and flocculation use ultrafiltration on hydropho membranes with a pore size of 0.03; 0.05; 0.08 μm and it is carried out by the continuous method, and further concentration of the extract and its liberation from low molecular weight impurities (phenolic substances, inorganic salts) is also carried out in a continuous way on a hydrophilic type ultrafiltration membrane followed by diafiltration with demineralized water on the same membrane, which allows get high purity arabinogalactan up to 96.5-98.0%.