CS272897B1 - Method of xylan's extractive insulation - Google Patents

Abstract

The invention concerns a method of extractive isolation of xylan from maize cobs. The principle of the invention is that ground maize cobs with a particle size of 2 to 3 mm are extracted in the first phase for 30 to 60 minutes at 65 to 70 degrees C in 20 to 30 times the volume of an aqueous alkaline solution containing 0.10 to 0.13 % by weight of sodium or potassium hydroxide and 0.05 to 0.l % by weight of sodium or potassium disulphite, whereupon the insoluble particles are filtered off and extracted in the second phase, 25 to 35 times the amount of aqueous alkaline solution containing 5 to 7 % by weight of sodium or potassium hydroxide and 0.l to 0.2 % by weight of sodium or potassium disulphite for 60 to 120 minutes at 65 to 70 degrees C, whereupon the reaction mixture is pre-filtered and xylan is precipitated from the filtrate after cooling by addition of l.5 to 2 times the volume of concentrated ethanol, then it is filtered off and processed in the usual way. The invention can be used for preparation of very pure xylan for further applications, particularly for preparation of a substrate suitable for setting xylanase enzymic activity and other applications in the pharmaceutical and textile industries.

Description

The invention relates to a method of extracting isolation of xylan from corn cob.

The polysaccharide D-xylan is found in considerable amounts in the cell walls of mainly deciduous trees, re sp of annual plants. As a rule, however, it does not occur pure, but is accompanied, in particular, by 4-O-methyl-D-glucuronic acid, respectively. as L.arabino-D-xylan.

12 to 34% of xylan is found in the cell walls of plants, from which it is isolated by appropriate procedures, taking into account both the degree of lignification of the raw material used, its physical structure and the understandable quality criteria of the resulting product.

There are also known methods for isolating xylan from T.E. Timell: Adv. Carbohydrate Che. 255 (1964), AO no. 195 527, AO no. 231 686 and procedures for isolating xylan from annual plants of O.B. Gerisch: US Pat. 3,879373 (1975) and U. Casier, Brit. pat. No. 1,332,903 (1973), AO no. 244,591 (1988), which have the common drawback of poor product purity, reduced molecular weight, low yields and, last but not least, the environmental performance of the proposed process technology for industrial application.

These drawbacks are solved by the proposed process by which xylan of high chemical purity, whiteness, with a molecular weight close to native xylan in the raw material used, can be prepared in a manner which can essentially be the basis of waste-free technology for industrial isolation of xylan from corn cob.

SUMMARY OF THE INVENTION The ground corn seeds having a particle size of 2 to 3 mm are first extracted for 30 to 60 minutes at a temperature of 65 to 70 ° C in a 20 to 30-fold volume of aqueous alkaline solution containing 0.10 to 0.13 % wt. % sodium or potassium hydroxide and 0.05 to 0.1 wt. sodium or potassium bisulfite, whereupon the insoluble particles are filtered off and extracted in a second step by 25 to 35 times the quantity of an aqueous alkaline solution containing 5-7% by weight. % sodium or potassium hydroxide and 0.1 to 0.2 wt. sodium or potassium bisulfite for 60 to 120 minutes at 65 to 70 ° C, then the reaction mixture is filtered and the filtrate, upon cooling, precipitates xylan by the addition of 1.5 volumes of concentrated ethanol, then filtered and worked up in a manner known per se.

It has been found that corn cobweed milled to a particle size of optimally 2 to 3 mm is a very good raw material for isolating xylan. They contain 34 to 36 wt. xylan, which can be selectively advantageously isolated by direct alkaline extraction without prior delignification of the feedstock.

It has also been found that the whiteness of the isolated xylan is substantially increased by the use of a brewing extraction step with a dilute alkaline solution prior to the loud alkaline extraction, in which undesired mono and oligosaccharides are extracted from the feedstock. thereby reducing the whiteness and chemical purity of the precipitated xylan. The inclusion of a bitter purification extraction step also has a more positive effect on the main xylan extraction. Indeed, the marrow portions of the maize corn flakes are very hard and slowly swell in alkaline solutions, but in dilute alkali they swell well at a temperature of about 70 ° C, thereby positively affecting the diphtheria processes of the subsequent main extraction, i.e., xylan.

It has been experimentally confirmed that the molecular weight of xylan does not decrease during the isolation and if the extraction is done with a solution having reducing properties, i. eliminates oxidative degradation reactions of carbohydrates in alkaline aqueous solutions.

The addition of 0.2 wt. potassium or sodium bisulfite, calculated on the extraction solution. It has also been confirmed that, in view of the chemical purity of the isolated xylan, it is preferable to use lower concentrations of alkaline solutions of up to 7% by weight. and not as generally used a higher concentration of 10 to 12% by weight, since at higher concentrations the isolated xylan contains isocyanates and lignin, which dissolve better at higher concentrations of the extraction alkaline solution.

As far as the temperature of the main extraction stage is concerned, it is optimal to operate in the range of 65 to 70 ° C for 1 to 2 hours. At higher than optimal extraction temperatures, the resulting xylan has a lower whiteness. The lowering of the temperature and the extraction time result in higher whiteness and chemical purity of the final product, but at a slightly lower yield.

The main advantage of the new process is that it makes it possible to prepare xylan of high chemical purity, whiteness and higher molecular weight than in the known processes. An important advantage is the fact that the process is practically waste-free and therefore meets the strict environmental criteria of industrial technology applied today.

Example 1

100 g of corn cobs ground to 2-3 mm particles are poured into a solution of 2 liters of distilled water with 2 g of NaOH and 1 g of Na2SO4 and allowed to stir at 70 [deg.] C. for 1 hour with stirring. The reaction mixture was then filtered through gauze. The insoluble wet residue is transferred to a reaction glass vessel and topped up with distilled water to a total volume of 3 liters, mixed well and 6 g of sodium metabisulphite and 150 g of solid sodium hydroxide are added and extracted with stirring for 2 hours at room temperature. temperature 65 ° C. After completion of the reaction, the reaction mixture is filtered through a fabric filter cloth and the insoluble residue is washed on the filter with 500 ml of distilled water heated to 65 ° C. The combined 3 liter filtrate was cooled to 20 ° C. ° C and quenched with 4.5 L of concentrated ethanol. The precipitated xylan settles rapidly, the supernatant is carefully decanted to recover ethanol, and the xylan is aspirated and defibrated in 2 liters of ethanol (2 parts ethanol and 1 part water) in a kitchen blender. Repeat these operations several times until the supernatant after settling is colorless. In the last operation, the reaction mixture is neutralized with conc. acetic acid using phenolphthalein as an indicator. After neutralization, the insoluble xylan is filtered off on the filter, washed several times with conc. ethanol and the filtered product is dried in the air or in a vacuum oven at a temperature of up to 60 ° C. The dried final xylan with a yield of 30 g is chemically very pure (it contains only a structurally stoichiometric amount of arabionose but no hexoses, and the lignin content is below 0.3%). Molecular weight 26.000.

Example 2

The procedure as in Example 1, except that 200 g of potassium hydroxide and 6 g of potassium bisulphite is used in the main extraction step, is extracted at 70 ° C for 1.5 hours. 34 g of the final xylan are obtained, which has a higher whiteness and similar properties as the xylan in Example 1.

The invention has utility in the preparation of very pure xylan for other applications, in particular for the preparation of a chromolytic substrate suitable for determining xylanase enzyme activity, possibly as pure standards for structural research needs.

Claims (1)

OBJECT OF THE INVENTION A method for extracting isolation of xylan is characterized in that the ground corn cob with a particle size of 2 to 3 mm is extracted in a first step for 30 to 60 minutes at 65 to 70 ° C in a 20 to 30-fold volume of aqueous alkaline solution containing 0.10 to 0.13 wt. % sodium or potassium hydroxide and 0.05 to 0.1 wt. sodium or potassium bisulfite, whereupon the insoluble particles are filtered off and extracted in a second step by 25 to 35 times the quantity of an aqueous alkaline solution containing 5 to 7% by weight of water. % sodium or potassium hydroxide and 0.1 to 0.2 wt. sodium or potassium bisulfite for 60 to 120 minutes at 65 to 70 ° C, then the reaction mixture is filtered and after cooling the xylan is precipitated by the addition of 1.5 to 2 volumes of concentrated ethanol, then filtered and treated according to known procedures.