NL1002525C2 - Method for oxidizing dry starch using ozone. - Google Patents

Description

Title: Method for oxidizing dry starch using ozone.

The invention relates to a method of oxidizing starch using ozone.

The oxidation of polysaccharides has been described in various variants. Known oxidizing agents for this purpose are periodic acid, peracetic acid, perborate, persulphate, potassium permanganate, lead (IV) salts, hydrogen peroxide, chlorite and hypochlorite.

The most common method for the oxidation of polysaccharides uses hypochlorites. This method has the drawback that large quantities of salts are formed in the process, which causes problems in the processing of the waste water. In addition, the yield of oxidized polysaccharides is often insufficient and long reaction times are required.

Dutch patent 43493, European patent application 0 427 349 and international patent application 91/17189 describe the oxidation of polysaccharides with a catalytic amount of bromide to form oxidized polysaccharides.

The bromide is thereby converted into hypobromite by hypochlorite or electrochemically. The method in which hypochlorite is used again produces many salts. The process of electrochemical regeneration is complicated; it requires a reservoir with at least 2 compartments and the anode and cathode quickly become dirty.

There is a great need for a process in which polysaccharides and in particular starches, such as potato starch, can be oxidized in systems containing as few solvents as possible and in particular water. After all, water and other solvents have to be removed for many applications, which entails high 1002525 - 2 - (drying) costs. In addition, a dry or semi-dry process has the advantage that it is not necessary to suspend the product to be oxidized and to filter it off, while in general the reaction volumes can be greatly reduced. Furthermore, no washing water has to be used, so that purification and labor costs can be saved.

It is known that ozone can be used as an oxidizing agent for starch, sometimes even suggesting anhydrous oxidation to be suggested.

For example, Szymanski in the Journal of Applied Polymer Science (1964), 1597-1606 discloses a method of oxidizing corn starch using ozone. Oxidation with ozone is carried out under dry conditions (10% water), in aqueous suspension and in an organic solvent.

The oxidation reactions were carried out at decreasing pH.

In particular, the final pH in the reaction mixture appears to be between 1 and 2.5.

The purpose of the study described in this article by Szymanski was to introduce a large amount of aldehyde groups into the corn starch. Because a considerable amount of ketone groups were formed in addition to the intended aldehyde groups, the target was not achieved according to the author.

It is further noted that the degree of oxidation is low when less than 65% by weight of water is present. It is explicitly stated that no tests have been carried out with anhydrous starch. The influence of water on the oxidation of corn starch is said to be complex; water can act as a solvent, hydrating agent for hydroxyl groups or as a catalyst.

In an article by Angibeaud et al. In "Cellulose, lts Derivatives" ed. J.F. Kennedy, Horwood Chichester Publishing 35 ü.K. (1985) entitled "Cellulose and Starch Reactivity with Ozone" it is concluded that the use of ozone as an oxidizing agent for carbohydrates, citing starch as 1007525-3 example, is prevented by the absence of selectivity. Both carbonyl and carboxyl groups are formed, while glycosidic bonds are broken. In order to gain some more insight into the mechanisms underlying ozone oxidation, the ozone oxidation of amylose is then studied. Carboxyl groups are reported in addition to depolymerization in a suspension of amylose buffered at pH 7. It is expressly stated that the results are not consistent with the results found by Szymanski for corn starch, namely the incorporation of aldehyde groups.

Incidentally, US Pat. No. 3,208,851 discloses a method for providing a batter for foods to be fried, which batter better adheres to the food to be fried. This batter is prepared by dry oxidizing starch using an oxidizing gas. One of the examples of such an oxidizing gas is ozone. In the examples, when ozone 20 is used, only corn starch is treated with it. No details are given regarding the starch product obtained.

Furthermore, it is disclosed in U.S. Pat. No. 3,361,741 that starch in an aqueous suspension can be oxidized by tetravalent lead ions, these lead ions being obtained by oxidation of divalent or trivalent lead ions with ozone.

German Offenlegungsschrift 22 33 977 describes the oxidation of carbohydrates using an aqueous basic solution of a silver oxide system. In the presence of this silver oxide system, the carbohydrates can be oxidized by a variety of means, including ozone.

The object of the present invention is to provide methods in which starch in dry or semi-dry state can be selectively oxidized. More particularly, the invention relates to a method in which 1002525-4 starch is treated with an oxidizing agent in the dry or semi-dry state, wherein the reaction yield is greatly increased.

This object is achieved by oxidizing those starches for certain starches by passing ozone through.

The invention therefore relates to a method for oxidizing root starch, tuber starch or sticky cereal starch and its derivatives, in which ozone is passed through an amount of dry or semi-dry starch.

Carrot starches, such as tapioca starch, tuber starches, such as potato starch and sticky cereal starches (derived from amylopectin-rich grains such as waxy maize and waxy rice) are used, because these starches are characterized by a low content of lipids and proteins.

The derivatives of the said starches used in the process according to the invention must be compatible with ozone under the reaction conditions used. Examples of such derivatives are cross-linked starches, starches with esterified or etherified groups thereon; or physically modified starches such as roll-dried or extruded starch.

It is often easier to first oxidize the starch and only then (chemically) derivatize or modify it. Very good results are obtained if the starch is subjected to a drum drying treatment before it is treated with ozone. Roller drying may increase the active surface area of the starch granules, making the carbon centers to be oxidized more available or accessible for the reagent ozone.

By the term "dry or semi-dry starch" is meant in the case of tuber starch, for example potato starch, starch containing up to 25% by weight of water and in the case of root starch, such as tapioca starch, and tacky starches starch containing up to 15% wt. % water. The term "starch" also includes the derivatives of these starches.

1002525 - 5 -

In a preferred embodiment, the dry or semi-dry starch is treated with ozone in a fluidized bed. A known flux, for example Aerosil®, can optionally be incorporated in this fluid bed.

At least a portion of the primary hydroxyl groups are selectively oxidized.

C6 oxidation in particular has been found to introduce carbonyl groups. This can be demonstrated using gas chromatography / mass spectrometry technique (Hewlett Packard, gas chromatograph GC 5890 series II and mass spectrometer MS 5989A).

The products with a high content of carbonyl groups obtained according to the method of the invention can be used in adhesives, in paper (eg coating, surface gluing), in textiles (eg strengths).

Moreover, carbonyl groups formed according to the invention can be converted according to conventional methods to e.g. amines, imines, acetals, and the like.

The advantage of the aforementioned method is that a starch with a high content of aldehyde groups is obtained while the glucoseation remains intact; this in contrast to known oxidation processes which lead to dialdehyde starch (DAS), as described for example in WO-A-93/01905. This has a beneficial effect on the biodegradability and application properties of the product. A further advantage of this method is that an oxidation product can be obtained without the intrinsic viscosity being greatly reduced and thus without the starch chains being severely degraded. The intrinsic viscosity of a substance is the degree to which one molecule of that substance in solution can increase the viscosity and is determined by measuring the hydrodynamic volume of that substance. The intrinsic viscosity is shown in dl / g.

In a preferred embodiment of the invention, a buffer is added to the starch and distributed homogeneously therethrough to increase the reaction efficiency. As a buffer, the usual buffer systems can be used, such as citric acid / phosphate buffers, phosphate buffers, acetate buffers, boric acid buffers in amounts of up to 5% by weight of dry buffer on the basis of the starch present. The pH during the reaction should not exceed 10.5 because ozone decomposes at higher pHs, and not lower than 1 due to starch hydrolysis. According to the invention, the pH is preferably between 5 and 8, because the reaction efficiency is then highest.

Furthermore, in a preferred form, bromine and iodine compounds can be used as a catalyst to increase the reaction efficiency. Preferably the bromine compounds are bromides or oxybromides, while the iodine compounds are iodides, oxyiodides and iodic acid compounds. These catalysts are used in amounts of up to 10% by weight of dry catalyst based on the starch present. The catalyst can be used in combination with a buffer. It is noted here that salts are thus introduced into the intended product, which is not desirable in all cases.

Instead of adding a buffer, caustic can also be applied continuously to the product to keep the pH constant.

The reaction can be run at temperatures to the point where ozone decomposes too quickly. Preferably, it is oxidized at a temperature of 0 to 60 ° C and most preferably between 5 and 40 ° C. The reaction time is between 10 minutes and 20 hours and depends on the desired degree of oxidation.

The invention will be further illustrated by the following non-limiting examples.

The oxidation products are analyzed in the following manner.

The content of carboxyl groups (DSCOOh) is expressed in the number of moles of carboxyl per mole of anhydroglucose units and is determined titrimetrically.

1002525 - 7 -

To this end, the sample material is brought into H + form with 1N HCl and titrated to pH 8.6 with 0.1 M NaOH. The titration is performed in 0.5 M NaCl.

5 The content of carbonyl groups (DSC.C) is expressed in the number of moles of carbonyl per mole of anhydroglucose units and is determined by determining the dextrose equivalent DE (in mg / g) of the sample material by Luff-Schoorl method and then as follows to calculate: (DSC_0) “DE / (1000-DE).

The intrinsic viscosity (IV) is expressed in g / dl.

It is determined in the usual manner with a Viscotek Y501B in 1 M NaOH as a solvent.

15

Example 1

Semi-dry ozone oxidation of potato starch at 2 0 and 3 0 ° C

1.0 kg (800 g dry matter) of potato flour was placed in a 15 1 rotor reactor with blade. Then ozone (100 l / h) was passed through the rotary reactor at 30 ° C for 6 hours. The reaction was repeated at 20 ° C.

After the reaction, part of the product (400 g based on

dry matter) suspended in 500 ml demineralized water. This suspension was neutralized to pH 5.5 with 4.4% sodium hydroxide solution. After filtration, the product was washed with 2.0 L of demineralized water. Finally, the product was dried and this dried material was analyzed.

1002525 - 8 -

Table 1

Oxidation of potato starch with ozone at 20 and 30 ° C

DScooh DSC-O IV

20eC 0.006 0.024 1.01 30®C ÖTÖÖ6 0.023 0.90

The intrinsic viscosity of native potato starch is around 2.60. The product has an IV of about 1 and yet a high degree of oxidation. This indicates less degradation of the starch chain than occurs by ozone oxidation in suspension or solution.

10 Example 2

Semi-dry ozone oxidation of potato starch in the presence of various catalysts and buffers. The catalyst (or buffer) was dissolved in 51 ml of demineralized water. This solution was added dropwise to 949 g (742 g of dry matter) potato starch in a Hobart mixer.

After 1 week, the oxidation reaction at 30 ° C was carried out with the mixtures as described in Example 1

The following catalysts and buffers were used: - NaBr (10 g) - HIO3 (5 g, pH of the solution adjusted to 3.0) 25 - Acetate buffer pH 4.5 (8.0 g NaOAc and 2.0 HOAc) - Acetate buffer pH 6.0 (10.0 g NaOAc) - Phosphate buffer pH 6.0 (1.0 g Na2HP04 and 9.0 g KH2P04) - Phosphate buffer pH 7.5 (8.0 g Na2HP04 and 2.0 g KH2P04) After the reaction, part of the product was washed and dried as described in example 1. The suspension was neutralized to pH 5.5 with 4.4% sodium hydroxide solution or 6 M hydrochloric acid.

1002525 - 9 -

Washing, neutralization and drying were performed because the presence of catalysts and buffers can interfere with the assays.

5 Table 2

Oxidation of potato starch with ozone in the presence of catalysts or buffers

catalyst / buffer DScooh DSc-o IV

0.006 0.023 0.90

NaBr 0.008 0.041 0.37 HI03 0.008 0.035 0.51

Ac buffer pH 4.5 0.002 0.010 0.91

Ac buffer pH 6.0 0.008 0.044 0.71

Phos buffer pH 6.0 0.010 0.039 0.70

Phosphate buffer pH 7.5 0.010 0.043 0.70 10 At a pH around 6, an increased degree of oxidation can clearly be observed.

1002525

Claims (5)

A method for oxidizing root starch, tuber starch or sticky corn starch and derivatives thereof, wherein the starch is brought into contact with ozone in the dry or semi-dry state. A method according to claim 1, wherein potato starch and / or tapioca are started from. A method according to claim 1 or 2, wherein a buffer is used. 4. A method according to claim 3, wherein use is made of a reaction system buffered at a pH between 5 and 8. Process according to claims 1-4, wherein use is made of a catalyst from the group consisting of bromine and iodine compounds. 1002525 COOPERATION TREATY (RCt) REPORT ON NEWNESS RESEARCH OF INTERNATIONAL TYPE IDENTIFlKATlE OF OE NATIONAL APPLICATION Characteristic of the applicant ol of α · gemacnsgae Nw 8315 Dutch application no. Among other things, her request for an onoerzoex of niamaeonaai type By the msanse for iniemaeenai Research (ISA) to nel request for an investigation of mameeoneai type toe genera no. SN 27271 NL I. CLASSIFICATION OF THE SUBJECT (specify when verxcnülanoe ctassiocaooeey da damb. ) According to the mtemaoonaie ciasailicaae (IPC) Int.Cl.6; c 08 B 31/18 II. UNRESERVED FIELDS OF OE TECHNOLOGY _.___ Unsurpassed mmimum document «ie_ Classification system I Assassination symbols Int.Cl.6: C 08 B Onoarzocme anoare oocumentaoe to the mmimum doumentaae insofar as such documents are included in the anaerzocma areas III. ! ί NO EXAMINATION FOR ANY PARTICULAR CONCLUSIONS (comments on supplement). IV. ! 1 LACK OF UNIT OF INVENTION (comments on pollution charge) I l '' orm PC T / ïSA / 231 fa i CS 19S *