MICRONIZATION OF POLYOLS

Micronization of polyols

Technical Field

The current invention relates to micronization of polyols. Polyols with improved properties can be obtained and can be applied in food, feed, cosmetic and pharmaceutical applications.

Background of invention

Polyol powders are prepared according to different technologies. Polyols can be crystallised, freeze-dried, extruded, spray-dried, or steam-agglomerated.

US 4,408,041, US 6,120,612, US 5,932,015 all relate to different processes for crystallising maltitol.

US 5,160,680 describes a method of preparing directly compressible granulated mannitol wherein mannitol powder is subjected to an extrusion treatment.

EP-A-1430887 describes the preparation of inhalable powders for use in the administration of therapeutically-active substances by inhalation. These powders are formed by mixing a coarse powder having an average particle size of 17 to 50 μm with a fine powder having an average particle size of 2 to 8 μm.

WO 2004/067595A discloses a process for preparing a granular polyol, e.g. maltitol, involving milling a dried composition to give a particle size of from about 200 to about 2000 μm.

WO 2006/127560A relates to a chewing gum composition comprising polyols. The average particle size of the polyol composition disclosed ranges from about 30 μm to about 600 μm.

It is, further, known to produce a lactose powder having a particle size distribution of 10 to 50 μm using a micronizer, "Sanitary Design Micronizer, USDA- accepted Jet Mills", 2005 STURTEVANT, INC.

Currently there is a need for a simple, cost-effective process, which allows a polyol of high quality to be obtained.

The current invention provides such a process. Summary of Invention

The current invention relates to a micronized polyol having a particle size distribution (dso) of from 20 to 60 μm, and a fiowability below or equal to 5 s/100 g, preferably below 5 s/100 g.

The current invention further relates to a process for micronizing a solid polyol, said process comprising the following steps: a) taking a solid polyol, b) feeding the polyol into a jet mill and applying pressure with nitrogen gas, collecting the micronized polyol.

It further relates to a food, feed, cosmetic or pharmaceutical composition containing the micronized polyol of the current invention, in particular to a chewing gum composition.

Detailed description

The current invention relates to a micronized polyol having a particle size distribution (dso) of from 20 to 60 μm, and a fiowability below or equal to 5 s/100 g, preferably below 5 s/100 g.

Although there is no fixed definition, the term "micronized" is generally used to describe particles having an average particle diameter of less than 10 microns, usually with the majority of the particles being between 2 and 5 microns. The present invention, however, relates to a different particle size distribution and, in the context of the present invention, a micronized polyol has a particle size distribution (dso) of from 20 to 60 μm.

The test for measuring the fiowability is described in the examples.

The micronized polyol of the current invention may be compared favourably with the corresponding milled polyol. Although the micronized polyol has a smaller particle size distribution (dso) than the corresponding milled polyol, surprisingly its fiowability is improved.

The polyol of the present invention is, typically, one having the chemical formula C_nH2n₊2θ_n, and, also typically, is a solid material at temperatures between 20 to 25°C.

This chemical formula is typical for hydrogenated (reduced) carbohydrates but the polyol of the current invention is not necessarily obtained by hydrogenation of the carbohydrate. Some of these polyols (e.g. erythritol) are obtainable via other chemical processes and/or microbial processes or fermentation.

Typically, the polyol is selected from tetritols, pentitols, hexitols, hydrogenated disaccharides, hydrogenated trisaccharides, hydrogenated tetrasaccharides, hydrogenated maltodextrins and mixtures thereof.

More specifically, the polyol may be selected from the group consisting of erythritol, threitol, arabinitol, xylitol, ribitol, allitol, altritol, gulitol, galactitol, mannitol, sorbitol, talitol, maltitol, isomaltitol, isomalt, lactitol, and mixtures thereof.

In a preferred embodiment, the polyol is selected from the group consisting of maltitol, isomalt, mannitol, sorbitol, xylitol, erythritol and mixtures of one or more thereof. In more specific embodiments, the polyol is erythritol or mannitol.

The micronized polyol of the present invention is further characterised in that it has a compressibility index equal to or higher than 40. The compressibility index is described in the examples.

According to a particularly preferred embodiment, the present invention relates to micronized erythritol having a particle size distribution (dso) of from 20 to 60 μm, and a flowability below or equal to 5 s/100 g, preferably below 5 s/100 g. It, further, has a compressibility index higher than 40.

According to a different preferred embodiment, the present invention relates to micronized mannitol having a particle size distribution (dso) of from 20 to 60 μm, and a flowability below or equal to 5 s/100 g, preferably below 5 s/100 g. It, further, has a compressibility index higher than 40. This compressibility index makes it a potential candidate for application in tablets.

The present invention further relates to a process for micronizing a polyol which comprises the following steps: a) taking a polyol having the chemical formula C_nH_2n+2O_n, and which is a solid material at temperature between 20 to 25°C, b) feeding the polyol into a jet mill and applying pressure with nitrogen gas, c) collecting the micronized polyol, Jet mills encompass any equipment, which allows the micronization of particulate material and, in particular, the micronization of polyols. Typically suitable equipment is one which allows the reduction of the particle size by mechanical methods and is capable of providing the micronized polyol with a particle size distribution (dso) of from 20 to 60 μm. More typical equipment can encompass jet mills, such as spiral jet mills and opposed jet mills. A typical suitable equipment comprises a cylindrical grinding chamber into which a high velocity gas is introduced via jet nozzles situated around the walls of the chamber. A particulate material to be micronized is introduced into the grinding chamber propelled by a pressurized gas and, inside the chamber, is accelerated around the internal walls of the chamber by virtue of the introduction therein of the high velocity gas. The movement of the gas within the chamber results in the creation of a vortex within which the particulate material is entrained. The particles of the particulate material are, thus, caused to undergo repeated collisions between themselves and, as a result, the particle size distribution (dso) of the particulate material becomes reduced. The reduced-size particles, i.e. the micronized product, exit the chamber carried by the exhaust gas and, typically, are passed to a suitable cyclone filter.

The particle size distribution of the micronized product is determined largely by the gas pressure in the chamber and the feed rate of the solid particulate material into the grinding chamber.

Micronization is currently used mainly in the industrial sector (in the production of cement or pigments for paints) and in the pharmaceutical industry for producing solid inhalation products. In these uses, the aim is to produce ultra-fine powders (e.g. particle sizes in the range of from 1 to 10 μm, or even smaller). In order to be able to achieve such small particle sizes, very high gas pressures (>7 bar) are necessary.

The present invention has demonstrated that suitable products are obtained by applying nitrogen gas.

The present invention is concerned with producing micronized powders of polyols which are particularly useful in the manufacture of edible products, such as food or feed compositions, or of cosmetic or pharmaceutical formulations. Such applications require the micronized polyols to have a particulate size distribution (dso) preferably from 20 to 60 μm. In order to achieve such particle sizes, moderate gas pressures are used, typically from 2 to 6 bar. The feed polyol whose particle size is reduced according to the process of the invention typically has a starting particle size distribution (dso) in the range of from 50 to 500 μm.

In the present invention, we have achieved good results using either a Micronet MlOO jet mill from Nuova Guseo S.r.l. or a Micronizer Jet Mill from Sturtevant Inc. In carrying out the present invention, a dry particulate polyol is typically fed into the grinding chamber of the jet mill through a Venturi injector and conveyed by a pressurized dry, nitrogen gas. Preferably, the feed rate is in the range of 0.5 to 7 kg/hour (in a 10 cm diameter chamber). The particulate polyol is accelerated into a vortex inside the circular chamber of the jet mill by virtue of the injection, into the chamber, of a high velocity, dry nitrogen. The repeated particle-on-particle impact caused under the gas pressure in the chamber of the mill grinds the polyol particles to the desired particle size.

The micronized polyol obtained has excellent properties. For instance, since the particle size reduction is achieved without the external application of heat and without the need to use any processing aids, which are commonly used in the micronizing of particulates, the product is not subjected to contamination. Furthermore, by using dry, inert gases in the jet mill, the micronized product is dry and, thus, not vulnerable to lump formation during storage.

Advantages of micronization over conventional hammer mills include the finding that micronized fine powders show much better flow properties (flowability) and stability at storage (absence of lumps after 3 months storage - without any anti-caking agent addition). Micronization also improves confectionery applications and/or pharmaceutical applications, for example, chewing gum compositions or tablets.

The present invention further relates to a chewing gum composition which contains a micronized polyol according to the invention, preferably micronized mannitol. A further characteristic of the chewing gum composition comprising micronized mannitol, according to the invention, is the improved hardness of the chewing gum composition. More specifically, it has a hardness of equal to or higher than 3500 g after 24 hours of production, preferably higher than 4000 g.

The present invention is further illustrated by way of the following examples: EXAMPLES

Example 1

Crystalline mannitol, having an average particle size of 67 μm, was fed into a Micronizer having a 10 cm diameter grinding chamber using a flow of dry nitrogen. The feed rate of the crystalline mannitol into the Micronizer was 3.1 kg per hour. Dry nitrogen was injected through nozzles into the chamber to maintain a gas pressure (P2) in the chamber of 2 bar (2 x 10⁵ Pa). A dry, free-flowing micronized mannitol, having consistently an average particle size of 33 μm, was obtained.

Example 2

The procedure described in Example 1 was repeated except that the crystalline mannitol fed to the Micronizer had an average particle size of 82 μm, the feed rate was 1.1 kg per hour and the pressure (P2) of the N2 in the chamber of the mill was 1.5 bar. The micronized product, again, had an average particle size of 33 μm.

The effect of the feed rate of the crystalline mannitol, at two different particle sizes, is shown in the following Table 1.

Table 1

Crystalline mannitol

Example 3

Using a procedure similar to that described in Example 1 above, other polyols were successfully micronized as shown in the following Table 2.

Table 2

Other Polyols

The micronized erythritol prepared according to example 3 was further analysed for its flowability and compressibility index (%) according to the test procedures described.

The compressibility index (%) is a measure of several properties of a powder: bulk density, particle size and shape, surface area, moisture content and cohesiveness. All of these can influence the observed compressibility index.

The compressibility index (%) of the samples of micronized polyol according to the present invention was determined according to the following procedure.

lOOg of a sample of polyol powder was placed in a 250ml volumetric cylinder. The apparent volume (Vo) of the unsettled powder in the cylinder was noted. The cylinder containing the powder sample was then mechanically tapped causing the powder in the cylinder to settle. Tapping was continued until no further volume change, due to settling, was observed. The final volume (Vf) of the settled powder in the cylinder, after tapping was concluded, was noted.

Using the observed values Vo and Vf, the compressibility index (%) is calculated according to the following equation:

/ Vo - V_f compressibility index (%) = 100 x ^ Vo An average of three determinations is used.

The flowability of a powder is measured as the rate of flow of the material through an orifice. It can be used only for materials that have some capacity to flow and is not, therefore, useful for cohesive materials.

The flowability (s/100g) of the samples of micronized polyol according to the present invention was determined according to the following procedure.

Apparatus

The apparatus used was a Pharma Test PTG-I from Pharma Test Apperatebau, Hainburg.

The apparatus comprised a flow funnel having, at its bottom, a nozzle (orifice) and provided internally with a stirrer. The flow funnel is suspended vertically above a container provided on a balance. The apparatus provides a choice of orifices of different diameters, e.g. 10mm, 15mm and 25mm. The stirrer can be used to help the powder pass through the nozzle and can be used at speeds from 5 to 25 rpm.

The sample of micronized polyol was placed in the flow funnel. The orifice diameter used in the test procedure was 25mm. The stirrer was operated, in the test procedure, at a speed of 25 rpm. The nozzle was opened and the time for lOOg of the sample to flow through the nozzle into the container was noted.

An average of three measurements was used for each sample.

The results obtained for flowability and compressibility index (%) are shown in the following table.

Example 4 - Chewing gum preparation

The following recipe was applied for preparing chewing gum.

Flowability of the micronized mannitol, after storage in a cabinet at 40% Relative Humidity for one year, was again measured. No deterioration in the flowability of the material, after storage, was observed.

The chewing gum composition was formed into sheets and they were stored at room temperature and in a cabinet at 40% Relative Humidity.

The quality of the chewing gum sheets was further determined by measuring the hardness of the chewing gum sheets. For comparison, sheets made using a composition wherein standard fine milled mannitol was used instead of the micronized mannitol of the invention were also subjected to the testing procedure.

Hardness measurement

Equipment: Texture Analyser Profile TA XTPlus

TA-XTPlus Settings:

Mode: Measure Force in Compression Option: Return to Start Pre-Test Speed: 0.8 mm/s Test Speed: 0.8 mm/s Post-Test peed: 3.0 mm/s Distance: 2mm Trigger Force Type: 30.Og Data Acquisition Rate: 250pps

Accessory: 2mm Cylinder Probe (P/2) using 25kg load cell Heavy Duty Platform (HDP/90) with blank plate

Test Set-Up: Place the Heavy Duty Platform onto the machine base. Position the sample chewing gum sheet on the platform, centrally under the probe, and commence the test.

Observations: The probe approaches the sample and once the 30.Og trigger force is attained, a rapid rise in force is observed, as the probe penetrates into the chewing gum sheet. The probe returns to its original starting position when a penetration distance of 2mm from the trigger point is reached. The mean penetration force is measured as an indication of the hardness.

The tests were carried out, at ambient temperature, on samples of chewing gum sheets stored at room temperature (22⁰C) in an air-conditioned room for 24 hours, one week and one month after preparation. The results are shown below.