Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
2001-10-01
2004-06-29
Bell, Mark L. (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C127S067000, C127S069000, C127S070000, C127S071000, C536S102000, C536S106000, C536S124000
Reexamination Certificate
active
06755915
ABSTRACT:
The present invention relates to a method for the preparation of starch particles by means of which small starch particles having a particle size of 50 nm to a few mm can be obtained in a simple manner. In particular small starch particles having a particle size of 50 nm to 100 &mgr;m, so-called nano- or micro-particles, are highly desirable for a broad range of applications. Small starch particles can be used in pharmacy, cosmetics, foods, paints, coatings, paper, inks and many other applications.
Up to now small particles of this type have been prepared using polymers as starting materials by means of (multiple) emulsion cross-linking or solvent evaporation, spray-drying and other methods (Jiugao, Y. et al., Starch 46 (1994) 252; Arshady, R., Pol. Eng. Sci., 29 (1989), 1747). A number of routes are described in the following patents: PCT/GB/01735, PCT/GB95/00686, PCT/GB92/01692, PCT/GB93/01421, EP 0 213 303 B1. In EP 0 213 303 B1 two immiscible aqueous liquid phases are used as the starting material. In the case of emulsion cross-linking a great deal of mechanical energy is required and it is very difficult to separate off and to purify the particles, which leads to high production costs (for example in PCT/GB93/01692). Evaporation and spray-drying are also expensive techniques which demand the use of large quantities of (usually organic, volatile) solvents. A polymer or starch dissolved in water is always used as the starting material. In PCT/GB95/00686 a combination of a water-soluble and water-insoluble polymer is used as the starting material. However, both are dissolved in two different solvents.
The present invention now provides a method for the preparation of starch particles using a two-phase system with starch as a third main component. The method comprises at least the following steps:
a) preparation of a first phase comprising a dispersion of starch in water;
b) preparation of a dispersion or emulsion of the first phase in a second liquid phase, with the proviso that the second phase is not water;
c) cross-linking of the starch present in the first phase;
d) separating the starch particles thus formed.
According to the present invention starch is understood to be native starch, granular starch, fractions and derivatives of starch and agricultural raw materials which are rich in starch, (containing at least 80% starch wt./wt.), such as wheat flour. The starch can originate from a wide variety of natural sources, such as wheat, corn, amylocorn, wax corn, potatoes, quinoa, rice, etc.
Preferably, the starch is granular starch which can be native or modified, for example physically, chemically or enzymatically modified. The starch does not have to be soluble in water cold. Optionally the starch can also be fully or partially gelatinised or melted. A mixture of various types of starch can also be used. For instance, partially soluble, (pre-)gelatinised or modified starch can be added to native starch.
Partially or completely fractionated starch, such as starch enriched in amylose or, on the contrary, enriched in amylopectin, can also be used. Derivatives which can be used are partially or completely hydrolysed starch, such as maltodextrins, in which context hydrolysis can be under the influence of heat or acid, basic or enzymatic hydrolysis, oxidised starch (carboxy, dialdehyde, etc.), carboxylated, chlorinated or sulphated starch, starch that has been rendered hydrophobic (esters, such as acetate, succinate, half-esters, phosphate esters) and phosphated starch, starch ethers (hydroxyalkyl), and the like. Furthermore, starches with combinations of the abovementioned modifications, i.e. bifunctional or multifunctional starch, can also be used. The derivatives can also be granular.
Other carbohydrates or polymers can be used as auxiliaries. These auxiliaries make up at most 15%, preferably 1-10% (wt./wt. based on starch solids). Said auxiliaries include, in particular, other carbohydrates such as alginates, pectins and carboxymethylcellulose.
According to a first aspect of the present invention, the second phase is a hydrophobic phase. Said second phase is dispersed or emulsified in the first phase (starch-in-water) in such a way that an oil-in-water (O/W) emulsion is produced (step b) i)). Said O/W emulsion is then inverted to a water-in-oil (W/O) emulsion (step b) ii)). This process is referred to as “phase inversion” in this application. In the W/O emulsion the aqueous phase consists of the first water-in-starch phase. The starch can be granular, partially gelatinised or dissolved here. Following the phase inversion step, the starch particles are cross-linked and then separated.
The cross-linking reaction can already have been started before or during phase inversion. This method can be used in particular if the conditions for the cross-linking reaction are such that the cross-linking reaction proceeds slowly. Complete cross-linking in general takes place after phase inversion.
The starch does not yet have to be completely gelatinised at the start of the method. According to a preferred embodiment of the invention, partial or complete further gelatinising of the granular starch is effected during, before or after phase inversion. The starch can remain partially granular during cross-linking. Gelatinising can be effected by means of raising the temperature or by adding salts, such as hydroxides, or by a combination thereof.
It is advantageous if in step b) the ratio of hydrophobic phase:water in the O/W emulsion is of the order of magnitude of 80:20 to 20:80. Preferably, the ratio of hydrophobic phase:water in the O/W emulsion is between 60:40 and 40:60 (V/V).
All liquids which are not miscible with water are suitable as hydrophobic phase. Examples of these are hydrocarbons (alkanes, cycloalkanes), ethers, esters, halogeno-hydrocarbons, di- and triglycerides, fats, waxes and oils. Examples of oils or fats are palm oil, kernel oil, sunflower oil and salad oil. A number of apolar liquids are octane, dodecane, toluene, decalin, xylene, higher alcohols such as pentanol and octanol, or a mixture thereof. Paraffin oil, hexane or cyclohexane are preferably used. Preferably the viscosity of the hydrophobic phase is close to the viscosity of the starch/water phase. The miscibility of the water/starch phase with the hydrophobic phase preferably has to be as low as possible.
Preferably the O/W emulsion is stabilised with the aid of a surfactant. Phase inversion, i.e. the inversion from O/W emulsion to a W/O emulsion (step b) ii)), can take place in various ways. 1) If a surfactant is used which is temperature-sensitive, the phase inversion can be induced by raising the temperature. 2) The O/W emulsion can be destabilised by adding another surfactant. This surfactant stabilises a W/O emulsion. 3)
Phase inversion can be obtained by adding a hydrophobic liquid. 4) Phase inversion can also be obtained with the aid of the addition of salts.
Phase inversion by means of raising the temperature may be mentioned first. Raising the temperature gives rise to a shift of the surfactant molecules at the O/W interface towards the oil phase. The result of this is that the protection which the polar head provides against coalescence of the hydrophobic phase also decreases. At a certain temperature, which is dependent on, for example, the hydrophobic phase, type of surfactant and type and concentration of starch in the aqueous phase, the protection has decreased to such an extent that all oil droplets coalesce and the emulsion changes over or inverts from O/W to W/O.
The phase inversion temperature (PIT) is dependent on the chosen (water/starch)/oil (hydrophobic phase)/surfactant system. The surfactant concerned must preferably have an equal affinity for water and the hydrophobic phase, for example an oil. This is expressed in the HLB (hydrophilic-lipophilic balance) value. Preferably surfactants are used which have a HLB value of 8 to 20 or more preferentially of 10 to 15. The higher the HLB value the greater is the affinity of the surfactant for the aqueous phase. If this value becomes too high
Feil Herman
Gottlieb Kornelis Fester
Stappers Frank Hubertus Maria
Van Schijndel Renée Josie Gide
Van Soest Jeroen Johannes Gerardus
Bell Mark L.
Ecosynthetix Inc.
Hailey Patricia L.
Young & Thompson
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