 |
Description  |
|
|
INTRODUCTION
The present invention relates to a novel composition of matter, usually in
particulate form, and a process for producing the same. More particularly
when the composition is in particulate form it comprises generally
spherical capsules, usually less than 400 microns in diameter. Regardless
of the form in which the product is prepared, it comprises a glassy solid
cellular matrix, usually water soluble but sometimes deliberately not
readily soluble, e.g., of a polysaccharide and a polyhydroxy compound,
having oil droplets, in many cases of about 1 micron diameter, in the
cells dispersed therethrough in a proportion that may be limited only by
the maximum oil content that can be maintained in the internal phase of an
emulsion from which the solid state product is produced by removal of
moisture. In practice the oil content of the product is limited to a
maximum of about 80% by volume. The product is produced by converting the
emulsion of oil droplets in a solution of the matrix ingredients to the
solid state with removal of moisture largely if not entirely while the
matrix is at least plastic. Where the product is particulate, the
particles or capsules are preferably produced by a spray drying process
characterized by high recovery of the oil in the capsules which have low
extractable oil upon exposure to non-polar extracting liquids.
BACKGROUND OF THE INVENTION
Many proposals have been made to encapsulate core materials that require
protection until time of use in a protective covering. Cf. Nack,
Microencapsulation Techniques, Soap and Sanitary Chemicals, Vol. 21, pp
85- 98, Feb. 4, 1970. Among process for making somewhat globular capsules
that have been described in the technical literature and patents are
coacervation and spray drying.
The coacervation process generally involves three steps: (1) formation of
three immiscible chemical phases, a liquid manufacturing vehicle phase, a
core material phase that can be dispersed or emulsified in the vehicle
phase, as droplets, and a coating material phase, (2) depositing the
coating material phase around the droplets of the core material phase and
(3) rigidizing the coating to form the self-sustaining particles. The
typical resulting particle is a globule of core material surrounded by a
wall of coating material. Size may vary from about 5 to 5,000 microns. The
core material may be liberated by mechanically breaking the outer wall by
external or internal force, by degradation of the outer wall by melting,
decomposition or dissolving or by diffusion of the core material through
the wall. Particles produced by this method have found successful
application in a number of industries, e.g., coated duplicating papers and
sustained release drugs, but have not been widely accepted for flavors and
fragrances in the food and cosmetic industry because they are relatively
expensive and not rapidly soluble in water, Cf. Bakan, Microencapsulation
as Applied to Pharmaceutical Products, Eastern Regional IPT Section,
Academy of Pharmaceutical Sciences, Philadelphia, Pa., Oct. 4, 1968.
In the spray drying process particles are produced by a three step
Operation comprising (1) forming an emulsion of the liquid core material
in a solution, usually aqueous, of the normally solid coating material and
(2) breaking up the emulsion into droplets of desired size, e.g., in a
spray nozzle, from a spinning disc, or apertured centrifugal atomizer, and
(3) removing moisture in a drying environment to solidify the coating
material in the droplets to form solid particles. The drying environment
may be hot drying air, e.g., in a spray drying tower, a dehydrating
liquid, e.g., propylene glycol; a bed of dehydrating powder, e.g., dry
starch powder; or the like. The particles produced by this process, while
they may be of various sizes and shapes and may be "hollow" or "solid",
are characterized by cellular structure comprising many dispersed globules
of the core material in a matrix of the coating material. "Solid" in this
context means that a particle has more or less uniform structure
throughout, as opposed to the "hollow" form of particle which has a shell
surrounding a void, but it does not imply absence of pores or cells in the
body thereof. Particles or capsules produced by this method have been used
commercially in many applications, including foods where the core material
is a flavoring oil and cosmetics where the core material is a fragrance
oil. Cf. Balassa, Microencapsulation in the Food Industry, CRC Critical
Review Journal in Food Technology, July 1971, pp 245-265; Barreto, Spray
Dried Perfumes for Specialties, Soap and Chemical Specialties, December
1966; Maleeny, Spray Dried Perfumes, Soap and San Chem, Jan. 1958, pp 135
et seq.; Flinn and Nack, Advances in Microencapsulation Techniques,
Batelle Technical Review, Vo. 16, No. 2, pp 2-8 (1967); Merory, Food
Flavorings, Avi Pub. Co. (1960), pp 274-277.
One of the best of the known processes for producing microcapsules involves
spraying into a drying atmosphere globules or droplets of an emulsion or
solution containing, in a continuous aqueous phase, a hydrophilic colloid
such as dextrin or gum Arabic as the coating material, with the addition
if necessary of an emulsifier, and a volatile or non-volatile core
material of organic liquid, hereafter sometimes referred to as oil or
oils, in a dispersed phase. The products of this process are dry, somewhat
porous powders consisting of roughly spherical, convoluted particles with
the coating material in the solid state and with the organic liquid either
dispersed as minute droplets throughout the particle, or dissolved in a
solid matrix, or both, depending on the compatibility of the oil and
coating material.
In the conventional spray drying process of producing capsules the surface
of the sprayed globule of the emulsion dries to form a solid outer crust
almost immediately on contact with the drying atmosphere and further
evaporation of entrapped moisture normally causes the particle to shrink,
forming craters and cracks in the crust.
Capsule manufacture by this process of spray drying has been accompanied by
loss of considerable proportions of oil by evaporation during spray drying
and the capsules produced have been characterized by relatively high
extractable oil. The maximum practical proportion of oil to wall material
that can be used in the emulsion is usually limited (1by factors inherent
in the mixture, particularly the ability of the aqueous phase to hold oil
as the dispersed phase, and (2) by the losses in processing. These
practical considerations have limited the oil to a fraction of the highest
proportion the particles theoretically are capable of containing and such
oil as is originally encapsulated can gradually escape from the dry
particle, perhaps by diffusing through the relatively porous, cracked and
cratered wall material. A quick test of the potential loss during storage
may be made by determining, in the manner hereinafter described, the
percent "extractable oil". While the mechanism of the oil losses has not
been fully established, both modes of oil loss, i.e., the loss during
spray drying and during storage, may be due to the relatively poor barrier
afforded by the walls of the particles produced by conventional spray
drying procedure using conventional wall materials.
SUMMARY OF THE INVENTION
It has now been discovered, quite unexpectedly, that significant advantages
and benefits are achieved by using combinations of matrix forming
materials characterized by (1) the ability of forming the continuous phase
of an emulsion in which a high proportion of oil can be held in the
dispersed phase, and (2) plasticity or flowability in the drying
temperature range during which a solid is derived from the emulsion by
removal of moisture, e.g., when the emulsion is converted into particles
by a spray drying procedure. The particles or capsules obtained by spray
drying such an emulsion are largely spherical without substantial oil
escape paths in the wall formed from the dissolved combination of matrix
forming solids in the continuous phase of the emulsion due to
discontinuties such as craters or pits, cracks, fissures, pin holes and
the like. The result is high oil recovery and low extractable oil content.
The practical upper limit of oil in the solid matrix is obtained by
properly removing moisture from an emulsion having the maximum oil content
that can be maintained in the dispersed phase. This oil content varies
somewhat in different combinations of the matrix forming material but the
maximum content for any particular combination is easily determined by
observation of the mixture which undergoes a phase inversion when the oil
content thereof is increased above this maximum limit.
The matrix resulting from removal or moisture from the emulsion, whether in
the form of a sheet, block or particles, appears to have a glassy,
amorphous cellular structure characteristic of materials that remain in
liquid phase during moisture removal and solidify without substantial
subsequent shrinkage. The body of the matrix in section is a honeycomb of
spherical cavities or cells holding tiny globules of oil that may be of
the order of one micron in diameter, although other diameters are
obtainable by varying the technique of forming the emulsion.
One combination of matrix forming materials which gives these unexpected,
new results comprises mixtures of polysaccharides and polyhydroxy
compounds as hereinafter defined which form with the oil emulsions that
(a) have a plastic or flowable state over a substantial range of
temperature that is in a critical range over which water is readily
removed between the fully liquid and fully solid states, (b) form a
surface that selectively permits removal of water and (c) become, on
removal of moisture, a cellular matrix of the polysaccharide and
polyhydroxy materials in solid state with oil fixed in the cells thereof.
Materials other than polysaccharides and polyhydroxy compounds that, in
combination, satisfy criteria (a), (b) and (c) may be substituted for part
or all of one or both of these materials. The invention includes the novel
product and the process of producing the same.
DETAILED DESCRIPTION OF THE INVENTION
The novel composition and process of producing the same will be described
in conjunction with the drawings in which:
FIG. 1 is an electron photomicrograph of capsules of the present invention
at a magnification of 200 diameters;
FIG. 2 is an electron photomicrograph of a portion of the same field as
FIG. 1 at a magnification of 500 diameters;
FIG. 3 is an electron photomicrograph of a smaller portion of the same
field as FIG. 1 at a magnification of 1000 diameters;
FIG. 4 is an electron photomicrograph of the portion of the surface of the
particle in the foreground of FIG. 3 surrounding the disc-shaped area of
different texture slightly above the horizontal equator at a magnification
of 5000 diameters;
FIG. 5 is a graph of % powder yield versus % theoretical oil load obtained
by a typical procedure of the present invention;
FIG. 6 is a graph of the % oil load actually contained in the capsules
versus % theoretical oil load obtained by the same procedure of the
present invention;
FIG. 7 is a graph of oil factor versus % theoretical oil load, where oil
factor is defined as the ratio of total oil recovered to total oil input,
obtained by said procedure of the present invention;
FIGS. 8-11 are graphs of melting behavior of typical two-component systems
comprising materials A and B as a function of % B in A;
FIG. 12 is a graph showing the melting range, % powder yield and
extractable oil at 60% oil loading plotted as ordinates versus %
polyhydroxy compound plotted as abscissa for one system of the invention;
and
FIG. 13 is a linear plot of % extractable oil versus time for lemon oil in
capsules produced by the procedure of the present invention at 45% oil
loading.
The polysaccharides employed in admixture with polyhydroxy compounds in
products of the invention are solids characterized by solubility in water
and by at least partial solubility in, or capability of at least partially
dissolving, the polyhydroxy compound within the ranges of proportions
used. They are primarily not the sweet, readily soluble saccharides like
sugar but higher polysaccharides that may be natural, such as gum arabic
and similar vegetable gums, or synthetic, such as degradation and modified
products of starch, which usually form colloidal solutions. Certain starch
degradation products such as dextrinized starch which are suitable
polysaccharides for use in the invention contain a wide spectrum of
saccharides of different molecular weights including a sufficient
proportion in the polysaccharide molecular weight range to be good
encapsulants and varying proportions of lower saccharides such as mono-,
di- and trisaccharides which are polyhydroxy compounds, as later defined.
When such polysaccharides are used it may be necessary to make adjustments
in the proportion of added polyhydroxy compound in order to obtain the
proper balance of polysaccharide and polyhydroxy compounds to assure
proper melt characteristics as later described since the proportion of
lower saccharides in the starch degradation products, while usually too
low to satisfy the requirements of the invention for polyhydroxy compound,
may be large enough to affect significantly the amount of added
polyhydroxy compound required to obtain the said proper proportion of
polyhydroxy compound to polysaccharide in the product.
Among the polysaccharides that may be used are dextrins derived from
ungelatinized starch acid esters of substituted dicarboxylic acids
represented diagrammatically by the formula:
##EQU1##
in which R is a radical selected from the class consisting of dimethylene
and trimethylene and R.sup.1 is a hydrocarbon substituent of R selected
from the class consisting of alkyl, alkenyl, aralkyl and aralkenyl groups.
These ungelatinized starch-acid esters are prepared by reacting an
ungelatinized starch, in an alkaline medium, with a substituted cyclic
dicarboxylic acid anhydride having the following formula:
##EQU2##
in which R and R.sup.1 represent the so designated substituent groups just
defined. Examples of such anhydrides are the substituted succinic and
glutaric acid anhydrides. Such a polysaccharide will be referred to
hereinafter as polysaccharide X.
Other useful polysaccharides include products derived from dextrinized
starch which will be referred to hereinafter as polysaccharide Y and
hydrolyzed starch which will be referred to hereinafter as polysaccharide
Z. In general these products contain minor proportions of lower
saccharides such as dextrose and it is customary to classify them as to
sweetness by a dextrose equivalent (DE) rating, number or range which for
solids (as opposed to syrups) is in the approximate range of 10 - 25,
although some manufacturers produce solid products having higher DE
ratings for several purposes in the food field, e.g., ice cream and other
frozen desserts, cake toppings, cream substitutes, confections and the
like.
The polysaccharide content may comprise a single polysaccharide or mixture
of two or more polysaccharides as illustrated hereinafter.
The polysaccharide should possess emulsifying properties either inherently
or by reason of the presence of a minor proportion of a suitable
emulsifying agent. Further definition of emulsifying agents is unnecessary
because they are well known to those skilled in the art. Examples of
satisfactory emulsifying agents are sodium diisooctyl sulfosuccinate and
sodium caseinate. If emulsifying agents are added, proportions in the
range of 0.1 to 10% based on the weight of polysaccharide in the mixture
are satisfactory. An important property of the polysaccharide or
polysaccharide-emulsifier combination is that when dissolved in water with
the polyhydroxy compound, the aqueous phase (a) is capable of emulsifying
oil to form the dispersed phase of an oil-in-water emulsion with the oil
globules having diameters largely within but not limited to the range of
about 0.5 to 5 micron and (b) has sufficient stability not to invert or
coalesce prior to moisture removal, e.g., by spray drying.
The polyhydroxy compounds employed in admixture with polysaccharide
material in products of the invention are characterized by (a) solubility
in water and at least partial solubility in the polysacchride material or
capability of at least partially dissolving such material, (b) forming
with the polysaccharide material a liquid melt having a softening range at
appropriate temperatures with the ranges of proportions used, (c) forming
with the polysaccharide material a continuous aqueous phase in which oil
is dispersible as a discontinuous phase to form a stable emulsion, (d)
plasticity of the surface of the particle formed from the emulsion as
water is removed through a drying operation and (e) forming with the
polysaccharide material a mixture that is in the solid state at the
temperature of use. The useful polyhydroxy compounds can be classified in
three groups:
1. Polyhydroxy alcohols, including glycerine, sorbitol, mannitol,
erythritol and ribitol.
2. Sugars from plant sources, including monosaccharides such as glucose,
disaccharides such as maltose and sucrose, trisaccharides such as
raffinose, and ketosaccharides such as fructose. These will be referred to
as plant-type sugars whether actually derived from plants or produced
synthetically.
3. Polyhydroxy compounds containing other functional groups including
glucuronolactone (lactone), sorbitan and mannitan (monoethers) and
methylglucopyranoside (acetal).
In general, the proportion of polyhydroxy compounds is at least 20% of the
matrix.
The suitability of mixtures of these matrix forming materials, e.g.,
polysaccharide material (referred to as A) and polyhydroxy compounds
(referred to as B) for use in the present invention may be determined by
the following test procedures:
1. Solubility Test
A. Dissolve A and B separately in water.
B. Combine the two solutions in proper amounts to give various proportions
of A:B on a solids basis over a sufficient range of proportions, in some
cases varying the proportions from pure A to pure B, to determine if there
are proportions that are useful in the invention.
C. Evaporate water from the mixture, leaving a residue in solid state.
D. Place some of the residue on the hot stage of a microscope and observe
the melting behavior as it is heated. If the residue remains essentially
homogeneous throughout the softening and molten range, it will be
satisfactory for use in the present invention, providing the criteria of
the softening range test are met.
2. Softening Temperature Range Test
A. Determine the plastic or softening temperature range of each mixture of
A and B, and use these data to construct a simple two component melt
diagram for each system as shown in FIGS. 8, 9, 10 and 11 which are
typical melting behavior curves for mixtures used in the invention, and
which are described in detail hereinafter.
B. The softening, plastic or flowable state of A:B mixture must occur
within the temperature range consistent with the drying technique used. It
should be noted that the temperature range within which moisture removal
occurs, e.g., the temperature of sprayed particles during drying of the
emulsion, is not necessarily the same as or overlapping the range
determined in 2A, since the melt during moisture removal is a quaternary
mixture of A, B, oil and diminishing proportions of water whereas on
reheating it is a ternary mixture of A, B, and oil.
The systems of FIGS. 8 - 11 are as follows:
Fig. A B
______________________________________
8 Polysaccharide X
Mannitol
9 " Sucrose
10 " Sorbitol
11 Gum Arabic Mannitol
______________________________________
The data on melting behavior for these four different combinations of A and
B are plotted in FIGS. 8 to 11 in which the ordinate is temperature and
the abscissa the present of B in A. In these plots the lower lines connect
the temperature of the beginning of softening for the various mixtures and
the upper lines connect the temperatures of complete fluidity of each of
these mixtures, both of which vary with the proportion of B in A. It will
be seen from the plots of temperatures vs. proportions of B in A for the
systems shown in FIGS. 8, 9 and 11 that the combinations of ingredients
used therein form systems having eutectice within the range of proportions
shown whereas the combination used in FIG. 10 does not. The minimum and
maximum proportions of A and B that can be used to obtain the benefits of
the present invention vary from system to system and are affected also by
the oil load. In general the polyhydroxy compound added to the
polysaccharide should be at least 20% and in some cases these results are
not achieved until considerably more than 20% is present. The effective
and optimum proportions of polyhydroxy compound to polysaccharide can
readily be ascertained by routine determinations carried out according to
the procedures disclosed herein. Products produced from such mixtures have
unique technical advantages in that the oil yield and oil contents of the
products are a maximum and extractable oil percentages are minimal as
illustrated by plots of data of these properties in FIG. 12 for the
eutectic composition of FIG. 8.
Visual evidence of the flowability during drying of the compositions of
this invention is most clearly obtained from scanning electron microscope
photographs of which FIGS. 1, 2, 3 and 4, described more fully
hereinafter, are examples. The smooth, rounded nature of the surfaces of
spray dried particles of the invention demonstrates that the compositions
from which they are derived remain plastic during the drying process. Pits
or craters, cracks, fissures, pin holes and like that ordinarily develop
during the drying process tend to be prevented or sealed by flow of the
plastic combination of materials, thus minimizing the escape of oil both
during the drying process and during the lifetime of the resulting solid
matrix.
Moisture removal may be carried out over a suitable temperature range by
any reasonable process such as vacuum drying, belt drying, slab drying or
spray drying; the latter including variations such as water dehydration by
a fluent dehydrating agent such as starch. Preferably, the softening
temperature range should be such that the material, e.g., particles,
remain plastic until almost all of the water has been removed. This
softening temperature range should be compatible with the vapor pressure
of the material in the dispersed phase.
By extractable oil is meant the oil that is not fixed or stably held within
the matrix, e.g., the spray dried particles. A suitable procedure for
determination of extractable oil comprises:
1. Agitate at 10 gram sample of the encapsulated product with stirring for
10 minutes in 20 milliliters of trichloromonofluoromethane (CCl.sub.3 F)
at 20.degree..
2. Filter the sample through a Buchner funnel with gentle vacuum
(approximately 10 mm. mercury pressure).
3. Wash the powder with 2 separate 10 ml. portions of CCl.sub.3 F.
4. Determine the weight of the oil in the solvent. This can be done in any
manner that gives dependable results. One way is gently to evaporate the
filtrate on a steam bath until the CCl.sub.3 F is completely volatilized
and weigh the oil residue after evaporation of the solvent, Another way is
to read the percentage of oil directly on a properly calibrated wide line
nuclear magnetic resonance spectrometer and calculate the extracted oil
weight. However determined, the weight of extracted oil is recorded as
extractable oil weight.
The percent of extractable oil is calculated from the following expression:
##EQU3##
The stability of the product, i.e., the ability of the product to retain
oil or to resist the loss of oil on storage is believed to be related to
extractable oil. Product produced in accordance with the invention is
stable on storage and has very little extractable oil as may be seen from
the curve in FIG. 13 which is a plot of extractable oil versus time for a
product of the invention which will be described in detail hereinafter.
The extractable oil in this product of the invention is 3.3% at 10 minutes
and does not significantly increase with extraction time up to four hours
(4.0%). In general, the percentage of extractable oil from particles of
the invention at oil levels above 30% is less than 5% in 4 hours. This is
in strong contrast to typical prior art products which show much higher
extractable oil ranges at the same high oil loadings.
By percent yield is meant the percent ratio of the weight of product
removed from the tower to the weight of the ingredients introduced into
the tower in the emulsion other than the solvent or vehicle, usually
water, i.e., the encapsulating agent and oil.
The oils that can be encapsulated in accordance with the present invention
include non-volatile as well as volatile oils such as have been
encapsulated by prior methods but the greatest advantages over the prior
art are obtained with volatile oils because of the low loss on spray
drying, the low extractable oil and high oil recovery. The oils are
characterized by being insoluble but dispersible (emulsifiable) in water
and they may be volatile or non-volatile under drying conditions which
include elevated temperature and low relative humidity in the air stream.
They are usually liquid at the temperature of the emulsion but petroleum
jelly can be successfully encapsulated by the process of the invention
since it is readily broken up into tiny particles in an emulsifying
machine producing high shear. Among the volatile oils that can be
encapsulated effectively by the present invention are natural and
synthetic essential oils or compounded fragrance oils such as citrus
(orange, lemon, lime, and the like), spice oils (cascia, clove,
wintergreen and the like), mint oils (spearmint, peppermint, and the
like), woody oils (vetiver, patchouli, and the like); perfume oils and
individual components thereof, such as linalool, methyl salicylate,
limonene, menthol, decanol, diethyl phthalate, carvone, citral, and the
like; fruit flavors, such as imitation orange, raspberry, apple, banana
and individual components thereof, such as benzaldehyde, isoamyl acetate,
ethyl butyrate, alpha-ionone, or cis-3-hexenol, and the like; and other
imitation flavors or aromas such as nut, meat, vegetable, beverage (such
as coffee and tea), condiment, onion, and the like. The oils may also be
the carrier for suspended solid particles that may be desirable in the
finished product, e.g., fungicides, pigments, and the like.
The proportions of oil to encapsulate or matrix ingredients may vary widely
from small but effective amounts to as high as 80% by volume. The
principal benefits of the present invention in high yield and low
extractable oil are realized in greatest measure where the oil amounts to
at least 30% of the composition.
The solvent or vehicle preferably used in the invention to dissolve the
polysaccharides and polyhydroxy compounds is water. The viscosity of the
emulsion can be modified by varying the proportion of water therein.
Additives may be used in the mixtures of matrix forming ingredients
provided the properties described above are not substantially impaired. In
some cases the favorable properties of the products are enhanced by the
presence of additives. For example, in systems comprising polysaccharide Z
having a DE in the range of 10-25 and sucrose at a level within the range
of 20% to 60% of the combination of matrix forming ingredients, partial
replacement of the polysaccharide by a protein derivative such assodium
caseinate, e.g., up to 50% thereof (i.e., 1 part of polysaccharide Z
replaced for each part of sodium caseinate), has no substantial
deleterious effect on yield or extractable oil over an oil load range from
15 to 75%. At lower proportions, e.g., 2-10%, sodium caseinate serves as
an emulsifying agent, as described above, and at higher levels it also
contributes to wall strength and integrity. Other protein derivatives
which function similarly are polymers of about 10 to 100 amino acids
joined by peptide bonds between the carboxy carbon of one acid and the
amino nitrogen of the adjacent acid by elimination of water. A preferred
polypeptide is derived from collagen having at least 15% nitrogen (of
which 9% is amino nitrogen), 8% maximum water, a maximum ash content after
16 hours at 550.degree.C of 6%, iron less than 5 parts per million (ppm),
heavy metals less than 50 ppm, average molecular weight of about 10,000
and a Lovibond color in 1% solution not darker than 2.5 yellow and 0.5
red. The referred proteins are characterized by emulsifying properties in
the polysaccharide-polyhydroxy compound system and, at higher proportions,
also as contributors to wall strength and particle integrity.
The mixtures of the polysaccharides and polyhydroxy compounds useful in the
invention all satisfy the solubility and softening temperature range tests
given above but not all of them exhibit an eutectic within the desired
composition range or optimum performance at the eutectic as in the case in
the polysaccharide X - mannitor system of FIG. 12. There is, however, a
range of proportions of A to B for all satisfactory mixtures which gives a
minimum extractable oil content and a maximum yield and this range is
easily determined for each mixture of A and B by plotting these values as
ordinates for each proportion of B to A as abscissa on graph paper in the
manner illustrated in FIG. 12 for the polysaccharide X - mannitol system.
Other satisfactory binary mixtures of A and B include:
A B
______________________________________
Polysaccharide X Sorbitol
" Erythritol
" Fructose
" Sucrose
" D-Glucoronolactone
" Glucose
" Glycerine
" Maltose
" Mannitan
" Methyl-A-D-Glucopyranoside
" Raffinose
" Ribitol
" Sorbitan
Gum Arabic Fructose
" Sorbitol
" Sucrose
Polysaccharide Y Mannitol
" Sucrose
______________________________________
A preferred process of making the particulate compositions of the invention
comprises dissolving the polysaccharide and polyhydroxy material as
defined hereinabove in water, with additions of a surface active material,
if necessary, emulsifying the oil in the aqueous phase so as to form a
dispersion of droplets having a diameter of the order of about 0.5 to 5
micron, for many purposes preferably about 1 micron, spraying the emulsion
into a spray drying tower operating under conditions that will form
droplets having the desired diameter, e.g., about fifty (50) microns,
removing the moisture content of the droplets to about 2% or less by
weight of the resulting solid paraicles by means of the heat and low
relative humidity in the drying air, while maintaining the particles at a
temperature such that the entire particle, and in particular the surface,
remain liquid until the moisture content has attained a low level, e.g.,
about 5% or so, then solidifying and/or cooling the particles to a glass
by evaporation of the remaining few percent of water, or by cooling with
air, or both.
In the preferred process the emulsion is prepared in a single vessel
equipped with an agitator capable of emulsifying the o/w emulsion to a
desired droplet size, e.g., about 1 micron or less. The agitator may be an
open blade type or a closed turbine type.
The required quantity of water is placed in the vessel and the solid wall
materials are added slowly with agitation. Agitation is continued until
solution is complete. The oil is added slowly, e.g., to the vortex
produced by the agitator, while the agitator speed is gradually increased
to the maximum required. Agitation is continued until the emulsion reaches
the required droplet size. Care should be taken not to overheat the
emulsion during agitation which could cause rapid coalescence when
agitation is stopped. The emulsion may be diluted with an appropriate
amount of water to give the desired viscosity. The emulsion is transferred
to a holding vessel where it remains with or without agitation as desired
until pumped to the dryer.
In the preferred process the emulsion is dried, preferably by spray drying,
at temperatures that maintain the particles entirely in a flowable state
until nearly all the moisture has been removed. Then the particles are
solidified either by cooling or by increasing the solidification point of
the mixture by further removal of water, or both, depending on the
specifications for the product and the type of equipment being used.
To accomplish moisture removal by spray drying, any suitable spray drying
tower may be employed. Typically spray drying towers comprise an upper
cylindrical portion where the emulsion to be dried is introduced by
rotating discs, nozzles, and the like, and a lower conical portion leading
to the product outlet at the bottom of the cone. The drying medium,
usually heated air, may be introduced at the top with the emulsion to be
dried, the so-called concurrent type, or adjacent to the bottom, the
so-called countercurrent type. In general for products of the invention in
the form of very fine powders it is preferred to use the concurrent system
with centrifugal separation of product from the air after the product has
been removed at the bottom of the conical portion of the spray tower. The
air used in the drying process is ordinarily taken from the atmosphere and
passed over heated surfaces before being introduced into the drying tower.
These surfaces may be heated electrically, by flame, by steam, or the
like, in accordance with the usual techniques which are understood by
those skilled in the spray drying art. Ordinarily the air at the time it
is introduced in the tower will have a temperature between about
125.degree. and 300.degree.C but on account of rapid evaporation of the
moisture in the emulsion, the heat in the air is absorbed so quickly as
latent heat of evaporation that the temperature of the particles from
which the moisture is being removed remains within the plastic range
throughout the drying operation and the particles then become discrete
solids.
Drying may also be effected by spreading a layer of the emulsion on a
suitable substrate, e.g., on a heated drum, or on a belt which is then
passed through a heating tunnel or subjected to vacuum drying, or on the
article where a layer of product is desired and removing moisture
therefrom. When drying by means other than a spray tower and on the
article where it is desired, it is ordinarily necessary to grind the
resultant dried material to the desired particle size. In general spray
dried particles ma have a spectrum of sizes up to about 400 microns in
diameter but preferably the predominant size for many purposes is about 40
microns in diameter.
The appearance and properties of the products produced by the preferred
spray process of the invention are unique and distinct and represent a
significant improvement over products produced by spray drying according
to the best known commercial techniques in prior use. The unique
appearance is readily seen and can be photographed under a scanning
electron microscope at various magnifications.
Referring to FIGS. 1, 2, 3 and 4 it will be seen that the product produced
in accordance with the present invention is characterized by well defined
spherical shape believed to result from the surface tension in the free
plastic particles during the drying operation. When one such free plastic
particle strikes another there is an infolding of the plastic surface
around the striking particle that may hold the two particles together, as
may be seen in FIG. 2. As seen in FIG. 1 some of the smaller spherical
particles tend to associate in clusters. The surface of all the particles
is smooth and glassy and fine pores visible in product produced by prior
procedures are absent in the particles of the present invention as shown
in FIGS. 1, 2, 3 and 4. The product from which the photomicrographs
reproduced in FIGS. 1, 2, 3 and 4 were made was obtained as described in
the Example 4e hereafter.
The following examples are given to illustrate the invention but they are
not to be considered as limitations on it except as specifically so
stated.
EXAMPLE I
A solution of an encapsulant comprising 32 parts glucoronolactone and 48
parts polysaccharide X is prepared by dissolving them in 250 parts of
water with agitation at high speed in a household type Waring blender.
Single fold orange oil containing 1% butylated hydroxy anisole as
antioxidant is slowly added to the resulting solution until 120 parts are
incorporated while continuing high speed agitation for 3 minutes, at which
time an oil/water emulsion had formed with an average droplet diameter of
0.5 microns. The | | |
