Note: Descriptions are shown in the official language in which they were submitted.
S685
Thi5 in~ention relates to a novel method of encapsulating
water~soluble material~ in water~oluble encapsulants via a spray
drying technique.
It is known to encapsulate a variety of materials in water-
soluble matrix-forming polymers such as gum arabic, starch, pec-
tin, casein, gum tragacanth and gelatin. In most o the known
càses, the encapsulation is carried out by dispersing the matexial
to be encapsulated in a solution of the wall-forming polymer in a
,
solvent which is not a solvent for the material being encapsulated.
10 Upon drying of this dispersion or emulsion, the wall-forming
materia~ forms the desired protective shell about the oil droplet. ~ ~-
Upon removal of the sol~ent, encapsulated small particles are re-
covered.
- The procedure which has just been described is useful only
with materials which are not soluble in the solution of wall- -
forming material. I the encapsulate and the wall-former are mut-
ually soluble, coprecipitation takes place upon removal of the
water phase with the result that the material sought to be pro-
tected by encapsulation is distributed relatively uniformly ~
20 throughout a matrix rather than being encapsulated. In such a ~;
case, the encapsulate is readily extracted from the matrix and,
even worse, any volatile components of the encapsulate can easily
evaporate out of the matrix either during the drying step or in
storage.
U.S. patent 3,539,465 teaches encapsulating water-soluble
materials in a water~soluble wall-forming polymer via a coacerva-
tion process. In this method the water-soluble encapsulate is
emulsified in a water-i~iclcible oil such as a vegetable, animal
or mineral oil with the assistance of a surfactant. The resulting
30 emulsion is then dispersed in a solution of the wall-forming poly-
mer and caused to coacervate by addition of appropriate agents
whereby liquid-liquid phase separation takes place, forming poly-
mer rich droplets dispersed in polymer~poor solution as a contin-
uous phase. The polymer~rich coacervate must then be hardened,
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usually by addition of a hardening agent, but sometLmes by means of tempera-
ture adjustm~nts, prior to removal from the continuous aqueous system.
In accordance with the present invention, it has been found that,
by making use of a specific nonionic surfactant, it is possible to effect
encapsulation of water-soluble materials or materials having a significant
water-soluble fraction, in water-soluble wall-forming polymer~ without the
necessity of going through the manipulative steps required in a coacervation
process.
Specifically, the invention provides a method of encapsulating a
liquid water-soluble material in a water-soluble, wall-forming polYmer, which
method comprises emulsifying the liquid water-soluble material in a non-polar,
water-immiscible oil to form an emulsion in which the oil is the continuous
phase, using, as an emulsifier, polyoxyethylene (20) sorbitan tristearate,
dispersing the resultant emulsion in an aqueous solution of a wall~forming
polymer which is insoluble in the said non-polar, water-immiscible oil and
spray drying the dispersion under conditions whereby substantially all water
is removed and the water-soluble material is encapsulated.
In carrying out the process of the invention, it has been found that
the surfactant employed to emulsify the water-soluble material in the water-
immiscible oil is highly critical. Of the commercially available nonionic
surfactants, only the specifiea ethoxylated sorbit~n tristearate has been
found effective. The designation polyoxyethylene (20) indicates that each
mole of sorbitan tristearate contains about 20 moles of ethylene oxide. The
; ethoxylated sorbitan tristearate useful in this invention is commercially
available under the trade names "Tween* 65" by ICI A~erica, Inc. and "Durfax*
65" by Durkee-Glidden Corp. In the first operative step of the invention, the
water-soluble material to be encapsulated is emNlsified in a non-polar, water-
i~miscible oil. Substantially any non-polar, water-immiscible oil can be
employed, depending upon the application contemplated for the encapsulated
material. m us, various vegetable oils, such as coconut oil, corn oil and
sunflower oil, as well as mineral oils, can be employed.
~Trade Mark
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" ~V8S68~;
The polyoxyethylene ~20) sorbitan tristearate i9 preferably dis- ~.
persed in the oil in a surfactan~ to oil ratio of about 1/1 to 2/1 by weight.
Blending is carried out with agitation at a temperature
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o about 40 to S0C, ~ime and temperature o~ blendiny are not
particularly signiicant so long as they are sufficient to assure
homogeneous dispersion of surfactant throughout the oil phase.
When the water~immiscible oil and the polyoxyethylene ~20)
sorbitan tristearate are thoroughly blended, the water-soluble
material is added to the oil/surfactant dispersion, again with
agitation, until all of the water-soluble material is taken up in
the surfactant droplets to form an emulsion wherein the oil is
the continuous phase. Blending can be accomplished at tempera-
10 tures up to about 50C., depending upon the volatilit~ of thewater-soluble material, In both of the blending steps employed
in the preparation of the emulsion of water-soluble material in
water-immiscible oil, it is preferred that blending be carried
out with a relatively high degree of shear in order that the sur-
factant droplets be as small and finely dispersed as possible.
~ f the water-soluble material to be encapsulated is a norm-
ally liquid~material, it can be added directly to the oil-surfac- ~ `~
tant blend for emulsification. If it is a normally solid mate-
rial, it can first be dissolved in water. In this case, it is ~ ;~
20 preferable to usethe minimum amount of water that is effective toaccomplish dissolution.
The amount of water-soluble material included in the oil
phase is determined by the amount that the surfactant is capable
of retaining in suspension. This will, of course, vary with dif-
ferent water-soluble materials. Generally, the amount will be
about 50 to 95% total water-soluble material ~including solvent
water, if any) in the oil, based on the total weight of the oil
phase. It will be recognized that the lower limit is not critical
except for economic reasons.
The emulsion of water-soluble material in oil is thPn added
to an aqueous solution of a wall forming polymer and blended
thoroughly to disperse the oil emulsion throughout the solution.
The wall-forming material is a water-soluble, oil-insoluble poly-
meric material capable of forming a film. Starch and modified
5685
starches, gum arabic~ carboxymethyl cellulose and gum tragacanth
are typical wall-forming materials which can be employed. These
can all be used alone or in combination with each other or with
other materials as, e.g., lower molecular weight polyhydroxy com-
pounds such as maltose, dextrose, sucrose and the like.
Most of the water-soluble, wall-forming materials possess
inherently some emulsifying properties. If the wall-forming mate-
rial being used possesses no or insufficient emulsifying proper-
ties, a minor amount of another known emulsifier can be added to
10 the solution. The emulsification capacity need be only sufficient
to assure that the oil phase can be dispersed as small droplets
and is stable enough that the emulsion will not invert prior to
water removal.
At this point, the only step remaining to complete the en-
capsulation is spray drying, No other manipulative steps, such as
; addition of an electrolyte or other precipitating or coacervation
aid are required. Removal of water via spray drying deposits a
film of wall-forming material on the oil droplet.
Any suitable spray drying e~uipment can be used in accord-
20 ance with techniques well known to those skilled in this art. Con-
ditions of spray drying can be selected to yield dried powder par-
ticles of substantially, any desired size. Drying is normally `
accomplished at dryer inlet temperatures between about 140 and
250C. and out temperature between about 70 and 90C., depending
upon the wall-forming matexial being employed, the volatility of
the encapsulate, and other factors. ~-
The proportion of encapsula~ed material (oil plus surfac-
tant plus water-soluble material) to encapsulant can vary widely
from about 1% to about 80~ by weight, The principal benefits of `
30 the invention so far as good yields and low extractable oil as de-
fined below ars concerned are realized when the encapsulated mate-
rial amounts to about 1 to 50% of the product.
The effectiveness of the process is evaluated principally
through dryer yield (TDY) and storage stability of the products.
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8S685
In both areas the products of thi~ invention are ~uite good.
By yield is meant the ratio of the weight of product re-
covered from the spray drying operation to the weight of the in-
gredients introduced into the tower in the emulsion other than the
solvent water, i.e., the ratio of product recovered to encapsula-
ting agent and oil introduced into the dryer
The method of the invention can be employed to encapsulate a
wide variety of commercial materials. One area in which the method
is particularl~ useful is flavors and fragrances for use in oods,
10 beverages, cosmetics, detergents and personal are products. Other
types of water-soluble products which can be encapsulated include,
e.g., agricul~ural chemicals, vitamins and other pharmaceutical
products, and various pesticides.
Example 1
About 3.3 grams of coconut oil and 6.7 grams of sorbitan tri-
stearate plus 20 moles ethylene oxide ~Tween 65) were blended with
agitation at about 45C. for about 15 30 minutes until smooth. The
blend ~as cooled to room temperature with continued agitation. At
-`room temperature 90 g. of an imitation sherry wine flavor contain-
20 ing, among other things, 30% by weight of acetic acid, was added.
With the mixture at room temperature, agi~ation was continued until
the sherry wine flavor was completely dispersed throughout the oil-
surfactant mixture and taken up by the surfactant droplets. A
clear, thin liquid was present at this point. When one drop of
this liquid was added to an excess volume of water, the drop did
not disperse. A white, opaque film formed around the droplet with
no visible sign of components leaching out into the aqueous phase.
.
;About 100 g. of the clear liquid oil-surfactant flavor mix-
;~- ture was added to a solution containing 400 g. water and 400 g. of
30 a 3/1 by weight mixture or corn starch having a 10% dextrose equi-
valent and a chemically modified starch prepared from ungelatinized
starch acid ester of substituted dicarboxylic acid represented by
formula O R'
Starch-O-C- R~COOH
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where R is di~ or trimethylene and R' is alkylr alkenyl, aralkyl
and aralkenyl, This mixture was emulsified under shear conditions
to reduce droplet size to about 1 to 2 microns~ -
Upon spray drying of the emulsion at about 180~ inlet and
80C. outlet temperature, a dry free-flowing powder was recovered.
Yield of encapsulated product was about 87%.
The odor intensity of the encapsulated dry sherry wine ~lavor
was substantially suppressed when compared with the liquid flavor-
ing material. Upon dissolving in water to form a sherry wine
10 drink, the organoleptic qualities of the product were found to be
excellent and comparable to those of the initial liquid product.
A parallel experiment was conducted in which the flavorant
was encapsulated using propylene glycol as the oil phase (the
flavor was not sufficiently soluble to be encapsulated in coconut
oil) without the assistance of the ethoxylated sorbitan tristear-
- ate surfactant. The attempted flavor load was 12.5% but this
material yielded only 70% through the dryer yield. Its organolep-
tic properties were considerably inferior to those of the material
prepared according to this invention at equivalent theoretical
20 flavor strengths. The odor intensity of this dry product, al-
though it contained only about half the amount of active flavor- -
' ant, was significantly higher than that of the product prepared
'' - according to the invention with the sùrfactant incorporated there-
in, indicating that encapsulation and entrapment of the flavor was
less efficient without the surfactant. ~
- Example 2 ~';
A natural maple flavor extract was emulsified in coconut
oil in a fashion similar to that described in Example 1. In this
case the oil phase consisted of 11 parts of coconut oil, 22 parts
. .~.. : .
30 Tween 65 and about 67 parts of the maple flavor extract. The oil
phase was dispersed in 254 parts of an a~ueous solution of the
mixed starches described in Example 1 and then spray dried at 180 ~`
- inlet and 80 outlet temperature. Encapsulated small particles
were recovered. The yield and the flavor characteristics were
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comparabl~ to those of the unencapsulated maple flavor.
A parallel experiment was performed in which the same flavor
material was encapsulated in the same starch without the assist-
ance of the coconut oil and the surfactant. A product having ap-
proximately 25% flavor load was recovered at a 50% yield. The
product prepared according to the invention was judged to have
about 2.5-3 times the flavor impact of the control sample indicat-
ing that some important components of the flavor were lost during
encapsulation of the control.
Example 3
Using substantially the same procedures usedin Examples 1 and
2, a core ma~erial containing about 93.7% of an imitation honey
; flavor, 4.2% sùrfactant and 2.1% coconut oil was prepared. This
material was emulsified in the modified starch and spray dried ;
yielding about 84% of a product containing about 31% of the imita-
tion honey flavor. This material was judged to have about ten
, times the organoleptic flavor strength of a control material en-
capsulated without the aid of the surfactant and the coconut oil
which yielded an 80% through the drier yield.
- 20 Exam~les 4 - 7 -
., Using the procedures outlined in Example 1 above, the fol-
lowing materials, each containing a substantial water-soluble
fraction, were encapsulated.
Table
` ` % Sur-
Ex Oil fact~
; No Materlal %* Phase tant* Intended A~plication
4 St. John's bread 78.9 Coconut 14.5 Tobacco flavoring
flavor oil
5 Naringin flavor 74.2 " 17.2 Beverage powder
substitute
6 Spearmint flavor 90.O " 10.0 Chewing gum
7 Potato flavor 50.0 " 37.6 Instant mashed
potato mix
- * Based on total oil phase -~
- Exam
A mixture was prepared comprising about 88 parts by weight
of coconut oil and 12 parts of a commercial water-soluble mustard
flavoring material. One hundred parts of this mixture was mixed
56~5
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thoroughly with 17~6 parts of polyoxyethylene ~20) sorbitan tri~
stearate until a smooth emulsion was formed.
The emulsion was added to a starch solution and spray dried
as taught in Example 1. Simultaneously, a portion of the oil/
flavor mixture without the emulsifier was added to an identical
starch solution in the same proportions of oil and flavor to
starch and spray dried.
Specimens of each of the spray dried products were agitated
gently in trichlorofluoromethane ~CC13F) for 10 minutes at 20C.
10 and the amount of flavor extracted therefrom was determined. The
product prepared according to the invention was found to have only
about 1.8% extractable oil (also sometimes referred to as "surface
oil"). The product prepared wi-thout the polyoxyethylene (20) sor-
bitan tristearate had 8.6% extractable oil.
In addition to the lower level of surface oil associated
with the product prepared according to the invention, it was noted
that the dry powder had no discernible mustard odor. By contrast,
the product prepared without polyoxyethylene (20) sorbitan tri-
~ .
stearate had a very distinct, pungent mustard odor associated with
; 20 it.
;i ExamE~e 9
The procedure of Example 8 was repeated with a mixture of
85 parts of hydrogenated~fractionated vegetable oil having a melt- ~'~
; ing point between 59 and 67F., and 15 parts of the water-soluble
mustard flavoring material. This was emulsified with about 17
parts polyoxyethylene (20) sorbitan tristearate, mixed with the
starch solution and spray dried.
The dry product exhibited no mustard odor but, when added to
~- water, a strong mustard flavor and odor was released.
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