Controlled Release in the Food and Cosmetics Industries - American

Chapter 3

Controlled Release in the Food and Cosmetics Industries

Downloaded by UNIV OF MISSOURI COLUMBIA on August 22, 2013 | http://pubs.acs.org Publication Date: March 5, 1993 | doi: 10.1021/bk-1993-0520.ch003

Lisa Brannon-Peppas Biogel Technology, P.O. Box 681513, Indianapolis, IN 46278

Encapsulation techniques are used in the food and cosmetic industries both to control the delivery of encapsulated agents as well as to protect those agents from environmental degradation. In foods, the most important applications of encapsulation include: (i) encapsulation of flavors, (ii) shielding of oxygen- or water-sensitive components such as vitamins, and (iii) isolation of reactive ingredients until their release is desired (1). A l o n g similar lines, the cosmetics industry utilizes encapsulation to: (i) trap fragrances for controlled or sustained release, (ii) protect particularly volatile components, and (iii) provide release at a delayed time. The preparation methods for these microcapsules may be similar, whether they contain flavors, fragrances, or drugs. This paper w i l l present an overview of the uses of microcapsules i n the cosmetics and food industries, with an emphasis on the materials used and the goals and uses of the final products.

Controlled release systems have been developed in the past thirty years for a variety o f " t r a d i t i o n a l " applications, i.e. applications i n pharmaceutical and agricultural applications. However, it may not be realized that applications o f microencapsulation in the "nontraditional" areas of cosmetics, food, fragrance, paper technology, and other fields have been prominent for far longer. Encapsulation has been used in the food industry for nearly sixty years. Encapsulation by spray drying was first used for flavor enhancement and protection in the 1930's (2). Concentric nozzle techniques were developed in the 1930's and 1940's to protect vitamins. In fact, several recent marketing surveys (3) indicate that the market for these products is significantly higher than for pharmaceutical and agricultural products. T h i s review w i l l present encapsulation techniques and uses o f flavors, fragrances, food additives and agents for cosmetic applications. Most of the techniques w i l l not be described in extreme detail, since they are presented elsewhere in this volume. However, any differences between these techniques and those usually found in pharmaceutical applications will be emphasized.

0097-6156/93/0520-0042$06.00/0 © 1993 American Chemical Society

In Polymeric Delivery Systems; El-Nokaly, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

3. BRANNON-PEPPAS

Controlled Release in Food & Cosmetics Industries

Controlled Release in "Nontraditional" Applications Controlled release devices and systems used in the so-called "nontraditional" areas are used i n the following applications:


( 1) (2) (3) (4) (5)

fragrance and flavor release systems, flavor and active ingredient release in food applications, active ingredient release for cosmetic applications, bioactive agent and fragrance release for pet products, active ingredient release of bleaching and fragrance products i n cleansing products, (6) release of fragrances and related compounds for air fresheners, space release systems, botanicals, potpourri, and household devices, and (7) release systems related to paper technology including pressure sensitive flavor-releasing systems and carbonless paper.

Depending upon the formulation that is used for the release system, the systems may be described as: (1) (2) (3) (4)

encapsulated (shell or core) systems, microparticulate matrix systems, cylindrical and planar matrix devices, and osmotic and other membrane systems.

O f the above mentioned systems, microencapsulated devices (category 1) continue to be the most attractive systems in the consumer products field. Indeed, about 8 5 % of products in the markets in those fields are encapsulated products (3). The reason for this preference is that microencapsulation has been a well-understood and relatively easily applied technique that can be used to prepare release systems for a variety of volatile and non-volatile, stable and sensitive, biological and nonbiological products. Since 1956, when the first patents of B . Green for N C R on the development of carbonless paper for microencapsulation of inks appeared (4,5), the field has grown in sophistication and variety of products. Mechanisms of Release. A very important classification of the controlled release devices i n this field is based upon the mechanism of release or method of triggering the release behavior. From this point of view, controlled release devices i n the consumer products field can be divided into the following ten categories (as shown i n Table I): (1) Diffusion controlled release devices: Controlled release devices based on diffusion control are systems where the release of the volatile or non-volatile active ingredient is controlled by the diffusional process of this ingredient through the polymer carrier. Such diffusion may be through the polymer proper (carrier of the device) or through pores preexisting in the polymer. If the component is a volatile material (eugenol release from a base polymer of a chewing gum) the release can be augmented by the evaporation characteristics of the active ingredient. Such diffusional mechanisms can be found in a variety of consumer products. For example, the release of various fragrances from strips of polymers i n air fresheners or the transport of flavorings in chewing gums are classical diffusional mechanisms. It must be noted that this diffusional process does not have to occur through a polymer in order for the release process to be controlled by the carrier. In fact, many food applications are based upon the utilization of the food itself as the


43

44

POLYMERIC DELIVERY SYSTEMS


carrier for the release. In this field, where only a small number of carriers have been approved by F D A for human consumption, the food itself is modified by a number of processes (e.g. freeze drying, other drying techniques) in order to impart porosity or other characteristics which would lead to controlled delivery of incorporated flavors. Thus, Reineccius and his associates have reported on various ingenious techniques of delaying the release of orange oil from food products by either modification of the food itself or by incorporation of small amounts of porous silica or other materials (6). Orange o i l is the least stable flavor and is often used as model systems to ascertain the viability of a controlled delivery system.

Table I.

Mechanisms of Release from Controlled Delivery Systems in Consumer Products

Diffusion Controlled Release Membrane Controlled Release Pressure-Activated Release Tearing- or Peeling-Activated Release Solvent-Activated Release Osmotically-Controlled Release p H Sensitive Release Temperature-Sensitive Release Melting-Activated Release Hybrid Systems

(2) Membrane controlled systems: Encapsulated controlled release devices are in principle membrane (reservoir) systems. A s most of these systems are microspherical, containing a core of active ingredient, and surrounded by an extremely thin membrane of the encapsulant polymer, one would expect that the release behavior would be controlled by the same principles as for the classical controlled release systems (7). In theory, this would means that if all microcapsules were of the same external diameter and the same wall thickness, and if they were all placed i n a fluid and released under perfect sink conditions, they should give zeroorder release behavior. In reality, this is almost impossible as the microcapsules are of a wide size range and may have different wall thicknesses (8). Still, the rate of release is controlled by the concentration difference across the wall of the microcapsules, the thickness of the wall, permeability of the active ingredient through the wall and, of course, the diffusion coefficient of the active ingredient with respect to the surrounding environment. A l l of the microencapsulation systems that w i l l


3. BRANNON-PEPPAS



release their contents by that classical release process may be considered to be membrane-controlled release systems. (3) Pressure-activated controlled release systems: A number of controlled release systems, including many of those used in paper technology, are triggered by the application of pressure on the walls. Such systems are usually microencapsulated devices but their walls are rather dense and the incorporated active ingredients are relatively non-volatile. Thus, neither diffusional release due to concentration gradients nor evaporation of active ingredient through any pores should be expected to contribute to the release mechanism. Instead, the prominent mechanism of release is rupture of the wall due to application of external pressure. Such is, for example, the case with microencapsulated inks adhering to the back of a paper in carbonless paper. The pressure applied by a pen on the front of the paper ruptures the microcapsules, immediately releasing their contents. Similar systems are those based upon Scratch ' n Sniff technology where, again, a shear action of a fingernail on a piece of paper would rupture the microcapsules. (4) Tearing or peeling activated systems: Tearing or peeling activated release systems are an unusual type of controlled release devices which have been finding more and more application in the field of fragrance release or i n applications related to print media advertising. In such systems, microcapsules are usually placed, with an adhesive, between two layers of paper or polymer film. The microencapsulated systems may contain fragrance oils, inks, colorants, and other related agents. The user usually applies a peeling action by pulling apart the two layers of paper (or polymer film) thus rupturing the microcapsules and releasing their contents. Such systems have found wide use i n various systems including the technologies of Microfragrance, Colorburst, and Fragrance Burst. (5) Solvent-activated systems: A number of controlled release products and devices in the consumer field are based upon diffusion of the surrounding fluid through the surrounding polymer carrier. Typically, water or a related aqueous solution penetrates the polymer carrier, swells it, and leads to a faster release of the incorporated active ingredient. In some cases, the polymer (or other encapsulating material) w i l l completely dissolve. Thus, the swelling process controls the overall release of the incorporated active ingredient. A number of consumer products reported in the patent literature utilize this system, especially in the field of fragrances and flavor release. This is a particularly favored mechanism in a large number of Japanese patents (9-77 ). (6) Osmotically-controlled devices: Certain types of microencapsulated controlled release devices are triggered by a large osmotic pressure that is created in the interior of the capsule due to the presence of an osmotically active agent. Indeed, if a chemical compound encapsulated in a particular device has a very high solubility in water, a large osmotic pressure can be created. Narkis and Narkis (12) and Theeuwes (13) have calculated the typical values of osmotic pressure that can be created by some of these compounds. If the osmotic pressure created is higher than the mechanical integrity of the microcapsule walls, then the microcapsules w i l l burst, releasing their contents. A typical device triggered by such an osmotic phenomena would be a microencapsulated device containing bleaches that would not release during the early stage of the washing cycle, but would release only after a certain time due to osmotic rupture. (7) p H sensitive systems: In the field of cosmetic products, there has been a recent explosion with respect to intelligent devices that respond to changes i n p H of


45

46



the user. For example, systems have been reported in the patented literature (14) that are sensitive to changes of the p H of the skin. A s a result, of that change, the polymer carrier collapses, thus "squeezing out" its active contents. This process is, i n principle, reversible. Systems like these are still at their infancy in the cosmetic area (15), but there is a strong indication that they w i l l be more acceptable in the future because the cosmetic market is one where the mark-up is extremely high, thus allowing for a higher cost of production (due to the relatively high cost of p H sensitive materials) if the final product is to exhibit unusual properties such as p H sensitivity. (8) Temperature-sensitive systems : Certain types of controlled release devices are being researched which are based on polymeric carriers that are temperature sensitive. In recent presentations, both Miles and Peppas (15,16) have noted that certain polymeric materials are sensitive to small changes to temperature, around room temperature, leading to either expansion or collapse of their structure. Such systems, could therefore exhibit dimensional reduction leading to exudation of their contents upon a small change of temperature. A s in the previous category, such systems could be beneficial in the cosmetic and personal care fields. It must be noted that the temperature sensitivity is centered around the critical temperature of the polymeric carrier and does not involve melting. (9) Melting-activated release systems: A number of controlled release systems for consumer applications are based upon a phenomena of melting of either the polymer carrier itself or the active ingredient. The most useful case, is that of melting of the encapsulant walls, leading to an abrupt release of the content of the microcapsules. Again, systems like this have been proposed for release in cleansing products, especially in situations where one would expect a particular ingredient to be release only during a drying cycle or during ironing. In addition, such encapsulated products are also used in baking mixes and are designed to be released only during baking. (10) H y b r i d systems: Numerous controlled release devices may exhibit a combination of several triggering events and release mechanisms. F o r example, a novel deodorant stick device may contain microencapsulated fragrance oils which would release by a combination of temperature increase, sweat production, and p H change. Such systems are presently under development and are even commercially available. Encapsulation in the Food Industry The effectiveness of encapsulation of flavors depends strongly on the concentration of the flavor as well as the method of encapsulation. The most successful encapsulant must be molecularly impenetrable to the flavor within it. In addition, the wall surrounding the flavor must have outstanding physical integrity which allows for no undesired breakage. The encapsulant should also be impenetrable to oxygen to increase the oxidation stability of the flavor. Methods of Encapsulation of Essential Oils. Encapsulated flavors are produced by a variety of techniques, depending upon the desired final form of the controlled release system as well as the nature of the flavor (usually an essential oil) to be encapsulated and the encapsulating material. In addition to controlled release and flavor protection, microencapsulation of flavor may provide an additional advantage i n that it converts liquid material into a solid which is significantly easier to handlef 17). Approximately 30 million pounds of encapsulated flavoring are used i n


3. BRANNON-PEPPAS


the United States each year. These products may be formed by spray drying, extrusion, molecular inclusion, or coacervation. A summary of the advantages and disadvantages of each method are given in Table II. The methods used to encapsulate fragrances are similar, if not identical, to the methods used to encapsulate flavors. The essential oils, which are the active agents in both applications, are closely related and sometimes the same oil may be used for applications in both both flavor and fragrance controlled release.


Table II.

Encapsulation Processes for Flavors

Advantages

Disadvantages

Spray Drying

L o w cost Availability of equipment Good protection Variety of wall materials

Small particles (dispersibility) Not for extremely low boilers Limited shelf life (oxidation)

Extrusion

Excellent shelf-life Visible "pieces" of flavor

L o w flavor load (8-10 wt%) Slowly soluble (variable) High temperature process

L o w process costs Very stable

L o w flavor load (6-15 wt%) L o w solubility Nonuniform component binding Cost

True encapsulation High load (25-97 wt%) L o w cost Good shelf-life

Large particle size (20/*m-2mm) Material and wall must be immiscible Boiling point limitations

Microencapsulation Technique

Molecular Inclusion

Coacervation

The characteristics of spray dried products are highly dependent upon the processing conditions of the encapsulation procedure. The oxidation of the essential oil in the final microcapsule (and therefore its shelf life) is directly related to the nature of the encapsulating material (usually a wax), the storage time, and the emulsion size prior to the spray drying. The factors which most directly influence the shelf life of these products are the presence of surface o i l , microcapsule porosity, the presence of trace pro-oxidants or anti-oxidants, and the quality of the o i l . Spray dried products are readily producible at low cost, with available equipment, but tend to have a shorter shelf life than other encapsulated systems due to their lack of oxidation protection for the essential oil. Extruded products are usually formed by passing a mixture of the essential o i l , a sugar-starch hydrolysis mixture as an encapsulant, and possibly an antioxidant,


47

48


through an extrusion die into a bath of non-sol vent where the extruded pieces are broken into particles by impact breakage. This preparation procedure yields products with an excellent shelf-life (1500 days or more at 25°C), but with a low flavor load (8-10 wt%).


Molecular inclusion is accomplished by trapping an essential oil within the center of molecules of cyclodextrins. This process involves s o l u b i l i z i n g the cyclodextrin to be used, adding the essential o i l , mixing, filtering, and drying. The process is very simple, giving a very stable product which, unfortunately, has a low flavor load (6-15 wt%), is expensive, and exhibits nonuniform binding. Coacervation may produce microcapsules with walls of waxes, fats, proteins, carbohydrates, or gelatins. These procedures are usually more complex than those previously mentioned, with a multitude of ingredients necessary: essential o i l , antioxidant, surfactant, hydrophilic colloid (wall material), plasticizer, oxygen scavenger, and séquestrant. However, the flavor loading may reach 25-97 wt%, unlike other methods. The procedures utilize available equipment and well-developed processes, so they are comparatively low cost. In addition to essential oils, hydrophilic and hydrophobic solids as well as suspensions may be encapsulated using coacervation. Uses of E n c a p s u l a t e d F l a v o r s . There are several hundred types of microcapsules being used as food additives in the U.S. today. Direct, intentional addition of artificial flavors, natural flavors, spices, nutrients, preservatives and other additives to enhance or alter the appearance, composition, and quality of food is widespread ( 18). Encapsulation is used to protect flavors and to retard their release so that the flavor of a food product w i l l last for a longer time than with unencapsulated flavor. Some food products which may use encapsulated flavors are dry beverage mixes, food mixes (cakes, biscuits, pastries), and instant or ground coffee. In addition, chewing gums almost always contain encapsulated flavors, and may well contain more than one flavor. Aspartame, an artificial sweetener, is usually encapsulated because it easily decomposes due to the presence of water, elevated temperatures, and may react unfavorably with other flavoring compounds. The most common release mechanisms for release of flavors (and other food additives) are: (1)

Compressive force which breaks the capsule open by mechanical means (i.e. pressing or chewing),

(2)

Shear force which breaks open the capsule (i.e. as in a blender),

(3)

Dissolution of capsule wall (i.e. dissolution of dry beverage mix in water),

(4)

Melting of capsule wall (i.e. during baking), and

(5)

Core diffusion through the wall at a slow rate due to presence of external fluid (i.e. water) or elevated temperature.

These and other methods of release for consumer products are summarized in Table I and have been fully described earlier in this chapter. E n c a p s u l a t i o n of O t h e r F o o d Ingredients a n d A d d i t i v e s . Other encapsulated food additives may serve as preservatives, antioxidants, redox agents,


3. BRANNON-PEPPAS



acidity buffers, colors, nutrients, and enzymes. The methods already described for encapsulation of flavors (see Table I) may be used as well for entrapment within sugar crystals of compounds which are strongly absorbed physically or chemically (19). The triggers to release these additives are usually temperature or moisture levels (for hydrophilic encapsulants) or temperature level alone (for fat-based encapsulants). Other, less common, release triggers are p H , enzymatic release, ultrasonics, grinding and photo-induced release. Cheese Ripening and Flavor Enhancement. A slightly different approach to the encapsulation and controlled release of enzymes in food applications is the use of liposomes to immobilize enzymes. These enzyme-loaded lipid vessicles may assist in improved flavor as well, through controlled modification of enzymatic processes. One of the most useful applications of this technology is the use of these encapsulated enzymes i n cheese ripening (20). Both milkfat-coated microcapsules and liposomes have been used to successfully encapsulate cell-free extracts, viable cells, purified enzymes, and spores. Different techniques have been used to achieve the goals of acceleration of cheese ripening and improvement of cheese flavor. C e l l free extracts of Streptococcus lactis subsp. diacetylactis were encapsulated with substrate and cofactors for generation of diacetyl and acetoin, two of the flavors found i n cheeses. It was found that cheese containing the intact microcapsules contained up to eight times more acetyl than control cheese (21). Other cell-free extracts have been studied which can enhance the production of other cheese flavors such as 3-methyl butanal and 3-methyl butanol (22). Therefore, by including appropriately encapsulated cell extracts, the flavors of cheeses may be enhanced and modified by creating a cheese with different ratios of flavoring compounds than would be found in the control cheese. A number of methods for reducing the ripening time for cheese have also been investigated (23-25). One method (23) is to encapsulate enzymes such as neutrase to protect them during curd formation, but to encourage release during ripening and therefore to lead to an increased hydrolysis of β-casein and faster ripening. These capsules are well retained in the cheeses (90%) and, if used appropriately, can cut the ripening times in half. Encapsulated enzymes have proven to be significantly more useful i n cheesemaking than unencapsulated enzymes (19). Unencapsulated enzymes, added to the m i l k prior to cheesemaking, produce a cheese with poor textural quality, high levels of whey contamination and a low yield. Unencapsulated enzymes, added to the curd, produce a better cheese yield, but the distribution of the enzyme is poor and the cheese is crumbly. Encapsulated enzymes may be added to the milk before cheese-making and do release the enzymes appropriately to increase cheese yield as w i l l as to decrease ripening time. Unfortunately, the encapsulation efficiency of these techniques must be increased (currently < 35%) before encapsulated enzymes will be widely used in cheese manufacture. In addition, more research must be conducted to evaluate the findings that these capsules migrate to areas between the fat globules and casein matrix and whether or not that is the optimal location for enzyme release during cheese production. Meat Acidulant. Especially in meat products such as sausages, it is desirable to acidify the meat after processing to stabilize the meat and inhibit undesirable bacterial formation (26). In the past, this has been accomplished by inoculating the sausage with lactic-acid producing bacteria, direct acidification, addition of glucono delta lactone, and coating of granular acids with fat or starch before incorporation. A l l of these methods have their disadvantages, with the two coated systems either releasing their acidulant too quickly (starch coating) or too late if at all (fat coating melting at 100-150 °F, which only occurs during some cooking processes). A n


49

50


improved encapsulation method uses a fluidized bed to coat granular acid with a 40:60 mixture of hydrogenated vegetable o i l and water-soluble glycerides. These microcapsules have been shown to keep the p H of sausage in the acidic range (4.48.85) for up to 24 hours at 80 °F and 48 hours at 32 °F.


Encapsulation in the Cosmetics Industry In many fragrance and cosmetic applications described in this chapter, it is interesting to note that one product may contain more than one encapsulated product, prepared by different technologies. For example, a liquid makeup foundation may very well contain encapsulated fragrance, sunscreen, humectant, and a sebum oil absorber. The most emphasis w i l l be placed on the release of fragrances, since encapsulated fragrances are used significantly more often in cosmetics products than any other encapsulated materials. Encapsulation of Fragrances. Fragrance release is of importance not just i n perfumes, colognes, and related products. In fact, a report on cosmetics raw materials states that the fragrance ingredients are the crucial materials for all cosmetics, with the influence of scent extending far beyond that of the classic perfume blends (27). Controlled release of fragrance is far more pervasive than most realize. A list of some products which currently use encapsulated fragrance i n marketed products is shown in Table III. This list, even though it is lengthy, probably does not include all of the currently marketed applications of controlled fragrance release and it certainly does not even touch on potential markets (28). What is most interesting to note is that, almost unseen, controlled release has become a major part of everyday life i n the use of these products. The methods by which fragrances can be released are similar to that of flavor release and have been summarized in Table I and already have been described in detail.

Table III.

Products Currently Using Controlled Release of Fragrance

Laundry Care Specialty Cleaners Pet Products Bath Products Soaps Skin Care Products Deodorants Potpourri Cologne

Paper Products A i r Fresheners Hair Care Products Body Powders Lipsticks Antiperspirants Athlete's Foot Powders Perfume Fragrance Samplers

S O U R C E : Adapted from ref. 28.

Two major advantages in utilizing controlled release of fragrances, which are not as important i n flavor release, are fragrance marketing and cost savings. Fragrance samples, as included in magazines, give consumers an opportunity to try a fragrance (29). The consumer is then more likely to purchase that perfume, if they like the perfume, than if they had not had the opportunity to sample the product before purchase. For most fragrances, and especially the finer fragrances which can cost


3. BRANNON-PEPPAS


51


more that $6000 per kilogram, encapsulation w i l l stabilize the fragrance and controlled release w i l l prolong the lifetime of one application. Therefore, an encapsulated product w i l l have a longer shelf life (of benefit to manufacturer and consumer) as well as a longer utility per application (of benefit to consumer). Encapsulation of Other Agents in Cosmetic Applications. Other than fragrances, humectants and "anti-aging" compound have been most often formulated in controlled release systems in cosmetics (30). Typical coatings for encapsulated products are shown i n Table IV. Mixtures of these materials may also be used as coatings. T h e release from these formulations is usually triggered by shear force (rubbing), temperature, volatility, solubility and diffusivity (31). The "anti-aging" products are also often formulated i n liposomes and have sales of $100 m i l l i o n per year i n the United States alone. It is in the release of these agents such as retinoic acid that the distinction between cosmetics and pharmaceuticals narrows (27). These agents actually increase the turnover rate of skin cells, leaving skin in better condition when the use is stopped.

Table IV. Typical Coatings for Encapsulated Products in Cosmetics

Acrylates Aminoplasts Cellulose Acetate Phthalate Ethylcellulose Gelatin Gelatin Complexes

Glycolide Copolymers Gum Arabic Shellac Starch/Dextrin Polystyrene Waxes

S O U R C E : Adapted from ref. 30. Conclusions Controlled release, especially i n the form of microencapsulated products, has been used for fragrance and flavor release for decades. In fact, controlled release is significantly more widespread i n such applications i n consumer products than i n pharmaceutical and agricultural applications. Microencapsulated products have enhanced the flavor, stability, and ease of use of products as various as baking mixes, drink mixes, sausage, magazine perfume samples and sunscreens. The challenges of producing large amounts of encapsulated product at very low costs has developed technology which can be and has already been transferred to many pharmaceutical encapsulation processes, to the benefit of all concerned. Literature Cited

1. 2. 3.

Langer, R.; Karel, M. Polymer News 1981, 7, pp. 250-258. Thies, C. Second Workshop on Controlled Delivery in Consumer Products: Encapsulation Processes for Controlled Delivery Applications, Controlled Release Society, May 13-15, 1992. Second Workshop on Controlled Delivery in Consumer Products: Encapsulation Processes for Controlled Delivery Applications, Controlled Release Society, May 13-15, 1992.


52

4. 5. 6. 7.


8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.


Green, B. U.S. Patent 2,730,456. Green, B. U.S. Patent 2,730,457. Bolton, T.A.; Reineccius, G.A. Perfumer and Flavorist 1992, 17(2), pp. 1722. Langer, R.; Peppas, N.A. J. Macromol. Sci.-Rev. Macromol. Chem. Phys. 1983, C23, pp. 61-126. Sparks, R. Microencapsulation, Book of a Short Course, Center for Professional Advancement, 1983. Yamazaki, S. Japanese Patent 79 70,373, June 6, 1979. Miyashita, T. Japanese Patent 62 67,016, March 26, 1987. Kumagai, S. Japanese Patent 61 60,605, March 26, 1986. Narkis, N.; Narkis, M.; J. Appl. Polym. Sci. 1976, 20, pp. 3431-3436. Theeuwes, F. J. Pharm Sci. 1975, 64(12), pp. 1987-1991. Manning, A.J. Mathur, K.K., Berman Patent 2,551,891, July 8, 1976. Miles, J. Second Workshop on Controlled Delivery in Consumer Products: Encapsulation and Delivery of Perfumes and Fragrances, Controlled Release Society, May 13-15, 1992. Peppas, N.A.; Brannon-Peppas, L. J. Membr. Sci., 1990,48, pp. 281-290. Reineccius, G. First Workshop on Controlled Delivery in Consumer Products: Flavor Encapsulation, Controlled Release Society, October 18-19, 1990. Versic, R.J. In Flavor Encapsulation; Risch, S.J., Reineccius, G.A., Eds.; American Chemical Society, Washington, D.C., 1991; pp. 1-6. Karel, M.; Langer, R. In Flavor Encapsulation; Risen, S.J., Reineccius, G.A., Eds.; American Chemical Society, Washington, D.C., 1991; pp. 177-191. El Soda, M.; Pannell, L.; Olson, N. J. Microencapsulation 1989, 6(3), pp. 319-326. Magee, E.L.; Olson, N.F. J. Dairy Science 1981, 64(4), pp. 616-621. Braun, S.D.; Olson, N.F. Lindsay, R.C.; J. Food Biochemistry 1983, 7, pp.23-41. Law, B.A., King, J.S. J. Dairy Research 1985, 52, pp. 183-188. Piaro, J.C.; El Soda, M.; Alkahalaf, W.; Rousseau, M.; Desmazeaud, M.; Vassal, L.; Gripon, J.C. Biotech. Letters 1986, 8(4), pp. 241-246. Kirby, C.J.; Brooker, B.E.; Law, B.A. Int. J. Food Sci. Tech. 1987, 22, pp. 355-375. Reineccius, G. First Workshop on Controlled Delivery in Consumer Products: Controlled Delivery Applications in the Food Industry, Controlled Release Society, October 18-19, 1990. Layman, P.L. C & E News 1988, April 4, pp. 12-19. Miles, J. First Workshop on Controlled Delivery in Consumer Products: Encapsulation of Fragrances, Controlled Release Society, October 18-19, 1990. Fraser, A. First Workshop on Controlled Delivery in Consumer Products: Controlled Release Technology in Print Media Advertising Controlled Release Society, October 18-19, 1990. Magill, M.C. First Workshop on Controlled Delivery in Consumer Products: Controlled Delivery in Cosmetic and Personal Care Products, Controlled Release Society, October 18-19, 1990. Abrutyn, E. Second Workshop on Controlled Delivery in Consumer Products: Polymeric Transport Systems for Personal Care Applications, Controlled Release Society, May 13-15, 1992.

R E C E I V E D October 5, 1992


Controlled Release in the Food and Cosmetics Industries - American

Recommend Documents