An overview of encapsulation

technologies for foodapplications

By: Nooshin Noshirvani

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Encapsulation definition

defined as a process to entrap active agents within a carrier material (wall material)a useful tool to improve delivery of bioactive molecules and living cells into foodsa technology in which the bioactive components are completely enveloped, covered and protected by a physical barriera technology of packaging solids, liquids, or gaseous materials in small capsules that release their contents at controlled rates over prolonged periods and under specific conditions Produced particles usually have diameters of a few nm to a few mmThe development of microencapsulation products started in 1950s in the research into pressure-sensitive coatings for the manufacture of carbonless copying paper Encapsulation technology is now well developed and accepted within the pharmaceutical, chemical, cosmetic, foods and printing industries. In food products, fats and oils, aroma compounds and oleoresins, vitamins, minerals, colorants, and enzymes have been encapsulated

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Trends in microencapsulation technologies

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The main purposes of encapsulation

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The substance that is encapsulated may be called the core material, the active agent, fill, internal phase, or payload phase.

The substance that is encapsulating may be called the coating, membrane, shell, carrier material, wall material, capsule, external phase, or matrix.

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Two main types of encapsulates• The reservoir type:• has a shell around the active agent.• This type is also called capsule, single-core, mono-core or core-shell type.• The matrix type• The active agent is much more dispersed over the carrier material; it can be in the

form of relatively small droplets or more homogenously distributed over the encapsulate.

• Active agents in the matrix type of encapsulates are in general also present at the surface (unless they have an additional coating)

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The reasons why to employ an encapsulation technology?

provide barriers between sensitive bioactive materials and the environmentmask bad tasting or smelling, stabilize food ingredients or increase their bioavailabilityprovide improved stability in final products and during processing. less evaporation and degradation of volatile actives, such as aromamask unpleasant feelings during eating, such as bitter taste and astringency of polyphenolsprevent reaction with other components in food products such as oxygen or waterimmobilize cells or enzymes in food processing applications, such as fermentation process and metabolite reduction processesimprove delivery of bioactive molecules (e.g. antioxidants, minerals, vitamins, phytosterols, lutein, fatty acids, lycopene) and living cells (e.g. probiotics) into foodsmodification of physical characteristics of the original material for (a) allow easier handling, (b) to help separate the components of the mixture that would otherwise react with one another, (c) to provide an adequate concentration and uniform dispersion of an active agent

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Protective shell specifications

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Materials used for encapsulation

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Encapsulation techniques

Since encapsulating compounds are very often in a liquid form, many technologies are based on drying.

Different techniques are available to encapsulate active agents like: • Spray drying• Spray-bed-drying• Fluid-bed coating• Spray-chilling• Spray-cooling • Melt extrusion• Melt injection• Coacervation

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Spray drying

• one of the oldest processes to encapsulate active agent• achieved by:• dissolving, emulsifying, or dispersing the active in an aqueous

solution of carrier material• atomization and spraying of the mixture into a hot chamber• Film formation at the droplet surface • a porous, dry particle is formed• retarding the larger active molecules while the smaller water

molecules are evaporated.

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Spray drying

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The size of the atomizing droplets depends on the surface tension and viscosity of the liquid, pressure drop across the nozzle, and the velocity of the spray.

The carrier material used should meet many criteria, such as:• Protection of active material• High solubility in water• Glass transition and crystallinity• Good film forming properties• Good emulsifying properties• Low costs

Examples of carrier material include natural gums (gum arabic, alginates, carrageenans, etc.), proteins (dairy proteins, soy proteins, gelatin, etc.), carbohydrates (maltodextrins and cellulose derivatives) and/or lipids (waxes, emulsifiers).

Spray-drying and agglomeration

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Spray drying

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Production of larger particles than those produced by spray-drying (in general about 10–150 μm).

An option is fluidized bed spray granulation (also called spray-bed-drying)

spray drying step is followed in one or two steps by a secondary agglomeration step in a fluid bed.

Another option is to spray-dry onto another carrier powder.

In both cases, the spray-dried particles are not fully dried after the first stage, and therefore remain sticky to facilitate agglomeration during the second phase. Alternatively, a binder solution (e.g., water) can be sprayed onto powder particles .

Agglomeration or granulation

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Fluid bed coatinga coating is applied onto powder particles in a batch process or a continuous set-up. The powder particles are suspended by an air stream at a specific temperature and sprayed with an atomized, coating material. 5–50% of coating is applied, depending on the particle size of the core material and application of the encapsulate

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Fluid bed drying (Würster set-up)

the coating is sprayed in an the bottomThe air flow rate is typically 80% in the center and 20% in the peripherywhich brings the powder particles into circulation. This increases the drying rate and reduces agglomeration. The bottom spray reduces the distance between the powder and the drops of coating solution, thereby reducing the risk of premature drying of the coating.

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The coating material must have an acceptable viscosity to enable pumping and atomizing, must be thermally stable and should be able to form a film over a particle surface.

The coating material might be an aqueous solution of cellulose derivatives, dextrins, proteins, gums and/or starch derivatives

A molten lipid can be used as a coating material, Such as hydrogenated vegetable oils, fatty acids, emulsifiers and/or waxes.

Care must be taken to prevent solidification of the lipid before it reaches the powder. This might be done by heating not only the storage vessel from which the molten lipid is pumped, but also the line, the nozzle, and atomizing air.

Fluid bed coating

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Film formation with the fluid bed coating

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The particles to be coated by fluid bed should ideally be spherical and dense, and should have a narrow particle size distribution and good flowability.

Spherical particles have the lowest possible surface area and require less coating material for the same shell thickness than nonspherical ones.

Sharp edges could damage the coating during handling.

Fine and low-dense particles might face the risk of accumulating on the filter bags in the top of the machine.

Fluid bed coating

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Carbohydrate materials can be mixed with an active when molten, at a temperature above 100°C

pressed through one or more orifices (extrusion) finally quenched to form a glass in which active agent have relatively little

mobility

two processes to encapsulate active agent in a carbohydrate melt can be distinguished.

One is melt injection, in which the melt (composed of sucrose, maltodextrin, glucose syrup, polyols, and/or other mono- and disaccharides) is pressed through one or more orifices (filter) and then quenched by a cold, dehydrating solvent. This is a vertical, screwless extrusion process.

Melt injection and melt extrusion

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isopropanol, and also liquid nitrogen, is used as the dehydrating solvent. The coating material hardens on contact with the dehydrating solvent, thereby encapsulating the active.

The size of the extruded strands is reduced to the appropriate dimensions inside the cold solvent during vigorous stirring, thereby breaking up the extrudates into small pieces. Any residues of active agent on the outside will be washed away by the dehydrating solvent.

Encapsulates made by melt injection are water-soluble and have particle sizes from 200 to 2,000 μm.

Melt injection and melt extrusion

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using an extruder with one or more screws in a continuous process. very similar to melt injection the main differences: melt extrusion utilizes screws in a horizontal position and that the extrudates are not surface washed.

Extruders are thermomechanical mixers that consist of one or more screws in a barrel. Most often, double screw extruders are preferred

Extrudates can be composed of starch, maltodextrins, modified starches, sugars, cellulose ethers (like hydroxypropyl cellulose or hydroxypropyl methyl cellulose), proteins, emulsifiers, lipids, and/or gums.

melt extrudates for use in food products are composed of “thermoplastic” starch.

Melt injection and melt extrusion

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In the feed zone, a low pressure is generated to homogenize the feeding. In the subsequent zone(s), a gradual increase in pressure is achieved via the screw design to melt, further homogenize, and compress the exrudate. In the final part of the barrel, a constant screw design helps to maintain a continuous high pressure to ensure a uniform delivery rate of molten material out of the extruder. The barrel is also divided into sections to allow for section-controlled variation in temperature.Addition of the active ingredient might be in the mixing/dispersing zone of the extruder at about halfway to minimizes the residence time of the active ingredients At the end of the barrel, a “pre die” and “die head” determine the shape of the final product (e.g., sheets, ropes or threads). It can be equipped with a chopper/cutter to obtain granular extrudates.

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Extrusion

• exclusively for the encapsulation of volatile and unstable flavors in glassy carbohydrate matrices• this process is the very long shelf life imparted to normally oxidation-prone flavor compounds, such as citrus

oils, because atmosphere gases diffuse very slowly through the hydrophilic glassy matrix, thus providing an almost impermeable barrier against oxygen.

• Carbohydrate matrices in the glassy states have very good barrier properties and extrusion is a convenient process enabling the encapsulation of flavors in such matrices

• allows the encapsulation of heat-sensitive material, such as Lactobacillus acidophilus, which cannot be achieved in a typical carbohydrate matrix because of the much higher processing temperatures typically used.

• The very low water content in the extruding mass prevents the degradation of the enzyme even at high temperatures for short periods of time.

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very long shelf life to oxidation

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Extrusion

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Spray-chilling or spray-cooling

• to produce lipid-coated active agents. • The active agent could be dissolved in lipids, present as dry particles or present as

aqueous emulsions. • Firstly, droplets of molten lipid(s) are atomized into a chilled chamber (e.g., via

nozzle, spinning disk or (centrifugal) co-extrusion), which results in solidification of the lipids and finally their recovery as fine particles.

• The initial set-up of spray cooling is quite similar to spraydrying but no water is evaporated here.

• The spray cooling is a technique with possibility to achieve high yields and it can be run in both continuous and batch processing modes.

• In case of spray-chilling, the particles are kept at a low temperature in a set-up similar to the fluidized bed spray granulation .

• The difference between these two techniques is the melting point of lipids. In spray chilling it is in range of 34–42°C and for spray cooling temperature is higher.

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Spray-chilling or spray-cooling

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Spray-chilling or spray-cooling

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Spray-chilling or spray-cooling benefits

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typically referred to as ‘matrix’ encapsulation for are aggregating the particles of active ingredient buried in the fat matrix

while ‘true’ encapsulation is usually reserved for processes leading to a core/shell type of microencapsules.

• A matrix encapsulation process leaves a significant proportion of the active ingredient is lying on the surface of the microcapsules or sticking out of the fat matrix, thus having direct access to the environment.

• A strong binding of the ingredient to the fat matrix can prevent the release of the ingredient even thought the fat matrix is melted and/or damaged during processing.

• An illustration of this phenomenon is the improved thermal stability of feed enzymes achieved by spray cooling in monoglycerides, but the non-release and of the fat-bound enzymes

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Spray-chilling or spray-cooling

a significantnumber of active ingredient particles are located at the surface of the microcapsules or have direct accessto the environment

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Coacervation

• original method of encapsulation

• was the first encapsulation process studied and was initially employed by Green &• Scheicher (1955) to produce pressure-sensitive dye microcapsules for the

manufacturing of carbonless copying paper.

• consists of the separation from solution of colloid particles which then agglomerate into separate, liquid phase called coacervate

• the core material used in the coacervation must be compatible with the recipient polymer and be insoluble (or scarcely soluble) in the coacervation medium.

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Coaveration

• a unique and promising microencapsulation technology because of the very high payloads achievable (up to 99%) and the controlled release possibilities based on mechanical stress, temperature or sustained release.

• Mechanism: phase separation of one or many hydrocolloids from the initial solution and the subsenquent deposition of the newly formed coacervate phase around the active ingredient suspended or emulsified in the same reaction media.

• The hydrocolloid shell can then be crosslinked using an appropriate chemical or enzymatic crosslinker, if needed.

• A very large number of hydrocolloid systems has been evaluated for coacervation microencapsulation but the most studied and well understood coacervation system is probably the gelatin/gum arabic system.

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Applications

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Coacervation in gelatine/gum acacia systemdissolving gelatin and gum arabic at a 1:1 ratio and at a 2–4% of each polymer to make o/w emulsion adjusting the pH from neutral to about 4 under turbulent conditions in a stirred vessel at >35°C, (above the gelation temperature of gelatin)creating three immiscible phases (oil, polymer-rich, and polymer-poor phase), deposition of polymer rich phase droplets on the emulsion surfaces because of interfacial sorption. Alternatively, complex coacervation can be induced by dilution instead of pH adjustment oil is emulsified in a 8–11% (w/w) gelatin solution, followed by addition of gum arabic and dilution water.Upon cooling well below 35°C , the deposited gelatin and thus the shell will solidify.

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Principle of the complex coaveration method

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A coaverated flavor oil

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Factors affecting the process

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polymer concentrationspHturbulence of the systememulsion sizeionic strengthtemperature.

Liposome

• consist of one closed vesicle composed of bilayer membranes which are made of lipid molecules, such as phospholipids (lecithin) and cholesterol.

• They form when (phospho)lipids are dispersed in aqueous media and exposed to high shear rates by using, e.g., microfluidization or colloid mill.

• The underlying mechanism for the formation of liposomes is basically the hydrophilic–hydrophobic interactions between phospholipids and water molecules.

• Active agent can be entrapped within their aqueous compartment at a low yield, or within or attached to the membrane at a high yield.

• The particle size ranges from 30 nm to a few microns.

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Advantages• Advantages: high encapsulation efficiency, simple production methods and good

stability over time. • The great advantage of liposomes over other microencapsulation technologies is

the stability liposomes impart to water-soluble material in high water activity application: spray dried, extruded and fluidized beds impart great stability to food ingredients in the dry state but release their content readily in high water activity application, giving up all protection properties.

• Another unique property of liposomes is the targeted delivery of their content in specific parts of the foodstuff.

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Applications• Liposomes are now used as drug delivery systems.

• their use in foods is quite limited due to its chemical and physical instability upon storage, low encapsulation yield, leakage upon storage of liposomes containing water-soluble active agent, and the costs of raw materials

food applications:• enhance ripening of hard cheeses• enzymes for tenderization of meat (Bromelain)• Encapsulation of vitamin C• significant improvements in shelf-life (from a few days to up to 2 months)

especially in the presence of common food components which would normally speed up decomposition, such as copper ions, ascorbate oxidase and lysine.

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Molecular inclusion• Inclusion encapsulation generally refers to the superamolecular association of a

ligand (the ‘encapsulated’ ingredient) into a cavity-based material(‘shell’ material). The encapsulated unit is kept within the cavity by hydrogen bonding or hydrophobic effect.

• best known example is cyclodextrin• Another cavity material: Amylose ligand-binding proteins such as the milk protein b-lactoglobulin.

• Cyclodextrins are cyclic oligosaccharides of 6–8 d-glucose molecules, which are enzymatically joined through alpha 1–4 linkages to form a ring

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• Cyclodextrins have a lipophilic inner pocket of about 5–8 A in which an active molecule with the right size can be reversibly entrapped in an aqueous environment. this characteristic limits its loading capacity

• Temperature, time, the amount of water, and the particular active and cyclodextrin control the loading rate and efficiency.

• the use of cyclodextrin might be limited by regulatory rules.

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The most used methods

1) stirring or shaking a cyclodextrin with flavours in aqueous solution and filtering off the precipitated complex

2) blending solid cyclodextrin with guest molecules in a powerful mixer, and bubbling the flavours, as vapours, through a solution of cyclodextrin

3) Kneading the flavour substance with the cyclodextrin- water paste.

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Co-crystallization

• Spontaneous crystallization of supersaturated sucrose syrup at high temperature (above 120 C) and low moisture (95– 97 Brix) and active agents can be added at the time of spontaneous crystallization

• The crystal structure of sucrose can be modified to form aggregates of very small crystals that incorporate the flavours; either by inclusion within the crystals or by entrapment.

• The granular product has a low hygroscopicity and good flowability and dispersion properties

• Although the product had a free-flowing property, the addition of a strong anti-oxidant was necessary to retard development of oxidized flavours during storage.

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Co-crystallization

• is relatively simple• Economic• flexible• Fruit juices, essential oils, flavours, brown sugar

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• Encapsulation can be employed to retain active agents

The retention of active agent is governed by factors related to:• the chemical nature of the core• including its molecular weight• chemical functionality• polarity and relative volatility• the wall material properties • the nature and the parameters of the encapsulation technology

• Many factors such as the kind of wall material, ratio of the core material to wall material, encapsulation method, and storage conditions affect the anti-oxidative stability of encapsulated agent

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Encapsulation of flavoring agents Flavor is one of the most important characteristics of a food product, since people

prefer to eat only food products with an attractive flavor• Aroma consists of many volatile and odorous organic molecules. Most of them are

in a gas or liquid state• Aroma can be encapsulated to improve aroma functionality and stability in

products.

• The possible benefits of encapsulated aromas are

Superior ease of handling (conversion of liquid aroma oil into a powder, which might be dust free, free flowing, and might have a more neutral smell)

Improved stability in the final product and during processing (less evaporation, degradation or reaction with other components in the food product)

Improved safety Creation of visible and textural effects Adjustable aroma properties (particle size, structure, oil- or water-dispersable) Controlled aroma release

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Encapsulation Technologies for Aroma

• Spray-Drying• Agglomeration or Granulation• Fluid bed Coating• Spray-Chilling/Spray-Cooling• Melt Injection• Melt Extrusion• Coacervates• Microspheres• Co-extrusion• Yeast Cells• Cyclodextrins• Co-crystallization/Co-precipitation

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Characteristics of the major wall materials used for flavour encapsulation

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Benefits of carbohydrates for flavor system

• starches, maltodextrins, corn syrup solids and acacia gums

to bind flavours their diversity low cost and widespread use in foods low viscosities at high solids contents good solubility

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Microencapsulation of Fish Oil

• Fish oil contains several special types of fatty acids, the so called long-chain polyunsaturated fatty acids (LCPUFA, with more than 20 carbon atoms) and Omega-3 fatty acids

• Food Fortification with LCPUFA is a useful method for preventing heart and mental deasease

• Unsaturated fatty acids are sensitive to oxidation

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Microencapsulation of Fish Oil Preventing the lipid oxidation by preventing contact between lipids and oxygen, metal ions and preventing direct exposure to light.

Increasing the storage stability.

Entrapment and reducing of volatile off-flavors.

Conversion of a liquid into a powder, which may ease the handling during supply chain or incorporation into food powder products.

Increasing bio-availability in the human gastro-intestinal tract.

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Encapsulation of Iron Iodine, vitamin A and iron deficiencies are important global public health problems

(preschool children and pregnant women in low-income countries) Co-fortification of foods with iron, iodine and vitamin A is a successfull application

of microencapsulation in food industry. Vitamin A, together with iodine, may reduce thyroid hyperstimulation and risk for goiter.

The main advantage of Fe encapsulation is that it may allow addition of Fe compounds of high bioavailability to difficult-to-fortify food vehicles, such as cereal flours, milk products and low-grade salt

Fe encapsulation may decrease Fe-catalyzed oxidation of fatty acids, amino acids, and other micronutrients that can cause adverse sensory changes and decrease the nutritional value of these foods

Also, it may reduce interactions of Fe with food components that cause color changes and lower Fe bioavailability, such as tannins, polyphenols and phytates

A number of encapsulated Fe compounds are in development or commercially available. These include forms of ferrous sulfate, ferrous fumarate, ferric pyrophosphate, and elemental Fe

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• Water-soluble coating materials, (maltodextrin and cellulose) do not provide adequate protection against iron oxidation in moist environments.

• most encapsulated Fe compounds are coated with hydrogenated oils that provide an effective water barrier at relatively low cost.

• These hard fat encapsulates can be prepared by fluid bed coating, or spray chilling/spray cooling

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controlled release of the FCs in at the intestinal wall

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controlled release

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Microencapsulation of Fe

(1) dispersing(2) mixing (3) spray chilling or spray drying

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Microencapsulation of Fe

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Microencapsulation of carotenoids

• due to their unsaturated chemical structures, Carotenoids are very sensitive to: heat, oxidation, and light

• They are almost insoluble in water and only slightly oil soluble at room temperature (about 0.2 g/Loil), but their solubility in oil increases greatly with increasing temperature

• due to the fact that carotenoids in the nature exist as crystals or are bound in protein complexes, minor part of the carotenoids in raw fruits or vegetables is absorbed in the intestines

• In contrast, carotenoids dissolved in vegetable oils show a higher bioavailability

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Microencapsulation of carotenoids Increasing solubility

Increasing stability against heat, oxidation and light.

Increasing bioavailability.

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Microencapsulation of carotenoids

(O/W) emulsions containing carotenoids dissolved in finely dispersed oil droplets can be produced

For preparing carotenoid-loaded O/W emulsions, the carotenoid is dissolved in a vegetable oil or in an apolar solvent at elevated temperatures

emulsified with an aqueous phase containing an emulsifier to stabilize the droplets.

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Microencapsulation of carotenoids

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Microencapsulation of carotenoids

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Encapsulation of Probiotics for use in Food Products

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• Probiotics can be delivered commercially either as nutritional supplements, pharmaceuticals or foods.

• A large number of probiotic products are available in the market in the form of milk, drinking and frozen yoghurts, probiotic cheeses, icecreams, dairy spreads and fermented soya products.

• International standards require that products claimed to be ‘probiotic products’ contain a minimum of 106–8 cells/g viable probiotic bacteria per gram of product when sold,

• However, many products failed to meet these standards when they are consumed. This is due to death of probiotics cells in food products during storage, even at refrigerating temperatures. Consequently, industrial demand for technologies ensuring stability of bifidobacteria in foods remains strong, which leads to the development of immobilized cell technology to produce probiotics with increased cell resistance to environmental stress factors

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Protection Needs of Probiotics

Processing conditions, like high temperature and shear. Desiccation if applied to a dry food product. Storage conditions in the food product on shelf and in-home, like food matrix,

packaging and environment (temperature, moisture, oxygen). Degradation in the gastrointestinal tract, especially the low pH in stomach (ranging

from 2.5 to 3.5) and bile salts in the small intestine.

• Microencapsulation technologies have been successfully applied to protect the probiotic bacterial cells from damage caused by the external environment and bile salts in the small intestine.

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The ability of probiotic microorganisms to survive and multiply in the host strongly influences their probiotic benefits.

The bacteria should be metabolically stable and active in the product, survive passage through the upper digestive tract in large numbers and have beneficial effects when in the intestine of the host.

Microencapsulation could be able to increase the stability of these sensitive microorganisms against adverse conditions.

The so-called stabilization of microorganisms means providing metabolic activity after storage and intake by a new host

Encapsulation increases not only their bioavailability, but more importantly functionality.

Encapsulation of Probiotics

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Most techniques used for encapsulation of probiotics

Spray dryingFluid bed coatingFreeze or vacuum dryingSpray cooling

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Encapsulation of Probiotics in Microspheres (Gel-Particle Techniques)

mixing of bacterial culture with a polymer solution to create bacteria-polymer suspension extruding through a needle to produce droplets Collecting the droplets in a bath where gelation occurs (ionotropic or thermal),or dispersed in a continuous phase applying mixing to create stable w/o emulsion.

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Typical carrier materials

Alginate K-Carageenan Chitosan) dairy proteins ( protein isolates) gum Arabic pectin skim milk powder non-fat dry milk solids modified starch maltodextrin sugars

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• However, there is no wide choice of encapsulation technologies that can be applied for living cells, as it is case in most molecules which are resistant to heat. One among ‘gentle’ approaches for encapsulation is the extrusion technique

• Except extrusion, mostly used encapsulation techniques are spray-, freeze- or vacuum-drying.

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Encapsulation of Enzymes and Peptides

Formulate them in a solid form to increase the stability and decrease the transportation cost.

Controlled release and extend enzyme activity.

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