MICROENCAPSULATION (7,8)

INTRODUCTION

• Definition: encapsulation is a process where a continuous thin coating is formed around is formed around solid particles, liquid droplets, or gas cells that are fully contained within the capsule wall

• Has been used in the food industry for more than 60 years as a way to provide liquid and solid ingredients an effective barrier for environmental and or chemical interaction until release is desired.

• Range size– Microcapsule: 0.2 – 5000 μm– Nanocapsule: < 0.2 µm– Macrocapsule: > 5000 μm

INTRODUCTION

• Microcapsule composition: core material and shell material.

• Widely used in dry flavor production while the vast majority of flavor compounds used in industries are in the form of liquid at room temperature.

• Factors to be considered in choosing shell material: cost, availability, processing ease and inherent barrier properties.

• Parameter to characterize microcapsule: particle size, size distribution, geometry, active content, storage stability and core material release rate

INTRODUCTION

• Factors to be considered in designing encapsulation process:– Type of functions encapsulated ingredients can provide to the

final product product.– The different processing condition that the product will go

through before release.– Optimum concentration of the active ingredient– The mechanism of release– The final particle size, density and stability– The cost

•Wide range of geometries and structure.

ADVANTAGES

• Controlling the release of encapsulated ingredients– gradual release of flavors during microwaving, leavening agents

in baking, and citric acid and release during sausage manufacture.

• Enhancing stability to temperature, moisture, oxidation and light– Aspartame protection during baking, oxidation barrier for beta-

carotene, protection during freeze and thaw cycles, and increased shelf life

• Masking undesirable flavors– Taste-masking of potassium chloride for nutritional supplements

ADVANTAGES

• Reducing negative interaction with other compounds– Microencapsulation of such acidulants as citric acid, lactic acid,

ascorbic acid to maintain color, texture, nutrient content and flavor of foods and encapsulation of choline chloride to inhibit interaction with vitamins in premixes.

• Promoting easier handling of the core or interior material by preventing lumping, improving flowability, compression and mixing properties, reducing core particle dustiness and modifying particle density.

• Encapsulation of spray drying and extrusion depend primarily on the carbohydrates used for encapsulation matrix.

• Gum is usually used as texturing ingredients, stabilize emulsions, control crystallization and inhibit syneresis thereby improving coating properties.

• Lipid are generally used for encapsulation for water soluble ingredients

• Protein is mostly used in coacervation (gelatine)

• Unencapsulated food acids can react with food ingredients to produce many undesirable effect → decreasing shelf life of citrus oil flavored foods and starch containing foods, loss of flavor, degradation color and separation of ingredients.

• Encapsulated acid reduce hygroscopicity, reduce dusting and provide a high degree of flowability without clumping.

• Other example : encapsulated lactic acid and citric acid as dough conditioner and in meat processing (curing of meat).

• Encapsulated enzyme→ maintain the viability for extended periods of time, avoiding their exposure to ions, protons, free radicals or other type of deleterious agent.

• Encapsulated sweeteners reduce hygroscopicity, improve their flowability and prolong their sweetness perception.

• Encapsulated flavoring agent (citrus oil, etc) → provide enhanced stability to oxidation, volatilization and light and controlled release, resistance to clumping and longer shelf life.

• Encapsulated sodium chloride (eg by hydrogenated vegetables oil) is used to control color degradation, rancidity, water absorption and yeast growth.

• Encapsulated leavening agent (sodium bicarbonate) protects the base from premature reaction with acid or water, and delays the release of its content until optimum baking condition are present

• Encapsulated colors are easier to handle, and offer better solubility, stability to oxidation and control during dry blending. Its shelf life is extended at least 2 years compared to 6 months for the uncoated form.

• Encapsulated vitamins and minerals are added to nutritional dry mixes to fortify a variety of foods such as breakfast cereals, dairy products, baby formulas and pet foods.

MICROCAPSULES: THEIR STRUCTURE AND RELEASE MECHANISMS

• Can be divided into three main classification in term of their conformation : single particle structure (regular or irregular), aggregate structure and multi-walled structure.

• A sphere of the active ingredient surrounded by a thick uniform wall or membrane, resembling the shell of a hen’s egg (single particle structure).

• An aggregate structure is formed when several distinct core particles are enclosed within the same capsule wall.

• Two main function of microcapsule: – Keeping and protecting the core material inside during storage– Releasing the core material at the right time.

ENCAPSULATION METHOD

• SPRAY DRYING• EXTRUSION• MOLECULAR INCLUSION IN CYCLODEXTRINS• COACERVATION• CENTRIFUGAL EXTRUSION• AIR SUSPENSION COATING• SPRAY CHILLING AND SPRAY COOLING• CENTRIFUGAL SUSPENSION-SEPARATION• FREEZE DRYING• CO-CRYSTALLIZATION

Classification of encapsulation process

SPRAY DRYING

• 1932, The English company, Boake, Roberts & Co Ltd produced firstly spray-dried flavor powder in which the flavors were encapsulated by a thin film of gum arabic.

• It is often used to produce commercial capsules loaded with fragrance or flavor oils.

• The shell material must have properties like good emulsifying, low viscosity at high solid level (< 500 cps at conc > 45% solid level) and exhibit low hygroscopicity.

• Shell material : gum arabic, hydrolyzed and modified (esterification) starches, dextrin, gelatin or non-gelling protein.

• Gum arabic is traditionally used

SPRAY DRYING

• Modified starches often have an undesirable off-taste and do not afford good protection for oxidized flavor.

• Hydrolyzed starches have DE range from about 2 to 36.5.

• Hydrolyzed starches are inexpensive, blend in flavor, have low viscosity at high solid content and afford good protection against oxidation. The major disadvantage is the lack of emulsification properties (mixed with gum arabic or hydrolyzed starches)

• A 20% flavor load is mostly used.

Flow diagram of spray drying process for flavor encapsulated

EXTRUSION• Used commonly for flavor encapsulation (where a flavor emulsion

is forced through a die at pressure less than 700 kPa and temperature lower than 115 oC.)→different from extruded cereals based product processing (high pressure and high temperature).

• The core material are not strictly encapsulated but locked into a matrix of long-chain molecules having much the same effect as a continuous capsule walls.

• Principle :The process consist of dispersing the core material the core material in a molten carbohydrate mass, then forcing it through a series of dies into a bath of dehydrating liquid (vegetable oil). Upon contacting the liquid, the coating material that forms the encapsulating matrix hardens to entrap the core material

EXTRUSION

• Shell material : high DE corn syrup and a combination of sucrose and maltodextrin.

• Modified starches with emulsification properties may be used to replace sucrose producing a sugar free product that has some advantage in marketing a finished food product.

• Anti caking agent (tricalcium phosphate)is added to maintain free flow ability of finished product.

• The major advantage of extrusion is its outstanding protection of flavor against oxidation compared to other method.

EXTRUSION

• The limitation :– High cost– Low flavor loading (10%).– Low solubility in cold water– High process temperature.

MOLECULAR INCLUSION IN CYCLODEXTRINS

• Take place in molecular level• Cyclodextrins are enzymatically modified starch

molecules.• Cyclodextrin can be produced from starch via

fermentation by microoganism such as Bacillus macerans and Bacillus circulans (enzyme cclodextrintransglycosidase convert the partially hydrolyzed stach into three typical cyclodextrin: alpha, beta and gamma containing six, seven and eight glucose molecules in the ring.

MOLECULAR INCLUSION IN CYCLODEXTRINS

• The interior of the molecule is formed by hydrogen atoms and glycosidic oxyygen bridge atoms, which give the cavityy hydrophobic character and interact with various organis molecules or moieties.

• Guest molecules with suitable dimensions to fit inside the interior can be included into the cyclodextrin moleculess to form agen-cyclodextrin complexes.

• The core materials: aroma compound

MOLECULAR INCLUSION IN CYCLODEXTRINS

• Example: encapsulation of flavor (principle)A 2:1 ethanol:water mixture is prepared and heated up to 50-55

oC. The beta cyclodextrin is added to the solution at soluble concentration of more than 10% (by weight). Immediately upon the addition of flavoring , the beta cyclodextrin complex enclosing the flavor molecule start to precipitate. With the continuous agitation the temp of the solution is allowed to drop to room temp and finally to 4 oC in a refrigerator. The cold, precipitated complex is collected from the solvent by filtering, dried by air then dried at 50 oC for 16 h. The final product is a free flowing cyclodextrin/flavor complex containing 6-15 % (w/w) flavoring.

MOLECULAR INCLUSION IN CYCLODEXTRINS

• Cyclodextrin provide exceptional protection to enclosed flavors in term of evaporation loss and oxidation.

• Cyclodextrins are very expensive and have low flavor loading (6-15% flavor on dry basis).

• Are not approved for food use in the USA, western & eastern Europe and Japan.

COACERVATION

• The oldest method of encapsulation.• Coacervation is a colloidal phenomenon which may be

defined as “the partially misciblity of two or more optically isotropic liquids, at least one of which is in the colloidal state.

• True microencapsulation process since the coating material completely surrounds the core with a continuous coating.

• The basic mechanism is the formation of an emulsion and subsequent precipitation of the continuous phase around the droplet of the discontinuous phase.

COACERVATION

• It employs a three phase system: a manufacturing vehicle (solvent), the material to be encapsulated and the coating material.

• Three stages in coacervation process:(Principle)1. Formation of three immiscible phase while mixing under

controlled condition

2. Deposition of the coating material around the core material (involving interfacial sorption of the hydrophylic phase on the droplets of the core material. To form the capsule, the pH and temp must be adjusted to cause the encapsulant to come out of solution so it can coagulate and form a cell wall. At this stage the cell wall is still liquid and needs hardening).

3. Shrinkage and solidification of the liquid coating to form the solid microcapsules (heating, desolvation or cross linking)

COACERVATION

• Simple coacervation = one shell material(e.g. only gelatin)– E.g. The encapsulation of citrus oil in gelatin :the gelatin is firstly

dispersed in water, the the core material is (hydrophobic citrus oil) is added and the blend is agitated. The solubility of gelatin is reduced by lowering the temp or adding sodium sulfate. Two phase created : one phase:the colloid rich phase, appearing as an amorphous cloud and second phase: the colloid poor aqueous phase. The citrus oil is in the phase of colloid rich phase. The capsule wall is liquid and must be hardened to form the final solid-like capsules (by adjusting pH and temperature) then the final steps in the process include collecting, washing and drying the now stable citrus oil capsules.

COACERVATION

• Complex coacervation = more than one shell material (e.g. gelatin and gum acacia).– E.g. core material : flavor oil, shell material : gelatin and gum

arabic. The core material is firstly suspended in first shell material, then gelatin or gum arabic solution is added into the system. The pH is adjusted to 3.8-4.3 (gelatin has positive charge and gum arabic has negative charge) and the system is cooled to 5 oC. As the gelatin and gum arabic react, viscous liquid microdoplets of polymer coacervate will separate and form a wall on the core particles. The still liquid gelled capsules walls can be hardened by glutaraldehyde or other hardening agents. The hardened microcapsules are collected, washed and dried.

Complex Coacervation

CENTRIFUGAL EXTRUSION

• Has been developed since 1960.• Principle : The core and shell material are extruded

through concentric cylinder, then because the head rotates, centrifugal force impels the rod outward, causing it to break into tiny spherical particles. By the action of surface tension, the coating material encircles the core material, forming a continuous coating. While the droplet are in flight, the molten coating wall is hardened through solvent evaporation from the wall solution and collected either solid or liquid solvent which can cushion the impact, protect the particles and serve additional function.

AIR SUSPENSION COATING

• Also called spray coating or fluidized bed processing.• First developed in 1950’s for coating pharmaceutical

tablets.• Principle :spraying of the droplet to impinge on and coat

solid particles.• The more spherical the particle (core material) the better

the encapsulation will be.• Particle with irregular shapes normally require structure

modification to improve their shape prior to using this method.

• Denser particle with narrow particle size distribution and good flowability are the most suitabe for encapsulation.

AIR SUSPENSION COATING

• The size range : 35 to 5000 μm (depend on the turbine capacity of the fluid bed and the porosity of the air exit filter).

• The shell material : cellulose derivatives, dextrin, emulsifier, lipids or protein and starch derivatives

SPRAY CHILLING AND SPRAY COOLING

• Similar to spray drying.

• The difference: the temperature of the air (cooled or refrigerated) used in the drying chamber and the type of coating material.

• The cool or chilled air in the chamber causes the coating material to solidify around the core (there is no evaporation of water).

• The shell material : molten fractionated and hydrogenated vegetable oils with a melting point of 32-42 oC (in spray chilling), while vegetable oils or other material with the melting point of 45-122 oC are often used

SPRAY CHILLING AND SPRAY COOLING

• Most often used to encapsulate solid food additives such as vitamins, minerals, or acidulants.

• The end product are water insoluble but can release their content at or around the melting point of the coating material.

• Secondary coating of spray-dried flavors to retard their volatile component during thermal processing.

• Spray chilled product have application in bakery product, dry soup mixes, and foot containing high levels of fat.

• Disadvantage: there is little or no barrier to the flavor loss by diffusion if the flavor is soluble in fat.

CENTRIFUGAL SUSPENSION-SEPARATION (CSS)

• Principle: It consists of forming a suspension of core particles in a coating liquid and passing this suspension over a rotating disk atomizer. The larger core particles with a layer of coating material and the smaller droplet of pure coating material are formed at the edge of the rotating disk atomizer, which is mounted at the top of a drying or cooling tower.

• CSS is a continuous, high production rate process that takes seconds to minutes coat core materials.

• It can coat particles of wide size range, from 30 µm several milimeter (smaller size, difficult to separate)

FREEZE DRYING

• Desirable process for the dehydration of almost all heat sensitive materials including flavors.

• It also has been used for encapsulating water soluble essences.

• High retention of volatile compound• Principle : E.g encapsulated citrus oil: dissolving various

blends of corn syrup solid and sugar in the aroma solution and then going through freeze-drying, retaining the aroma in the carrier.

CO-CRYSTALLIZATION

• Sucrose is used as a matrix for the incorporation of core materials.

• Involving spontaneous crystallization, which produce aggregates of micro-or fondant size crystal ranging from 3 to 30μm, while entraping non-sucrose materials within or between sucrose crystals.

• Principle : a saturated sucrose syrup concentrate is mixed with a predetermined amount of core material.The process finally followed by drying.

• The core will remain located primarily in the interstices between crystals.

• Also mentioned in the example of agglomeration.

The End