What are the different types of microcapsules?

01.Microcapsules

Refers to a micro-container or package with a polymer shell. Its size generally ranges from 5-200μm and its shape varies, depending on the raw materials and preparation methods.

02.Microencapsulation technology

Refers to the technology of encapsulating solids, liquids or gases in tiny and sealed capsules so that they can only be released at a controlled rate under specific conditions.

Among them, the encapsulated substance is called the core material, including flavors and fragrances, acidulants, sweeteners, pigments, lipids, vitamins, minerals, enzymes, microorganisms, gases and other additives. The material that encapsulates the core material to achieve microencapsulation gelation is called the wall material. ‍

03.Wall material

Natural polymers, semi-synthetic polymers and synthetic polymers can be used as microcapsule encapsulation materials. Depending on the properties of the encapsulated substance (capsule core), oil-soluble core materials need to select water-soluble wall materials, and water-soluble core materials need to select oil-soluble wall materials, that is, the core material and the wall material are insoluble and non-reactive.

The microcapsule wall material should comply with national food additive standards, be non-toxic, have good film-forming properties, fluidity and low hygroscopicity, and should not chemically react with the core material.

Therefore, wall materials can often be divided into the following categories:

Due to the different core materials, wall materials and microencapsulation methods, the size, morphology and structure of microcapsules vary greatly. The particle diameter of microcapsules ranges from a few microns to several thousand microns, generally 5 to 200um, and the capsule wall thickness is 0.5 to 150um. At present, millimeter-scale microcapsules ranging from several millimeters in size to nanometer-scale microcapsules ranging from 0.1 to 1nm have been achieved.

The sizes of microcapsules prepared by several different methods are shown in the following table:

There are many methods of microcapsule technology, but the application in the food industry mainly includes interfacial polymerization, sharp hole method, spray drying method, spray cooling method, extrusion method and air suspension method.

01.Interfacial polymerization method

The core material is emulsified by a suitable emulsifier and added to the wall material solution. The reactant is added to initiate polymerization, a polymer film is formed on the surface of the droplet, and then the microcapsules are separated from the oil phase or the water phase. The microcapsules prepared by this method have good density, mild reaction conditions and fast reaction rate.

02.Sharp hole method

First, the core material is dissolved in the wall material solution, and then it is solidified and formed by a certain vessel and added to the solidifying liquid. It is solidified and formed by coprecipitation, and vacuum drying is used to obtain the microcapsule product. Usually, a curing agent is added or thermal condensation is used, and curing can also be achieved by complexing polymers with different charges.

03.Spray drying method

The core material is added to the pre-liquefied wall material solution to form a thermal dispersion system and spray dried in a hot air flow to evaporate the wall material and fix the capsule membrane to form the required substance. This method is suitable for heat-sensitive substances, with low cost and simple process, but the active substances are easily inactivated, the encapsulation rate is low, and the energy consumption is high.

04.Mist cooling method

The core material is mixed with molten oil to form a molten liquid, and after forming microcapsule fine particles with an atomizer, the wall material is quickly cooled with cold air to solidify into microcapsules. This method is suitable for heat-sensitive substances to protect the activity of the core material.

05.Extrusion method

The core material is dispersed in the melted sugar material, and then put into the dehydration solution after extrusion and drawing. The sugar material solidifies and the core material is embedded in it. Then, the microcapsule product is obtained by crushing, separating and drying. The wall material of this process generally uses sucrose, maltodextrin and modified starch, which is mainly used for microencapsulation technology such as flavoring materials and essential oils, but the embedding rate is low.

06.Air suspension method

First, the solid granular core material is dispersed and suspended in the carrier airflow, and then the wall material is sprayed on the circulating core material in the encapsulation chamber. The encapsulation material is suspended in the rising air flow, and the product is dried by relying on the humidity regulation of the carrier airflow itself. This method is only applicable to the packaging of solid core materials, and is generally used for flavors, spices and fat-soluble vitamins.

Due to its unique advantages, microencapsulation technology has been widely used in various types of food, which has successfully solved problems that traditional processes cannot solve and promoted the rapid development of the food industry.

01.Microencapsulation of oils and fats

Oils and fats are important substances in people's daily life and food processing, but they are easily oxidized and deteriorate to produce bad flavors, and have poor fluidity, which makes packaging and consumption inconvenient. Therefore, it is necessary to use microencapsulation technology to maintain their functional properties.

02.Microencapsulation of flavors and spices

Flavors and spice extracts are highly volatile and easily oxidized to change their flavors. Therefore, in order to prevent the volatilization of flavors and reactions with other substances, microencapsulation methods can be used to convert liquid spices into solid powders to improve stability and practicality.

Generally, gelatin, gum arabic, carboxymethyl cellulose, ethyl cellulose, dextrin, etc. can be selected as wall materials, and microencapsulation products of flavors and spices can be prepared by sharp hole method, extrusion method, spray drying method, spray cooling method, etc.

03.Microencapsulation of pigments

Many edible pigments are oil-soluble and have poor stability. In particular, natural pigments are very sensitive to light, heat, oxygen, and acid and alkali, and are prone to fading or discoloration. Microencapsulation can avoid environmental factors that cause pigment changes, and can also improve the dispersibility and solubility of oil-soluble pigments in aqueous solutions.

04.Microencapsulation of probiotics

The activity of probiotic products will be reduced under the action of gastric acid, and microencapsulation technology can protect probiotics against adverse environments. Enteric wall materials are used to prevent damage by gastric juice, so that as many live bacteria as possible can reach the intestines, which is truly beneficial to health.

05.Microencapsulation of antioxidants

Antioxidant substances such as vitamins, flavonoids, tea polyphenols, BHT, etc. are widely used in food, but these substances are relatively unstable and easily affected by the external environment. Therefore, it is necessary to change their characteristic properties through microencapsulation technology.

06.Microencapsulation of acidulants and sweeteners

Acidulants can promote food oxidation, affect the original pH of food, and cause food spoilage. Therefore, acidulants can be encapsulated through microencapsulation technology to avoid direct contact with food and extend the shelf life of food.

The production of microencapsulated acidulants usually uses physical methods, such as using hydrogenated oils, fatty acids and other materials to encapsulate acidulants and cool them to form microcapsules. This technology has been widely used in the processing of pie fillings, pastry powders, solid beverages and meat.

Microencapsulated sweeteners can reduce hygroscopicity, improve fluidity, and prolong the sweetness. The sweetener in Wrigley's chewing gum is a microcapsule coated with hardened oil, which improves stability and storage time.

07.Microencapsulation of leavening agents

Using microencapsulation technology to encapsulate leavening agents can make the leavening agents react only under appropriate conditions to avoid reactions before baking.

08.Microencapsulation of enzyme preparations

Enzyme preparations are widely used in food, but they are easily damaged by the external environment. Therefore, certain polymer substances can be used as wall materials to encapsulate a variety of enzymes in the form of microcapsules in semipermeable membranes. Microencapsulated enzyme preparations are made to maintain enzyme activity, prolong the action time, and realize continuous enzymatic production or fermentation.

09.Microencapsulation of preservatives

Adding preservatives directly to food will affect product quality, so these substances can be microencapsulated before adding them to food. Using hardened grease as the wall material to embed sorbic acid can not only avoid direct contact between sorbic acid and meat products, but also slowly release sorbic acid through the sustained-release effect of the wall material to play a role in preservation and sterilization.

HSF Biotech's VegeLipi^® micro-encapsulated lipid powder is based on its patented micro-encapsulation technology, aiming at the challenges that have been facing the market of functional lipids, such as instability of active ingredients, difficult handling and flowing ability, poor solubility in water, bad taste, and etc.

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