Encapsulation of Bioactive Compounds for Food and Agricultural Applications

1The characteristics of foods depend on several factors, such as forms of presentation, nature, texture, flavor profiles, and major composition, among others. However, many evolutions have been observed in recent years toward providing a wider range of products for consumers, with singular characteristics and properties. Minimally processed foods have shown characteristics similar to natural ones due to these developments in the aspects of engineering, nutrition, science, and technology. Accordingly, these foods have shown longer shelf life, nutritional functionality, different textures, and specific flavors, among other benefits.

2In the same trend, the growing demand for biological products in agriculture encourages research on novel formulation techniques and especially the production of biological capsules. This has occurred due to the stability of these bioproducts and higher reactivity of active ingredients, which minimizes volatility losses.

3Based on this scenario, the encapsulation of bioactive substances (essential oils, plant extracts, fungal metabolites, etc.) in food and agricultural areas allows them to be protected against external factors and degradation. The encapsulation allows the biological integrity of the products and supports environmental conditions during storage, ensuring the viability of active ingredients for long periods. For example, microbial agents are susceptible to abiotic and biotic factors that reduce the effectiveness of these living organisms and their metabolites when exposed to ultraviolet radiation and adverse temperatures, resulting in the loss of toxin integrity and spore viability. In this sense, encapsulation is an alternative to these adversities. In the agricultural area, it allows for reducing losses by volatility, having better biological integrity, increasing efficiency, improving commercial viability, and increasing formulation stability, among others. Therefore, the use of bioactive compounds as agents in the production of bioinsecticides, bionfungicides, bioherbicides, and biofertilizers is a promising strategy.

4For encapsulation, many polymers are used as wall materials to protect the core, generally formed by bioactive compounds. Chitosan, gums (gum Arabic, Xanthan gum, gum acacia, and Shellac, for instance), maltodextrin, pectin, starch, whey protein, sodium alginate, cellulose and carboxymethylcellulose, zein, pullulan, galactomannan, and sodium caseinate, among others, are used for this purpose. The polymers favor the retention of desired compounds in the systems formed during the processes and help to prolong the release of bioactive compounds for longer times or under specific conditions, such as certain pH ranges, for example.

5Therefore, this review presents polymer matrices for the incorporation of bioactive compounds and discusses the characteristics of encapsulation systems. The data cited in the text were obtained from the scientific literature through the main scientific databases. The search was mainly focused on the five past years to have a recent scenario of findings and evolutions. Some figures were created by the authors to express the authors’ viewpoint and tables were compiled based on other referenced works.

6Encapsulation is described as a process where a core material (a liquid, solid or gaseous compound) is packaged in a wall material to create capsules that are effective against chemical and environmental interactions. Encapsulation is an alternative for problems of physical or chemical instability of compounds. It can inhibit volatilization and protect the encapsulated material against unfavorable environmental conditions, reducing the sensitivity to the degradation of plant materials and their bioactive compounds. In such case, food biopolymers are used in the encapsulation process. Biopolymers are classified into three classes: synthetic polymers derived from petroleum, synthetic polymers derived from renewable resources, and naturally produced renewable polymers,. Many polymers (synthetic and natural) are used as a coating material for encapsulating bioactive compounds, such as polyethylene, polyethylene glycol, poly(vinylpyrrolidone), polyvinyl alcohol, polyacrylic acid, polylactic acid, polyhydroxyalkanoates, β-glucans, dextran, starch, alginate, cellulose, chitin, chitosan, pectin, collagen, gums, zein, hyaluronic acid, and gelatin, among others. Table 1 presents some examples of polymers and encapsulated bioactive compounds.

7The deacetylation of the chitin polymer allows for producing chitosan, in which the acetyl groups of the chitin chain are removed to compose amino groups. The degree of deacetylation is directly interconnected with the performance of chitosan in its different uses. Chitosan is a natural and non-toxic polysaccharide widely used due to its characteristics of biocompatibility, chemical resistance, and biodegradability. Moreover, it has the property of forming films without dependence on additives. The high availability of chitosan is an important factor, which is the second most numerous natural polysaccharide biopolymer found in nature.

8Chitosan still has antimicrobial and antioxidant activity. The antimicrobial activity of chitosan depends on some parameters that affect its properties, such as pH, molecular weight, type of microorganism, source of chitosan, concentration, degree of deacetylation, complexes with certain materials, food components, and chitosan derivatives. Chitosan is an excellent coating material used in the encapsulation of multiple bioactive compounds due to its characteristics and properties, having applications in food, pharmaceutical, agricultural, biomedical, environmental, and industrial segments, among others. This polymer is used in the encapsulation of essential oils, lipids, different food ingredients, vitamins, medicines, vaccines, hemoglobin, and microbial metabolites, among others. In agriculture, chitosan and its encapsulated compounds have been widely used as an ecological alternative in agricultural production, such as biofertilizers, biopesticides, seed treatment agents, soil conditioners, and growth promoters. Chitosan has been used as a co-encapsulating material for curcumin and resveratrol and in the development of nanocomposite films to inhibit the growth of fungi, such as Penicillium chrysogenum, Aspergillus flavus, Aspergillus niger, and Aspergillus parasiticus, resulting in the control of these pathogens.

9Cellulose is a natural polysaccharide with properties of high interest, e.g., biodegradability and biocompatibility. In terms of chemical composition, cellulose is a homopolysaccharide, which is formed by many monomers of glucose. Cellulose is found in plants, microorganisms, such as fungi and bacteria, and algae. It is the most abundant naturally occurring polysaccharide. Methylcellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, and hydroxypropylcellulose are synthetic derivatives of cellulose, which are also used for the encapsulation and manufacture of edible food films. These films are usually used to protect fruits and vegetables through the use of barrier layers.

10In addition to the synthetic derivatives of cellulose, generally carried out by etherification or esterification of hydroxyl groups, it is possible to produce cellulose derivatives from agricultural and agro-vegetable residues. New biopolymers that have unique characteristics and properties compatible with synthetic polymers can be used for their replacement with non-degradable polymers, combining their applications with environmental preservation. Cellulose can be used as nanocomposites. Especially, the nanocrystals can be used as reinforcing agents in the preparation of composite materials due to their characteristics such as high reactivity, high strength and modulus, rigidity, renewability, low density, biodegradability, and no toxicity. Cellulose nanocrystals can compose films, food packaging, fibers, hydrogels, and drugs. Also, it can be used as a transport vehicle for agrochemicals and in many other segments of biotechnology.

11Starch is a natural polymer, which is the main polysaccharide reserve material existing in photosynthetic tissues and other parts of plants such as fruits, seeds, tubers, and roots. Therefore, depending on its botanical origin, starch can have a different molecular structure, as well as distinct characteristics and properties, in addition to exhibiting diversity in the shape, size and composition of its granules.

12Starch is characterized as a polymeric compound consisting of glucose monomer, while it is present in abundance in foods, such as grains, corn, potato, and rice. This polymer has 20–25% amylose and 75–80% amylopectin, presenting hydrophilic granules. It is a material with multiple applications due to its biodegradability, availability, and abundance, in addition to presenting competitive cost compared to other polymers.

13Alginate is a natural hydrophilic polymer isolated from brown algae and is used in food applications due to its film-forming, gel-making, thickening, and stabilization properties. Alginate exhibits antimicrobial properties, moisture absorption, gelation, biocompatibility, and application in various segments (pharmaceutical, cosmetic, food, and biomedical industries) as a consequence of its multiple materials such as films, hydrogels, microspheres, fibers, and microcapsules, among others.

14Alginate is also widely used with other polymers to improve or obtain new properties through the integration of materials, such as the production of edible films from the composition of alginate and fish gelatin, resulting in the improvement of the mechanical characteristics of the film and increasing antioxidant capacity. The manufacture of bilayer films based on sodium alginate and tea tree essential oil incorporated in TiO2 nanoparticles is reported, aiming at improving postharvest quality and reducing anthracnose in banana fruits. The use of alginate for the encapsulation of vegetable oils is quite widespread, such as the use of alginate-based microparticles structured with other biopolymers such as pectin to improve the encapsulation efficiency of essential oils from olive leaves.

15Shellac is a natural polymer refined from lac resin that is excreted from insects, mainly from the species Kerria spp. As it is a natural resin, shellac exhibits non-toxic and biodegradable properties. It is characterized as a semi-crystalline polymer but with less regular alignment, less dense, and brittle, presenting itself as an alternative to synthetic polymers. Moreover, it has potential in the area of green technologies.

16Shellac is composed mainly of oxyacid polyesters, being an amphiphilic biomacromolecule. This biopolymer has been widely used in several segments due to its characteristic of amphiphilicity and pH responsiveness. Examples of applications are food coating, biodegradable films, manufacturing of food waxes, preparation of food delivery systems (coated carriers, microcapsules, nanoparticles, and microparticles), and as an oil gelling agent.

17Many studies report the use of shellac with other materials to improve the efficiency of the delivery of bioactive compounds through a synergistic effect between the substances. One example is the combination of shellac and tannic acid to prolong the shelf life of post-harvested mango and improve its quality. Another example is the interaction of oat protein granules and shellac to the development of gels at near neutral pH to protect and release sensitive bioactive compounds. The preparation of microspheres composed of shellac and chitin to obtain high-efficiency enzymatic immobilization with great potential in biotechnology is also highlighted. Furthermore, the development of films composed of shellac and gelatin to extend the shelf life of banana fruits and improve post-harvest quality has been studied, thus presenting satisfactory results. The use of zein and shellac composite particles to improve curcumin encapsulation efficiency can be cited, among others.

18Pectin is a natural heteropolysaccharide found in the meristematic tissue and the parenchyma. The amount of pectin in the cell wall and its quality change according to the plant source. Pectin is composed of poly α−1–4 galacturonic acid residues with degrees of methylation of carboxylic acid residues. It is also composed of sugars, such as arabinose, galactose, and rhamnose.

19The degree of esterification is a factor that influences the processing conditions and pectin characteristics. It is the percentage of the number of esterified carboxyl groups in relation to the degree of methylation. Pectin is separated into high methoxyl pectin (degree >50%) and low methoxyl pectin (degree < 50%).

20Pectin is a food safety active ingredient and presents several benefits, such as gelling agent, emulsion stabilizer, and binding capacity agent. It is not digested by intestinal enzymes, while it is mucoadhesive. This biopolymer has anti-inflammatory, non-toxic, biodegradability, and biocompatibility properties. It can be found as a hydrogel, fiber, composites, and injectable cell vehicle.

21Gum Arabic is a natural source of mineral salts (potassium, magnesium, calcium), fiber, and carbohydrates (arabinose and galactose). It is a heteropolysaccharide often used as a coating material due to its characteristics, such as retention of volatiles, emulsification, low cost, negatively charged properties, low viscosity, high solubility, easy use, inhibition of oxidation reactions, and colorless characteristic of solutions. Gum Arabic is mainly used in the pharmaceutical area to concentrate syrups. In the food industry, it is used as a stabilizer, while in the agricultural industry it is mainly used to produce microcapsules containing bacteria.

22Xanthan gum is a polysaccharide biopolymer consisting of glucose, mannose, and diglucuronic acid, which is produced using some inexpensive nutrients such as sucrose, sugarcane molasses, and whey. Xanthan gum is a novel generation of extracellular metabolites produced by bacteria such as Xanthomonas campestris.

23This gum is easily dissolved in cold and hot water and produces a concentrated solution, even in a small amount. Xanthan gum is used in many segments such as chemical, petroleum, cosmetic, food, and agricultural products. This gum is also used in some beverages, candies, and frozen and canned foods. Factors, such as temperature, pH, carbon sources, high pressure, polymer concentration, and viscosity, in the presence of galactomannan influence the production of this gum.

24Dextran is a linear polysaccharide biopolymer that contains hydroxyl groups used for the covalent bonding of some organic groups, such as hydrophobic compounds. The modified dextran becomes insoluble or soluble in water and can form self-organized nanoscale particles by increasing the degree of substitution. This biopolymer can be used for the production of nanocarriers to encapsulate active materials with different hydrophobicities. Despite its great potential, the nanoencapsulation of food bioactive compounds using modified dextrans polymers should be better studied.

25Protein-based polymers, in addition to presenting mechanical properties of films equal or superior to other polymeric materials, have excellent gas barrier properties, which are widely used for food packaging. In this context, milk proteins are used, which can be separated into caseins and whey proteins. Casein is the main and high-quality milk protein, found naturally in milk in micellar supramolecule structures. It constitutes approximately 80% of the total milk protein, while whey proteins represent approximately 20% of the total milk protein, and are normally obtained as a by-product (whey) of cheese production.

26Milk proteins demonstrate several favorable characteristics for biotechnological, food, and agricultural applications due to their multiple functional and structural properties, benefiting the development of macro, micro or nano structures. Among its various functional properties, the emulsifying and foaming properties are the most important. Milk proteins are used as nutraceutical vehicles, acting in the stabilization of bioactive compounds in foods, in the delivery of nutrients, in the improvement of food quality (sensory, color, flavor, texture), and the improvement of food safety. These proteins are found in different structural forms and levels, such as nanofilms, hydrogels, microcapsules, nanocomposites, nanocoatings, and microspheres, among others.

27In the agricultural area, the encapsulation of an insecticide, Cydia pomonella granulovirus used in organic arboriculture, was performed with sodium caseinate, a hydrophilic milk protein. Lipophilic polyglycerol polyricinoleate and sodium caseinate concentrations larger than 1 wt% were very interesting for applications because the encapsulation remained at a high level for at least 300 days. In addition, the encapsulation of neem seed oil extract within polymeric shells formed by whey protein isolate/maltodextrin was performed using spray drying. Neem seed oil contains azadirachtin as its main bioactive component, a compound having efficient insect repellent and insecticidal properties. As a result of the study, encapsulation efficiencies for neem seed oil were demonstrated higher in smaller microcapsules, with efficiency values of 60–92%. The association of botanical insecticides within biopolymer cores such as milk proteins presents a remarkable potential for increasing agricultural production levels and reducing impacts on human health and the environment.

28Bioactive compounds can be found in vegetables, fruits, cereals, legumes, roots, rhizomes, and other plant sources. In this sense, to improve their stability and applicability in both food and agriculture, encapsulation is a feasible technique. Microencapsulation and nanoencapsulation are the two most used technologies to encapsulate bioactive compounds.

29For the encapsulation process of bioactive compounds, the selection of the appropriate encapsulating material and the encapsulation technique should be considered. Some reported techniques are emulsification, anti-solvent precipitation, electrospinning, and coacervation, among others. Coating materials influence emulsion properties, such as droplet size, viscosity, stability, and powder characteristics. Nanoencapsulation presents a particle size of less than 1 micron, microencapsulation presents a particle size between 1 to 1000 microns, and microencapsulation produces a particle size higher than 1000 microns.

30Microencapsulation protects core bioactive compounds in a heterogeneous or homogeneous matrix. The technique and the type of coating materials play a significant role in the feed and powder properties. Droplets of liquid or small particles are coated by a polymer to produce particles, such as microspheres or microcapsules. They are used in the industry as pharmaceuticals, chemical, and food agents. Microspheres are dense matrix systems, while microcapsules are hollow internally possessing a reservoir system. The microparticles can present many morphologies, which depend on the properties of the core with bioactive compounds, coating material, and microencapsulation technique. The main types of encapsulation methods, physical, chemical, and physical-chemical, are presented in Figure 1.

31Emulsion techniques are rather used in the food industry. Recently, Pickering emulsions have gained importance because they have higher stability to coalescence. The Pickering emulsion technique for preparing microspheres, microcapsules, and foams is broadly studied because it is easy to operate and economically feasible. However, there are other emulsion techniques (Figure 2).

32Encapsulation allows active ingredients such as polyphenols, carotenoids, pigments, fatty acids, phytosterols, probiotics, vitamins, minerals, and bioactive peptides to be trapped within a matrix of different carriers. Generally, the stability of these bioactive compounds is low, and encapsulation generates a powder with higher stability against variations in temperature, light, pH, or oxygen, increasing the release rate of these active ingredients.

33Bioactive peptides are found in an inactive form in the structure of the original proteins and are activated after the cleavage of the proteins. In most cases, the peptide chain comprises the amino acids arginine, proline and lysine together with hydrophobic residues. They can be classified as exogenous endogenous substances. Endogenous peptides are produced in different cell types, like neural, immune, or glands throughout the body. Exogenous peptides came from a variety of sources, such as food, supplements, and drugs.

34Peptide fractions and protein hydrolysates can be used as nutraceuticals, functional foods, or ingredients in food products. Some factors can affect bioactive peptides, limiting their application, e.g., pH, enzymatic degradation, low water solubility, interaction with the food matrix, hygroscopicity, and possible bitter taste. In this sense, encapsulation of peptides with some coating polymers can improve these aspects. Some studies have presented that encapsulation of peptides increases their stability, bioactivity, solubility and sensory characteristics, and reduces hygroscopicity. In addition, the various colloidal systems used to encapsulate peptides have presented good encapsulation efficiency and stability.

35These bioactivities depend on the amino acid and the peptide sequence, which comprises 2 to 20 amino acids. Bioactive peptides can be obtained by hydrolysis of protein of animal or vegetable origin, by chemical or enzymatic hydrolysis. Nowadays, peptides are mainly applied in the food industry to obtain functional and nutraceutical foods. Additionally, bioactive peptides have functional properties and can be used as additives, such as solubility, emulsification, foaming, and water/oil binding capacity.

36Encapsulation techniques are a promising alternative to increase stability and control the release of peptides for food applications. Also, encapsulation of peptides in nanocarriers increases the sensory characteristics by masking their bitter taste, increasing the solubility, and decreasing the hygroscopicity. Some peptides can be used as natural food preservatives to prolong shelf life or incorporated into bioactive packaging in the form of coatings and edible films to improve the safety of some foods due to their antioxidant and antimicrobial properties. An overview of the bioactive peptides microencapsulation process and characterization, sources of the bioactive, coating materials, encapsulation method, process conditions and results in terms of process parameters, encapsulation efficiency, particle size, and retention of their functional properties is shown in Table 2.

37Vegetable oils rich in unsaturated fatty acids are prone to oxidation, which produces free radicals called hydroperoxides. The encapsulation system reduces their degradation and/or masks certain undesirable, preserving the bioactive compounds and improving their controlled release, solubility, and bioavailability. Moreover, micro- and nano-encapsulation of extracts and essential oils can enhance their functional properties in new-generation foods. Applications for the encapsulated essential oils have been emphasized, including antimicrobials, pesticides, natural insecticides, repellents, food packaging and taste preservation, and lipid oxidation.

38Vitamin E is a fat-soluble vitamin from plants with health benefits. This vitamin is made up of eight isoforms, including α-, β-, γ-, and δ-tocotrienol, and α-, β-, γ-, and δ-tocopherol. The most prevalent vitamin E homolog in nature is α- tocopherol. Tocopherols are found in high-fat foods such as nuts (almonds, peanuts, hazelnuts), seeds (sunflower, cottonseed), cereals (rice, oat, wheat), and vegetable oils (palm oil, wheat germ oil). Moreover, it is found in vegetables and fruit, such as spinach, tomatoes, green beans, broccoli, turnip, pumpkin, cranberries, carrots, avocado, kiwifruit, and raspberries.

39Vitamin E is a weakly water-soluble bioactive component, which restricts its absorption in the gastrointestinal system and its total bioavailability. There is an interest in developing vitamin E fortified foods and beverages. Therefore, encapsulation is necessary to increase its absorption. Furthermore, α-tocopherol is very susceptible to oxidative reactions, mediated by oxygen, light, heat, and free radicals.

40Spray-drying is a known encapsulation technique because it allows for a continuous operating procedure. For improving vitamin E oral bioavailability, the spray freeze-drying method has shown to be effective. The food industry uses encapsulated -tocopherol as antioxidants to extend the shelf life of fat-based bakery products. Various studies have suggested that a vitamin E concentration beyond the advised daily allowance can have positive benefits on human health and may prevent reproductive, nervous system, inflammation, and immune system problems.

41Recent studies on the encapsulation of bioactive peptides, fatty acids from vegetable oils, and vitamins (tocopherols) are presented in Table 2.

42Polyphenols include a heterogeneous group of bioactive compounds containing at least one phenolic ring, naturally found in fruits, rhizomes, cereals, coffee, and tea, among others. Anti-inflammatory, antioxidant, and anticancer properties have been associated with them, and they also participate in the prevention of diabetes, cardiovascular diseases, and cancer. During its encapsulation, biopolymers are used, which stand out for being biodegradable, biocompatible, and high nutritional value vehicles. Among the most widely used biopolymers are carriers based on proteins, polysaccharides, and lipids.

43Proteins represent excellent carriers of polyphenols due to their functional properties of emulsification, amphiphilicity, gelation, and foam formation. They can form nanoemulsions, nanogels, nanoparticles, nanofibers, and nanofilms, producing hydrophilic and hydrophobic polyphenolic compounds. Likewise, polysaccharides, due to their structure and physiological activity, represent very suitable nanocarriers for encapsulating and administering polyphenols. Lipids represent one of the most important vehicles for the protection and supply of fat-soluble polyphenols due to their high biodegradability and biocompatibility. Through the use of liposomes, nanoemulsions, and solid lipid nanoparticles, the bioavailability of fat-soluble polyphenols can be improved. In general, for the encapsulation of plant polyphenols, different types of biobased nanocarriers can be used, such as nanomicelles, nanoemulsions, nanoparticles, nanogels, and liposomes, including soy protein, albumin, zein, cellulose, starch, and lipids, which efficiently manage and protect polyphenolic compounds, as well as improve their bioavailability.

44Carotenoids are isoprenoid compounds found in plants, bacteria, fungi, and algae, as well as in foods such as fruits, vegetables, and fish. There are more than 600 fat-soluble carotenoids that differ by structural changes in their polyene skeleton, subdividing them into carotenoids, xanthophylls, and lycopene. Different biological actions are attributed to it, such as important antioxidant activity in the prevention of age-related macular and cardiovascular diseases, as well as participating in the strengthening of the immune system, proper functioning of the reproductive system, regression of malignant lesions, and inhibition of mutagenesis. They are sensitive to degradation by heat, light, and temperature. Likewise, the presence of oxidizing agents and oxygen could cause their decomposition, demonstrating the necessity to encapsulate them to stabilize and properly administer these bioactive ingredients.

45Among the methods used for its preservation, microencapsulation is one of the most used. It allows stabilizing and reducing the volume of the product, thus reducing storage and transport costs, as well as favoring its administration. Among the oldest and most widely used carotenoid microencapsulation methods, the spray-drying allows for obtaining a product with the appropriate characteristics by varying the drying parameters such as feed flow rate and temperature, while different agents can also be used as carriers. Currently, among the most modern methods for the encapsulation of carotenoids, supercritical micronization is used, which allows for controlling the particle size and distribution of the particles, stability, and bioavailability of the product.

46Anthocyanins, carotenoids, betalains, and chlorophylls are natural pigments widely used in the food industry. Among them, anthocyanins are water-soluble pigments that compose the vacuoles of several plant tissues, mainly in flowers and fruits, leaves, stems, and storage organs. The total content and composition vary substantially between different plant species. However, they are susceptible to degradation during processing and storage due to pH, light, heat, oxygen, and interaction with other food components, decreasing their bioavailability and biological activity. Microencapsulation using biopolymers based on proteins and polysaccharides of food origin is one of the most common methods to stabilize and protect anthocyanins from degradation. However, in a physiological environment, these systems could be unstable, due to high particle size and low efficiency of encapsulation of anthocyanins and zeta potential. Currently, for the stabilization of anthocyanins, nanosystems, such as nanoemulsion and nanoliposome, are being used. Unlike conventional emulsions, nanoemulsions provide higher stability against aggregation and gravitational separation due to their high surface area. Likewise, nanoliposomes made from conventional liposomes, in which the particle size has been reduced by ultrasound, high-pressure homogenization, maintained the stability, bioavailability, and controlled administration of anthocyanins.

47Betalains are found in leaves, flowers, fruits, roots, stems, bracts, petioles, and seeds. They are synthesized from tyrosine and are divided into two subclasses: betaxanthins and betacyanins. Antioxidant and anticancer properties have been attributed to them. However, they are highly unstable and can be degraded according to variations in temperature, light, oxygen, and pH. It has been reported that the encapsulation of betalains allows storage stability of up to 6 months. Moreover, the encapsulated betalains could be resistant to degradation and added to liquid or solid substances.

48For the encapsulation of betalains, different matrices have been used, such as polysaccharides and proteins, or a combination of both, due to the high solubility of most polysaccharides and the high capacity of these compounds to protect betalains from oxidation. Among the techniques used for the encapsulation of betalains, the most common are lyophilization, emulsions, ionic gelation and spray drying. The latter is the most used due to its cheaper cost and faster processing. However, it requires that the carrier be soluble in easily evaporable solvents at high temperatures, which could degrade some bioactive compounds. The lyophilization technique presents a higher loading efficiency and stabilization of betalains compared to spray drying. Likewise, it is reported that guar gum is suitable for encapsulating betalains with the lyophilization technique. However, it is not suitable for use with the spray-drying method.

49Encapsulating efficiency is the ratio of a core material that is trapped inside an encapsulate as opposed to the initial core content that was introduced to an encapsulation process. It was determined using Equation (1): where represents the amount of integrated core material and represents the total amount of core material originally added during preparation.

50Spectroscopic or chromatographic methods can be used to determine and. Encapsulation method and particle size distribution can influence encapsulation efficiency. The criteria that can affect encapsulation efficiency are wall and core specifications, core/wall ratio, emulsion properties (such as viscosity and droplet size) and drying parameters. Encapsulation efficiency can be improved by selecting wall materials with different functional properties, and it is preferable to use various combinations of wall or shell materials. Low efficiency might lead to low stability since capsules are not protected from adverse storage conditions. Currently, the primary focus of food component micro/nano-encapsulation is on enhancing encapsulation efficiency and prolonging product shelf-life.

51Bioactive components are released from encapsulants in three steps: surface release, diffusion via a swelling matrix, and matrix erosion. More mechanisms were discussed, such as matrix degradation induced by enzymes and pH, fissure development, hydrostatic pressure, and geometric changes brought on by shear forces. Surface release may be caused by inadequate entrapment inside the matrix or by a polar bioactive compound’s tendency to partition toward the hydrophilic surface of an emulsion.

52Concentration-time profiles are frequently used to qualitatively evaluate release kinetics, with a focus on the quantity released after a certain length of time. There have been several mathematical models developed, that describe the release of bioactive components. The following kinetic models were used: The zero order (Equation (2)), first order (Equation (3)), Hixson–Crowell (Equation (4)), and Korsmeyer–Peppas (Equation (5)): where is the quantity released after time t; is the initial quantity which is usually zero; is the cumulative release at time t; is the cumulative release at infinite time;,,, represent the zero-order, first-order, Hixson–Crowell, and Korsmeyer–Peppas kinetic constants, respectively; n represents the diffusion exponent in the Korsmeyer–Peppas model. To characterize release from porous matrixes, the zero-order and first-order models are commonly utilized. In the Hixon-Crowell model, a linear graph of the cubic root of the unreleased fraction of capsule vs time demonstrates that the surface area of the composite changes during the release process. According to R2 values, the Hixson-Crowell model was comparable to zero-order and first-order kinetics. The Korsmeyer–Peppas model is typically utilized when the release mechanism is unknown or when the release process is regulated by more than one sort of release mechanism.

53The releasing action is therefore known to be triggered by a range of internal (such as diffusion, degradation, and swelling) and external stimuli (such as changes in temperature, pH, light, ultrasound, ionic strength, and magnetic field). It is evident that numerous models have been established that may predict the release profile of active agents into the environment by taking into account the occurrence of different kinetic rates. Several researchers have attempted to forecast their experimental release data using various models such as the zero-order, first-order, Korsmeyer–Peppas model, and Hixson Crowell model. The Korsmeyer–Peppas model of bioactive compounds release is found to be used in the majority of investigations on the release of corrosion inhibitor from nanocontainers.

54The encapsulation efficiency, release kinetics of bioactive compounds, stability of capsules, and matrix characteristics are all essential features that are affected by the technique and encapsulation materials. The size of the encapsulating does not directly affect the efficiency of encapsulation, but it does affect the controlled release of bioactive compounds as well as the physical and chemical characteristics of encapsulants. This is due to the fact that smaller particle sizes result in bigger contact surfaces, resulting in more release than larger particle size encapsulates. Preferably, wall material should be insoluble, not react with bioactive components, good at producing films, and possess the appropriate protective qualities against a variety of external factors.

55Finally, it has been found that most study include the encapsulation efficiency in their results, as it is one of the crucial parameters to assess the preservation of the core material (bioactive compound). However, there are few studies that cover the characteristics and release kinetics of bioactive compound microcapsules in food and agricultural applications, because kinetic models are more used in the realization of a simulation, evaluating the diffusion process that occurs through the nanocontainer, and making some assumptions appropriate for a specific application.

56The population is demanding healthy foods with higher added value, such as functional foods or foods that contain special nutrients. The food industry faces technological changes to meet the needs of consumers. For these reasons, the technology must be appropriate to process these types of foods. The micro- and nanoencapsulation of bioactive compounds, such as antioxidants, carotenoids, tocopherols, phenols, and bioactive peptides, among others, is mostly done by spraying. Currently, lyophilization is also used to microencapsulate bioactive compounds. Extrusion is another technique that has been used in this food and agricultural field.

57In this sense, different techniques can be used to microencapsulate bioactive compounds. The selection of the technology depends on several factors, such as the types of bioactive compounds to be encapsulated, the sensitivity of the bioactive compound, the encapsulating agent, and the costs of the technique. Each microencapsulation technique presents different results in the final product. The bioactive compound in the final product may have properties in terms of shape, structure, size, distribution, and bioavailability. Microencapsulation has some uses expressed in Table 3.

58Currently, supercritical microencapsulation is also known as “micronization”. Supercritical micronization uses mild temperatures, which avoids reducing the quality of bioactive compounds. CO2 is the most used solvent in this technique, followed by water. CO2, under supercritical conditions, has become increasingly popular in the microencapsulation of bioactive compounds of interest to the food and agricultural industries.

59Complex coacervation is an encapsulation technique that consists of the interaction of two polyelectrolytes of opposite charges in an aqueous medium. The chemical complex of a protein or carbohydrate nature is formed around the bioactive compound to be encapsulated. This interaction is formed under specific conditions of ionic strength, temperature, pH, polymer concentration, the proportion of biopolymers, the molecular weight of biopolymers, and the degree of homogenization. This technique allows for obtaining particles, where the core (bioactive compounds) is protected by a layer of an encapsulating agent of a protein or carbohydrate nature.

60The application of vitamin C (ascorbic acid) has demonstrated beneficial effects in agriculture, such as reducing the effect of nickel and cadmium in barley, alleviating drought stress in sweet pepper and Cucumber, and improving the qualities of apples. It allows for mitigating the salinity stress and providing better growth performance in barley. In this context, the encapsulation of ascorbic acid through spray chilling has been reported as an effective technique, showing retentions over 90% and controlled release of vitamin C in aqueous solutions. These authors employed a combination of fully hydrogenated palm oil and palm oil to obtain flexible particles. The technique involves heating the fully hydrogenated palm oil to 80 °C to make it liquid and mixing it with the ascorbic acid to pass immediately through the spray dryer and be cooled to 5 °C.

61Some essential oils have the potential to be applied in agriculture as biopesticides. Rosemary oil has the potential to be used as an insecticide. It has been encapsulated by spouted bed drying using a mixture of Tixosil and maltodextrin as drying carriers and Teflon beads for drying and with microcrystalline cellulose cores. Neem oil has shown insecticide activity, and it can be effectively nanoencapsulated to control pests, showing enhanced properties.

62Encapsulation materials consist of a variety of synthetic or natural polymers, the former still being the most used elsewhere. Otherwise, an increase in the use of natural polymers is seen, and non-hydrolyzed biopolymers have been widely used in agriculture due to their availability and low cost. Among them, hydrolyzed starches stand out as agents in the encapsulation of Bt pesticides (metabolites produced by Bacillus thuringiensis) because they protected environmental factors and improvement in the formulated product. Moreover, encapsulation can be efficient for formulations of biofungicides, biopesticides, and/or biofertilizers in agricultural fields, becoming an economically viable technique for farmers. The encapsulation can have several advantages in the agricultural sector, as shown in Figure 3.

63Taking into account agricultural applications, report Trichoderma harzianum as a biological control agent very sensitive to biotic and abiotic factors due to the presence of live spores. Consequently, encapsulation shows an improvement in activity against phytopathogens such as in the control of Sclerotinia sclerotiorum (white mold). In another study, spores of the Trichoderma species were encapsulated in biologically based lignin for the treatment of diseases of the vine trunk, demonstrated by in vitro tests that the spores remain at rest until germination is triggered by the fungus itself at the correct time. Additionally, the fungus Trichoderma spp. was encapsulated in a sodium alginate matrix to guarantee good stability of the biopesticide formulations. The encapsulation strategy resulted in the survival of the fungi during the production and storage stages. After 14 months, the stored samples still had good conditions and viable cells.

64In the case of microencapsulation by Pickering emulsion of Metarhizium conidia for the mortality of Spodoptera littoralis larvae, better cell distribution in leaves and control of the agricultural pest were observed. Furthermore, in a study carried out, a formulation of Bacillus thuringiensis aizawai (BtA) encapsulated by Pickering water-in-oil emulsion was obtained. The efficiency of 92% in the mortality of Spodoptera littoralis larvae in the first instar was reported.

65Similarly, it was shown that inoculating two strains of Pseudomonas fluorescens in potatoes using an alginate-gelatin capsule resulted in higher plant protection against harmful soil conditions and establishment in the rhizosphere. Likewise, Pseudomonas spp. was encapsulated in sodium alginate and with salicylic acid containing zinc oxide nanoparticles, in which the efficiency in the antifungal activity against Sclerotium rolfsii was demonstrated. Following this trend, a formulation of biopesticides with UV protection capacity in the encapsulation of fungal conidia in oil/water emulsion and stabilized by titanium dioxide (TiO2) was developed. Satisfactory efficiency in their germination rate was achieved when exposed to natural UV light compared to unprotected conidia (not encapsulated).

66Azadirachtin found in the neem tree (Azadirachta indica), which is a natural pesticide molecule, was encapsulated via nanoemulsification with whey protein isolate. This strategy demonstrated a positive effect on the mortality of Spodoptera frugiperda, a caterpillar that affects the soybean crop. Moreover, the encapsulated essential oil extracted from orange peel effectively inhibited the growth of Staphylococcus aureus and Escherichia coli.

67Regarding the encapsulation of biofertilizers, a study showed that formulations containing Burkholderia cepacia and Pseudomonas fluorescens encapsulated with phosphate alginate presented better growth conditions for wheat plants in semi-arid and salt-stressed areas. The study demonstrated that biofertilizers consisting of Pseudomonas fluorescens and Azosprillum brasilense encapsulated with polymers of montmorillonite (clay mineral) and sodium alginate resulted in higher control of the formulation. Furthermore, slow release of the active compounds was reached, thus contributing positively to the growth of the wheat crop with an increase in the biomass and aerial part of the plants.

68Regarding the food industry, food encapsulation has been widely used over the years. The encapsulation technique aims to protect and deliver the bioactive compounds to the target tissue of the human organism. This approach results in better stability and bioavailability of the bioactive compounds and increases their use and benefits for the human body. Figure 4 shows some foods used in encapsulation technology. As presented in the scheme, the main interesting compounds for the food encapsulation technique are dyes and flavorings (candies), vitamins (vitamin A, D, E), antioxidants (citrus fruits and cereals), enzymes (lipase, invertase), bioactive peptide (milk), and polyunsaturated fatty acids (omega 3), and some mineral elements (iron, potassium), among others.

69In addition to substances produced by microorganisms, substances found in herbal extracts and essential oils are also targeted to be encapsulated because they have antimicrobial and insecticidal properties, among others. The control of the high volatility of oils and extracts is a challenge for biotechnology. Therefore, the encapsulation of essential oils and volatile extracts in the development of bioproducts for agricultural use is of great interest because the release of these compounds to the target agent is desirable to be slow and continuous.

70Essential oil from savory leaves (Satureja hortensis L.), for example, was encapsulated with different natural polymers such as apple pectin, gum arabic, and gelatin. A higher encapsulation efficiency for all polymers was reported. Consequently, the efficiency of herbicidal activity in amaranth (Amaranthus retroflexus L.) and tomato (Lycopersicon esculentum Mill.) was increased. Another active oil has been encapsulated and tested over time against bacteria oxidation: pepper oil. The encapsulation of such oil by gum arabic/maltodextrin resulted in an inhibitory effect against Pseudomonas aeruginosa, Enterococcus faecali and Staphylococcus aureus. The microencapsulation using these polymers contributed to a higher protection of pepper oil against the oxidation process during storage.

71Curcumin extracted from turmeric was encapsulated by the Supercritical Anti-solvent (SAS) technique using various polymeric matrices to formulate a dye containing turmeric extracts. The encapsulating polymers tested were Eudragit® L100 (Evonik-Germany), Pluronic® F127 (BASF-Germany), and polyvinylpyrrolidone or mixtures of these materials. The dye formulation had a curcumin content of 4.45 µg mL−1 with a mean diameter of amorphous particles of approximately 5.7 µm. Also, the best dye solubility of 211 μg mL−1 of total curcuminoids was obtained at pH 4. Economic evaluations have also been developed in this area to provide information that can boost applications on larger scales and transfer the technology to the industrial scale. In this case, the technical-economic feasibility of the SAS technique for food applications was evaluated in terms of the precipitation of a vitamin complex containing riboflavin, δ-tocopherol, and β-carotene in zein microcapsules. The results showed that the average size of the microcapsules ranged from 8 to 18 µm, with spherical morphology, while the precipitation yield ranged from 410 to 820 g kg−1. The simulated manufacturing cost for the microcapsules ranged from USD 0.38 g−1 to USD 0.50 g−1, while these values may reduce with the possibility of reducing the mass flow of CO2 during precipitation.

72Poly(ε-caprolactone) particles containing resveratrol were developed using the Gas Anti-solvent (GAS) technique, having heterogeneous characteristics. Encapsulation was positive because it did not change the chemical structures or the antioxidant activity of resveratrol. In addition, the microparticles maintained a constant release for 48 h and, in the thermal oxidative analysis, the difference between the samples and the control was 2.57 times smaller than the difference between pure resveratrol and the control sample. Curcumin nanoparticles were also produced by encapsulation in Shellac by the GAS technique. After 2 months of storage at room temperature (25 °C), the aqueous nanodispersions of the particles with the encapsulated bioactive substance (Cur@Lac) showed long-term stability without agglomeration or sedimentation. Furthermore, the final retention rate of curcumin was over 85%. Colored drinks made from fruit syrup (pH = 4.0), fruit soda (pH = 6.0) and sparkling water (pH = 8.3) were prepared using Cur@Lac as a dye, which has a yellow-orange color.

73An overview of the latest research, technologies, and advances regarding the application of the encapsulation of bioactive compounds for food and agricultural applications is presented. The main forms of encapsulation are microencapsulation, followed by nanoencapsulation. A crescent interest exists in the development of micro or nanocapsules loaded with polyphenols, carotenoids, fatty acids, phytosterols, probiotics, vitamins, minerals, and bioactive peptides from natural sources, for the food industry. However, for applications in agriculture, the development of particles loaded with essential oils, lipids, phytotoxins, medicines, vaccines, hemoglobin, and microbial metabolites is the focus. The main purposes of the encapsulation strategy are to improve stability, solubility, bioavailability, sensorial properties, retention of bioactive properties and microstructure, reduction of hygroscopicity, and increase shelf life. The most widely used polymers for their high performance are gum Arabic, starch, and chitin, while the most commonly used technologies for encapsulation are emulsions-spray drying, emulsions-freeze drying, complex coacervation, followed by others, such as the emerging technology known as supercritical microencapsulation. More studies are needed on bioavailability for food applications and the effectiveness of bioactivity in agricultural applications, as well as scale-up studies at both pilot and industrial levels. However, the potential of encapsulation into polymeric matrices makes it a good strategy to protect bioactive compounds and broaden their use in both food and agriculture.