Electrospinning for Encapsulating Functional Ingredients

Name: Krishnaben Parimalkumar Mandawala

Topic: Electrospinning has been applied for encapsulating functional ingredients. Critically review the development in the above area. You are expected to provide a summary on the wall materials and bioactive components that were studied. At the final section of the review, comment on the advantages/ disadvantages and suitability of this method for encapsulating functional ingredients for food application.

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Abstract:

The electrohydrodynamics processes such as electrospinning is the most promising encapsulation technologies for delivering bioactive compounds effectively and for entrapping. In food industry, encapsulation is highly used in order to delivering bioactive compounds into different food matrices, protect them from unfavorable environmental conditions and increase the shelf life and subsequently maintain the health promoting properties of product formulation. The progress in developing encapsulating technology for functional ingredient delivery is done with the help of electrospinning technique. There is a tremendous development in the field of encapsulating functional ingredient such as successfully incorporation of gallic acid into zein ultra-thin fibers, stabilization of omega-3 fatty acids by encapsulation of bioactive ingredient such as DHA (Docosahexaenoic acid) in zein ultra-thin fibers, encapsulate Bifidobacterium strains for functional food applications and applied for the oxidative stability of encapsulated fish oil. The selection of proper encapsulating material plays a vital role, in which they are selected on the basis of physical and chemical nature of core, wall material, interaction between them and the relative proportion in the formulation of capsules. In current years, electrospinning technology have drawn attention to many researchers’ interest due to their possible applications in food industry. With the help of electrospinning process, it is potential for making micro- and nanosized particles and fibers which are highly applicable for encapsulating bioactive compounds. However, there are complicating issue by using electrospinning technique is the multitude of optimizable factors. There are only few parameters which can be controlled as some of the parameters complicated are either derive from the polymer solutions or highly interdependent. For industrial purposes, there is a big challenge for electrospinning process remains the scaling. This review provides the discussions about the potential of food ingredient-based applications of electrospinning process on encapsulation as well about the encapsulation efficiency and morphology of carrier matrix.

Introduction:

In Food industry, the expansion of nanotechnology field, behavior of components and sensory attributes provides the new insights into the delivery of bioactive, design of a new encapsulated bioactive. Various advanced methods are developed for production of nanomaterial in which electrospinning is one of the modern method suited to the production of fibers using large and complex molecules. Electrospinning is a simple, flexible and one of the most known techniques which involves in the production of ultrathin fibers. These ultrathin fibers possess high surface area to volume ratio and high porosity. These fibers are produced by the application of strong electric field between the two electrodes and imposed on a polymer solution or melts up to the diameters in the order of some ten nanometers, they are widely used as drug delivery, wound dressings, enzyme immobilization and biosensors. The components involve in the process of electrospinning as shown in Figure 1. In the process the polymer solution is ejected through needle and a high voltage is applied after the small drop is formed at the tip. Thus, the electrostatic repulsion counteracts the surface tension and at a critical point, a stream of liquid erupts from the surface which is called Taylor cone. The polymer solution may take complex path, solvent is removed and polymer thread elongated which is deposited in the form of membrane. The spiral movement of the stream leads to increases the path between the needle and collector, results in significant stretching shown in Figure 2. The initialization of electrospinning process requires overcome of surface tension of solution by electric interaction between charges. The most important conditions for the electrospinning is that the viscosity should be above some critical value to prevent the breakage of the jet. However, the higher molecular weight of polymer results in more entanglements and prevents the breakage of fibers and formation of fibers. The production of nanofibers by electrospinning is highly applicable in analytical chemistry, filtration techniques, tissue engineering, electronic or environmental engineering. Nanofibers are also used for drug delivery system or vascular surgery.

Figure 1. A schematic diagram of the electrospinning process. (Athira et al, 2014. Fabrication of poly(caprolactone) nanofibers by electrospinning.) Random fibers, b) aligned fibers at an angle and c) aligned fibers.

Figure 2. Electrical instability formed path of jet. (Fred et al., 2015. Electrospinning: principles practice and possibilities. Royal Society of Chemistry. 2015. Ch-1.)

However, Tan et al., 2007 reported that because of the electrospinning techniques showed their extremely high surface area and trapping efficiency and electrosprayed structures have been proposed a wide range of bioactive protective applications and Shen at al., 2011 showed that the integrated materials in the ultrathin fibers can improve and increase the functionality due to nano-scale effects. The electrohydrodynamics methods have been enrolled for the encapsulation of various food and bioactive compounds such as pharmaceuticals. However, Aceituno-Medina et al., 2015 reported that the encapsulated bioactive compounds kept their antioxidant capacity to a high level in comparison with the non-encapsulated ones during in-vitro digestion. Most of the common proteins which is used in electrospinning as encapsulating material are whey protein concentrate (WPC), whey protein isolate (WPI), zein-gallic acid system, soy protein isolate, gelatin and casein. However, Kayaci el at., 2012 focused on electrospinning of edible biopolymers and less on edible polysaccharides for controlled release of bioactive. Altogether, electrospinning technique had shown auspicious outcome as an efficient and potent method for the production of sub-micron structured encapsulated functional ingredient which may be useful in the food industry. The most interesting benefit of electrohydrodynamics processes is that they can obtained high encapsulation efficiencies without the application of heat treatment. The main objective of this literature is about the development in the Electrospinning technique which is highly applied for the encapsulating functional ingredients.   

Discussions:

Electrospinning has been applied for encapsulating food grade antioxidant based on zein-gallic acid system:

Electrospinning of zein shows an exceptional outlook for its application in the stabilization of light and oxygen sensitive food components. Zein is a hydrophobic protein which is extracted from corn grains and it is well known for great oxygen barrier properties and high thermal resistance and in the plant kingdom, gallic acid is considered as a naturally occurring phenolic acid and it imparts the characteristics such as antioxidants which shows antimicrobial and anti-inflammatory abilities. Neo et al., 2013, reported the successfully incorporation of gallic acid into zein ultra-thin fibers by using electrospinning and developed an encapsulation technology for functional ingredient delivery. However, Liu et al., 2009, was represent for the first time and reported that by using electrospinning, encapsulation of this naturally occurring antioxidant for the production of sub-micron structured ingredients and because of their geometric confinement it can exhibit different physical properties. For the electrospinning process, the solution of Zein electrospun fibers containing varying concentration of gallic acids were placed in a syringes and the power supply was connected to a syringe and grounded collector as a result fibers were collected and examined using a Scanning Electron Microscopy (SEM).

The prepared gallic acid-zein fibers were assessed for various physicochemical characteristics such as morphology, thermal stability etc. The interaction between the gallic acid and zein as well as radical scavenging properties of gallic acid after electrospinning were investigated. Neo et al., 2013, showed the evidence of encapsulation of gallic acid in electrospun fibers with varying gallic acid content which is shown in Table 1.

Table 1. SEM and TEM images of gallic acid loaded zein electrospun fibers. (Neo et al., Encapsulation of food grade antioxidant in natural biopolymer by electrospinning technique: A physicochemical study based on zein-gallic acid system.)

Thus, from the above results they revealed that with the increasing gallic acid content, the fiber diameter as well as viscosity of the solutions also increased and thus eventually increased the number of molecular entanglement in solution which was shown in electrospun diameter and the similar result was concluded by the Neo et al., 2012 and the antioxidant activity of the fibers in which the in which the DPPH scavenging abilities of gallic acid loaded zein varied from 58% to 89% and neat zein exert a 6% of inhibition which is shown in Table 2. Thus, it can be concluded that the incorporated gallic acid has showed its antioxidant activity, without being affected by the interactions that took place between the gallic acid and zein after electrospinning.

Table 2. Antioxidant activity of (%AA) of electrospun fibers. (Neo et al., Encapsulation of food grade antioxidant in natural biopolymer by electrospinning technique: A physicochemical study based on zein-gallic acid system.)

Thus, from the above observation it is revealed that by the distribution and deposition of gallic acid within the fibers shows confirmation about the successful encapsulation of gallic acid within the zein fibers containing antioxidant activities Thus, the formation of sub-micron by electrospinning connects the rising world in food nanotechnology which may apply in packaging materials and scaffolding for microbial cultures. However, Fernandez et al., 2009, reported that the encapsulated β-carotene which is a good source of provitamin A with antioxidant properties and by electrospinning technique reported that the encapsulated β-carotene was well dispersed and stable within ultrathin zein fiber matrix and had significantly higher light stability than the non-encapsulated control.

Electrospinning has been applied for the encapsulation of living bifidobacteria:

Amongst the probiotics, one of the interesting genus called Bifidobecterium have been allow for various intense researches due to their favorable effects attributes to some strains and leads to the incorporation into the food products. However, Shah et al., 1995 reported that the direct incorporation of bacteria into the food leads to the damage of product during their storage period, as they are metabolically active and generous in product. Thus, encapsulation is a believable option as it increases the viability of bacteria and allows proper handling of cells and controlled dosage. López-Rubio et al., 2012, has been carried out the probiotic encapsulation by electrospinning/electrospraying technique using a carbohydrate-based matrix (pullulan) and protein-based matrix (whey protein concentrate) for functional food applications. They compared the morphological features and the viability of encapsulated probiotic and same bacterium in liquid medium (phosphate-buffered saline or skimmed milk) and freeze dried followed by storage at various temperatures and humidity conditions. As pullulan dissolved in PBS, which is not suitable for the electrospinning because during analysis of carbohydrate concentration, there is unstable in jetting and only drops were collected whereas, WPC exhibits greater protection ability as encapsulation material than pullulan as it is highly effectively extend the survival of cells and developed the hydrocolloid-based microcapsules by an electrospinning technique for the protection of living Bifidobacterium.

Electrospinning has been applied for the oxidative stability of encapsulated fish oil:

Numerous studies displayed the advantageous effects of consuming omega-3 fatty acids, despite their conspicuous sensitivity to oxidative degradation. However, Moomand and Lim, 2014, showed that the fish oil can be encapsulated in electrospun zein fibers to provide stability of the lipid and also showed that electrospun zein fibers contribute a greater oxidative stability in comparison to non-encapsulated fish oil. These demonstrate that electrostatic encapsulation technique is very versatile in order to prepare zein encapsulant polymer to protect bioactive compounds. The electrospinning used in this study as shown in Figure 3. The spinneret was connected to the positive electrode. For minimizing charge leakage, the syringe was covered with a rubber insulation.

The present electrospinning technique shows a wide ranges of advantages as compared as compared with other encapsulation techniques. Kolanowski, et al., 2005 showed that fish oil was encapsulated in a cellulose by emulsifying oil in the polymer solution, followed by spray drying and increase in fish oil stability after encapsulation. Whereas, Augustin et al., 2006 reported that Maillard reaction products were used to encapsulate fish oil by heating proteins and carbohydrates, with the increase of Maillard browning leads to the reduction in oxidation of fish oil, but did not improve the encapsulation efficiency. In addition, Li et al., 2009 showed that encapsulated (-)-epigallocatechin gallate (EGCG) in electrospun zein fiber to stabilize the polyphenol during simulated food processing conditions as well as also reported the successful immobilization of EGCG occurred when the fibers were aged for 24h under dry conditions at ambient temperature.

Figure 3. Schematic diagram of the electrospinning setup used in this study. (Moomand and Lim, Oxidative stability of encapsulated fish oil in electrospun zein fibres.)

Electrospinning has been applied for the encapsulation of Ultrathin Zein Prolamine for stabilization of Nutraceutical Omega-3 fatty acids:

The world food market is presently involved in foods that contributes not only in promoting health benefits but also taking care of its nutritive value. Natural substances are treated as safe as they occurred in plant foods. Among these, fish or marine oils are admirable dietary sources of nutritional functional ingredients which is called polyunsaturated fatty acids (PUFAs) more specifically, omega-3 fatty acids (ω-3). Torres-giner et al., 2010, showed stabilization by encapsulation of bioactive ingredient (Docosahexaenoic acid) in zein ultrathin capsules. Docosahexaenoic acid (DHA) which is a long chain polyunsaturated fatty acid of the omega-3 series (ω-3) which shows a healthy impact on the human health. The various advantageous effects of DHA are blood pressure reduction, inflammation modulation, reduction of cardiovascular diseases and inhibition of platelet activation. Therefore, nowadays it is highly recommended for the consumption of DHA. Encapsulation consist of creating droplets of liquid or solid which are packed into the matrix and protect it from deterioration and subsequently, allow to release under suitable conditions. The techniques for encapsulation explore to increase the stability against degradation, controlled release of bioactive food ingredients and raise bioavailability. Shukla and Cheryan, 2001, showed the amphiphilic character and emulsification properties of proteins are essential to encapsulate the oil-based materials and also showed the properties of Zein such as high thermal resistance, satisfactory mechanical and oxygen and aroma barrier properties and low water uptake values. According to Torres-giner et al., 2010, used the electrospinning technique to prepare ultrathin zein Prolamine capsules containing bioactive-DHA which is a functional ingredient of ω-3 fatty acids. The stability of free and encapsulated DHA has been evaluated aa a function of zein concentration, temperature and relative humidity. The images of electrosprayed ultrathin matrices of zein-DHA and zein are shown in Table 3.

Table 3. Optical images of the electrosprayed ultrathin matrices of zein and zein-DHA. (Torres-giner et al., Stabilization of a Nutraceutical Omega-3 Fatty Acid by Encapsulation in Ultrathin Electrosprayed Zein Prolamine.)

These observations support the fact that zein entrapped the DHA oil drops with relative efficacy into the capsules. However, mass of ultrathin irregular zein-based beads is also observed which is shown in Table 4.

Table 4. SEM images of capsules obtained from electrospraying of zein and zein-DHA.(Torres-giner et al., Stabilization of a Nutraceutical Omega-3 Fatty Acid by Encapsulation in Ultrathin Electrosprayed Zein Prolamine.)

For the capsules containing nutraceutical, it is also observed that the surface beads seem to be smoother and homogenous. Thus, the incorporation of nutritional functional ingredient did not exhibit any effect on morphology as from above result, the morphology of electrosprayed zein-DHA capsules had similar morphology to this of pure zein. Therefore, by choosing the appropriate electrospinning conditions showed that the resultant morphology is close to beads rather than the usual long fibers. As this morphology demonstrate the micro-encapsulated bioactive particles have a uniform and superior incorporations in food emulsions and suspensions as they can more easily disperse and homogenized. It represents that decrease in the size of capsules to the micro-range leads to increase the flavor retention and shelf-life stability. However, water also plays a vital role in encapsulation because it highly influences the oxidation rate as well as plasticize polymers and specifically biopolymers such as proteins and polysaccharide. Table 5. shows the changes in the degradation rate constant as function of %RH.

Table 5. Rate constant and induction time as a function of relative humidity and temperature. (Torres-giner et al., Stabilization of a Nutraceutical Omega-3 Fatty Acid by Encapsulation in Ultrathin Electrosprayed Zein Prolamine.)

From Table 5, it shows that k rate decreases from 0.45 to 0. 34 per hour for free DHA and from 0.17 to 0.10 per hour in zein encapsulated DHA, with increasing %RH. Thus it reveals that the ω-3 deteriorates faster under dry conditions and stable at high %RH as well as matrix of zein provides excellent degradation protection against high water. This is supported by the fact that the zein prolamine can maintain water molecules in a closer contact with the bioactive components. This enhanced protection may implicit preservation of bioactive oxygen sensitive compounds and antioxidants, specifically in high foods like beverages, salads, or refrigerated meals. This shows that electrospinning technology is a potential new stage for enhanced stabilization by encapsulation of ω-3 PUFA and oil particles of DHA which is an oxygen-sensitive compound could be encapsulated in ultrathin layers of zein prolamine to enhance chemical stability.

Advantages and Disadvantages of Electrospinning:

It is noted that the electrospinning is a continuous process and leads to the formation of longer fibers as compared to fibers prepared by other physical or chemical methods.

Advantages:

• There is a possibility of scaling the process as well as to control the fiber morphology.
• Nearly, all kind of polymers with high molecular weight can be processed by electrospinning.
• The process of electrospinning has been applicable in many fields such as filtration, textile manufacturing, catalysts, medical applications, water and air filtration membrane.
• The different materials can easily have mixed together for spinning into fibers.
• The deposition of fibers on the collector to have a low static charge, they have been routinely deposited on surfaces such as glass, metal, water and microfibrous mat. There is ease of fiber deposition onto other substrates.

Disadvantages:

Electrospinning currently has some limitations:

• The variety of polymers are used during electrospinning process in order to prepare nanofibers is limited as well the structure and performance of nanofibers are not well researched.
• The process depends on many variables as well as the solvents which are used can be act as toxic.
• Electrospinning has been implemented at the industrial level in order to produce fibers, however, it is inferior to traditional methods due to its higher cost to produce fibers with large diameters. Moreover, it remains a challenge to fabricate fibers with diameter of less than 10nm by electrospinning, which is reported by the S, et al., 2010.
• It is highly problematic to obtain 3D structures and adequate size of pores needed for biomedical applications.
• The application of nanofibers has been limited due to their powdery after calcination, even though nanofibers have a potential application in the fields such as efficient catalysis, biological tissue engineering, energy devices, high temperature filtration etc.

Conclusion:

In this review, electrospinning technology in food related applications were discussed. The use of electrospinning technique for the encapsulation of food bioactive compounds aims to improve their stability, controlled release properties, shown great potential of making micro- and nanosized particles and fibers. The encapsulation efficiency, microstructure of the carrier structure and morphology are highly affected by the polymer solution characteristics and process parameters. The emerging electrospinning technology, are gaining popularity due to their high encapsulation efficiency, ability to preserve heat and oxidation sensitive ingredients. From the above it can also suggest that the fibers which are formed during the electrospinning is not widely explored in food industry and it is highly needed to optimize the operating conditions and solution properties for the effective encapsulation of various bioactives. Thus, the incorporation of bioactive compounds within the food matrices in which the food hydrocolloids act as encapsulated matrices is highly preferred, results in improving consumer perceptions for these formulations as well as achieve a better integration of the capsules in foodstuffs. There is highly demand to enhance our understanding on interactions of core and wall materials as well as on relationships between process parameters, solution properties and functionality of particles which is derived from the electrospinning technique. It is therefore important to analyze the relations between the particle microstructure, controlled release phenomena of the entrapped ingredients and stability of the core material i.e., upon storage in different environmental conditions and encountered in the gastro-intestinal tract under conditions. Although, the use of biopolymers often involves the electrospinning process due to their limited solubility, lack of sufficient molecular entanglements and poor viscoelasticity behavior in solution and therefore, it is needed to do more research to modify solution properties in order to improve the spinning of food grade biopolymers. Thus overall it can be said that the electrospinning process which is a simple and straight forward process, had shown the auspicious results as a productive, profitable, competent and valuable methods for the preparation of sub-micron structured encapsulated functional ingredient that may be highly use in food industry.

References:   

Aceituno-Medina, M., Mendoza, S., Rodríguez, B.A., Lagaron, J.M., LópezRubio, A., 2015. Improved antioxidant capacity of quercetin and ferulic acid during in-vitro digestion through encapsulation within food-grade electrospun fibers. Journal of Functional Foods, 12, 332-341.

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