Probiotic bacteria have been shown to provide numerous health benefits, but their efficacy can be affected by processing, storage, and the gastrointestinal tract. To address this issue, microencapsulation technology has been utilized to enhance the survival and stability of probiotics. Membrane emulsification is a precise and energy-efficient method that allows for the production of uniformly sized droplets on demand, providing greater control over emulsion size and morphology. Encapsulation of Lactobacillus casei YIT 9018 using membrane emulsification has been recently investigated. The resulting microcapsules had excellent viability and stability, with a constant viable count of encapsulated cells through incubation time and a higher viability of encapsulated cells compared to non-encapsulated cells during a storage stability test. Membrane emulsification technology has broad applications in the food, pharmaceutical, and cosmetic industries. This innovative technique can revolutionize emulsion formation and provide novel opportunities for product design and development. This report highlights the potential of membrane emulsification in the microencapsulation of probiotics, which could improve the delivery and effectiveness of probiotics in various products.
Sheet Pile Wall Design and Construction: A Practical Guide for Civil Engineer...
Membrane emulsification
1. 1
Food Engineering
NFS 4005
Graduate Student Presentation
Professor Sathivel, Subramaniam
Title: Probiotic Microencapsulation
by Membrane Emulsification Technique: A
New Trend in Food Engineering
Processing
Tharindu Trishan Dapana Durage
04/12/2023
2. 2
Abstract
Probiotic bacteria have been shown to provide numerous health benefits, but their efficacy can
be affected by processing, storage, and the gastrointestinal tract. To address this issue,
microencapsulation technology has been utilized to enhance the survival and stability of
probiotics. Membrane emulsification is a precise and energy-efficient method that allows for
the production of uniformly sized droplets on demand, providing greater control over emulsion
size and morphology. Encapsulation of Lactobacillus casei YIT 9018 using membrane
emulsification has been recently investigated. The resulting microcapsules had excellent
viability and stability, with a constant viable count of encapsulated cells through incubation
time and a higher viability of encapsulated cells compared to non-encapsulated cells during a
storage stability test. Membrane emulsification technology has broad applications in the food,
pharmaceutical, and cosmetic industries. This innovative technique can revolutionize emulsion
formation and provide novel opportunities for product design and development. This report
highlights the potential of membrane emulsification in the microencapsulation of probiotics,
which could improve the delivery and effectiveness of probiotics in various products.
4. 4
1. INTRODUCTION
1.1 Overview
Probiotics are described by the World Health Organization (WHO) as “live organism, which
when administered in adequate amounts confer health benefits to the host” (IGEM, 2009).
However, the significant reduction in their viability during food storage and gastrointestinal
transit limits their effectiveness (Razavi et al., 2021). This can result in a decreased number of
viable probiotics reaching the colon, which is the primary site of their action. To overcome this
challenge, microencapsulation can be used to enhance the resistance of probiotics to
unfavorable conditions (Yao et al., 2020). This technology involves encapsulating the
probiotics with food-grade materials to protect them from harsh environmental conditions and
increase their mucoadhesive properties. A range of oral delivery systems, including embedding
and coating systems, have been developed to increase the level of probiotics reaching the colon.
Microencapsulation of probiotics is important because it can increase their ability to colonize
the colon and provide health benefits. The stress-tolerance properties of microencapsulated
probiotics and the efficiency of probiotic delivery systems can be evaluated using suitable in
vitro and in vivo models (Kailasapathy, 2006; Rajam & Subramanian, 2022).
1.2 Probiotic encapsulation techniques
Numerous encapsulation technologies are currently available to protect probiotic cells during
food production, processing, and storage. However, before selecting a specific technology,
several critical factors should be considered, including: (i) the conditions that affect the
viability of probiotics, (ii) the processing conditions used during food production, (iii) the
storage conditions of the food product containing the encapsulated probiotics prior to
consumption, (iv) the necessary particle size and density for proper incorporation into the food
product, (v) the triggers and mechanisms of release, and (vi) the cost constraints (Heidebach et
al., 2012; Rajam & Subramanian, 2022).
In terms of conditions affecting probiotic viability, it is important to consider factors such as
moisture content, high temperatures, and agitation. To minimize the impact of these factors,
food matrices should be produced under mild conditions, with low temperature, controlled
agitation, small presence of oxygen, and moderate pH. Before incorporating particles into food
matrices, it is essential to determine the most suitable storage conditions, which are often tested
at 4°C or room temperature. Particle size is also a crucial consideration, as it must be sufficient
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to protect probiotics without causing gritty mouthfeel. Soft, rounded particles have been shown
to be imperceptibly gritty up to 80 µm. The mechanism of release depends on the encapsulation
technology and material, with pH changes, chelating agents, and enzymatic action being the
most common triggers. Finally, the balance between cost and benefit should also be taken into
account, as some technologies may require specific devices or materials that increase
production costs (Martín et al., 2015).
1.2.1 Extrusion technique
This technique involves forcing a mixture of bacteria and a matrix material through a small
orifice to create a capsule. The high shear forces during extrusion help to break down bacterial
clusters and disperse the bacteria throughout the matrix material.
1.2.2 Emulsion technique
In this technique, bacteria are mixed with a matrix material and then dispersed in an aqueous
phase to create small droplets that are subsequently hardened to form capsules. The matrix
material stabilizes the droplets and protects the bacteria during subsequent processing steps.
1.2.3 Fluid bed technique
This technique involves suspending bacteria in a stream of hot air while coating them with a
matrix material to form capsules. The hot air helps to evaporate the solvent and solidify the
matrix material around the bacteria.
1.2.4 Rennet-gelled protein encapsulation technique
In this technique, proteins are used to encapsulate bacteria by forming a gel matrix around the
cells. Rennet enzymes are added to the protein solution to create a stable gel matrix.
1.2.5 Freeze drying technique
This technique involves freezing bacteria and then dehydrating them under vacuum to create a
dry powder that can be easily stored. The frozen bacteria are subjected to sublimation to remove
the water, which helps to preserve their viability.
1.2.6 Spray drying technique.
This technique involves dispersing bacteria in a solution and then spraying them into a hot
drying chamber to create small particles. The hot air in the drying chamber helps to evaporate
the solvent and form dry particles.
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1.2.7 Hybridization system technique
This technique involves encapsulating bacteria in a hydrogel matrix and then further coating
them with a polymer layer to enhance stability and protect against environmental conditions.
The hydrogel matrix provides mechanical stability, and the polymer coating helps to prevent
degradation.
1.2.8 Impinging aerosol technology technique
In this technique, bacteria are dispersed in a solution and then sprayed onto a solid substrate to
create a thin film. The substrate helps to support the bacteria and facilitate their encapsulation.
1.2.9 Electrospinning technique
In this technique, bacteria are suspended in a solution and then electrospun to create a fibrous
scaffold that can be further coated with a polymer layer to form capsules. The electrospinning
process generates a high electric field that draws the solution through a spinneret, creating
fibers that can be manipulated into various shapes.
Emulsification techniques are the most widely used techniques over other techniques,
considering their cost, simplicity, mild process conditions, and possibility of yielding
microparticles. Membrane emulsification and microfluidic emulsification are two recently
developed technologies to encapsulate probiotics and apply them in the food industry.
1.3 Objectives
The overall objective of this report is to discuss the membrane emulsification technique, its
engineering aspects, and its potential use in the food industry.
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2. MEMBRANE EMULSIFICATION TECHNIQUE
2.1 Overview
Membrane emulsification is an innovative technique that deviates from the conventional
approach of repeatedly breaking down droplets to smaller sizes. Instead, it enables the
production of droplets at the desired final size, individually and on demand. This 'made-to-
measure' approach has several advantages over the traditional method, such as reduced energy
consumption and minimized thermal and shear stresses on the constituents of the emulsion.
Moreover, it provides greater control over the size and distribution of the emulsion droplets,
allowing for the creation of customized emulsion structures in a single step. The membrane
emulsification process involves the use of microporous membranes to generate droplets of
uniform size and morphology. The resulting emulsions have superior stability, uniformity, and
functionality, making them ideal for various applications in the food, pharmaceutical, and
cosmetic industries. Therefore, membrane emulsification is an evolving technology that has
the potential to revolutionize emulsion formation and provide novel opportunities for product
design and development (Joscelyne & Trägårdh, 2000).
Figure 1. Flow diagram of membrane emulsification (Camelo-Silva et al. (2022)
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2.2 Principal Mechanism and its Engineering Aspects
2.2.1 Overview
Membrane emulsification is a process that utilizes microporous membranes to form uniform
droplets or emulsions with controlled droplet-size distribution. There are two types of
membrane emulsification: direct membrane emulsification (DME) and premix membrane
emulsification. In DME, the disperse phase is pressed through a microporous membrane, and
droplets are formed at the opening of the pore on the other side of the membrane, which is in
contact with the continuous phase. Droplets can detach either by spontaneous deformation or
by shearing by the continuous phase flowing parallel to the surface. In premix emulsification,
the predominant formation mechanism is droplet disruption within the pore (Giorno et al.,
2009).
The droplet size, its dispersion, and the droplet-formation time depend on several parameters,
such as membrane parameters, operating parameters, and phase parameters. Membrane
parameters include pore-size distribution, pore-border morphology, number of active pores,
porosity, and wetting properties of the membrane surface. Operating parameters include
crossflow velocity, transmembrane pressure, disperse-phase flow, temperature, and the
membrane module used. Phase parameters include dynamic interfacial tension, viscosity,
density of processed phases, emulsifier types, and concentration (C. Charcosset et al., 2004;
Catherine Charcosset, 2009; Giorno et al., 2009)
The production of monodisperse emulsions is related to the size distribution of membrane pores
and their relative spatial distribution on the membrane surface. The geometry of the module in
which the membrane is located is also an important parameter since it determines, in
conjunction with the crossflow velocity, the wall shear stress. The droplet-size distribution and
disperse-phase percentage determine the emulsion properties characterizing the final
formulation for an intended use (Giorno et al., 2009).
Membrane emulsification is an efficient process, and the energy density requirement is low
with respect to other conventional mechanical methods, especially for emulsions with droplet
diameters smaller than 1 mm. The lower energy density requirement improves the quality and
functionality of labile emulsion ingredients, such as bioactive molecules, as the shear stresses
calculated for a membrane system are much less, making it possible to process shear-sensitive
ingredients.
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2.2.2 Probiotic encapsulation
The review by Camelo-Silva et al. (2020) states that the basis of this method for
microencapsulating probiotic bacteria is driving the dispersed phase of an emulsion through a
membrane's pores into the continuous phase. Droplets expand at pore exits until they reach a
particular size and then separate. Shear pressures can also be used to encourage the separation
of these droplets from the surface of the membrane. A continuous phase envelope forms on the
surface as the hydrocolloid droplets separate, creating the emulsion (W/O). The hydrocolloid
gelation is then made possible by adding this emulsion to an acetic acid solution.
The review has also discussed the most important factors to be considered in membrane
emulsification technique related to probiotic encapsulation as follows:
2.2.3 Pore size
The average pore size has a big impact on droplet size. It is assumed that there is a linear
relationship (Eq. 1), where c is dependent on the operating circumstances, exists between the
droplet diameter, dg, and the average membrane pore diameter, dp. If the membrane's pore size
distribution is narrow enough, monodisperse emulsions are able to form.
Eq. 1
2.2.4 Membrane wettability
The mean size as well as the distribution of droplets are influenced by membrane wettability.
Emulsions having a high degree of dispersion and greater average droplet size frequently occur
on membranes that are not thoroughly wetted from the continuous phase. To ensure the
effective creation of monodispersed emulsions, pore wetting by the dispersed phase needs to
be avoided. To reduce the spread of the dispersed phase on the membrane, the membrane in
the formation of W/O emulsions should be fully moistened by the continuous oil phase
(Catherine Charcosset, 2009).
2.2.5 Membrane surface porosity
Since it controls the distance between two neighboring holes, the membrane surface's porosity
is crucial. According to some research, pores should be spaced apart by a factor of 10 times
their size. This rule prevents two nearby developing droplets from coming into touch with one
another, which might result in coalescence.
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2.2.6 Emulsifier
In order to create an emulsion, the presence of emulsifiers or surfactants in the phases is
important for two reasons: first, it lowers the interfacial tension between the oil and the water,
which makes droplet distribution easier and, in the case of membranes, lowers the minimum
emulsification pressure; second, it stabilizes the drops, so they don't coalesce. The primary
emulsifying substances used to stabilize probiotic emulsions include Sorbitan monooleate,
Polysorbates, PGPR, and Panodan SDK. Lecithin and Saccharomyces cerevisiae bioemulsifer
have also been investigated as probiotic emulsion surfactants. The dispersion and ultimate
droplet size of probiotic emulsions produced by membrane emulsification have not yet been
studied in the literature in relation to emulsifier type or concentration (Matoušková et al., 2016).
2.2.7 Viscosity
The effectiveness of the membrane emulsification process is significantly impacted by the
viscosity of the dispersed phase. In accordance with Darcy's law (Eq. 2), the dispersed phase's
flux (Jd) is inversely proportional to its viscosity, meaning that when the viscosity is high, the
flux will be low and the droplet diameter will be larger than the average pore diameter.
Eq. 2
where K is the permeability of the membrane, ▲Ptm is the transmembrane pressure, µ is the
viscosity of the dispersed phase, and L is the membrane thickness.
2.2.8 Shear rate
The use of continuous phase shear stresses facilitates the separation of the dispersed phase
droplets, which are generated at the membrane/continuous phase contact, as was previously
indicated. As the shear stress rises, the droplet size decreases. To reduce the number of
microorganisms that die during the encapsulation of probiotics, excessive shear rates should be
avoided. Cell lysis can result from damaged cell walls caused by high shear rates. According
to certain research, shear rates between 200 and 250 rpm can be recommended (Vinner et al.,
2019).
2.2.9 Hydraulic pressure
Hydraulic pressure is needed during the membrane emulsification process to push the dispersed
phase through the membrane and onto the continuous phase side. The variation between the
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pressure within the phase to be dispersed (Pd) and the mean pressure in the continuous phase
which passes through the module of the membrane is known as the transmembrane pressure
(▲Ptm) (Eq. 3).
Eq. 3
where Pc,in and Pc,out are, respectively, the pressures of the flowing continuous phase at the
membrane module's intake and outflow. Given that the membrane pores are assumed to be
perfect cylinders, it is possible to calculate the applied transmembrane pressure using the
capillary pressure (Eq. 4):
Eq. 4
where dp is the average pore diameter, Pc is the critical pressure, is the O/W interfacial tension,
is the contact angle of the oil droplet against the membrane surface thoroughly wetted with the
continuous phase and is the O/W interfacial tension.
Darcy's law (Eq. 2) states that an increase in pressure will result in an increase in the dispersed
phase flux across the membrane. This is because the dispersed phase flux, Jd, is correlated with
the difference in pressure applied to the membrane. Since high fluxes tend to create droplets
with bigger size distributions and diameters due to the rise in the coalescence of the droplets
on the membrane surface, the pressure applied to the membrane must be carefully selected.
Additionally, very high fluxes will produce distributed phase jets rather than probiotic-
containing droplets. It is also important to note that probiotic cells' plasmatic membranes can
be harmed by extremely high pressures, which lowers the number of viable cells.
The size of the droplets formed in a dispersion dead-end cell has been predicted using a
mathematical model (Eq. 5)(Consoli et al., 2020). The capillary force (function of interfacial
tension/ pore size) and the drag force (function of shear stress / droplet size) acting on a severely
deformed droplet at a membrane pore are balanced to determine the droplet diameter (x).
Eq. 5
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where rp is the pore radius, T is the maximal shear stress, and γ is the interfacial tension. The
maximal shear stress over the entire membrane area is calculated according to Eq. 6.
Eq. 6
where µc is the continuous phase viscosity, ὠ is the angular velocity, rc is the critical radius,
which corresponds to the point where the rotation changes from a forced vortex to a free vortex,
at which shear stress is greatest, calculated using Eq. 8, and δ is the boundary layer thickness,
given by Eq. 7.
Eq. 7
where D is the stirrer diameter, T is the tank (cell) diameter, b is the blade height, nb is the
number of impeller blades, and Re is the Reynolds number, given by Eq. 9.
Eq. 8
Eq. 9
where ρ is the density of the fluid, V is the average flow velocity in the channel, D is the diameter of
the channel, and µ is the viscosity of the fluid.
Figure 2. Important parameters for membrane emulsification based probiotic encapsulation.
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2.3 Example studies
2.3.1 Study 1: This study was done by (Morelli et al., 2017),
Dispersion Cell ME (membrane emulsification) technique was used to produce water-in-oil
(W/O) emulsions with hydrophobic membranes of 30 µm pore diameter and 200 µm pore
spacing. Aqueous dispersed phases composed of gelatin and chitosan mixtures, or just gelatin
with yeast cells, were used as an example of encapsulating a living organism. The oil
continuous phase used to inject the encapsulated cells was 2 wt% SPAN 80 in kerosene.
Monodispersed emulsions with coefficient of variance below 25% were obtained with drops
sized between 70 and 340 µm. The emulsion drop size and uniformity were not affected by the
addition of the cells in the disperse phase, and the yeast cell encapsulation efficiency was 100%.
The process of solid microparticle formation consisted of thermal gelation and/or ionic
crosslinking using sodium hexametaphosphate. Eudragit S100 coating was performed on
gelatin microparticles encapsulating cells using the oil-in-oil solvent evaporation method. The
dissolution of the yeast loaded particles was checked at different time intervals in acidic (pH
1.2), neutral (pH 7), and slightly basic (pH 8) environments. The Eudragit coated particles
survived the acidic environment for 2 h without dissolving or releasing the yeast cells. After
surviving acidic conditions, dissolution of the particles occurred at pH 7 within 3 h and within
1 h at pH 8, with subsequent yeast release. The cell viability after release was demonstrated by
the ability of the yeast to metabolize up to 90% of glucose added to the growth medium in 24
h. Yeast cells were chosen as a proof of concept showing that ME is a promising method for
cell encapsulation, and the process can be applied to a variety of micro-organisms according to
the cell type and specific requirements, provided that the membrane structure is non-tortuous
as this does not filter the yeast cells from the injected phase within the matrix of the membrane.
The Polytetrafluoroethylene (PTFE) coated membrane gave smaller drops than the Fluoro
Alkyl Silane (FAS) coated membrane, but the PTFE coated membrane is less favorable for
repeated use after cleaning.
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2.3.2 Study 2: This study was done by (Song et al., 2003),
The study aimed to encapsulate Lactobacillus casei YIT 9018 using microporous glass (MPG)
membrane emulsification. The process parameters of membrane emulsification were varied to
produce a stable emulsion. The continuous phase was a highly viscous alginate solution in
which the viscosity was 20 times higher than the viscosity of water. In order to examine the
effect of membrane pore size (Dm) on droplet diameter (Dp), MPG membranes with different
pore dm were used. Results showed that Dp varied with Dm,
and a narrow size distribution of emulsion droplets was
obtained. Furthermore, a linear relationship existed between
the droplet size and the microcapsule size. The microcapsule
size was approximately 1.5 times larger than the droplet
diameter in the emulsion.
In the study, the viability of the encapsulated cells was
tested under artificial gastric acid and bile. The results
showed that the viable count of encapsulated cells was
constant through the incubation time, while the count of
non-encapsulated cells was significantly decreased. This
indicates that encapsulation is effective in protecting the
probiotic cells from harsh digestive conditions in the
stomach and intestine.
Moreover, a storage stability test was performed at different
temperatures to test the viability of the encapsulated cells.
The results showed that the viability of encapsulated cells
was 3 to 5 log cycles higher than the viability of non-
encapsulated cells. This indicates that encapsulation using
MPG membrane emulsification can improve the shelf-life
and stability of probiotics.
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2.4 Pros and cons
One of the significant advantages of this technique is the consistent droplet size, which is
crucial in the food industry for creating stable emulsions with desirable textural and sensory
properties. Additionally, emulsions produced by membrane emulsification have increased
stability due to the small droplet size and homogeneity of the emulsion system. This technique
is also highly efficient and requires less energy and time compared to traditional emulsification
methods. Furthermore, it reduces the amount of waste generated during the production process,
resulting in cost savings and environmental benefits. Another advantage of membrane
emulsification is its flexibility as it can be used with a variety of different materials and can be
easily scaled up for industrial production.
However, there are also some limitations to using membrane emulsification in the food
industry. Firstly, the initial investment required to set up a membrane emulsification system
can be high, which may be a barrier for smaller companies or start-ups. Additionally, the
technique requires specialized equipment and expertise, which may limit its accessibility to
smaller companies or those with limited resources. Membrane fouling is a common issue in
membrane emulsification, which can lead to reduced performance and increased maintenance
costs. Membrane emulsification can also be sensitive to changes in the product being
emulsified, such as changes in viscosity or composition, which may affect droplet size and
stability. Finally, membrane emulsification is typically used for the production of small
droplets, which may not be suitable for all applications.
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3. CONCLUSION
Membrane emulsification technique has shown significant potential in the food industry for the
production of stable emulsions with small droplet sizes. This technique can also be applied to
the encapsulation of probiotics in food products. Encapsulation is a crucial step in the
development of probiotic food products as it protects the probiotics from harsh environments
and ensures their survival during processing, storage, and consumption. The use of membrane
emulsification for probiotic encapsulation can result in improved probiotic viability, stability,
and delivery. Additionally, it can provide a way to produce uniform-sized droplets that can
enhance the sensory properties and texture of the final product. Therefore, it can be
recommended that the food industry explore the use of membrane emulsification for the
encapsulation of probiotics in food products to improve their quality and health benefits.
Further research can help to optimize the process conditions, such as the choice of membrane,
emulsifier, and processing parameters, to ensure the successful encapsulation of probiotics and
to enhance the functionality of the final product.
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