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Engineering Aspects of Emulsification and Homogenization in the Food Industry

Rayner, Marilyn LU and Dejmek, Petr LU (2015) In Contemporary Food Engineering Series
Abstract
Preface

Motivation in short for this book
o Emulsions are used widely and produced in large volumes. Thus, emulsion formation or emulsification is an important unit-operation.
o Emulsification is of interest for a broad audience, both because of its influence on the functionality of emulsion based products, and because it is generally energy intensive running at low efficiency.
o Today, there is no comprehensive treatment available in English of emulsification describing state-of the-art technology and bringing together aspects from physical chemistry, formulation, fluid mechanics and chemical engineering. Together these aspects are the foundation needed for understanding emulsification at more than a rudimentary... (More)
Preface

Motivation in short for this book
o Emulsions are used widely and produced in large volumes. Thus, emulsion formation or emulsification is an important unit-operation.
o Emulsification is of interest for a broad audience, both because of its influence on the functionality of emulsion based products, and because it is generally energy intensive running at low efficiency.
o Today, there is no comprehensive treatment available in English of emulsification describing state-of the-art technology and bringing together aspects from physical chemistry, formulation, fluid mechanics and chemical engineering. Together these aspects are the foundation needed for understanding emulsification at more than a rudimentary level.
Emulsions and Emulsification
Emulsions can be found in a wide variety of food products such as in milk, cream, spreads, ice-creams, dressings and sauces. Emulsions are also common in many related areas such as in pharmaceuticals (e.g. topical formulation and nutritional emulsions) and in many house hold products (e.g. paints and cosmetics).
Emulsions bring many different forms of functionality to these products via their drops. Emulsion drops can be used to design bulk properties such as appearance, solubilization, mouth-feel, rheology, electrical properties and much more. Emulsions can also been used for bringing highly specific functionality to products such as in controlled delivery and in release of pharmaceuticals, in increasing bioavailability of nutrients, and in delivering flavor. All the above mentioned product properties are highly influenced by the characteristics of the emulsion. Emulsion character includes many different aspects such as drop size distribution and structure, type and amount of adsorbed emulsifiers etc. The properties of a given emulsion influenced to a large extent by the emulsification process through which it was created. Intensity and spatial/temporal distribution of the applied energy, time allowed for adsorption of surface active material and type of force acting to destabilize the interface will all influence the properties of the final emulsion. Hence, creating functional emulsions requires a fundamental and general understanding of the involved physical-chemical processes as well as specific information about the limits and possibilities for the different types of emulsifying equipment.
Emulsions are produced in large quantities. As an example approximately 270 million tons of liquid dairy products are annually treated with high-pressure homogenization (Tetra Pak Dairy Index Report, 2011). Emulsification is also a rather energy demanding unit operation, in absolute terms and particularly in relation to the theoretical energy requirements. The thermodynamically required energy for creating an emulsion is determined by the increase in free energy due to surface energy. For drops of a micrometer diameter this would amount to order of magnitude 103 J/m3, whereas the actual energy requirement for high-pressure homogenization is of order 107 J/m3. Taking the example of the dairy market this would correspond to roughly 600 GWh of energy of which only 0.01% is needed from a thermodynamic view. The conclusion from these large volumes and low efficiency must be that even a small incremental improvement in process operation would lead to substantial savings. Thus, there is a broad and large demand for better understanding emulsification processes.
The low thermodynamic efficiency is characteristic to all the high-energy methods such as rotor-stator based technologies, high-pressure homogenizers, microfluidization, ultra sonic systems and colloidal mills. Alternative low-energy flow processes, such as membrane based technology, have a higher efficiency but have not been able to reach the same productivity and extremely small drops as in the high energy technologies. However, the methods are developed continuously and an up to date comparison is much in need.
The emulsification process
The outcome of an emulsification process is generally a combination of two competing processes; disruption of the drop interface from dynamic destabilizing forces and thermodynamically driven coalescence. Studying the processes one at a time is not uncomplicated; the coupling is highly complex and poorly understood.
Emulsification also encompasses a large range of time-scales, from the very fast velocity fluctuations in high-pressure homogenization (100 MHz), ultrasonication (100 kHz), the adsorption times of surfactants (1 MHz) and macromolecular emulsifiers to the slower process of shear and drop detachment and all the way to the equilibrium thermodynamics which determines the long term fate of every emulsion.
From the discussion above it is clear that emulsification is truly a multidisciplinary phenomenon and an understanding must therefore spring from the combination of (at least) three different scientific specializations:
• Physical chemists have long studied interfaces between liquids and their relation to surface active molecules. This will be key aspects in the process of coalescence as well as understanding how surface active agents can aid in disruption.
• Fluid mechanics has developed theoretical and experimental methods for understanding the interplay between hydrodynamic forces and the drop interface. This is vital for understanding how differences in design can bring about different emulsification results.
• Research in chemical engineering has led to relations between operating conditions and emulsion characteristics and devised methods for measuring fragmentation or coalescence rates in bulk. This has obvious practical importance, but can also be used for comparison to the predictions from the more fundamental disciplines.
A comprehensive discussion on emulsification methods and their application must bring together aspects from all these different specialties.
The need for new literature on emulsification
The present literature on emulsification is to a large degree is influenced by the abovementioned division between the different topics. Many of the more general text books on surface and colloidal chemistry contains chapters on emulsions (e.g. Cosgrove, 2010; Goodwin, 2004; Holmberg et al., 2003). There is also a rather voluminous literature on emulsions per se, both in general (e.g. Sjöblom, 2006; Binks, 1998; Becher, 1983) and for food applications (McClements, 2005; Friberg & Larsson, 1997; Dickinson & Stainsby, 1992). These do, however, to a large extent focus on the physiochemical aspects of emulsions and the emulsification process in itself is not treated in sufficient detail. Similarly, books from the fluid dynamics section dealing with multiphase flow sometimes discuss implications on drop formation (e.g. Clift et al., 1978), however without the coupling to technical considerations/design and the advances in physical chemistry.
Steps towards this synthesis of different aspects can be found in the older literature (e.g. Gopal, 1968) and substantial advances were made by Walstra in a series of book chapters and review articles during the 80: ies and 90: ies (Walstra, 1983; Walstra, 1993; Walstra & Smulders, 1998), however, these works are now beginning to be outdated especially in relation to the coupling between process design and obtained emulsification result. Today, there is no comprehensive treatment of emulsification including state-of-the art developments and integration of all three aspects available in English. This book is aimed at filling that gap. The perspective will be that of the unit emulsification process, using fundamental theory from different fields to discuss design and function of different emulsification techniques.
References
Becher, P. (1983). Encyclopedia of Emulsion Technology. Marcel Dekker Inc.
Binks, B.P. (1998). Modern Aspects of Emulsion Science. Royal Society of Chemistry.
Clift, R., Grace, J.R., Weber, M.E. (1978). Bubbles, Drops and Particles. Academic Press.
Cosgrove, T. (2010). Colloid Science: Principles, Methods and Applications. John Wiley & Sons.
Dickinson, E., Stainsby, G. (1982). Colloids in Food. Applied Science Publishers.
Friberg S., Larsson, K. (1997). Food Emulsions. Marcel Dekker Inc.
Goodwin, J.W. (2004). Colloids and Interfaces with Surfactants and Polymers. John Wiley & Sons Ltd.
Gopal, E.S.R. (1968). Principles of Emulsion Formation. In: P. Sherman (ed.), Emulsion Science. Academic Press.
Holmberg, K., Jönsson, B., Kronberg, B., Lindman, B. (2003). Surfactants and Polymers in Aqueous Solution. Wiley,
McClements, J.D. (2005). Food Emulsions. CRC Press.
Sjöblom, J. (2006). Emulsions and Emulsion Stability. Taylor & Francis.
Tetra Pak Dairy Index Report, Issue 4, 2011
Walstra, P. (1983). Formation of Emulsions. In: P. Beacher (ed.), Encyclopedia of Emulsion Technology volume I: Basic Theory. Marcel Dekker Inc.
Walstra, P. (1993). Principles of Emulsion Formation. Chemical Engineering Science 48, 333-349.
Walstra, P, Smulders, P.E.A. (1998). Emulsion Formation. In: B.P. Binks (ed.), Modern Aspects of Emulsion Science. Royal Society of Chemistry. (Less)
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Contemporary Food Engineering Series
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@misc{d56b6b0e-8b31-48ac-a596-3f335ad3e15e,
  abstract     = {Preface<br>
<br>
Motivation in short for this book<br>
o	Emulsions are used widely and produced in large volumes. Thus, emulsion formation or emulsification is an important unit-operation.   <br>
o	Emulsification is of interest for a broad audience, both because of its influence on the functionality of emulsion based products, and because it is generally energy intensive running at low efficiency.  <br>
o	Today, there is no comprehensive treatment available in English of emulsification describing state-of the-art technology and bringing together aspects from physical chemistry, formulation, fluid mechanics and chemical engineering. Together these aspects are the foundation needed for understanding emulsification at more than a rudimentary level. <br>
Emulsions and Emulsification<br>
Emulsions can be found in a wide variety of food products such as in milk, cream, spreads, ice-creams, dressings and sauces. Emulsions are also common in many related areas such as in pharmaceuticals (e.g. topical formulation and nutritional emulsions) and in many house hold products (e.g. paints and cosmetics).<br>
Emulsions bring many different forms of functionality to these products via their drops. Emulsion drops can be used to design bulk properties such as appearance, solubilization, mouth-feel, rheology, electrical properties and much more. Emulsions can also been used for bringing highly specific functionality to products such as in controlled delivery and in release of pharmaceuticals, in increasing bioavailability of nutrients, and in delivering flavor. All the above mentioned product properties are highly influenced by the characteristics of the emulsion. Emulsion character includes many different aspects such as drop size distribution and structure, type and amount of adsorbed emulsifiers etc. The properties of a given emulsion influenced to a large extent by the emulsification process through which it was created. Intensity and spatial/temporal distribution of the applied energy, time allowed for adsorption of surface active material and type of force acting to destabilize the interface will all influence the properties of the final emulsion. Hence, creating functional emulsions requires a fundamental and general understanding of the involved physical-chemical processes as well as specific information about the limits and possibilities for the different types of emulsifying equipment. <br>
Emulsions are produced in large quantities. As an example approximately 270 million tons of liquid dairy products are annually treated with high-pressure homogenization (Tetra Pak Dairy Index Report, 2011). Emulsification is also a rather energy demanding unit operation, in absolute terms and particularly in relation to the theoretical energy requirements. The thermodynamically required energy for creating an emulsion is determined by the increase in free energy due to surface energy. For drops of a micrometer diameter this would amount to order of magnitude 103 J/m3, whereas the actual energy requirement for high-pressure homogenization is of order 107 J/m3. Taking the example of the dairy market this would correspond to roughly 600 GWh of energy of which only 0.01% is needed from a thermodynamic view. The conclusion from these large volumes and low efficiency must be that even a small incremental improvement in process operation would lead to substantial savings. Thus, there is a broad and large demand for better understanding emulsification processes. <br>
The low thermodynamic efficiency is characteristic to all the high-energy methods such as rotor-stator based technologies, high-pressure homogenizers, microfluidization, ultra sonic systems and colloidal mills. Alternative low-energy flow processes, such as membrane based technology, have a higher efficiency but have not been able to reach the same productivity and extremely small drops as in the high energy technologies. However, the methods are developed continuously and an up to date comparison is much in need. <br>
The emulsification process<br>
The outcome of an emulsification process is generally a combination of two competing processes; disruption of the drop interface from dynamic destabilizing forces and thermodynamically driven coalescence. Studying the processes one at a time is not uncomplicated; the coupling is highly complex and poorly understood. <br>
Emulsification also encompasses a large range of time-scales, from the very fast velocity fluctuations in high-pressure homogenization (100 MHz), ultrasonication (100 kHz), the adsorption times of surfactants (1 MHz) and macromolecular emulsifiers to the slower process of shear and drop detachment and all the way to the equilibrium thermodynamics which determines the long term fate of every emulsion.<br>
From the discussion above it is clear that emulsification is truly a multidisciplinary phenomenon and an understanding must therefore spring from the combination of (at least) three different scientific specializations:<br>
•	Physical chemists have long studied interfaces between liquids and their relation to surface active molecules. This will be key aspects in the process of coalescence as well as understanding how surface active agents can aid in disruption. <br>
•	Fluid mechanics has developed theoretical and experimental methods for understanding the interplay between hydrodynamic forces and the drop interface. This is vital for understanding how differences in design can bring about different emulsification results. <br>
•	Research in chemical engineering has led to relations between operating conditions and emulsion characteristics and devised methods for measuring fragmentation or coalescence rates in bulk. This has obvious practical importance, but can also be used for comparison to the predictions from the more fundamental disciplines. <br>
A comprehensive discussion on emulsification methods and their application must bring together aspects from all these different specialties. <br>
The need for new literature on emulsification <br>
The present literature on emulsification is to a large degree is influenced by the abovementioned division between the different topics. Many of the more general text books on surface and colloidal chemistry contains chapters on emulsions (e.g. Cosgrove, 2010; Goodwin, 2004; Holmberg et al., 2003). There is also a rather voluminous literature on emulsions per se, both in general (e.g. Sjöblom, 2006; Binks, 1998; Becher, 1983) and for food applications (McClements, 2005; Friberg &amp; Larsson, 1997; Dickinson &amp; Stainsby, 1992). These do, however, to a large extent focus on the physiochemical aspects of emulsions and the emulsification process in itself is not treated in sufficient detail. Similarly, books from the fluid dynamics section dealing with multiphase flow sometimes discuss implications on drop formation (e.g. Clift et al., 1978), however without the coupling to technical considerations/design and the advances in physical chemistry. <br>
Steps towards this synthesis of different aspects can be found in the older literature (e.g. Gopal, 1968) and substantial advances were made by Walstra in a series of book chapters and review articles during the 80: ies and 90: ies (Walstra, 1983; Walstra, 1993; Walstra &amp; Smulders, 1998), however, these works are now beginning to be outdated especially in relation to the coupling between process design and obtained emulsification result. Today, there is no comprehensive treatment of emulsification including state-of-the art developments and integration of all three aspects available in English. This book is aimed at filling that gap. The perspective will be that of the unit emulsification process, using fundamental theory from different fields to discuss design and function of different emulsification techniques. <br>
References<br>
Becher, P. (1983). Encyclopedia of Emulsion Technology. Marcel Dekker Inc. <br>
Binks, B.P. (1998). Modern Aspects of Emulsion Science. Royal Society of Chemistry.  <br>
Clift, R., Grace, J.R., Weber, M.E. (1978). Bubbles, Drops and Particles. Academic Press.<br>
Cosgrove, T. (2010). Colloid Science: Principles, Methods and Applications. John Wiley &amp; Sons.<br>
Dickinson, E., Stainsby, G. (1982). Colloids in Food. Applied Science Publishers.<br>
Friberg S., Larsson, K. (1997). Food Emulsions. Marcel Dekker Inc. <br>
Goodwin, J.W. (2004). Colloids and Interfaces with Surfactants and Polymers. John Wiley &amp; Sons Ltd. <br>
Gopal, E.S.R. (1968). Principles of Emulsion Formation. In: P. Sherman (ed.), Emulsion Science. Academic Press.<br>
Holmberg, K., Jönsson, B., Kronberg, B., Lindman, B. (2003). Surfactants and Polymers in Aqueous Solution. Wiley,  <br>
McClements, J.D. (2005). Food Emulsions. CRC Press.<br>
Sjöblom, J. (2006). Emulsions and Emulsion Stability. Taylor &amp; Francis. <br>
Tetra Pak Dairy Index Report, Issue 4, 2011<br>
Walstra, P. (1983). Formation of Emulsions. In: P. Beacher (ed.), Encyclopedia of Emulsion Technology volume I: Basic Theory. Marcel Dekker Inc.<br>
Walstra, P. (1993). Principles of Emulsion Formation. Chemical Engineering Science 48, 333-349. <br>
Walstra, P, Smulders, P.E.A. (1998). Emulsion Formation. In: B.P. Binks (ed.), Modern Aspects of Emulsion Science. Royal Society of Chemistry.},
  author       = {Rayner, Marilyn and Dejmek, Petr},
  isbn         = {978-1-4665-8043-5},
  language     = {eng},
  pages        = {332},
  publisher    = {ARRAY(0x8e85578)},
  series       = {Contemporary Food Engineering Series},
  title        = {Engineering Aspects of Emulsification and Homogenization in the Food Industry},
  year         = {2015},
}