Emulsifiers in Food Technology

Viggo Norn, Viggo Norn

• Publisher: Wiley-Blackwell
• Year: 2014
• ISBN:
  9781118921258
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

EMULSIFIERS IN FOOD TECHOLOGY

Emulsifiers are essential components of many industrial food recipes. They have the ability to act at the interface between two phases, and so can stabilize the desired mix of oil and water in a mayonnaise, ice cream or salad dressing. They can also stabilize gas/liquid mixtures in foams. More than that, they are increasingly employed in textural and organoleptic modification, in shelf life enhancement, and as complexing or stabilizing agents for other components, such as starch or protein. Applications include modifying the rheology of chocolate, the strengthening of dough, crumb softening and the retardation of staling in bread.

Emulsifiers in Food Technology, second edition, introduces emulsifiers to those previously unfamiliar with their functions and provides a state of the art account of their chemistry, manufacture, application and legal status for more experienced food technologists. Each chapter considers one of the main chemical groups of food emulsifiers. Within each group, the structures of the emulsifiers are considered, together with their modes of action. This is followed by a discussion of their production, extraction and physical characteristics, together with practical examples of their application. Appendices cross-reference emulsifier types with applications, and give E-numbers, international names, synonyms and references to analytical standards and methods.

Praise for the first edition of Emulsifiers in Food Technology:

"Very informative … provides valuable information to people involved in this field." International Journal of Food Science & Technology

"A good introduction to the potential of emulsifiers in food technology … a useful reference source for scientists, technologists and ingredients suppliers." Chemistry World

"A useful guide to the complicated array of emulsifiers presently available and their main functionalities and applications." International Dairy Journal

Chapter 1
Introduction to Food Emulsifiers and Colloidal System

Viggo Norn

Palsgaard A/S, Palsgaard vej 10, DK-7130 Juelsminde, Denmark

1.1 Introduction

This chapter provides a short introduction to the most important parameters involved in multiphase system. As an introduction, the forces that interact between individual molecules are briefly mentioned, followed by a short review of the factors responsible for formation of, and stability of, systems consisting of two or more incompatible phases, as illustrated by emulsions and cake batters. This illustrates how forces related to amphiphilic substances like food emulsifiers on a molecular level can be thought of as complex foods, or how models of food can be formulated and described to get an idea of how food emulsifiers can act in the complex food and benefit from the emulsifiers. For monographs dealing extensively with interface chemistry see, for example, Israelachivili [1] or McClements [2].

Food and food ingredients are made up of a huge number of different types of molecules, and most foods will be amalgamates of numerous different constituents, ranging from small-sized molecules to much bigger biopolymers, altogether forming the compounded food. This means a substance or individual component will be associated with a number of similar, as well as different, substances, and together they will give the food its texture, sensory and other characteristics. In the food or food ingredient, individual components can be present in various forms—either in similar constituents, or as a mix of discrete components. Often, they will be organized into separate structural entities at the interface between different phases, or may be dispersed as separate accumulated bodies or aggregates in a bulk phase. The food components can also be elements of a internal three-dimensional lattice, forming an integrated structure and thus giving the food the characteristic physical and chemical properties recognized as texture and organoleptic profile.

This means that the properties of food originate from the substances present. Due to intermolecular interactions and forces combined with external factors like temperature, stress, etc. they combine into structural organizations like dispersions, foams, emulsions, gels and other composite systems.

At the molecular level, individual molecules will interact due to a number of attractive as well as repulsing forces see Table 1.1 page 3 between the molecules. These forces are recognized as Van der Waal forces and, compared to intramolecular forces (i.e. covalent bonding), are approximately two decades weaker. However, although weak, they play and important role when considering interaction within neighbour compounds. The Van der Wall forces can be classified into three distinct groups: Orientation forces, Debye forces and London forces.

Table 1.1 Some molecular and intermolecular forces.

Type	Energy	Ratio vs distance	Type of forces
Covalent	<120 kJ	1/r (strong)	electrons are shared
Electrostatic	40–90 kJ	1/r (strong)	ion-ion, ion-dipole, dipole-dipole
Hydrogen bonds	6–25 kJ	1/r^6 (weak)	dipole-dipole + van der Waal
Van der Waal	2–10 kJ	1/r^6 (weak)	induction, rotation, dispersion

The first of these, i.e. the orientation forces, take their onset from electrostatic interaction arising from unsymmetrical charge distributions within electrically neutral molecules—a charge displacement causing a permanent dipole moment. The presence of a permanent dipole moment will induce an electrostatic interaction between the charged components or molecules possessing a dipole moment, and thus becomes a fundamental parameter in the orientation of substances and in molecular arrangements and organization.

The presence of a dipole moment in a substance can interact with other molecules by inducing a dipole moment in neighbouring substances, and in this way it can establish attractive or repulsive forces between the substances. In this case, the forces are recognized as Debye forces. A neighbour interaction can also take place when a dissolved ion, due to the presence of the electrical charge, induces an electronic distortion of a non-polar compound and, thus, turns the compound to a polarized species.

The third category is London forces, which originate in the movements of electrons within a molecule. The fluctuations of electrons generates an oscillation of a negative charge, forming dipole moments within the molecule, and the dipole moment will interact with neighbour molecules with a weak attraction or, in if the charge is similar, a repulsion.

An important force which can interact between molecules and have a power between the weak Van der Waal forces mentioned above and the forces of a covalent bond is hydrogen bonding. The hydrogen bond is a non-covalent bond formed from intra- as well as intermolecular interaction between a proton donor and a proton acceptor, the latter being an atom or moiety of higher electronegativity than the donor. As mentioned above, the hydrogen bond can be an intramolecular bond but, more interesting in the case of colloidal and food systems, it can be an intermolecular attraction or bonding between individual compounds. The hydrogen bonding is formed by interaction between an electron donor and an electron-deficient centre, and the bond strength is determined from the length, with a exponential decay in relation to the distance between the species. In addition, the angle of bond has an influence on the bonding strength.

Hydrogen bonds are not simple bonds, but are considered to be partly electrostatic and partly covalent of nature (see Gabowski [3]). Hydrogen bonding can be shown by spectroscopic methods (e.g. IR, UV and NMR) and are the explanation for the extraordinary high boiling point of water and a number of organic solvents. Other interactions worth mentioning are the electron pair donor and acceptor interaction (C. Reichardt [4]), which originate in the presence of high energy electron occupied and low energy non-occupied molecular orbitals. Also, solvophobic interaction, which is the inclusion of a hydrophilic substance in water, has to be considered.

Going from the interaction between two molecules to a system consisting of numerous molecules and where the materials are organized into structures or bodies formed from a high number of associated molecules, the interaction between the different colloid bodies can be simplified into attractive and repulsive forces between the individual colloid bodies. The interaction between colloid bodies originates from the molecular forces and will be an integration of the interaction between all the molecules of the colloid bodies, as well as interaction from molecules of the surrounding medium. This means that, in colloids, the interaction between the single colloid particles will originate from the same forces as those mentioned above. However, the overall interactions between the different colloid bodies are determined from the nature of the bodies and the surrounding solvent, both representing a huge number (and, often, a huge variety) of molecules.

In a multiphase system, the interaction between the discrete particles is related to two major forces, according to the DVLO theory of Derjaguin & Landau and Verweg & Overbeek . Here, the known Van der Waal interaction (i.e. the forces sourcing from the fluctuating dipole moments of neutral atoms) cause a polarizations of other atoms, and thus can establish an attraction between particles, thus acting as a driving force in flocculation into bigger bodies. The second force is the electrostatic repulsion between double layers, which is associated with an electrical charge, as in the case of ionic substances. The forces will counteract and equalize the Van der Waal interaction and will thus stabilize the colloid system (i.e. prevent the colloid from creaming and or flocculation). From a thermodynamic point of view, the system is unstable, but the counteracting forces between the particles bring the system into a metastable state which is, thus, kinetically stable. In addition to the two major forces of the DVLO theory, more detailed models include additional contribution from the steric repulsions and from hydrophobicity—interactions which also have to be taken into account when focusing on the overall interaction between colloid particles in a more complex picture of a colloid system.

In a colloid system, two or more individual phases are present, and the contact region of the two phases is known as the interface when the system is formed from two separate liquids or a liquid and a solid, or is described as a surface in a system formed from a liquid and a gas. Thermodynamically, such systems are unstable, and there will be a driving force favouring the energy of the system, which will divide the non-mixable substances into two separate bulk phases. Where a substance possesses an amphiphilic nature (i.e. having both hydrophilic as well as lipophilic moieties), the substance will migrate to, and organize, at the interphase. Thus, a migration takes place as long as the adsorption free energy can counteract opposite contributions from entropy and thermal energy. The adsorptions of molecules at the interface will increase the number of favourable thermodynamically interactions and, when equilibrium is reached, an optimum number of favourable interactions will have been formed.

The adsorption of a solutes such as an amphiphilic compound to the interface will also depend on the concentration of the solutes, as the adsorbed molecules will be in equilibrium with the molecules remaining in the bulk. This equilibrium has to be evaluated from a kinetic point of view, as the migration of small molecules takes place at different rates compared to big molecules like proteins. The small molecules are much faster in obtaining an equilibrium and can thus be an important parameter in forming and stabilizing an interface or a surface film. When the stabilizations come from polymers like proteins and or polysaccharides present in the system, the polymer will be associated to the surface of the colloidal particles, covering the interface/surface more or less.

Large biopolymers such as proteins often exhibit both lipophilic as well as hydrophilic segments and, when distributed in a multiphase system, the proteins will arrange themselves with the lipophilic moieties being in ...