Food Biopolymers and Colloids
November 13th and 14th, 2008
The purpose of the short course is to present the basic principles, concepts and techniques of emulsion science & technology that are relevant to those working within the food and related industries. The short course aims to show how emulsion science and technology can be used to understand, predict and control the properties of real food products and ingredients, and to develop novel food and nutraceutical products. In particular, we will focus on the principles of emulsion preparation, emulsion stability, emulsion rheology, and emulsion characterization. Web Link
Many foods consist either partly or wholly as food emulsions, or have been in an emulsified state sometime during their manufacture, including milk, cream, salad cream, mayonnaise, salad dressings, soups, sauces, butter, margarine, low-fat spreads, beverages, ice cream and coffee whitener. The bulk physicochemical properties of these foods (appearance, flavor, rheology and stability) depend on colloidal properties, such as droplet concentration, size and physical state, colloidal interactions and interfacial properties. Our laboratory is involved in a number of research projects aimed at improving the understanding of the molecular-colloidal basis of the bulk physicochemical properties of food emulsions. The influence of pH, ionic strength, droplet crystallinity, temperature, and ingredient interactions on the rheology, stability and appearance of oil-in-water emulsions is being investigated using a variety of experimental methods, including laser diffraction, particle electrophoresis, dynamic shear rheometry, ultrasonic spectroscopy, ultrasonic imaging and optical microscopy. Standardized methods are being developed to categorize the functional properties of food emulsifiers, which will enable food manufacturers to select ingredients in a more systematic and informed manner. Novel interfacial engineering technologies are being developed based on multiple-layer formation to improve the properties and stability of food emulsions.
Multi-Layered Emulsions. Two-stage mechanism for producing emulsion droplets coated by a two-layer interfacial membrane. First, a primary emulsion containing small droplets coated with an emulsifier membrane is formed by homogenizing oil, water and lecithin together. Second, a secondary emulsion is formed by mixing the primary emulsion with a chitosan solution to form droplets that are coated with a lecithin-chitosan membrane.
Encapsulation and Delivery Systems
Functional agents (such as vitamins, antimicrobials, antioxidants, flavors, colors, preservatives and nutraceuticals) are important components in a wide range of food products. Many functional agents have poor water solubility, poor compatibility with typical food matrices, are prone to chemical degradation or have relatively low bioavailability, which restricts their utilization as ingredients in food products. Consequently, there is a need for delivery systems that can: (i) encapsulate functional agents into water-dispersible forms that are compatible with food matrices; (ii) stabilize the component against chemical degradation (e.g. oxidation) during processing, storage and utilization; (iii) delivering the functional agent to its site of action (e.g., mouth, stomach, small intestine). We are developing a range of different types of delivery system that could be used to encapsulate functional agents for utilization in the food industry, e.g., micro-emulsions, macro-emulsions, multilayer-emulsions and multiple emulsions. These delivery systems are being constructed from food-grade ingredients (proteins, polysaccharides and lipids) using common unit operations (mixing and homogenization).
Biopolymer Solutions and Gels
The aqueous phase of many foods contains biopolymers that either enhance viscosity or cause gelation. The appearance and rheological properties of an aqueous phase is determined by the nature of the interactions between the biopolymer molecules (hydrogen bonding, hydrophobic interactions, van der Waals forces, electrostatic interactions and disulfide bond formation), as well as the kinetics of the aggregation process. Our research group is studying the molecular basis of the bulk physicochemical properties of biopolymer solutions, with the objective of designing functional ingredients with improved properties. We are also examining methods of producing novel structures in biopolymer solutions and gels by utilizing thermodynamic incompatibility and coacervation in biopolymer mixtures (see above picture of O/W/W emulsion).
Optical Microscopy Image of O/W1/W2 Emulsion. This emulsion consists of fish oil (O) droplets contained within a whey protein aqueous phase (W1) that is contained within a HM-pectin aqueous phase W2 (pH 7). This type of emulsion may be useful for encapsulation, controlled release, or production of reduced-fat products. ). Photograph taken using a Nikon eclipse e400 microscope (x 200).
Application of Micellar Technologies
Small molecule surfactants are often used in the food industry to enhance the formation and stability of oil-in-water emulsions. There are also a number of other potential applications of surfactants, which are based on their ability to form micelles in solution. A micelle is a dynamic aggregate of surfactant molecules in which the non-polar tails are located in the hydrophobic interior and the polar head-groups are located at the exterior (in contact with water). The ability of micelles to incorporate and transport non-polar molecules across an aqueous phase can be used to control flavor release, encapsulate non-polar flavor compounds in an aqueous environment, selectively extract certain non-polar molecules from emulsion droplets and catalyze certain chemical reactions. Our research group is studying the factors which determine the rate and extent of solubilization by surfactant micelles, and investigating potential applications of this technology in the food industry.
Association Colloids. Small molecule surfactants can form a variety of different association colloids in aqueous solutions depending on their molecular geometries. These association colloids can be used to encapsulate ingredients or control their release.
Ultrasonic Characterization of Foods
It is widely recognized that there is a lack of suitable on-line sensors for characterizing the physicochemical properties of foods during processing, and that this is holding back the implementation of new process control technologies that are needed for automated food production. Our laboratory has developed an on-line ultrasonic sensor for rapidly and nondestructively determining the size, concentration and solid fat content of droplets in food emulsions. This sensor can be used by food manufacturers to continually monitor the efficiency of food processing operations. Recently, we have developed an unique ultrasonic imaging device for non-destructively monitoring creaming and sedimentation in emulsions, and to follow diffusion of small molecules through aqueous solutions and gels. This technique is being used to study the kinetics of mass transport in food systems, and to elucidate the most important factors that determine these processes. We are also developing novel hand-held ultrasonic devices for use by the fishing industry that can be used to rapidly measure the composition of fish. Ultrasonics is an extremely powerful technique that has many advantages over alternative technologies, and will certainly find increasing utilization in the food industry.
Ultrasonic characterization. Ultrasonic velocity and attenuation measurements can be used to provide a wide variety of information about food systems, including composition, structure, phase transitions, and interactions.
LS230 (Beckman-Coulter) MasterSizer (Malvern Instruments)
These laser diffraction instruments are used to measure the particle size distribution of emulsions and colloidal systems. The measure the angular dependence of light scattered by a dilute dispersion of particles, and find the particle size distribution that gives the best fit between the experimental measurements and theoretical calculations (Mie theory).
ZEM5003 Zetamaster (Malvern Instruments)
This instrument is used to measure the sign and magnitude of the electrical charge (ζ-potential) on emulsion droplets and other colloidal particles. The ζ-potential is determined by injecting a dilute suspension of particles into the measurement chamber and measuring the direction and velocity of particle movement in a well-defined electric field.
CS10 (Bohlin Instruments)
This equipment is used to measure the rheology of solutions, emulsions and gels as a function of shear stress, temperature and time. It applies a controlled stress to the sample and measures the resulting strain.
VP-DSC (MicroCal Instruments)
This ultrasensitive differential scanning calorimeter instrument is used to monitor conformational changes and phase transitions, e.g., protein unfolding, polysaccharide conformational changes, and fat crystallization/melting.
VP-ITC (MicroCal Instruments)
This ultrasensitive isothermal titration calorimeter instrument is used to monitor enthalpy changes at fixed temperatures resulting from molecular events such as molecular association-disassociation events (such as biopolymer aggregation, demicellization of surfactants, or binding of surfactants, flavors or minerals to biopolymers) and conformational changes (such as unfolding). It can often be used to quantify the thermodynamics of these molecular events.
K10 (Kruss Instruments)
This instrument measures surface tension (liquid-air) or interfacial (liquid-liquid) tension. It is normally used to quantify the adsorption behavior of surface-active materials at air-water and oil-water interfaces.
Content last updated: December, 2007