9/6/2016 1 Food Emulsions, Colloids, Surface Interactions 1 Learning Objectives • To characterize dispersions & to classify emulsions • To discuss formation and destabilization of emulsions • To discuss colloidal interactions and understand their role in stability • To explain the role of emulsifiers & to recommend suitable emulsifier for various food systems 2 Characterization of Dispersions (food chem view) • Dispersion – system of discrete particles in a continuous liquid Particles System Gaseous Foam Liquid Emulsion Solid Suspension (Walstra & van Villet, 2008) 3 Characterization of Dispersions (colloid chem view) • Dispersion – system of discrete “particles” in a continuous fluid 4 Characterization of Dispersions cont. • Colloid – a dispersion containing particles larger than small molecules (1 nm to some μ m) • Colloids may be thermodynamically or kinetically stable • Dispersion may be spontaneous (at a certain temperature – kT energy) or require energy (e.g. emulsification) 5 Emulsion • Emulsion - system containing two immiscible liquid phases one of which is dispersed in the other – Dispersed phase – Droplets typically 0.1 and 50-100mm (INTERNAL PHASE) – Continuous phase - Matrix in which droplets are dispersed (EXTERNAL PHASE) – Surfactant stabilise emulsions – soaps, proteins, egg yolk (lecithin), etc … 6 wiki/Emulsion Immiscible liquids Emulsion Unstable emulsion
9/6/2016 2 Emulsions • Oil in water emulsions – oil/water o/w – dispersed phase (oil) & continuous phase (water) – conducts electricity, can be diluted with water – Milk • Water in oil emulsion – water/oil w/o – dispersed phase (water) & continuous phase (oil) – feel greasy, can be diluted with oils or solvent – margarine 7 Classification • Based on vol % of internal Phase • Internal phase ratio is defined as: F = Vi / (Vi + Ve) where Vi = volume of internal phase; Ve = volume of external phase • F < 0.3, Low internal-phase ratio (LIPR) – o/w: milk, ice cream, and cheese – w/o: butter and margarine • 0.3 < F < 0.7, Medium internal-phase ratio (MIPR) – Heavy cream • F > 0.7, High internal-phase ratio (HIPR) – Mayonnaise and salad dressing 8 Oil-in-Water Emulsion Droplet • Natural food emulsions – contain amounts of natural emulsifiers – In homogenised milk casein protein adsorbs on surface of milk fat globules and acts as a surfactant • Formulated food emulsions are processed from ingredient components 9 Complex Food Emulsions • Dispersed phase (oil) can be partially solidified – e.g., in dairy creams % solidification of fat depends on Temp. • Continuous phase may contain crystalline or gelled material – e.g., ice cream where ice crystals are present – e.g., gelled desserts where the continuous phase is a gel • Food emulsions affect food texture and sensory properties 10 Formation of Emulsions cont.
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- Chemistry, Emulsion, emulsions, Walstra, colloidal interactions, van Villet