‘Emulsion’ is one of the many terms that I learned from a food chemistry paper in my undergraduate study. Back then I was not aware that emulsion is the basis of many food products which influence our daily life. Food emulsions are used to deliver nutrients such as carbohydrates, proteins, fats, vitamins and minerals. In daily life we don’t often use the word ’emulsion’ but we do often consume emulsifiers, in food like milk, vinaigrettes, mayonnaise, whipped cream, ice cream, butter and margarine. Emulsion technology development is all about enhancing nutritional value, as well as improving taste and flavour in foods and beverages.
My interest in emulsion started when I worked as a product developer on edible oil products. I was astonished by the physics and chemistry on the formation of an emulsion. For examples, the mixing procedure can have almost no impact in some emulsions while in another instance, the emulsion can separate into oil and water within minutes. Emulsifiers, a minor component in the emulsion, can significantly influence the formation of emulsion and its appearance. However, the role and function of emulsifiers are often vague and dependent on the type of emulsifier. Even after spending a few years creating emulsifiers and using them to make emulsions, I still didn’t understand how emulsifiers work. About three years ago, I felt that I needed to take a break from work and do a PhD to obtain a deeper and more fundamental understanding about what happens during the formation of emulsions.
What is an emulsion? An emulsion is a mixture of at least two immiscible (unmixable) liquids such as oil and water. When oil mixes with water, it will float on top of the water as it is lighter (lower density) than water. Oil and water require an emulsifier to mix and form an emulsion.
What are emulsifiers? Emulsifiers are molecules with one water-loving (hydrophilic) head and one oil-loving (hydrophobic) tail. The unique structure of emulsifiers make it possible for water and oil to disperse as small droplets in each other, eventually forming a stable emulsion. Milk proteins can serve as an emulsifier to form many dairy-based foods and beverages. Fat-derived emulsifiers such as lecithin (extracted from egg yolk or soybean) and monoglycerides (modified from oil) form the basis of many food products in the supermarket.
How many types of emulsion are there? There are two types of simple emulsion, namely oil-in-water (O/W) and water-in-oil (W/O). An O/W emulsion contains many small oil droplets dispersed in a bulk of water, while a W/O emulsion has many water droplets in the oil.
How do we know the type of emulsion formed? A simple and quick way to determine the emulsion type is by adding the emulsion into a glass of water. An oil-in water emulsion will disperse quickly in the water, while a water-in-oil emulsion maintains the same shape or sticks to a spoon.
In my PhD study, I first investigated the interaction between milk proteins and monoglycerides and looked at how this affects the appearance and properties of a milk coffee beverage. The study showed that monoglycerides interact with milk proteins to form stable oil droplets that don’t cream. Creaming is the formation of a cream layer at the top of the emulsion due to upwards movement of oil droplets.
In the subsequent study, I selected a monoglyceride that shows improved creaming stability to create a new emulsifier system. This new emulsifier is a stable powder that readily forms an emulsion in water. It is currently under evaluation, and the early results are promising, showing enhancement of the appearance and properties of the emulsion, a positive development for future food technologies – especially for your future cappucinos.
Marcus Loi is a PhD Candidate in the Department of Food Science, University of Otago, under the supervision of Associate Professor John Birch, Dr Graham Eyres and Mr Pat Silcock.