Food Emulsions: An Important Mix
Food emulsions are everywhere in today’s food industry. From the milk poured with a bowl of cereal in the morning to the margarine used to flavor rolls at dinner, food emulsions are something that an individual will encounter on a daily basis. By formal definition, a food emulsion is defined as, “a colloidal dispersion of two liquids, usually oil and water, that are immiscible.” (Murano 2003). To better understand what this definition is stating, a colloidal dispersion must also be defined. A colloidal dispersion is a dispersion of food colloids, a dispersed phase, into a continuous phase such as water or oil. Keep in mind, however, that a colloidal dispersion is not a solution, and the two liquids are said to be immiscible, meaning unmixable. Food colloids are too large to be dissolved into a solution and are thus suspended in a continuous phase, similar to a mixture, but the particles are still small enough that they will not settle out like in a suspension. In a colloidal dispersion, the food colloids are each approximately 10 – 100nm in diameter, smaller than food particles contained in a suspension, but larger than those that can dissolve into a solution (Murano 2003). Some people regard foams as a type of emulsion, but this is not true. Foams are similar to emulsions, but occur when a gas is dispersed in a liquid, such as in whipped cream. Other dispersions similar to emulsions are gels, which are a liquid dispersed in a solid, and sols, which are solids dispersed in a liquid, an example being gravy. The history of food emulsions starts with milk. Milk is the oldest known food emulsion and can be dated back to 8000 BC with the domestication of sheep and cows in India, the Middle East, and Sub-Saharan Africa. The classification of oil-in-water and water-in-oil emulsions originated from a 1910 paper by Wolfgang Ostwald (Becher 1991). Milk, butter, and cheese were the pioneering emulsions and were created long before other emulsions such as margarine, mayonnaise, salad dressings, gravy, certain meats (frankfurters), and ice cream. Butter and cheese emulsions were discovered shortly after milk, when the domestication of goats and cows became more popularized. Mayonnaise is an emulsion that is made using lecithin as an emulsifier. Using a previous recipe from the town of Mahon in Spain, the French created the emulsion we now know as mayonnaise in the mid 1700’s. Margarine was also discovered in France and was produced shortly after in the early 1800’s. Today, emulsions can be very complex with the pasteurization of milk and the various types of cheeses, butters, and dressings produced using emulsions. The most typical types of emulsions found in foods that we consume on a daily basis are the O/W (oil-in-water) and W/O (water-in-oil) emulsions. An O/W emulsion occurs when oil particles are dispersed in a continuous phase of water. Some of the most common examples of O/W emulsions include products like milk, cheese, vinaigrettes, mayonnaise, and other dairy products. Milk, is a quite unstable when unpasteurized. Due to its instability it needs an emulsifier to create the emulsion. Once the milk passes through the pasteurization process, fat globules decrease in size and no longer clump together, creating a stable emulsion with no separation. Likewise, W/O emulsions occur when water particles are dispersed in a continuous phase of oil. W/O emulsions that we use on a daily basis and as ingredients in common foods are butters, margarines, and some specific oil products like cod liver oil. In addition to both O/W and W/O emulsions, two forms of more complex food emulsions exist. These emulsions are of the oil-in-water-in-oil form (O/W/O) and the water-in-oil-in-water-form (W/O/W). They are simply emulsions within emulsions, acting to stabilize the “multiple emulsion”. For instance, water droplets containing smaller oil droplets within them may be dispersed in a continuous phase of oil, thus...
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