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Bridget Skelly

on 28 April 2014

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Transcript of Lipids

Learning Targets:
Define saturated, monounsaturated and polyunsaturated fatty acids
List categories of lipids based on physical state and dietary sources
Relate physical characteristics of lipids to their performance in foods
Examine the functions of lipids in food preparation
Analyze the nutritional impact of lipids in the diet
Chemical Structure
Physical Characteristics
Functions of Lipids
Lipids are insoluble in water and have a greasy feel. Examples include: fats, oils, shortening and cholesterol.
Lipids contain carbon, hydrogen and oxygen.
Categories of Lipids
Categories based on molecular structure
Saturated fatty acids contain the maximum number of hydrogen atoms. They're SATURATED with hydrogen. Saturated fatty acids are solid at room temperature.
Unsaturated fatty acids do not contain all the hydrogen atoms they can hold. Unsaturated fatty acids are liquid at room temperature.
*Trans fatty acids are unsaturated fatty acids that are "hydrogenated" in order to change the state. This causes health concerns.
Categories based on physical state
Lipids that are solid at room temperature are commonly called fats
Lipids that are liquid at room temperature are called oils
Melting and Solidification Points
Solidification point for lipids is lower than the melting point
Lipids containing mostly saturated fatty acids have a higher melting point than lipids containing mostly unsaturated fatty acids.
Nonpolar Molecules
Lipids are nonpolar (equal sharing of electrons).
Water is polar (unequal sharing of electrons).
Polar and nonpolar substances do not attract; therefore water and oil do not mix unless there is an emulsifier (has polar and nonpolar portions)
Mayonnaise is an emulsion. Egg yolks are the emulsifying agent.

Homemade mayonnaise!
Tendency to Deteriorate
Lipids tend to react with oxygen. Auto-oxidation is a complex chain reaction that starts when lipids are exposed to oxygen. Auto-oxidation causes lipids to deteriorate and creates an unpleasant flavor and odor (rancidity-no health risks; just unappetizing)

To prevent rancidity, high fat foods are often vacuum sealed or antioxidants can be added to slow rancidity.
Functions of Lipids
Transfer heat
Lipids are an excellent heat medium! They transfer hear from cooking utensils to food quickly, evenly and at very high temperatures. Unlike water, lipids get hotter as you continue to heat them and can brown food-Careful! If you heat it too high it will start to smoke :(
Fats are used to tenderize baked products.
Aeration is the addition of air-saturated fats allow tiny air pockets to form when batters are beaten (butter+sugar creamed). Oils do not and therefore cannot typically be substituted for fats in recipes!
Enhance flavor
Fats add flavor to dishes! Butter, olive oil, bacon fat, NOM NOM NOM
Lipids lubricate food, making it easier for them to slide over one another. Also, the greasy texture make fats feel smooth to the tongue which causes food to seem moister. This is why we put butter or mayonnaise on bread- to add moisture without making the bread seem soggy!
While it is important to limit fat, please remember that fat is an important part of the diet. You want to avoid eating TOO MUCH of it, but you don't want to completely avoid eating fat!
Lipids provide 9 calories/gram (More than 2x what protein or carbs provide! Lipids take longer to digest and give a longer feeling of fullness.
Fat is necessary for providing energy and maintaining body temperature. Fat also cushions your vital organs and protects them from injury.
Fat is also necessary for cell production, transportation of certain vitamins, and production of hormones.
While fat is an important part of the diet, too much fat can be harmful. It is recommended that 20-35% of your daily calories come from fat. Most of these should come from unsaturated fat.
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