Chapter 10

The Glycerides: Monoglycerides Diglycerides Triglycerides Phospholipids Sterols Lipids are a category of organic compounds that are insoluble in water and have a greasy feel. There are three types of lipids with unique chemical structures:

 The core of lipids is the glycerol molecule.  Molecules that have a glycerol base are called glycerides.

 Fatty Acids are organic molecules that consist of a carbon chain with a carboxyl group at one end.  A carboxyl group is a carbon atom, two oxygen atoms, and a hydrogen atom.  The carboxyl group of a fatty acid will readily react with a hydroxyl group of glycerol.

Monoglyceride One fatty acid attached at the site of a hydroxyl group.

Diglyceride A glycerol with two fatty acids attached at the site of a hydroxyl group.

Triglyceride A glycerol with a fatty acid attached at each of the three hydroxyl sites. Major type of fat found in foods and in the body.

Can have 3 different fatty acids attached 20 fatty acids to choose from Create different characteristics Cooking performance Shelf life Nutritional value

 Is a glycerol base with 2 fatty acids and a phosphorus-containing acid attached.  The fatty acids are soluble in fats.  The phosphorus-containing acid is soluble in water.  Allows to mix w/both water-based and fat- based substances.  Phospholipids help fats stay mixed in water- based solutions  Keep foods like mayonnaise from separating.

 Are complicated molecules derived or made from lipids.  They include:  Cholesterol (most familiar b/c part of every cell in human body)  Vitamin D  Steroid hormones

Based on Molecular Structure Based on Physical State Based on Dietary Sources

 Saturated: when fatty acids have the maximum number of hydrogen atoms.  Butyric:  Stearic:  Unsaturated: when fatty acid does not contain all the hydrogen atoms it could contain.  Monounsaturated: fatty acids that have 1 double bond in the carbon chain.  Oleic:  Erucic:  Polyunsaturated: Fatty acids have 2 or more double bonds in the carbon chain.  Linoleic:  Linolenic: See page 273 in textbook

See page 278 in textbook

 One of the easiest ways to categorize lipids is by their physical state at room temperature.  Fats: lipids are solid at room temp.  Oils: lipids are liquid at room temp.  The #’s of hydrogen and carbon atoms on a fatty acid chain determine the temp. at which lipids liquefy.  More hydrogen = higher melting point  More double bonds = lower melting point  The type of fatty acid present in the largest amount has has greatest effect on characteristics of the lipid. (see page 277 in textbook)

 Melting point: temp. at which a substance changes from solid to liquid. Hydrogenated Vegetable Oils  Hydrogenation: the process of adding hydrogen atoms to an unsaturated lipid to increase its saturation level.  Used to make oils solid at room temp ▪ Ex : margerine  Achieved by bubbling hydrogen through liquid oil in the presence of a nickel catalyst.  Advantages include:  Longer shelf life than oil or lard  Greater stability than lard  Lower production cost than lard  Faster dissolving and setting properties in chocolate production.

Triglycerides come from 7 main groups of dietary sources. Milkfats: Lauric Acids: Vegetable Butters:

Oleic-linoleic acids: Linolenic acid: Animal Fats: Marine Oils:

Differing Melting and Solidification Points Nonpolar Molecules Tendency to Deteriorate

 Lipids do not have a specific melting point because most lipids are mixtures of different fatty acids.  Lipids will also become solids at different temps.  Solidification point: the temp. at which all lipids in a mixture are in a solid state.

 Lipid molecules have a equal or balanced sharing of electrons, which makes them nonpolar.  Nonpolar molecules readily mix with other nonpolar molecules but do not want to mix with polar molecules  This is why water and oil do not mix.  Lipids are large molecules with spaces between the parts of the molecules.  This causes lipids to be less dense than water. ▪ Ex: oil floats on water

 Lipids have a tendency to react with oxygen.  Auto-oxidization: complex chain reaction that starts when lipids are exposed to oxygen.  Oxygen will bind to the lipid molecules and then to other compounds. (domino effect)  Starts to form other compounds and makes food rancid (bad flavor, color, and odor)  Antioxidants: compounds that quickly react with oxygen to form new substances.  Will react with oxygen before lipids do. ▪ Ex: vitamins A,C, and E.

Transfer Heat Tenderize Aerate Enhance Flavor Lubricate Serve as Liquids in Emulsions

 Excellent heat medium  Temp. of lipids will continue to increase as heat is added.  Every lipid has a temp. at which the fatty acids begin to break apart and produce smoke. This temp. is called the smoke point.  Once oil starts to smoke, nothing should be cooked in it, or it should be discarded, because it will cause an unpleasant flavor.

 Flash point is the temperature at which lipids will flame (this occurs around 600 degrees F).  Do not salt food until after deep frying because it will lower the smoke point of the oil, reducing the time the oil can be used.

 Tenderize baked goods  Protein in baked goods have long strands and the lipids tend to shorten those strands.  That is why the solid white fate sold for baking is called shortening.  Fat to flour ratio will determine how flaky a baked product.  You cut in fats to dry ingredients and do not over mix or the dough will not be suitable for baked goods.  Will become a greasy ball

Aerate  The addition of air into a batter.  Saturated fats allow tiny air pockets to form when batters are sufficiently beaten.  Oils are not suitable for this because they will separate from the mixture.  In cakes:  You cream the ingredients together to aerate them. You cant heat them too high because you don’t want them to melt (then they act like oils).

 Fat is a major flavor enhancer.  Overeaten by most people in the U.S.  Used in preparation of many foods:  Salad dressings, sauces, soups, casseroles, etc.  When you want to taste more of the main food product and not the fat, use oils that have very little taste  Ex: soybean oil, canola oil, and sunflower oil.

 Makes meat easier to chew as the fat content increases.  Pleasant mouth feel  Feel slick or smooth to the tongue  Foods seem moister

 An emulsion is a mixture that contains a non- polar lipid and a water-based liquid, which is polar.  Another compound with a polar and nonpolar end must be added to emulsify  Phospholipids have this chemical structure and create emulsions.  Ex: mayo, phospholipid (lecithin) fount in egg yolks, prevents oil from separating.

Carbohydrates Versus Fats  Which is more fattening, 100 kilocalories of carbohydrates or 100 kilocalories of fat? See page 289 in textbook

Functions of Lipids in the Body Essential Fatty Acids The Role of Cholesterol Unsaturated Oils Dietary Recommendations

Calorie Density See page 293 in textbook