Saponification of Triacylglycerols

The hydrolysis of triacylglycerol in the presence of sufficient sodium hydroxide is called saponification. The fatty acids are released as sodium salts and the mixture of these salts of long-chain fatty acids is soap.

RANCIDITY

Oils and fats are liable to spoilage that results in the production of unpleasant odors and flavors; such spoilage is called rancidity. Different types of oil and fat show varying degrees of resistance to rancidity; thus most vegetable oils deteriorate only slowly whereas animal fats deteriorate more rapidly and marine oils, which are highly unsaturated, deteriorate so rapidly that they are useless for eating purposes unless they have been refined and hydrogenated.

One important type of rancidity is known as hydrolytic rancidity; it occurs as a result of hydrolysis (i.e. reaction with water) of triglyceride molecules to glycerol and free fatty acids and it is caused by the presence of moisture in oils. The rate of hydrolysis in the presence of water alone is negligible, but it is hastened by the presence of enzymes and microorganisms. Oils and fats that have not been subjected to heat treatment may contain enzymes, which hasten hydrolysis by acting as catalysts. They may also contain moulds, yeasts and bacteria present in the natural oil or they may become contaminated with them during processing. Such microorganisms hasten the process of rancidity.

The industrial process of frying food in deep fat in large kettles gradually causes rancidity to develop as hydrolysis. This will cause changes in the nutritional quality of the food and will be much more effective in doing this than the fresh oil or fats would be.

A different type of rancidity that can occur in foods is oxidative rancidity. In this type of rancidity the double bonds of unsaturated fats are selectively attacked by oxygen in the air. When unsaturated fats or oils are exposed to the atmosphere the oxygen (oxidized) after which the molecule breaks down further and tastes rancid chemically changes the double bonds in the fat or oil molecule.

Note: In rancidity process iron is a catalyst and therefore plain iron pots should be avoid. Although fats and oils have a high b.p., they are relatively fragile organic substances. They start to decompose before reaching the point where they would actually evaporate as a gas. The temperature at which a particular fats or oils starts to decompose is called its ‘smoke point’. Most glycerides do not reach 260 degree C (500 F) without starting to decompose.

Application of hydrogenation - Hardening

Hydrogenation is adding hydrogen to unsaturated fatty acids and resulting in changing oil to fat. (This is how margarine & shortening are made. It's generally only partial, thus we have "partially hydrogenated" fats and oils. This means that not all the possible hydrogens were added.) In soft magarine some of the double bonds remain: regulating the amount of hydrogenation can control the degree of softness.

Oils are usually highly unsaturated, and vegetable oils can be transformed into solid fats industrially by catalytic hydrogenation. During this processing, hardening, one can be selective, in which case hydrogen is added to the most reactive (i.e.: the most unsaturated) fatty acid chains. Therefore, not all partially hydrogenated oils are necessarily the same.

At the unsaturated place, the carbon chain is easily broken by oxidation from oxygen in the surrounding air, by light and by heat. This process raises the melting point and the oil becomes more stable and rather odorless and tasteless fat, which may be heated to 180 degree Celsius (360 F) and makes an excellent medium for deep frying. In short, fatty oils are liquid fats, or fats are solidified oils.

This selective process adds stability to otherwise unstable fats and oils and thus allows developers to use some fats and oils that they otherwise could not. Consumers want unsaturated fats when they eat fat and this gives the developer a way to be able to provide the consumer what he wants yet maintain a stable product.

It is difficult to selectively hydrogenate fish oil; thus fish oils are less available for use in the manufacture of food products.

Effect of Processing on Fats & Oils

POLYMERIZATION

This is the process whereby molecules combine and form large ones. Generally a problem in frying operations because it is accelerated by high temperatures.

Polymerization results in

increased viscosity

increased foaming

HEATING

Heating can result in :

1.free fatty acids

2.polymerization

3.darker color

4.autoxidation

5.rancidity

Function

The hydrophobic nature of lipids contributes significantly to the biological functions of these molecules. Their water insolubility allows lipids to serve as barriers to aqueous solution.

The cell uses lipids to give the membrane its hydrophobic nature. In fact, by selecting the right lipids, both the hydriphobic and hydrophilic portions of a membrane can be assembled.

Fat should account for 30 % or less of the calories consumed daily, with saturated fats accounting for no more than 10% of the total fat intake. Fats are a concentrated form of energy, which help maintain body temperature, and protect body tissues and organs. Fat also plays an essential role in carrying the four fat-soluble vitamins: A, D, E, and K. Excess calories from protein and carbohydrates are converted to and stored as fat. Even if you are eating mostly "fat free" foods, excess consumption will result in additional body fat. Fat calories in food are readily stored, while it takes energy to transform protein and carbohydrates to body fat. The only proven way to reduce body fat is to burn more calories than one consumes.

• Saturated Fat: tends to increase blood cholesterol levels. Most saturated fats tend to be solid at room temperature, with the exception of tropical oils. It is found mostly in meat and dairy products, as well as some vegetable oils, such as coconut and palm oils (tropical oils). Butter is high in saturated fat, while margarine tends to have more unsaturated fat.
• Polyunsaturated Fat tends to lower blood cholesterol levels. It is found mostly in plant sources. (safflower, sunflower, soybean, corn, cottonseed).
• Monounsaturated Fat tends to lower LDL cholesterol (the "bad" cholesterol). It is found in both plant and animal products, such as olive oil, canola oil, peanut oil, and in some plant foods such as avocado.

Facts

* Values are given as a percent of total fat

** Total unsaturated fatty acids = polyunsaturated fatty acids + monounsaturated fatty acids. The sum of total unsaturated fatty acids + saturated fatty acids will not add to 100 percent because each item has a small amount of other fatty substances that are neither saturated nor unsaturated.

*** Made with hydrogenated soybean oil + hydrogenated cottonseed oil.

**** Fat from white tuna, canned in water, drained solids.