Fats and oils may come from vegetable or animal source. Vegetable sources include coconut, palm, olive, peanut, corn, safflower, sunflower, cottonseed, and soybean oil. Animal sources include butter (from dairy), lard (from pork), tallow (from beef) and fish oil. Fats and oils provide a high source of energy and is used in the making of important bio-compounds such as cell membrane and non-protein hormones. They are also important in digestion of fat-soluble vitamins (A, D, E and K). Functional properties of fats and oils are described below.
Due to their low specific heat capacity and high boiling point, fats and oils can heat up quickly and reach very high temperatures. This allows them to be used in frying. High frying temperatures enables the development of brown colors and new flavors due to caramelization and Maillard reaction. At elevated temperatures, fats and oils smoke. This is called the smoke point. They say that where there is smoke there is fire so watch out. Continued heating beyond the smoke point will lead to ignition of the oil. This is called the flash point. Oil that has been abused to its smoke point should be thrown out due to the development of harmful breakdown products called free-radicals.
Most flavors are hydrophobic in nature, making fats and oils a good solvent for them. Hence foods that are fatty will taste better compared to low-fat foods which are generally bland. Consider the difference in flavor between skimmed milk and whole milk for example. Or, compare meats that have high marbling (i.e. high fat) versus those that have low marbling. The greater the marbling the more flavorful and desirable the eating quality.
Fats and oils improve not only flavor but also texture. Their ability to lubricate materials generate a juicy and tender mouthfeel. In food processing, shortenings texturize pastry by trapping tiny air bubbles during mixing, which then expand with heat to aerate and soften the final product. In addition, shortening can create flaky textures when layered between thin sheets of dough.
Fats can produce different textures due to the combination of fat crystal forms they contain. The three crystal forms are alpha (α), beta prime (β’), and beta (β) crystals. Alpha crystals are formed by rapid cooking of fat and are the most unstable crystals with the lowest melting point (54.7oC). β’ crystals are more stable and have a higher melting point (63.2oC). They are produced when cooled at a slower rate compared to α crystals. Shortening and margarine are high in β’ crystals and are excellent for creaming. β crystals are formed during even slower cooling than β’ crystals. They are most stable with a high melting point (73.5oC). The firmness of chocolate is due to the presence of high β crystals. Ultimately the type of crystal forms are dependent on the type of fatty acid present in the fat or oil.