According to Bahrami et al. (2001), solubility in NaOH is due to saponification. Saponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of a carboxylic acid. Saponification is commonly used to refer to the reaction of a metallic alkali (base) with a fat or oil to form soap. Saponifiable substances are those that can be converted into soap.
According to Meyer (1968), the use of bases and acids serves as solubility switches to convert an insoluble form of a compound to a soluble form and vice versa. Observing the solubility or insolubility of reactants and/or products serves as a means to monitor acid base reactions. The concept of a solubility switch will also serve as the basis for following the base (NaOH) catalyzed hydrolysis (saponification) reaction of an ester (methyl benzoate) to the subsequent water soluble carboxylate salt (sodium benzoate) and alcohol (methanol).
According to Bahrami et al. (2001), Generally fats are not soluble in water and in dilute acids but soluble in ether,chloroform, hot alcohol, hot acetone, C6H6 and CCl4. Oils are not soluble in water because Oils (Lipids) and Fats have higher molecular weights and when dissolved in water tends to float. Oil molecules don’t interact as well with water molecules as the water molecules do with each other. Water is polar while oil is non-polar. Oils are very soluble in chloroform because it is non-polar and it is also an organic solvent that is chemically used as a solvent for fats.
According to Bahrami et al. (2001), the specific gravity of all fats is less than one. Consequently all fats float on water.
Specific gravity is a good indicator of adulteration, because if a particular oil is said to be pure, its specific gravity must be of close to an accepted value, but if it is impure, the specific gravity varies. The refractive index is related to the ease with which light passes through an oil or fat. Temperature and degree of saturation affect the value. Butter’s refractive index value can be used as an indirect measurement of unsaturation.
As shown in the table above, oil is immiscible in water since it formed a two layered solution. The same is true with alcohol, but oil is slightly soluble in alcohol since there is turbidity in the sample. When we mixed the oil samples to toluene and chloroform there is no formation of two layers and there is no turbidity. Oils are readily soluble to organic solvents.
Oils at low temperature become lighter than water. Soya bean oil has higher specific gravity than olive. Olive has higher specific gravity than corn oil. And corn oil possesses the lowest specific gravity in all the oil samples.
According to Meyer (1968), The smoke point is the temperature at which the fat or oil gives of thin bluish smoke. The oil begins to breakdown creating acreolein, an obnoxious-smelling compound.
For a given sample of oil or fat, the temperature is progressively higher for smoke point, flash point and fire point. The temperatures vary with the amount of free fatty acids present in oil or fat, decreasing with increased free fatty acids present in oil or fat is important. The smoke point of a fat used for deep fat frying decreases with the use of fat. Fats and oils with lower molecular weight fatty acids have low smoke points, flash and fire points. The number of double bands present has little effect on the temperature required. Smoke, flash and fire points are particularly useful in connection with fats used for any kind of frying. (Meyer 1968)
Knowing the smoke point can also save you money, because each time you deep-fry, you lower its smoke point irreversibly. If your oil’s smoke point is just above 190 degrees C (375 degrees F), which is the normal deep-frying temperature, chances are its smoke point will drop below 190 degrees C (375 degrees F) after its first use, rendering it useless. If you want to save money by reusing oil as many times as possible, select one with a high smoke point.
The smoke point of various fats is important to note because a fat is no longer good for consumption after it has exceeded its smoke point and has begun to break down. Once a fat starts to smoke, it usually will emit a harsh smell and fill the air with smoke. In addition it is believed that fats that have gone past their smoke points contain a large quantity of free radicals which contibute to risk of cancer. Refining oils (taking out impurities) tends to increase the smoke point. The table below lists some ballpark values for smoke points of various common fats.
According to Bennion (1980), the presence of mono- and diglycerides in fats lowers the smoke point since these emulsifiers smoke at a relatively low temperature. Fats are used for frying should be chosen on the basis of their resistance to smoking at the temperatures used. The production of free fatty acids by hydrolysis of some triglycerides during the frying process causes a decrease in smoke point. The presence in the fat of small particles that come from the food being fried also lowers the smoke point.
A number of factors may contribute to a decrease in the smoke point of oil. The length of time the oil has been heated, the number of times the oil has been used, the presence of salt or any other impurities, improper storage, and if the oil is a generic blend of various oils may all contribute to lowering the smoke point.
There are different kinds of liquid oils have different smoke point due to different structure of each fat. On table 3, liquid oils have higher smoke point than solid fats. The number of double bonds has a little effect on the temperature required for the smoke point but it varies with the amount of free fatty acids present in oil (Bennion, 1980). Added to that, the highest smoke point was the soybean which means that it has the lowest chain of free fatty acids. And the lowest smoke point was the margarine due to its long chain of free fatty acids. This indicates that the lower the temperature, the higher the amount of fatty acids exists.
According to Fenemma (1996), the solidification of liquid and solid fats is generally affected by the number of carbon chains in their bonds and the degree of saturation they have. In general, the higher the number of carbon chains attached, the higher the solidification point. And the higher the degree of unsaturation the fat has, the lower the solidification point. This general acceptance is greatly influenced by the number of double and triple bonds. Such evidence pertains to the solidification of the coconut oil. Since coconut oil is mostly saturated fat, it readily solidifies at 20oC which is similar to solid fats. Animal fats are generally solid at high temperatures because of their chemical composition since most animal fats are composed of saturated fatty acids, they have higher solidification points than liquid oils. Marine fat, also dubbed as Fish oil, did not solidify though it came from animal sources since it is mostly made up of unsaturated fatty acids. The chemical composition of fish oil varies from the sources of fish. In a study of both freshwater and ocean fish oil preparations, it was observed that fish oil preparations
Ocean fish contained 35 unsaturated fatty acids with 1-6 double bonds. In contrast, freshwater fish oil preparations contained 14 unsaturated fatty acids having 1-5 double bonds. (A Study on the Fatty Acid Composition of Fish Liver Oil from Two Marine Fish, Eusphyra blochii and Carcharhinus bleekeri, Zafar S. SAIFY et.al.)
Results show that, liquid oils have lower solidification temperature compared to solid fats. Most of the liquid oils needed temperature lower than 0oC to be able to solidify, except for coconut oil. These happen because solidification of the oil was dependent on the fatty acid present in the oil sample. According to Zapsalis (1985) corn and soybean oil majority consists of linoleic fatty acid, while olive oil consists more of oleic fatty acid. These oil samples contain mostly of unsaturated fatty acid not like coconut oil, which mostly consists of lauric fatty acid, mostly contain saturated fatty acid. The results shown in table 4 implies that if the oil sample consists of more unsaturated fatty acid, the lower its solidification temperature.
Moreover, all solid fat solidified at temperature higher than 0oC. According to Zapsalis (1985), lard mostly consists of oleic fatty acid, while butter commonly consists of butyric fatty acid. Oleic fatty acid is a monounsaturated fatty acid but is a long chain fatty acid compared to the butyric fatty acid, which is a saturated fatty acid but a short chain fatty acid, so even if lard consists of unsaturated fatty acid, the lard has higher solidification temperature than the butter because of the length of the fatty acid.
Creaming is one way of knowing the plasticity of fats through the ability to trap air bubbles while specific gravity determines the relative density. One factor that affects the plasticity of fat is the solid contents, the higher the solid contents the lower is the workability. This verifies the specific gravity of the samples.
According to Meyer (1968), solid fats are plastic over fairly wide range of temperatures. By plastic we mean that they are soft and can be deformed, but do not have the ability to flow. The spreading quality of butter is the result of its plastic nature. The plasticity is due to the mixture of triglycerides, each with its own melting point. Some fats have been formulated so that their melting points are low and they can be spread straight from the fridge, e.g. soft margarine.
According to Mc Williams (1997), butter and margarine can also be creamed but it will be more difficulty. This was shown in the results of the experiment where in they have lower specific gravity compared to that of lard.
Plastic fats and oils have a water-holding ability; however, emulsifiers greatly enhance it.
When increasing amount of emulsifier, holding water ability rises. When an emulsifier is added at 5%, 1 to 2-fold amounts of water can be held. Especially for monoglyceride, when the unsaturation degree is high, the holding-water rate is high.
According to Griffin et.al . (1965), Emulsions are inherently unstable. This is because the system has a large interfacial surface area and an interfacial surface energy that is proportional to this area. A reduction of the total surface energy will bring the system into a more stable state. If dispersed droplets coalesce, surface energy is decreased various factors in emulsion preparation influence the stability of the finished product. Emulsion instability is evidenced by creaming (or sedimentation) and by phase separation. Since the dispersed particles are freely suspended in a liquid, they obey the laws of sedimentation. If the dispersed phase has lower specific gravity than the continuous phase, the dipersed particles will move upward. They will move downward if their specific gravity is gerater than that of of the dispersion medium. In an oil-in-water emulsion such as mayonnaise, the lower density of the oil particles causes them to move upward if creaming occurs. In general, the greater the difference of the specific gravity between the two phases, the more rapid and complete the separation will be. The dispersed droplets of an emulsion can carry an electric charge. Since all particles will carry the same charge, and like charges repel each other, this may be helpful in keeping dispersed particles separated. A high viscosity in the continuous phase and small particle size will also retard creaming of the dispersed particles
According to Lissant (1974). Lowering interfacial tension increases the ease of emulsion formation but contributes in a less than major way to the stability of the formed emulsion. The formation of a rigid interfacial film is a more important factor operating in stabilization. A mixture of emulsifiers are often more effective than a single agent forming a tightly packed strong film around the dispersed particles. Emulsifiers that ionize contribute a charge to the film. This may aid in stabilizing the emulsion by keeping the dispersed particles separated. Finely divided solids such as spices, can also stabilize emulsions by being adsorbed at the surface of the dispersed particles.
The creaming ability of fats is determined by the plasticity of fats and how the fats can incorporate and retain air bubbles. One good example of plastic fat is hydrogenated shortening. Melted fats and oil does not have the ability of plastic fats but can be aerated but cannot retain air bubbles because they lack the crystalline nature of plastic fats. One important use of creaming is in the baking industry. Creaming affects the textural and volume of baked products.
Creaming contributes to the leavens the bake products such as cakes, this leads to increase in volume and an acceptable texture.
According to Bennion (1980), emulsion instability is shown by creaming and by phase separation. A high viscosity in the continuous phase, a charge on the dispersed particles, and small particle size retard creaming. Phase separation involves breaking of the emulsion with coalescence of the dipersed particles. The proper choice of emulsifier, fine particle size, proper induced particle charges, and high viscosity of the emulsion and component phases contribute to a stable dispersion of the phase.
Chocolate bloom is a sign that chocolate has not been stored correctly. The most obvious is fat bloom, which looks like gray-white blotches and streaks on the chocolate and occurs when the chocolate is exposed to heat during storage.
Polymorphism refers to the triglyceride of the same chemical structure but will form crystals of different sizes and shapes. Essentially, it refers to those fats of identical chemcial structure but because of different cooling and stirring conditions it will form different types of crystals.
According to Bennion (1980), plastic fats contain both a solid phase and a liquid phase of the noncrystallized molecules. The ratio of solid to liquid fat depends on the temperature. Solid fats can exist in more than one crystallize form and are called polymorphic. Each crystal form has a characteristic melting point, size, and shape. Various forms are called alpha, beta prime, intermediate, and beta. Molecules that are alike can readily align themselves with each other and form relatively large crystals.
According to Hoerr (1960), The three forms are a, b’, and b. The a form is the least stable, the b form is the most stable, and the more stable can be obtained from the less stable, as follows, ag b’g b. the fact that the three forms of SSS have three different melting points has been known for over 100 years. Any difference in melting point from one of lower stability to one of higher stability is lower to higher melting point. A further unstable form is produced is form if the form is held for about an hour just below its melting point temperature, this is called b’ which will change to the b stable form in about a month at normal temperature. Butter fat occurs as natural ingredient in the milk solids of milk chocolate and it is has been shown to have valuable anti-bloom effect in dark chocolate. To prevent or delay bloom therefore it is necessary to prevent the growth of large b stable crystals and this can be encouraged by setting as much as possible of the cocoa butter in its stable form during the tempering and cooling process. If small, rapidly grown b crystals are formed the slow growth of large b crystals is avoided.
According to Miller (1998), cocoa butter exists in a number of polymorphic forms of increasing melting points: α-2, β’-2, β3V, and β-3VI. On the sample A, α-2 size of the fat was transformed into β’-2, which has coarser particle size, and from β’-2 to β3V, and lastly to β-3VI, which is a more stable crystals but forms bloom on the chocolate. Rapid cooling and the presence of “seed” crystals form small, unstable crystals. A predominance of the more stable crystals results if the partially crystallized chocolate is properly tempered to melt unstable α and β’ crystals which have begun to form followed by moderate cooling.