Oils, smoke points

Smoke Point. As oils or fats are heated, a thin bluish smoke appears. The smoke point is the lowest temperature, under controlled conditions, that the smoke becomes visible. Cottonseed oil s smoke, fire, and flash points, like other fats and oils, are almost entirely dependent on the free fatty acid content. Fats and oils smoke point results decrease when the triglycerides are split during hydrolysis to form free fatty acids and glycerol. The glycerol portion decomposes to form acrolein, which is the major portion of the smoke evolved from heated fats and oils. Like other long-chain fatty acid oils, cottonseed oil with 0.01% free fatty acid will have a smoke point of approximately 450°F. Additions of monoglycerides... 

Conventional Hydrofining of diesel oils does not improve octane number because octane number improvement, like smoke point improvement in kerosenes, requires samration of aromatics. Higher pressures are needed to gain appreciable aromatics samration and cetane number improvement. 

The smoking point of butter is the temperature at which partial combustion starts, yielding smoke. An oil or fat is only safe to cook with below its smoke point. 

Smoke flavoring, 12 48 Smoke generation tests, 19 588 Smoke point, of fats and oils, 10 822 Smoke retardants, molybdenum compounds in, 17 39 Smoke suppression, by ethylene-acrylic elastomers, 10 700 Smoking, age-related macular degeneration and, 17 659 Smoky quartz color, 7 337... 

Smoke Point A measurement of the burning quality of jet fuel, kerosene, and lamp oils. This value is determined by ASTM D-1322. 

Measurement of smoke, flash and fire points is carried out subjectively by observing the surface of an oil sample while the sample is being heated. (The critical temperatures are higher than the upper limit of the melting point range of a fat.) The smoke point is the temperature at which the sample begins to give off a continuous stream of bluish smoke, observable... 

BSI 1976b. British Standard Methods of Analysis of Fats and Fatty Oils, Part 1. Physical Methods, Section 1.8. Determination of smoke point. British Standards Institution, London. 

The volatile peroxides, other oxidation decomposition products, and odiferous compounds form reduced-boiling point azeotropes with water in the steam, at high temperatures, 250-260°C/482-500°F, and very low absolute pressures ( 3 mbar). This is above the smoke point of soybean oil, but below the flash point, and oxygen must be excluded. Considerable heat bleaching of yellow-red carotenoids also occurs at this temperature. Typically the deodorization process requires 20-40 min after come-up time, uses 0.5-2.0 percent spaiged steam (the higher level if tocopherols are recovered), operates at between 2 and 4 mbar, and produces a product with about 0.03-0.05 percent FFA.143... 

Smoke, Flash, and Fire Point—Cleveland Open Cup Method (Cc 9a-48) determines the temperatures at which fats and oils smoke, flash, or burn. Smoke point determinations sometimes are used to follow degradation of frying oils with use. 

Other physical properties such as the smoke, flash, and fire points of oils and fats are measures of their thermal stability when heated. The smoke point is important for the oils and fats used for deep-frying. The flash point and fire points are a measure of residual solvent in crude and refined oils and are also a safety requirement. 

Smoke point is another characteristic that is important if oils are with for frying. The temperature at which smoking is observed with actual frying or heating is measured with AOCS Method Ca 9a-48 (22). Smoke point depends primarily on the content of free fatty acids as they are more volatile than their corresponding triacylglycerols. 

The smoke point is the temperature at which a fat or oil produces a continuous wisp of smoke. This provides a useful characterization of its suitability for frying, and often 200°C is specified as the minimum by regulations (Table 13). 

The flash point defines the temperature at which the decomposition products formed from frying oils can be ignited. This temperature ranges from 275°C to 330°C for different oils and fats (Table 13). An increase in the content of unsaturated fatty acids usually decreases the flash and smoke points (60). 

Smoke point (98) is a function of acidity level in the oil. The smoke point for olive oil generally ranges from 150°C to 163°C. 

The smoke, flash, and fire points of soybean oil have been determined by the Cleveland Cup method and show considerable variation. Dickhart (117) reported a smoke point of 138°C while Detwiler and Markley (76) reported 241-250°C. 

Detwiler and Markley (76) found that the smoke point varied considerably with the degree of refining, especially the removal of free fatty acids, and also with the mode of oil extraction. Yen et al. (118) found a smoke point of 191°C, which was raised several degrees by the addition of phenolic antioxidants. The flash point of soybean oil, the temperature at which vapors coming from the oil will catch fire from an ignition source, were reported as 304°C (117), 326-331°C (76), 174°C (69), 318°C (70), and 320°C (119). The low value reported by Ali et al. (69) was obtained by using a Pensky-Martens closed tester and ASTM method 093-90. The flash points of hexane-soybean oil mixtures were determined and correlated with headspace gas chromatography data (120). 

Smoke Point, Fiash Point, and Fire Point The smoke point, flash point, and fire point of an oil are relevant parameters in deep-fat frying processes. The fatty acid composition of the oil is not relevant (unless the oil has short-chain fatty acids, as is the case of butter or coconut oil). The most important effect is generally that of free fatty acids (FFA) in the oil. The following values have been reported for fully refined sunflower oil (with 0.10% free fatty acids) smoke point = 209°C flash point = 316°C fire point = 341°C (5). 

The 3M Company of St. Paul, MN introduced the Shortening Monitor, which consists of a white strip of paper, measuring 0.3 x 3.75 inches, which has four blue bands across it. The strips are used as a dip test to measure accumulated free fatty acids in the oil. The tests were developed to provide users, especially those in the fast-food industry, with an inexpensive means to objectively measure FFA in the cooking oil. This test might be suitable for restaurants because the FFA in restaurant fryers tend to mn high and might be effective to predict the imminence of reduced smoke point in the fryer oil. 

Phospholipids, if not removed from oils before deodorization, can lead to dark-colored oils and serve as off-flavor precursors (53, 54). Chlorophyll (55), pheophytins and pyropheophytins (56), and metal ions (57, 58) are prooxidants that decrease oil stability. Iron and copper at levels as low as 0.01 and 0.1 ppm, respectively, are capable of lowering flavor and oxidative stabihty (59). Free fatty acids, besides representing a refining loss, have also been shown to act as prooxidants (60) and to lower smoke points (61) of oils during frying. Uinolenic acid has... 

Every oil has a different smoke point—the temperature after which it is no longer healthy and begins to smoke. Some oils, such as flaxseed oil, have a very low smoke point and, as a result, should never be heated. Olive oil smokes at just under 325°F, while macadamia nut oil reaches its smoke point at around 4io°F, allowing you to cook with it at higher temperatures without destroying the health benefits of the oil (unless the oil has been overheated during manufacturing). When oils become rancid or overheated, the beneficial fatty acids break down into other compounds such as hydrocarbons, ketones, and aldehydes, all of which can raise the acidity of our bodies. 

Never allow oil to get so hot it smokes. The temperature at which an oil will smoke varies from one type to another. The smoke temperature is the point at which the heat chemically alters the oil. If your cooking oil smokes, throw it out and start again. It is far better to use a lower temperature when cooking with oils and take a few extra minutes than to destroy the health properties of the meal by overheating it. Olive oil is a good choice for sauteing foods, as it can withstand temperatures up to about 325°F. Coconut oil can handle temperatures up to 350°F. 

Table III gives the physical and chemical properties of the M. oleifera oil. Some of the properties of the oil depend on the extraction medium. The M oleifera oil is liquid at room temperature and pale-yellow in colour. Electronic nose analysis shows that it has a flavor similar to that of peanut oil. The melting point estimated by differential scanning calorimetry is 19°C (15). The chemical properties of the oil depicted in Table III below are amongst the most important properties that determines the present condition of the oil. Free fatty acid content is a valuable measure of oil quality. The iodine value is the measure of the degree of unsaturation of the oil. The unsaponifiable matter represents other lipid- associated substances like, sterols, fat soluble vitamins, hydrocarbons and pigments. The density, iodine value, viscosity, smoke point and the colour of Moringa oil depends on the method of extraction, while the refractive index does not. Varietal differences are significant in all physical characteristics apart from refractive index and density (2). The heating profile of the M. oleifera seed oil using the differential scanning calorimetry (DSC) conventional scan rate shows that there is one major peak B and, two small shoulder peaks A and C...

---