Oil stability index

A widespread method for determining the induction period for autoxidation of oils and fats consists of passing a continuous stream of air through the heated sample and collecting the volatile acids evolved in a water trap, where they are determined on a real time basis. The time plot usually presents a flat appearance for a certain period and then takes off in an accelerated manner. This test is the basis of several national and international standards (e.g. AOCS Cd 12b-92—oil stability index" ISO 6886—accelerated oxidation test for oxidative stability of fats and oils ) and the design of the Rancimat equipment, where the end determination is based on conductivity measurements . In addition to oxidation stability as determined by the Rancimat method and POV, which negatively affects virgin olive oil stability, other nonstandard properties were proposed for better assessment of the quality of this oil, namely LC determination of Vitamin E (21), colorimetric determination of total polar phenols and UVD of total chlorophyll. ... 

A sample is heated, usually at or above 100°C, while air is bubbled through it, and the volatiles created are transferred to a water trap where conductivity is measured (Fig. D2.3.1). The induction period endpoint is determined by the time it takes for the sample to begin a rapid increase in conductivity. The time required for the sample to reach its induction period endpoint is termed the Oil Stability Index (OSI). The Oil Stability Index is Official Method Cd 12b-92 of the American Oil Chemists Society (AOCS, 1996). 

Figure D2.3.1 Schematic diagram of oil stability index (OSI) instrumentation.

Figure D2.3.2 Data from conductivity probe and determination of oil stability index (OSI) by Lipid Oxidation/ drawing tangents. Stability...

The oil stability index (OSI) method provides results in a matter of hours instead of months (required for studies done at ambient temperatures). These OSI results are useful as comparative measures of oxidative stability, i.e., to determine the effect of a treatment or antioxidant compared to a control sample. Meaningful predictions of the actual shelf lives of specific commodities require that such shelf life studies be performed at ambient conditions. If only accelerated tests are to be performed, two or more tests based on different principles of lipid oxidation measurement should be conducted the effect of accelerated storage temperature should also be investigated. 

Food deterioration desiccation/water activity, 61 -66 oil stability index, 541-545 primary lipid oxidation products,... 

Rancidity in food, measurement of oil stability index, 541 -545 secondary lipid oxidation, 531-539 Rapeseed oil, properties and composition of, 474 (table)... 

Anon. 1999. In Firestone, D. (Ed.), Official Methods and Recommended Practices of the AOCS, Cd 12b-92 Oil Stability Index (OSI) (5th ed.). Champaigne IL AOCS Press. 

Dunn, R. O. 2005a. Oxidative Stability of Soybean Oil Fatty Acid Methyl Esters by Oil Stability Index (OSI). /. Am. Oil Chem. Soc., 82, 381-387. 

Tan, C. P., Che Man, Y. B., Selamat, J., and Yusoff, M. S. A. 2002. Comparative Studies of Oxidative Stability of Edible Oils by Differential Scanning Calorimetry and Oil Stability Index Methods. Food Chem., 76,385-389. 

Dijkstra, A. J., Maes, P. J., Meert, D., and Meeussen, W. 1996. Interpreting the Oil Stability Index. Oleagineux Corps Gras Lipides, 3, 378-386. 

Active Oxygen Method for Fat Stability (AOM) (Cd 12-57) determines the time (in hours) for a sample of fat or oil to attain a predetermined peroxide value (PV) under the conditions of the test. The method is used to estimate the comparative oxidative stability of fats and oils. The method has been placed in surplus, in favor of Cd 12b-92 (Oil Stability Index), but retains official status and is still used in domestic industry. p-Anisidine Value (AV) (Cd 18-90) determines the amount of aldehydes (principally 2-alkenals and 2,4-dienals) in animal and vegetable fats and oils. These are degradation products of peroxides, which are not removed by bleaching. Some fats and oils chemists propose increased use of this method in purchase specifications. Bleaching Test for Soybean Oil (Cc 8e-s63) determines the color of a sample of soybean oil after treatment with a specified bleaching earth. Specific methods exist for other oil species. 

Fat oxidative stability is measured by the active oxygen method (AOM, AOCS Method Cd 12-57). Oil or fat is held at 97.8°C while air is bubbled through it. The time required to develop a peroxide concentration of 100 meq/kg is the AOM stability of the sample. A closely related method, the oil stability index (OSI, AOCS Method Cd 12b-92), also bubbles air through hot oil. One of the breakdown products is formic acid, which is trapped in a water cell. The machine continuously monitors conductivity of the water, and records the time when it rises sharply. Rancimat times obtained at 110°C are 40-45% of the AOM times, so an OSI stability of 4 h is equal to an AOM stabihty of 10 h. 

The main conclusions of the Round Robin were Karl-Fischer titration is recommended for analysing water in pyrolysis oils. Solids content as ethanol insolubles is accurate for white wood oils but a more powerful solvent, like a mixture of methanol and methylene chloride (1 1) is needed for extractive-rich oils. For the elemental analysis at least triplicates are recommended. Kinematic viscosity is an accurate method for pyrolysis oils. Stability index needs more clarification and testing,- Results of chemical characterisation were not very consistent. It may be necessary to prepare standard solutions with known aniounts of conqiounds for... 

Lipid hydroperoxides can be measured by peroxide value (PV) and 2-thiobarbituric acid (TBA) tests. The resistance of a fat or an oil to oxidative rancidity can be measured by the Schaal oven test, Swift test, and oil stability index (OSI) analysis. 

Coppin, E.A. and Pike, O.A. (2001) Oil stability index correlated with sensory determination of oxidative stability in light-exposed soybean oil. J. Am. Oil Chem. Soc., 78, 13-18. 

The Oil Stability Index (OSI) is another method to measure oil stability that can be conducted using AOCS Method Cd 12b-92 (AOCS, 2005) with a Rancimat instrument or an Oxidative Stability Instrument. The OSI may be run at temperatures of 100, 100, 120, 130, and 140°C. Although oil processors and food manufacturers are interested in rapid measurements of oxidation, the high temperature at which the procedure is conducted may not be relevant to ambient temperatures used for most oil storage. Frankel (1993) suggested that the variation in results at 110°C with the rapid analysis and ambient temperature storage may be because of differences in the oxidation mechanisms at the two temperatures. 

Knothe, G. R.O. Dunn. Dependence of oil stability index of fatty compounds on their strucrure and concentration and presence of metals./. Am. Oil Chem. Soc. 2003, 80, 1021—1026. 

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