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AACC Approved Methods of Analysis, 11th Edition -AACC Method 58-54.02. Oil Stability Index

AACC Approved Methods of Analysis, 11th Edition

Special Properties of Fats, Oils, and Shortenings

AACC Method 58-54.02
Oil Stability Index


Resistance of oil to oxidation depends on the degree of saturation, natural or added antioxidants, prooxidants, or prior abuse. Oxidation is very slow until this resistance is overcome, at which point oxidation accelerates and becomes very rapid. The length of time before the rapid acceleration of oxidation is the measure of resistance to oxidation, and is commonly referred to as the "induction period." This method determines the induction period. It is equivalent to Official Method Cd 12b-92 of the American Oil Chemists' Society (AOCS).

In this method, a stream of purified air is passed through a sample of oil or fat that is held in a thermostated bath. The effluent air from the oil or fat sample is bubbled through a vessel containing deionized water. The effluent air contains volatile organic acids, swept from the oxidizing oil, that increase the conductivity of water as oxidation proceeds. Water conductivity is monitored continuously until the point of maximum change in rate (or the second derivative) of conductivity with respect to time is obtained. The oil stability index (OSI) is the point of maximum change of the rate of oxidation. The OSI may be run at temperatures of 110-140°C and, because of this flexibility, results should specify the OSI time with the temperature (for example, "OSI 11.7 hr at 110°C"). This method is applicable to all fats and oils. See Note 1.