AB-408
Oxidation stability of fats and oils in solid foods using the Rancimat method
Summary
The Rancimat method is an accelerated aging test also known as the oxidation stability index (OSI). At a stable high temperature, air flows through a sample (e.g., vegetable oil) in the reaction vessel. During this process, fatty acids undergo oxidation. After the accelerated oxidation test concludes, volatile secondary reaction products form. These products are carried into the measuring vessel by the air stream and then absorbed into the measuring solution (deionized water).
The absorption of the reaction products increases the measuring solution's electrical conductivity, which is continuously recorded. This identifies their degree of oxidation. The induction time is the amount of time it takes to detect secondary oxidation products. It indicates the oxidative stability of food, for example oil samples like sunflower oil, corn oil, or virgin olive oil, as well as fats or unsaturated fatty acids.
In the food industry, quality control requires determining the stability of solid foods against oxidation. Determination of the oxidative stability by direct measurements of fats and oils in solid foods is performed whenever possible. If the samples cannot be measured directly, this can still be accomplished by using the isolated fat following cold extraction with petroleum ether.
Additionally, the innovative PEG (polyethylene glycol) method has proven to be the most successful approach for OSI testing with the Rancimat, aside from direct measurement or cold extraction. The PEG method is quite effective for products with challenging matrices or when the objective is to avoid laborious sample preparation.
A further method is the determination of the stability index (SI), which is a measure of the antioxidant capacity of a product. In the stability index method, the sample is mixed with a reference of antioxidant-free fat (e.g., pure lard), and the induction time is then compared with the reference alone as a control. It is evident that, owing to its inherent properties, the product exerts a retarding effect on the oxidation of the reference. In this study, pure lard was utilized as the reference material. This approach does not directly measure the oxidative stability of the sample; rather, it measures its influence on the oxidative stability of the reference. This method, which is the subject of a separate chapter in this Application Bulletin, is very comprehensive, but is no longer widely used because pure lard is not available in all countries and is not offered in a standardized form. Conversely, the aforementioned method employing PEG has demonstrated a high degree of reliability and ease of standardization.
This Application Bulletin provides a detailed description of all the mentioned Rancimat test methods and their requisite sample preparation steps.