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The oxidative stability of oils determined with Metrohm's
743 Rancimat
Fatty acids and antioxidants
Natural oils are normally mixed triglycerides
of saturated and unsaturated fatty acids. Common edible
vegetable oils are olive, soybean, peanut, sesame, cottonseed,
rapeseed, poppy seed and linseed oil. Oxygen can oxidize
fatty acids in a multi-step reaction that occurs in
principle according to a radical chain mechanism. The
oxidation products formed by this reaction (mainly formic
acid) are volatile. Antioxidants prevent
the degradation of oxidation-sensitive vitamins, amino
acids and unsaturated fatty acids.
Determination of the oxidative stability
The determination of the oxidative stability of natural
oils is a standard quality control method
in the food industry. Metrohm's
743 Rancimat offers an easy and fast method to determine
the oxidative stability index (OSI)
of natural oils. The Rancimat Method is considerably
less costly, less labour-intensive but as accurate as
the traditional active oxygen method (AOM). Air is blown
through the heated and thermostatted sample (50...220
°C) in order to oxidize it. The stream of air then
carries over the volatile oxidation products (normally
formed at the end of the oxidation process) to a measuring
vessel containing deionized water. The readings of the
conductivity measurement can be plotted as a function
of the time required for the oxidation. The inflection
point of this oxidation curve is known as the induction
time which serves as a measure of quality of the oil
tested.
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Product information
The 743 Rancimat is an instrument with two separate heating blocks. The temperature
of each block, containing four disposable sample vessels, can be controlled
separately. This setup allows the easy and time saving analysis of several different
oils simultaneously. In addition the 743 Rancimat allows predicting the shelf
lives of natural oils and fats.
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Tips
- The Rancimat method also allows the determination
of the antioxidant activity according to the
Application Bulletin 232 (Info
Center).
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For the Validation of the 743 Metrohm Rancimat using Standard
Operating Procedures see our Application Bulletin 278
(Info
Center).
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