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Reaction conditions for measuring oxidative stability of oils by thermogravimetric analysis

1985; Wiley; Volume: 62; Issue: 12 Linguagem: Inglês

10.1007/bf02541668

1558-9331

Mario Mikula, Ali Khayat,

Edible Oils Quality and Analysis

Abstract A method for evaluating the oxidative stability of oils based on heating the sample in an oven and periodically testing for weight gain has been known for over 100 years. Thermogravimetric analysis (TGA) with its highly sensitive recording electrobalance turns this simple method into a powerful technique for studying the relative thermooxidative stabilities of oils. This paper explores the potential of an isothermal TGA via evaluation of several freshly processed, unhydrogenated soybean oils. The objective was to define the parameters of the TGA experiment for fast routine measurement and to compare isothermal and dynamic experiments. The consideration of influence of temperature, specific surface area, air flow rate, sample volatilization and nature of the sample pan on the induction period (IP), which is a measure of the oil's resistance to oxidation, revealed that the temperature and specific surface area are the major parameters that affect the oxidation process. The Arrhenius plot in the range of 80–150 C has shown that the overall activation energy of the oxidation process for three freshly processed oils lies within the range of 21–22 kcal/mole. The rate of oxidation at 150 C is directly proportional to the specific surface area of an oil, suggesting that the rate of oxygen diffusion determines reaction rates at this temperature. A coefficient of variation of the IP better than 2% was found in a routine experiment (10 mg sample, 150 C, 60 ml/min air flow rate, aluminum pan) for typical oils which had an IP range of 25–31 min.