ANALYSIS At a certain interval of time,

 ANALYSIS OF OXIDATIVE STABILITY

Rancimat

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The vulnerability of oils towards oxidation was determined using rancimat test. It was performed on rancimat apparatus by measuring the induction period at 100-110ºC and the air flow rate was set at the desired level. The induction period was determined on the basis of the conductometric detection of volatile acids. 21,23

Schaal oven test

Oil sample (5g) was accurately weighed in a 250ml flask. The flask was placed in an oven at a temperature of 80ºC. During the heating process, the oils were protected from light. Caution was taken that the glass wares were clean and the flasks were evenly distributed in the oven. At a certain interval of time, the samples were randomly withdrawn. The peroxide value of the sample oils was determined and the result was expressed as meq peroxide per kg oil. 19

Active oxygen method (AOM)

Sample oil (40ml) was measured and transferred into a 50ml screw cap tube. It was then placed in an oil bath held at 112±1ºC. The two Pasteur pipettes were connected to a medical air tank via a plastic Y and clean tygon tubing. The pipettes were inserted into the oil 2cm from the bottom. Once the tubes were positioned into the bath air flow was started and the flow was measured. After a certain period of time, the sample was withdrawn and anisidine value was determined. 19

Oxidative stability index (OSI)

The OSI is defined as the hours for an oil sample to develop a measurable rancidity. The OSI is measured using a Rancimat instrument. The sample oil (4 mL) was transferred into the reaction tube and the oxidation is carried out after setting the temperature and airflow rate at the desired level. 27

 

ANALYSIS OF THERMAL STABILITY

Differential scanning calorimetry (DSC)

DSC has the possibility to be used as a non-chemical technique to determine the quality factors of the oil. Weigh the oil sample (5.0±0.5mg) in an open aluminum pan and then place in the sample chamber. The isothermal temperature can be programmed at different temperatures (110ºC, 120ºC, 130ºC, 140ºC). The purified oxygen was passed through the enclosed sample at the desired flow rate. 23,27,32

 

 

Thermogravimetry (TG) or Thermogravimetric analysis (TGA)

TGA can determine the quantity of weight alteration of a material, either as a function of elevating temperature, or isothermally as a function of time, in an atmosphere of nitrogen, helium, other gas or in vacuum. The oil sample was weighed and transferred into the TGA platinum pan. The pan was then placed in a furnace. The sample was heated in an air atmosphere. The temperature can range from 25ºC-900ºC. 5,33,37