2.7. Antioxidant assay using β-carotene-linoleate model system
The antioxidant activity of the pineapple extracts was evaluated
using β-carotene-linoleate model system as described by
Jayaprakasha, Singh, and Sakariah (2001) with some modification.
0.1 mg of β-carotene in 0.2 mL of chloroform, 10 mg of linoleic acid and 100 mg of Tween-20 (polyoxyethylene sorbitan monopalmitate)
were mixed. Chloroform was removed at 40 °C under vacuum and the
resulting mixture was diluted with 10 mL of water and was mixed
well. To this emulsion, 20 mL of oxygenated water was added. Four
milliliter aliquots of the emulsion were pipetted into different test
tubes containing 0.2 mL of extracts (50 and 100 ppm) and BHA (50
and 100 μg) in ethanol. BHA was used for comparative purposes. A
control containing 0.2 mL of ethanol and 4 mL of the above emulsion
was prepared. The tubes were placed at 50 °C in a water bath and the
absorbance at 470 nm was taken at zero time (t=0). Measurement of
absorbance was continued till the colour of β-carotene disappeared in
the control tubes (t=60 min) at an interval of 15 min. A mixture
prepared as mentioned above without β-carotene served as blank. All
determinations were carried out in triplicate.