Changes in repeatedly heated oils during deep fat frying.

To assess the stability of oils during repeated frying,
refined groundnut oil, raw groundnut oil, and refined groundnut
oil blended with raw sesame oil in the ratio 3 : 1 v/v
which were used for deep frying at regular intervals were investigated.
The oils were examined for % triglycerides, % diand
mono-glycerides, % free fatty acids. UV spectrum of triglycerides,
diglycerides and mono-glycerides at a regular intervals.
Glyceride composition revealed that as frying progressed,
degradation of triglycerides increased. The values for triglycerides
for samples A, B and C were found to be between 93.0
to 79.1, 93.2 to 79.6 and 93.0 to 80% respectively. Effect of
natural antioxidants like tocopherols and sesamol present in
groundnut oil and sesame oil have been studied. No significant
change in free fatty acids content was noticed. Ultra violet
spectrum of triglycerides and mixture of diglycerides and
monoglycerides have shown a strong absorption at 242 nm and
a weak absorption at 270 nm indicating the likely presence of
conjugated ene-one system generated after deep frying. Incorporation
of sesame oil in refined groundnut oil retarted the
progress of oxidation.