Abstract:
Palm oil is widely used in shops as the frying medium. This study was carried out
to evaluate the effect of continuous heating on the quality of the palm oil and the
effects of adding passion fruit (Passiflora edulis) leaf extract on its stability.
Antioxidants were extracted from the leaves using acetone. Negative control
(samples without any added antioxidants), positive control (samples added with
200 ppm of Butylated Hydroxytoluene (BHT) and test (samples added with 1000
ppm of extract) samples were prepared. All oil samples were evaluated for their
stability during continuous heating by heating the oil at 170±5 °C up to 24 h (30
min heating followed by 30 min cooling). The level of oxidation of the samples
was determined by evaluation of peroxide value, p-anisidine value, TOTOX value,
free fatty acid content, total polar compounds and fatty acid composition and
conjugated diene (CD) and conjugated triene (CT) values. The data were
analysed by performing ANOVA (α = 0.05) using SAS. The free fatty acid content
of the oil before heating was significantly higher (44.76±0.09%) than the
standard value (5%) indicating that the oil has undergone extensive hydrolysis
already. All parameters measured were increased in all three samples, however,
free fatty acid content, peroxide value, p-anisidine value and CD and CT values
were significantly less in the test samples than positive control and negative
control. The average rate of formation of polar compounds (% increase per
heating cycle) was significantly less in the test sample (1.29%) and positive
control (1.27%) than negative control (1.68%). These results indicate that
passion fruit leaf extract (1000 ppm) can more effectively control thermal
oxidation of palm oil than BHT during continuous heating. This study shows that
the fresh passion fruit leaf extract could be used as a potential source of
antioxidant to improve the oxidative stability of edible oils
