Some local natural sources of antioxidant such as orange peel extract (Citrus
sinensis), pomegranate peel extract (Punica granatum) and ginger extract
(Zingiber officinale L.) were evaluated during 5 days storage of refined palm oil
at 63°C as com
pared to the synthetic antioxidant such as propyl gallate. The
above extracts were obtained with ethanol and oil (palm oil). Those extracts
were added to the oil at two different levels (100 ppm and 200 ppm).
Antioxidant activity of natural extracts, synthetic antioxidant and the control
treatment without antioxidant under thermal treatment (Schaal test) was
assessed by measuring acid value (AV), peroxide value (PV), iodine value (IV)
and refractive index (RI) during 6 days storage of refined palm oil at
temperature mentioned above. Antioxidant activity also measured by studying
the stability of oil by the use of rancimat method. All treatments exhibited
antioxidant activity. Statistical analysis results were shown that the
pomegranate peel extract treatment was significantly (P<0.05) superior than
the orange peel extract and ginger extract treatments whereas, it was not
significant difference about propyl gallate treatment.
The phenolic compounds were extracted from leaves and flowers of Hops and grape
seeds from local production by soaking with different solvents (Methanol-ethanol-alcohol
and water mixture) . The polyphenols content in the methanol extracts for 100 g
dry matter
was 6.31 g for the grape seeds, 2.08 g for Hops leaves and 0.6 g for Hops flowers.
Methanol extracts were characterized by an antioxidant activity that appeared by their
ability to Reduce ions ferriques Fe+3, at a concentration of 2500 ppm, the Reducing Power
was 96.45% , 67.56% for the grape seeds and Hops leaves, respectively. The methanolic
extracts of grape seeds and Hops leaves at 80 ppm showed activity in scavenge free radical
DPPH. was 82.04% and 40.92% respectively. The methanolic extracts of grape seeds and
Hops leaves at 250 ppm gave the ability to protect linoleic acid from the oxidation process
of 78.98% and 48.41%, respectively. The antioxidant activity values of the extracts were
compared with standard samples of ascorbic acid and BHT.