1010
gradient used was as follows: 0-7 min 99.5% hexane and 0.5% isopropanol; 7-9 min linear gradient of 0.5-
1% isopropanol; 9-20 min 99.0% hexane and 1.0% isopropanol; 20-25 min reconditioning of the column
with 0.5% isopropanol isocratic for 10 min. The chromatographic run time for each analysis was 35 min.
Samples were dissolved in hexane, and aliquots of 20 μL were injected into the HPLC system.
Determination of the total phenolic content
The total phenolic content was quantified using Folin-Ciocalteu reagent, with minor modifications.
A 300-μL aliquot of extract solution was mixed with 5 mL of Folin-Ciocalteu reagent (10% in distilled
water). After 5 min, 4 mL of sodium carbonate (7.5% in distilled water) was added. The samples were
incubated for 2 h at room temperature in the dark. The absorbance was measured at 765 nm. A standard
curve was prepared with gallic acid solutions of know concentrations. The results were expressed as mg
gallic acid equivalents (GAE) per kg of extract.
Measurement of oxidative stability
The oxidative stability of the sample was evaluated with a Metrohm 743 Rancimat instrument
which measures the rate of oxidation under accelerated conditions. The tests were performed with 3 g
samples at a temperature of 130
o
C and flow of air 20 L/h. The oxidative stability was expressed as the
induction time for oxidation of the oils.
Results and discussion
Extraction yield
Different solvents have different resolving strength towards the plant constituents which
resulted in different yield as shown in Table 1. The extraction of methanol resulted with the
highest amount of yield. Oil palm fruit (100 g) used in methanol -polar solvent extraction obtained
the highest yield (5.41%) while the other yielded only 1.20 -3.58%.
Table 1
Yield of oil palm fruit (200 g) extracted using different types of solvents.
Solvents
Yield
gram
%
Acetone
4.84
2.42
Ethanol
7.16
3.58
0.05 mM Tris-HCl buffer (pH 8)
7.16
3.58
Methanol
10.82
5.41
Chloroform
2.40
1.20
Hexane
2.90
1.45
The extraction yield of palm oil fruit (this study) showed the similar pattern with the
result from Yin [13]. The extraction yield of leaves from
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gave the highest value
