Food & Nutrition

Arab Journal of Food & Nutrition
7. A Comparative Study of the Chemical and Physical Properties of Samples of
Nabali – Virgin Olive, and Olive Kernel Oils (1992)
Ala'a Izzat Farid Abu Al – Rub\ University of Jordan
Supervisor: Dr. Ayed S. Amr
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Four types of olive oil were studied: hexane extracted olive pulp, flesh and kernel
oils in addition to the mechanically – extracted virgin olive oil. The kernel oil showed
the most drastic differences among these oils in physical and chemical tests, it had a
significantly lower melting point and maximum - absorption wavelength at ultraviolet
range than other three oils. Kernel oil had a higher specific gravity value than flesh and
virgin olive oils, and was not significantly different from olive pulp oil. There were no
significant differences in the values of Bellier index, refractive index, iodine value and
saponification value among the four olive oils. Unsaponifiable matter content of flesh
oil was significantly higher than other olive oils tested in this study. The four olive oils
were separated by thin layer chromatography into their basic lipid classes, using silica
gel DG. All the olive oils studied were separated into seven lipid classes. However,
olive kernel oil showed two additional unidentified classes.
The methyl ester of triglyceride fractions as well as their respective oils were
analyzed by gas liquid chromatography (GLC) to determine their fatty acid
composition. Oleic acid percent was the highest in all the triglyceride fractions and
their unfractionated olive oils, although it was lower in the kernel oil than in the
others. Kernel oil and its triglyceride fraction had significantly higher levels of inoleic
acid than other types of olive oil. Trace amounts of α – linolenic acid were detected in
the triglyceride fraction of olive kernel oil as well as in the four whole unfractionated
olive oils. Olive kernel oil and its triglyceride fraction showed lower ratios of oleic to
linoleic, and palmitic to stearic acid than other olive oils and their triglyceride
fractions.
Four internationally recognized method used in the evaluation of the oxidative
rancidity of fats and oils were evaluated for their applicability and accuracy in
detecting oxidative rancidity in virgin olive oil in seven stages. These methods were:
Kreis Test (as Kreis Score), Kreis Absorbance, Thiobarbituric Acid and Peroxide
value. No single test of the four oxidative rancidity test could detect and evaluate
oxidative rancidity in the whole incubation period. On the other hand, peroxide value
test was the most efficient test in evaluating the oxidative rancidity in olive oil during
all the incubation periods except the decline stage and hence peroxide value correlated
highly (p 0.01) with the incubation time.
During the decline period Kreis absorbance test was the most efficient. However
Kries score was effective in detecting oxidative rancidity during the earlystages of
oxidation. Thiobarbituric acid test was most efficient during both acceleration and total
activation periods of oxidation profile.
Bellier index and Bellier test were used as adulteration tests to detect adulterant
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Volume 11, No. 25, 2011