Food & Nutrition

Arab Journal of Food & Nutrition
47. A Study of Some Chemical and Physical Changes in Soybean Oil and
Palmolein during Falafel Frying (1999)
Mai Adnan Abdullah\ University of Jordan
Supervisor: Dr. Ayed S. Amr
Palmolein and soybean oils were heated at separately 160, 190 and 220±10°C for
2, 6 and 10 hours alone, and with falafel being fried with and without skimming.
Chemical and physical properties of these oils were studied including the free fatty
acid and acid value, peroxide value, p- anisidine value, totox value, Kreis test, iodine
value, ultraviolet extinction at 230, 234, 268 and 275nm, melting point, viscosity,
specific gravity, refractive index, dielectric strength and color. Both temperature and
time of frying had significant effect (P≤0.01) on these chemical and physical
properties of palmolein and soybean oils.
Results showed a good performance stability of palmolein oil compared with
soybean oil, more deterioration took place in unskimmed oil, compared with skimmed
oil and more degradation at higher temperature, i.e. >190 ±10°C, and increased
duration of frying.
Tow colorimetric quick tests Rau®-test and Fritest® were evaluated for
predicting the deterioration of oil. Both could be used with sufficient accuracy as
quality control test. It has been found that palmolein oil was deteriorated after 10 hours
when heated at 190±10°C but soybean oil deteriorated after 6 hours at the same
heating temperature according to these colorimetric tests.
A good significant correlation (P≤0.01) was found between Fritest® and Rau®test
results and refractive index, free fatty acid, specific gravity, dielectric strength and
viscosity. Melting point, Kreis test, peroxide value and specific extinction showed low
or no significant correlation with the results of these tests.
Stepwise regression test was conducted to construct prediction equations for the
condition of the frying oil, the results show the complexity of the oil heating process,
the results varied according to the dependent variable (Fritest ®or Rue®-test) and the
type of oil used.
A survey was conducted in this study to evaluate the condition of oils used for
falafel frying in Amman in Feb-May. 1998 and some of the physical and chemical
changes that occur in palmolein and soybean oils used for commercial deep-frying of
falafel. It was found that 80% of ate samples were deteriorated according to Fritest®
where 60% of these samples were deteriorated according to Rau® test, thus revealing
the abuse of such oils during frying and reflecting their poor conditions.
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