The Effect Of Heat On Some Chemical Properties Of Vegetable Oils And Fats

ABSTRACT

Samples of oils and fats of different degree of unsaturation namely; shea

butter, palm oil and groundnut oil were heated at three different temperatures

(150°C, 110°c and 190°C) for 2, 4, 6, 8 and 1 Ohrs using a temperature

regulated, lidded-deep frying equipment. The changes in some chemical

properties were monitored. These chemical properties include acid value,

iodine value, saponification value, peroxide value and volatile content. The

total phosphorus contents were also monitored. Changes in some mineral

elements such as Zinc, Cobalt and Copper, in the samples were also followed.

The results showed that the changes in some of their chemical

properties are dependent on the heating temperature, heating time or duration

and the degree of unsaturation of the oil/fat. For example, acid value

decreased with temperature and heating time more in shea butter (80%

saturation) (from 14.95 to 8.70) than in groundnut oil (20% saturation)

(virtually no change). The deterioration of heated oil under storage, generally

depend on the degree of unsaturation of the oil/fat, the temperature at which it

was heated, and the duration of heating before storage. For example, all the

samples appeared to be more resistant to peroxide formation when heated at

190°C than when heated at 150°C. The depletion of total phosphorus

appeared to generally depend on the duration of heating rather than heating

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temperature, and this was noticeable in shea butter and groundnut oil. The

presence of high level of antioxidants may be responsible for the slight

stability of phosphorus in palm oil. There were no defined pattern(s) in the

changes in mineral content.

The result showed changes in these parameters which could be used in

online monitoring of heating processes in oil processing/use.