"The outcome of the present study suggests that crude olive juice can be used in practical operation to extend the frying life of frying oils," wrote lead author Radwan Farag from Cairo University.
The use of natural alternatives to synthetic preservatives, such as like butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT), to slow down the oxidative deterioration of food is gaining interest.
According to a 2003 report by Frost and Sullivan, the synthetic antioxidant market is in decline, while natural antioxidants, such as herb extracts, tocopherols (vitamin E) and ascorbates (vitamin C) are growing, pushed by easier consumer acceptance and legal requirements for market access.
This natural antioxidant range could potentially include the polyphenol-rich extract from olive leaves, suggests new research published in the International Journal of Food Science and Technology .
The Egyptian researchers compared the antioxidant performance of 400, 800, 1600, and 2400 ppm of olive polyphenols with BHT (200 ppm) on the stability of sunflower oil under heating conditions (180 degrees Celsius, five hours per day for five days).
Measures of physical and chemical characteristics as a result of adding the antioxidant ingredients showed that no significant effect on the colour of the oil occurred by addition of any level of olive polyphenols.
The formation of peroxides in the oil as a result of heating also decreased with increasing olive juice concentration, said the researchers.
"In fact, the peroxide value of the heated sunflower oil mixed with 2400 ppm of polyphenolics at the end of the heating process was about 11.3, 9.2, 2.8 and 11.4 times lower than that of the sunflower oil mixed with 400, 800, 1600 and control, respectively," they wrote.
Using the thiobarbituric acid (TBA) assay to measure lipid oxidation, the researchers report that the 400 ppm level of olive polyphenolics exhibited almost the same antioxidant activity as 200 ppm BHT, while 800 ppm of olive polyphenolics was superior to the synthetic antioxidant.
"Therefore, one would recommend adding 800 ppm of the phenolic compounds of olive leaf juice to increase oil stability," wrote Farag.
"The data indicate that the addition of olive leaf juice to sunflower oil heated at 180 degrees Celsius induced remarkable antioxidant activity and at 800 ppm level was superior to that of BHT in increasing sunflower oil stability," concluded the researchers.
The cost of the olive leaf juice could also add to the attractiveness of using the juice as an ingredient with antioxidant activity, suggested the researchers.
"One has to point out that the main goal of this work was to use a very cheap natural source to as antioxidant agent," wrote Farag.
"It is of interest to note that olive leaves used as a natural source for antioxidants in the present study are obtained by the annual pruning of olive plants."
Antioxidant revenues are predicted to grow from €46m ($55m) in 2004 to €58m ($70m) in 2008, according to Frost and Sullivan.
Source: International Journal of Food Science and Technology (Blackwell Publishing) Volume 42, Pages 107-115, doi: 10.1111/j.1365-2621.2006.01374.x "Use crude olive leaf juice as a natural antioxidant for the stability of sunflower oil during heating" Authors: R.S Farag, E.A. Mahmoud, A.M. Basuny