The health benefits arising from the consumption of tomatoes have been widely covered, with their antioxidant content linking them to the reduction of disease risk, such as the prevention of prostate cancer.
Tomato peel is an industrial waste product, but found by scientists to have the highest levels of the carotenoid lycopene, compared to the pulp and seeds.
The scientists concluded that enriching oils with tomato carotenoids and lycopene, in particular low quality oils like refined olive oils, could be an alternative approach to elaborate new functional foods.
The study, published in Food Chemistry, looked at the effects of adding tomato pulp to different edible oils.
While the incorporation of both improved the thermal stability of olive oil, but not extra virgin oil or sunflower oil, the peel resulted in more substantial health benefits.
"The results of this study show that the incorporation of tomato peel, as agro-industrial waste, is an efficient means to extract carotenoids and phenolics into the fatty substrate, to enhance their bioavailability, thus upgrading low quality edible oils," said the study.
The study Three types of oils were used for the study - low quality refined olive oil, extra virgin olive oil and BHT-free sunflower oil.
Tomato puree in the amounts of 1g, 2.25g, 5g and 8.6g were added to 20g of the edible oil samples, to give final concentrations of 5 percent, 10 percent, 20 percent and 30 percent respectively.
The peel was mixed with the refined olive oil only at ratios of 5 percent and 10 percent.
The phenolic profile and carotenoid content were then analysed.
Results Adding tomato puree or peel to the olive oils did not lead to any significant change in acidity or peroxide value.
While the sunflower oil showed a significant increase in its peroxide value after the inclusion of 5 percent tomato puree, there was no major change in its acidity.
The incorporation of tomato puree actually led to a decrease in the total polyphenols of the extra virgin olive oil mixtures.
A small but noteworthy decrease was also noticed in the refined oil.
The researchers said the decrease could be a result of the "dissolution of polyphenols into the aqueous phase of the tomato puree during centrifugation".
However, a significant improvement was observed with the addition of tomato puree to the sunflower oil and with tomato peel to the refined oil.
The carotenoid content of the oils tended to be significantly enhanced by incorporating the tomato puree and/or peel.
The authors wrote: "Tomato peel incorporation in refined olive oil was more efficient to enhance its content on lycopene and ß-carotenoids as compared to tomato puree .
"Moreover, tomato puree incorporation induced leaching of phelonic compounds, while tomato peel permitted to overcome this problem and enhance significantly the total phenol content of the refined olive oil."
Source Food Chemistry Volume 110, Issue 3, 1 October 2008, Pages 684-690, published online ahead of print, doi:10.1016/j.foodchem.2008.02.063 "Valorisation of low quality edible oil with tomato peel waste" Authors: Amar Benakmoum, Souheila Abbeddou, Ali Ammouche, Panagiotis Kefalas and Dimitrios Gerasopoulos