Student - April 16, 2009


Oil from the resin of the mastic tree limits the growth of bacteria and fungi. Lisa Gkokga from Greece demonstrated this in her graduate research project with the Food microbiology chair group. And her thesis has won the annual prize of the NVVL Network for Food Experts, a large Dutch professional association.

Lisa Gkogka’s graduate thesis on the antibacterial effects of essential oils went down well with the NVVL Network for Food Experts.
Gkogka studied the antibacterial effect of essential oils, and in particular the oil that is extracted in Greece from the resin of the Mediterranean mastic tree, a member of the pistachio family. ‘I have an obsession with spices’, she explains. ‘The aromatic resin of the mastic tree has been used for thousands of years as a spice in Mediterranean cooking, but it also has countless medicinal uses.’

Almost all the resin comes from the Greek island of Chios, and the oil is extracted from the ivory-coloured drops of resin known as the tears of Chios. At the most, three percent of the resin is made up of oil. Much as the Greeks enjoy the flavour, when Gkogka took some of the resin along for Dutch students to taste, they were not all so positive. Some of them thought it tasted like soap.

Gkogka wanted to do something new and decided to test the mastic oil for antibacterial properties. ‘I was curious what effect it would have on micro-organisms in food. The resin largely consists of aromatic hydrocarbons such as terpenes, which limit enzymatic processes and micro-organisms as well.’ In her prize-winning thesis, she placed her experimental findings in a broad context and compared the effectiveness of mastic oil with that of essential oils from other spices.

One of the obstacles for the planned exposure experiment was the fact that mastic oil is not soluble in water. This makes it difficult to apply it to micro-organisms, which grow on a water-based culture medium. The solution was to mix the mastic oil with a special, extra syrupy culture medium. ‘I like to think up analytical and experimental methods, and I see practical problems as a challenge’, says Gkogka.

The experiment showed that mastic oil curbs the growth of bacteria and, to a lesser extent, of moulds and yeasts. ‘Unfortunately, though, the effective concentrations were so high that it is not realistic to add the oil to foodstuffs as an antibacterial agent. The oil is far too expensive for that, too', says Gkogka, putting things in perspective. ‘Cinnamon and clove oil are much more effective and cheaper.’ So for the time being, the main use of the tears of Chios will be as a flavouring in Greek cooking.