The purpose of this paper is to describe the factors affecting olive oil composition and to overview the effect of its composition on nutrition and human health. It is well accepted that the high mono-unsaturation of olive oil and the presence of several other constituents such as phenols and tocopherols, chlorophyll and pheophytin, sterols, squalene, aroma and flavour compounds and others exhibit a significant role on the health. Olive oil, as a highly monounsaturated oil, is resistant to oxidation. Also the presence of phenols, tocopherols and other natural antioxidants prevent lipid oxidation within the body eliminating the formation of free radicals which may cause cell destruction. The aroma and the flavour compounds of olive oil, as well as the chlorophyll and pheophytin pigments, increase the stomach secretion and facilitate the absorption of the natural antioxidants, which furthermore protect the body tissues from oxidation. Epidemiological studies suggest that the high consumption of the monounsaturated olive oil in Mediterranean countries, is related with the low rates of cardiovascular disease (CHD), cancer of the breast and of high life expectancy.

1. MAIN OLIVE OIL CONSTITUENTS

   Olive oil contains triacylglycerols and small quantities of free fatty acits, glycerol, pigments, aroma compounds, sterols, tocopherols, phenols, unidentified resinous components and others (Kiritsakis, 1998). Among these constituents the usaponifiable fraction (Fig 1), which covers a small percentage (0,5-15%) plays a significant role on human health.
    

   1. Oleic Acid Olive oil contains a high percentage of the monounsaturated oleic acit. Thus, it is a natural monounsaturated oil. This particular fatty acid reduces LDL-cholesterol, which is responsible for the formation of the atherosclerotic plaque, and increases the HDL-cholesterol. The latter is removed from arterial cells.
       
   2. Hydrocarbon squalene The hydrocarbon squalene, and important metabolic factor, is present in high percentages in olive oil (Fig 1).
   3. Tocopherols  Olive oil contains the tocopherols a -, b -, g -, d - (a - tocopherol covers almost 88%). The tocopherol content of olive oil depends not only on the presence of these compounds in olive fruit but also on several other factors, involved in the transportation, storage and olive fruit processing. According to Viola (1997), the ratio of vitamin-E to polyunsaturated fatty acids in olive oils is better than in other edible oils.

      

      Figure 1: Unsaponifiable components of olive oil
       

   4. Pigments The colour of olive oil is mainly related to the presence of chlorophyll and pheophytin. Carotenoids are also responsible for the colour of olive oil. The presence of these constituents depend on several factors, such as cultivar, soil and climate, and fruit maturation as well as applied conditions during olive fruit processing.
       
   5. Phenolic compounds Olive fruit contains simple and complex phenolic compounds. Most of these compounds pass into the oil, increase its oxidative stability and improve the taste. Hydrohytyrosol, tyrosol and some phenolic acids are mainly found in olive oil (Kiritsakis, 1998). The phenol content and the specific composition of these phenols in olive oil depend on the altitude where the olive trees are grown, on the harvesting time and on the processing conditions (Cinquanta et al., 1997; Kiritsakis, 1998).
       
   6. Aroma components  Aroma and the taste of olive oil are its main sensory characteristics. These characteristics are attributed to a group of aroma compounds. Their formation occurs in olive fruit, via a series of enzymatic reactions (Kiritsakis, 1998). Figure 2 shows a gas chromatography mass spectroscopy (GC-MS) analysis of three different olive oil samples. In the sample of good quality (a), trans-2-hexenal is the predominant component. The other two samples (b,c) have defects (Tateo et al, 1993).
       
2. ASSIMILATION OF OLIVE OILS FROM THE HUMAN BODY

Olive oil is greatly assimilated by the human body. The assimilation of this 'natural fruit juice' by our body is mainly attributed to the high percentage of triolein. Also, the pigments chlorophyll and pheophytin and the aroma components present, facilitate its absorption from the human body. The latter differentiate the gastric fluid composition of the stomach and increase the digestive activity. The great assimilation of olive oil from the human body facilitates the absorption of vitamin-E and phenols as well.

Figure 2: Gas chromatography mass spectroscopy analysis of the flavour components of three samples of olive oil (a: fruity flavour, b and c: with defects) (Tateo et al, 1993).

The accumulation of free radicals, as a result of oxidation in the body, causes serious problems on human health. More specific, free radicals destroy the polyunsaturated fatty acids of the membranes and the DNA (Fig 3), which facilitates the aging process, causes damage to the liver and even cancer formation. Our body is protected from the free radicals by free radicals scavengers such as vitamin-E and phenols. The latter, present in significant amounts in olive oil, prevents the human’s cell destruction. Greeks and Italians, who consume large quantities of virgin olive oil, intake almost 25gr of phenols per day, which is a significant amount for preventing oxidation.

Figure 3: Effect of free radicals in polyunsaturated fatty acids of membranes and DNA. (Viola, 1997).

Recent studies showed that LDL-cholesterol oxidation promotes the atherosclerotic plaque formation (Kafatos, 1995; Lenart et al, 1998). Diets rich in olive oil on the other hand showed a stable ratio between total cholesterol and HDL, and a reduction of LDL-cholesterol. Even though the role of triacylglycerols in coronary disease is still unclarified, the substitution of olive oil with complex starches in the diet, decreases the triacylglycerols in blood serum. Greece, a member of the seven country study with the highest consumption of olive oil, shows the lowest number of deaths from coronary disease (Trichopoulou, 1993). Recent studies in South Italy, showed an increase in cholesterol content almost 2% every year, after the abundance of Mediterranean diet, in which olive oil is the major fat component.

In conclusion, oleic acid and mainly the unsaponifiable fraction of olive oil, such as phenol, tocopherols, chlorophyll, squalene and aroma components, exhibit a high nutritional and biological value, resulting in good human health.

Cinquanta, L, Esti, M, and Notte, E L, Evolution of phenolic compounds in virgin olive oil during storage, J Am Oil Chem Soc 74: 1259 (1997).

Kafatos, A Olive oil consumption in Crete. One of the main characteristics of the Mediterranean – Cretan Diet. Olivae: 56:22 (1995).

Kiritsakis, A. Olive oil – Second Edition, From the tree to the table. Food and Nutrition Press, Inc. Trumbull, Connecticut, 006611, USA.

Lenart, E B, Willet, and Kiritsakis A, Ibid.

Tateo, E, Brunelli, N, Cucurachi, S, and Ferillo, A, New trends in the study of the merits and shortcomings of olive oil in organoleptic terms, in correlation with the GC/MS analysis of the aromas. In Food Flavours, Ingredients and Composition, G Charalampous, editor, Elsevier Science publishers B V , Amsterdam (1993).

Trichopoulou, A, Katsoyanni K, and Gnardellis, C, The traditional Greek diet. European Journal of Clinical Nutrition (Suppl 1 ) 47:76 (1993).

Viola P, Olive Oil and Health. International Olive Oil Council, Madrid Spain (1997).