Lycopene content must be distinguished from lycopene bioavailability. The above mentioned studies are incomplete because they only measured the lycopene content, not its bioavailability, which is most important for the nutritional quality of the product. Therefore, the most stimulating object of research on lycopene is, perhaps, to evaluate the actual bioavailability for humans in the forms in which lycopene is present in processed tomato products.34
Although there are a number of comparative studies on the bioavailability of lycopene in tomato products, there are no proven methods for the quantitative assessment of carotenoid bioavailability, even of b-carotene which has been the most frequently studied. A few studies have been carried out on the bioavailability of lycopene in the human diet. Some of them indicate that the absorption of lycopene is greater from heat-treated tomato juice than from untreated juice, and others indicate that absorption from tomato paste is greater than from fresh tomatoes.
It has been clearly demonstrated that the physical state and processing history of a food item have a very marked effect on the availability of these compounds for absorption. This indicates that disruption of the food matrix and thermal history via the processing technique could be the most important factors affecting bioavailability. It is also known that the bioavailability of carotenoids is markedly affected by the fat content of the general diet, because the presence of lipids is essential for the extraction of carotenoids from the aqueous bulk of the food and for the formation of mixed micelles via which the carotenoids are then absorbed by enterocytes and transferred to the tissues (via plasma lipoproteins). Carotenoids are passively absorbed lipophilic compounds and their bioavailabil-ity is therefore affected by those factors that influence their mass transfer from food into the mixed micelles that can be absorbed by the intestine.35 Interestingly, absorption can be improved by cooking and homogenising the food, thus breaking down the cell structure, as long as the cooking is carried out in the presence of oil or fat.
As long as lycopene remains in the aqueous matrix and more so if it remains inside the undamaged cells it is very stable but has little reactivity. Its bioavail-ability is therefore small and its efficacy as antioxidant almost zero. In contrast, its high solubility in a lipid medium (for instance in certain products formulated with oil) imparts considerable reactivity as well as complete bioavailability. Its assimilation is decidedly better if foods are cooked and homogenised so as to disrupt the cells and even more so if this occurs in the presence of oils or fats.
However this effect is inevitably counteracted by a more rapid degradation of its antioxidant power.
When lycopene solubilises in a lipophilic matrix, it has considerable reactivity and more availability, thus enabling it to undertake its antioxidant activity. However, this greater reactivity also means that it is more unprotected against the degradation effects of environmental conditions (air, biological matrix components, temperature).
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