ABSTRACT
Recent epidemiological studies suggest a positive correlation between the ingestion of diets rich in vegetables and fruits and a reduced incidence of chronic diseases, such as cancer, cardiovascular disease, Alzheimer’s disease and cataracts. This beneficial effect is primarily attributed to the occurrence of vitamins, minerals and secondary phytochemicals, for example, carotenoids, anthocyanins, flavonoids, and other phenolic compounds that are widely distributed throughout the plant kingdom. Tomatoes are a source of antioxidants and they contribute to the daily intake of a significant amount of these compounds. One hundred grams of tomato can contribute 24-48%, 0.5-0.8% and 2.7-4.0% of the recommended daily intake of vitamin C, vitamin E and β-carotene, respectively. Tomato fruits are also considered the major source of lycopene. Mineral content is normally between 0.60 and 1.80%; the major elements are K, Na, Ca, Mg, P, Fe and Mn.
The main problem of the analysis of micronutrients and bioactive compounds in tomatoes is the selection of an adequate pre-treatment and clean-up method. In the case of fat-soluble vitamins and carotenoids, the main analytical difficulty is the isolation of these compounds from a large excess of 538physically hydrosoluble materials, and hence a great deal of effort has been made to improve extraction and clean-up procedures. Liquid-liquid extraction is frequently used. An attractive alternative to alleviate the risk of isomerization and oxidation of these compounds is supercritical fluid extraction.
There are several methods for measuring total antioxidant activity, and in general all of them imply the generation of radical species and the subsequent evaluation of the presence of antioxidants by the disappearance of these free radicals.
Although there are also official methods based on spectrometric quantification, liquid chromatography has proved to be one of the most useful techniques for the analysis of vitamins. This is a consequence of the versatility in column technology and detection methods. Reverse phase high performance liquid chromatography is the method most widely employed for analysis of carotenoids because of their hydrophobic character. C-18 columns, which are less selective, are preferable for less detailed analysis, while C-30 columns in combination with gradient elution are suitable for the separation of carotenoids and their different isomers with a wide polarity range. High performance liquid chromatography coupled with mass spectrometry improves the sensitivity and the selectivity of the analyses of micronutrients and bioactive compounds, especially with the introduction of modern ionization systems such as atmospheric pressure chemical ionization.
For analysis of minerals, classical methods (Kjeldahl method for total nitrogen and colorimetric method for phosphate analyses) are still routinely employed. On the other hand, when several elements need to be analysed in a plant over a large range of concentration, the analytical tool of choice is usually inductively coupled plasma-mass spectrometry (ICP-MS), followed by ICP-atomic emission spectrometry (ICP-AES) and atomic absorption spectrometry. ICP-AES allows simultaneous measurement of metals together with some non-metals, such as P or B. Thus, this technique has rapidly replaced colorimetric procedures for P and B determinations.
This chapter also describes the different analytical methods that can be applied for the determination of micronutrients and bioactive compounds in tomato fruits and tomato products taking into account trends of the future in analytical methods.
