Postharvest Biology and Technology 43 (2007) 335–342 Analysis of the main secondary metabolites produced in tomato (Lycopersicon esculentum, Mill.) epicarp tissue during fruit ripening using fluorescence techniques A. Lai a,∗ , E. Santangelo b , G.P. Soressi c , R. Fantoni a a ENEA, Divisione Fisica Applicata, Centro Ricerche Frascati, Via Enrico Fermi 45, 00044 Frascati, Roma, Italy b Consorzio Agrital Ricerche, Viale dell’Industria 24, 00057 Maccarese, Roma, Italy c Department of Agrobiology and Agrochemistry, Tuscia University, Via S.C. de Lellis s.n.c., 01100 Viterbo, Italy Received 14 July 2005; accepted 15 September 2006 Abstract Tomato (Lycopersicon esculentum L.) fruit are an important source of antioxidant (mainly pigment) compounds, as well as lycopene, - carotene, ascorbic acid and polyphenols. Differentiation of the final product in the market requires an accurate evaluation of these value-adding compounds. Because of this, we have undertaken a comparison of the spectral characterisation of the tomato fruit surface pigments from the immature to over-ripe stage, using spectroscopy techniques based on visible fluorescence emission upon excitation in the same or ultraviolet spectral regions. The aim was to verify the spectral band for optimal conditions for fruit harvesting using non-destructive techniques. The pattern of pigment composition changed markedly during ripening and showed progressive disappearance of chlorophyll with a concomitant increase in carotenoids until the fully ripe stage. The main fluorescence spectral features belonging to anthocyanins, flavonoids, carotenoids and chlorophyll a after excitation of skin tomato pigments at different laser wavelengths was identified. In comparing, the fluorescence spectral ratios at the excitation wavelength λ exc = 266 nm, significant differences were obtained for the spectral ratios of chlorophyll/flavonoids and carotenoids/chlorophyll. Positive correlation coefficients were found for the carotenoids/flavonoids (0.780) ratios and negative ones for the carotenoids/chlorophyll ratios (-0.513). Analysis of fluorescence resulted in determination of the most useful laser radiation for remote non-invasive measurements with laser- induced fluoresence (LIF): for the ripening stage, λ exc = 266 nm was the optimal laser wavelength, since the induced fluorescence spectra obtained appeared to differ with the physiological stage of the fruit. © 2007 Elsevier B.V. All rights reserved. Keywords: Lycopersicon esculentum; Fruit ripening; Skin pigments; Laser-induced fluorescence 1. Introduction Tomato (Lycopersicon esculentum L.) ripening involves a number of physiological processes that include the visi- ble breakdown of chlorophyll and build-up of carotenoids, with massive accumulation of antioxidant components such as lycopene and -carotene (Laval-Martin et al., 1975) within the plastids. Besides carotenoids, the contents of other important antioxidant compounds, such as ascorbic acid, - tocopherol and phenolics, vary during ripening, thus varying ∗ Corresponding author. Tel.: +39 06 94005207; fax: +39 06 94005312. E-mail address: lai@frascati.enea.it.it (A. Lai). the nutritional value and the antioxidant activity of the fruit (Giovanelli et al., 1999; Mart` ınez-Valverde et al., 2002; Raffo et al., 2002; Cano et al., 2003; Slimestad and Verheul, 2005). Ripening conditions affect both the antioxidant accumulation kinetics and the final contents, which are higher in postharvest ripened than in vine-ripened fruit (Giovanelli et al., 1999). Effective monitoring of crop production needs continuous information to be collected on the metabolic state and the physical and chemical cell environment of the fruit. Current imaging techniques allow monitoring of changes in the phys- iological state of plants to be performed on-line, in situ and even non-invasively. Non-destructive technologies for eval- uating the quality of a food might be helpful for improving 0925-5214/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2006.09.016