Lycopene and Hydroxymethylfurfural (HMF) Evaluation in Tomato Products

Color of tomato products is due to the pigments content of fruit together with browning compounds originated during processing. To get a final product with a good is color is necessary to use fruits with an appropriated coloration and to avoid the degradation of pigments during post-harvest and processing. Final color should be bright and characteristic of each fruit. Lycopene, a liposoluble thermostable compound, is the main carotenoid of tomato fruit and it is responsible of its red color. Although tomato concentrate, as an intermediate industrial product, has many advantages, during processing a very energetic treatment is applied, which may easily alter the product, basically by browning reactions, with the formation of hydroxymethylfurfural (HMF). Thermal treatment, together with the storage conditions and transportation can affect the chemical composition and final characteristics of the product. In this paper Lycopene and HMF content have been evaluated in commercial tomato products: juices and ketchup. Analytical methods applied were as follow: Lycopene by spectrophotometric determination at 503 nm, and HMF by a colorimetric method based on the thiobarbituric acid (TBA) color reaction with 5hydroxymethylfurfural measured at 443 nm, after clarification of samples with Carrez solutions. Lycopene concentrations in samples analyzed ranged between 6 – 15 mg/100g and HMF content ranged between 0,2 –4,0 mg/100g, with higher values for ketchups than juices in both parameters. INTRODUCTION Colour is the first attribute in consumer perception of foods, and one of the most important factors on the commercial quality of tomato products. This attribute is due to the presence of different pigments. Moreover, the effect of enzymatic browning reactions after the disruption of the cell membranes has to be considered. During processing of tomato products, thermal treatment, together with the storage conditions and transportation can affect their chemical composition as well as their final characteristics, with nutritional and sensorial quality changes. Lycopene, a liposoluble thermostable pigment, is the main carotenoid in tomato fruit (83 – 90 % of the total pigments present, according to Shi and Le Maguer, 2001), and it is responsible of red colour. Although lycopene has no provitamin A activity, it has been reported as a potent scavenger of singlet oxygen in vitro (double activity of other carotenoids). Its protector effect against certain cancer diseases has been shown in epidemiological studies as well as in animal and cellular models of carcinogenesis (Okajima et al., 1998; Jain et al., 1999; Sharoni et al., 2000; Gann et al., 1999; Shi and Le Maguer, 2000). Some hypolipemiant and immunomodulator effects have been also reported for lycopene (Arab and Steck, 2000; Watzl et al., 2000). For this reason, it can be considered as an important compound (Le Maguer et al., 1998) and the interest in its consumption has recently increased. Tomato almost exclusively represents the dietary intake of lycopene. Previous data on lycopene content in tomato juices range between 5 and 61 mg/100 g, while for ketchups these values are 3 – 41 mg/100 g (Lindner et al., 1984; Heinonen et al., 1989; Tavares and Rodríguez-Amaya, 1994; Tonucci et al., 1995; Schierle et al., 1996; Offord, 1998). Proc. 8 IS on Processing Tomato Eds.: B. Bieche and X. Branthome Acta Hort. 613, ISHS 2003 366 However, the bioavailability of this compound depends on several factors including food processing, with higher lycopene levels in plasma after the consumption of tomato paste or juice, compared to fresh tomato (Sies and Stahl, 1998). This fact has been partially attributed to heating, which improve the bioavailability of lycopene by breaking down cells walls and weakling the bonding forces between lycopene and tissue matrix (mainly lycopene-protein complexes). Thus making lycopene more accessible, and enhancing the formation of more absorbable and less metabolized (although less stable) cis-isomers. But also, the presence of a lipid food matrix in processed tomato causes a better extraction of lycopene into the lipophilic phase and results in a better absorption of this compound (Shi and Le Maguer, 2000). On the other hand, the energetic treatment applied for the obtention of tomato products may easily alter the product, with some isomerization and degradation of lycopene up to 17 % of its initial value (Miki and Akatsu, 1970; Shi and Le Maguer, 2000). Most common changes in fruit juices and concentrates color by browning reactions are: Enzymatic browning: It involves different hydroxylation – oxidation reactions of phenols compounds with the result of the formation of brown compounds. (Woodroof and Luh, 1986). Non enzymatic browning: a) Maillard reaction: substrates are the carbonyl groups of reducing sugars and amines with a decrease of aminoacids biodisponibility and the formation of dark compounds (melanoidins) (Ashoor and Zent, 1984; Dauberte et al., 1990). This reaction is accelerated in acid medium and with high temperatures, as it is the case of fruit juice concentrations (Toribio et al., 1984). b) Caramelization: When polihidroxyl compounds are heated at high temperature. c) Oxidation of ascorbic acid. Processing of tomato products enhances browning reactions, with the formation of hidroxymethylfurfural (HMF), an intermediate compound of Maillard reaction between sugars and aminoacids. This parameter, together with furosine is normally used by the industry to evaluate heat damage in food products (Hidalgo and Pompei, 2000). This work is focus on the evaluation of lycopene and HMF content in different commercial tomato products (juices and ketchups), as indicators of sensory characteristics of these products. MATERIAL AND METHODS Samples Tomato juices and ketchups from 4 commercial brand each were considered for analysis. Analytical Methods Dry matter: drying at 100 oC (FAO, 1989). oBrix: refractometric measurement Pulp and juice contents: Gravimetryc determination after centrifugation during 30 min at 3.000 r.p.m, and juice decantation Lycopene: spectrophotometric determination at 503 nm (Sadler et al.,1990). HMF: colorimetric method based on the thiobarbituric acid (TBA) color reaction with 5hydroxymethylfurfural measured at 443 nm, after clarification of samples with Carrez solutions (Guzman, et al. 1986). Statistical Analysis * Pearson Correlations between Variables: These correlation coefficients range between –1 and +1 and measure the strength of the linear relationship between the