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if o, ie Ag b-Carotene rtia in d 8 ma was our g p cherry tomatoes. Temperature was directly related to browning, ascorbic acid loss and HMF formation, while no clear influence could be found for carotenoid degradation. to prod ir valu tives to s can b d mark nume organic acids (Muratore, Licciardello, & Maccarone, 2005). Much research has been carried out in order to correlate the assumption of tomatoes and their derivatives, with the ability to prevent some kinds of cancers and cardiovascular diseases (Gio- vannucci et al., 1995; Giovannucci, 1999; La Vecchia, 1998). These studies have demonstrated that thermal treatment of tomatoes (in every commercial product) positively correlates with low risk for cancers of the digestive tract and prostate. Other works (Nakaga- large changes in total lycopene content, but during conventional tomato management, most lycopene can be converted from the all-trans form into the cis isomer which is less bioactive. The aim of this work was to examine the effects of the partial dehydration of cherry tomatoes at different temperatures, in a forced air oven, with special regard to the effect of a pre-treating solution on the main physical, chemical and organoleptic charac- teristics of the products, namely, colour, water activity, dry matter, L-ascorbic acid, lycopene, b-carotene and 5-hydroxymethylfurfural. Many studies deal with the drying of tomatoes, but none of these has considered cherry tomatoes as a partially dehydrated product * Corresponding author. Tel.: +39 95 7580210; fax: +39 95 7141960. Food Chemistry 111 (2008) 887–891 Contents lists availab he lse E-mail address: g.muratore@unict.it (G. Muratore). and processed forms. Processed products include ketchup, sauces, pastes and juice. Drying is not a popular way to process tomatoes due to its adverse effect on final product quality (Lewicki, Vu Le, & Pomaran´ska-Lazuka, 2002) such as tissue browning and remark- able changes in the flavour profile. Many differences in general composition have been highlighted between traditional varieties (big tomatoes) and the new small-sized varieties (cherry and plum tomatoes), the latter characterised by higher dry matter and solu- ble solid fraction, essentially due to the higher levels of sugars and lycopene acts as a ‘‘scavenger” against free radicals reducing the risk of cancer in humans. Lycopene, according to the findings of Gartner, Stahl, and Sies (1997) and Stahl and Sies (1992), is stable during heating and industrial treatment, and treatments are able to improve lycopene bioavailability. Nevertheless, research carried out by Shi, Le Ma- guer, Kakuda, Liptay, and Niekamp (1999) showed significant loss in lycopene content during the dehydration of tomato products. Processes like cooking, cooling and canning do not usually cause Lycopene Hydroxymethylfurfural 1. Introduction A significant part of cherry toma in a brief period during which the Therefore, producers aim at alterna produce, hopeful of some profit. Thi a new product, which is stable an Being a popular fruit, tomatoes find 0308-8146/$ - see front matter � 2008 Elsevier Ltd. A doi:10.1016/j.foodchem.2008.05.001 � 2008 Elsevier Ltd. All rights reserved. uction is concentrated e drops to below cost. commercialise excess e achieved by creating etable all year round. rous uses in both fresh wa, Yokozawa, Teresawa, Shu, & Raj Juneja, 2002; Russo et al., 2000) have confirmed that the consumption of natural substances capable of lowering oxidants, can protect against epithelial cancers and other diseases. Abushita, Hebshi, Daood, and Biacs (1997), Cro- zier, Lean, Mc Donald, and Black (1997), and Sies and Stahl (1998) have highlighted that the biological value of tomatoes is undoubt- edly related to their high concentration of antioxidants, such as carotenoids, ascorbic acid and phenolic substances; in particular, Partial drying L-ascorbic acid formation of 5-hydroxymethylfurfural were also determined as an index of sugar heat degradation. Treat- ment with a dipping solution protected both the nutritional and chemical qualities of the partially dried Partial dehydration of cherry tomato at d and nutritional quality of the products Giuseppe Muratore *, Valeria Rizzo, Fabio Licciardell Sezione Tecnologie Agroalimentari, Dipartimento di Orto-Floro-Arboricoltura e Tecnolog a r t i c l e i n f o Article history: Received 16 July 2007 Received in revised form 5 March 2008 Accepted 1 May 2008 Keywords: Cherry tomato a b s t r a c t This study concerns the pa obtain a product with 25% forced air oven at 40, 60 an immersion of the fresh to (10:10:24 g/l); the second suring their CIE L�a�b� col uate thermal damage durin Food C journal homepage: www.e ll rights reserved. ferent temperature, Emanuele Maccarone roalimentari (DOFATA), University of Catania, Via S. Sofia, 98 – 95123 Catania, Italy l dehydration of cherry tomatoes (Lycopersicon esculentum, var. Shiren) to itial water content. Two kinds of dried tomatoes were obtained using a 0 �C for different lengths of treatment. The first type was dehydrated after toes in an aqueous solution of citric acid, sodium and calcium chloride obtained with no pre-treatment. The products were characterised by mea- parameters and levels of L-ascorbic acid, lycopene and b-carotene to eval- rocessing under the different conditions. Moreover, water activity and the le at ScienceDirect mistry vier .com/locate / foodchem em with 25% initial water content. Today, the market shows increasing interest in products with intermediate humidity, which combine increased stability, due to lower water activity, with good nutri- tional and organoleptic characteristics. Partially dehydrated cherry tomatoes could be utilised as seasoning or to replace fresh toma- toes as the main ingredient in starters and other recipes. 2. Materials and methods 2.1. Sample preparation Cherry tomatoes, cultivar ‘‘Shiren”, were collected at a local farm when ripe. They were selected by colour and homogenous diameter (29–32 mm), washed with tap water and cut longitudi- nally in halves. The samples were divided into two batches, one immersed for 20 h in a solution of sodium chloride (10 g/l), citric acid (10 g/l) and calcium chloride (24 g/l) in tap water. The other was used as the control. Sodium chloride is used in ancient Sicilian tradition to prepare dried tomatoes, citric acid was used to guarantee lower pH for a longer shelf life, and calcium chloride was added because, according to a previous work, it increases the amount of water re- moved during dehydration (Lewicki et al., 2002). 2.2. Dehydration Cut tomatoes were placed on four grates. Drying was performed in a forced air oven G�-Therm 075 (Galli, Milan, Italy) with the fol- lowing characteristics: heating power, 1330W; volume, 75 l; forced air speed, 2000 rpm. The following drying temperatures were chosen for treated and untreated samples: 40, 60 and 80 �C. The tomatoes were dried to 25% of their initial water content. 2.3. Quantitative measurements For the fresh sample, pH, �Brix, dry matter and colour (CIE parameters) were determined. The partially dehydrated cherry tomatoes (16–20 halves, 160– 200 g), both raw and treated samples, were homogenised immedi- ately at the end of drying and their dry matter and colour were measured. Samples with similar weight and dimensions were packed in PET/PP bags (Plastar Pak s.r.l., Milan, Italy) in a partial vacuum to reduce headspace, and then thermally sealed (Delta model ‘‘Delta 30”, Brindisi, Italy) stored at �18 �C, and thawed at +4 �C before analysis. All the analyses were carried out in duplicate runs: dry matter was determined for 2 g homogenised samples in a thermo venti- lated oven at 105 �C until constant weight; pH was determined for five homogenised fresh fruits by digital pHmeter (MP 220, Met- tler Toledo, Greifensee, Switzerland); total soluble solids were measured at 25 �C by refractometer (2WAJ ABBE bench Refractom- eter, Optika Microscopes, Bergamo, Italy); the colour coordinates L�, a�, b�, C (colour chromaticity) and h (colour intensity) were measured by calorimeter NR-3000 (Nippon Denshoku Ind. Co. Ltd, Japan). The colour of fresh cherry tomatoes was measured from the puree of 8–10 halves for both fresh and dehydrated samples. Water activity was determined at 25 �C for fresh and partially dried sam- ples by hygrometer AwVC (Rotronic AG, Bassersdorf, Switzerland). 2.4. Carotenoids Carotenoids were extracted according to De Sio, Grimaldi, and 888 G. Muratore et al. / Food Ch Loiudice (1999); in particular, for partially dehydrated samples, the initial extraction was modified as follows: 2 g were mixed with 50 ml dichloromethane/methanol 2:1 (v/v) solution with 0.1% BHT and the extraction was repeated three times, using a total of 150 ml extraction solution. Quantification was performed by HPLC (Finnigan SpectraSys- tem P 2000, Thermo scientific, Waltham, MA, USA) equipped with a Diode Array Detector UV 6000 LP, a Waters-YMC C-30 col- umn for carotenoids (5 lm, 250 mm � 4.6 mm i.d.), and a 20 ll loop. Carotenoids were separated by 95:5 (v/v) methanol/H2O as mobile phase A and dichloromethane with 0.1% BHT and 0.05% triethylamine (TEA) as mobile phase B. The solvent pro- gram, at a flow rate of 0.8 ml/min, was: 95% A for 2 min; 95% A to 30% A linearly in 8 min; followed by 5 min isocratic; 30% A to 10% A linear increase in 5 min; 10 min isocratic and a return to 95% A at 40 min to restore the initial conditions. Triethylamine was used to reduce carotenoid misplaced in the column and to improve peak shape. The spectra were recorded in the range 320–480 nm, while chromatograms were acquired at wavelength (k) 480 and 460 nm to determine lycopene and b-carotene. Quantification was made by calibration using appropriate dilutions of external standard lycopene and b-carotene (Sigma-Aldrich, Milan, Italy). All solvents were HPLC grade (J. T. Baker, Deventer, Holland). 2.5. L-ascorbic acid Ascorbic acid was extracted and quantified by HPLC according to Nisperos-Carriedo, Buslig, and Shaw (1992). HPLC separation was by Finnigan SpectraSystem P 2000 (Thermo scientific, Wal- tham, MA, USA)) equipped with a Diode Array Detector UV 6000 LP, a Supelcosil LC-18 (5 lm, 25 mm � 4.6 mm i.d.) column and a 20 ll loop. Ascorbic acid was separated by 2% KH2PO4 buffer solution at pH 2.3 as mobile phase, at a flow rate of 0.5 ml/min. The spectra were recorded in the range 245–260 nm, where maximum absorbance for ascorbic acid is at 245 nm, but the acquisition of chromato- grams was set at 260 nm to avoid interference (Finley & Duang, 1981). The identification and quantification was made by the external standard method, using a pure commercial standard (Car- lo Erba Reagenti, Milan, Italy). 2.6. 5-Hydroxymethylfurfural (HMF) The extraction of HMF was performed by homogenising 10 g of sample with 20 ml HPLC grade water for 15 min; samples were fil- tered through 0.45 lm nylon filters, and injected into the HPLC. The HPLC was a Varian 9012Q liquid chromatograph equipped with a diode array detector (Varian, Star 330), a Merk Lichrospher 100 RP-18 (5 lm, 125 mm � 4 mm i.d.) column, and a 20 ll loop. HMF was separated using H2O/acetonitrile 95:5 (v/v) as mobile phase, at a flow rate of 1 ml/min. Chromatograms were acquired from 250 to 300 nm but HMF was monitored at 285 nm. Quantifi- cation was performed by external standard calibration using a cal- ibration line obtained with appropriate dilutions of commercial standard (Sigma, Milan, Italy). Water and acetonitrile were HPLC grade (Merck, Darmstadt, Germany). 2.7. Statistical analysis All analyses were carried out in duplicate. The experimental data was processed by Duncan test using Statgraphics Plus 5.1 software (Manugistic Inc. Rockville, MD, USA). The means and standard deviations were calculated. The data shown is the aver- age of all repetitions. The sets of data obtained for each param- istry 111 (2008) 887–891 eter were statistically treated to obtain a 95% confidence interval. 3. Results and discussion 3.1. Characterization of fresh and treated products The fresh cherry tomato var. Shiren is characterised by a pH of 4.05, 7.06% soluble solids and 8.15% dry matter. Standard deviation ranged within 6% of mean values. Table 1 reports temperatures and dehydration times to reduce water content to 25% of the initial va- lue and drying kinetics for both samples are shown in Fig. 1. Obvi- ously, the dehydration time was inversely proportional to the treatment temperature. For each temperature the dehydration was quicker for treated cherry tomatoes according to Lewicki et al. (2002). Treated samples showed higher dry matter content, probably due to the presence of salts in the pre-treatment solution (sodium chloride, citric acid and calcium chloride). The water activity changed from 0.97 in the fresh tomatoes to 0.93 in semi- dry ones. 3.2. Colour measurements Table 2 shows the CIE colour parameters. In particular the a�/b� ratio is often used as an indicator of colour development in toma- toes and redder hue, since it produces a good linear regression with Table 1 Temperatures, partial dehydration times and dry matter content Sample Temperature (�C) Time (h) Dry matter (g/100 g) Untreated 40 29 39.16 ± 0.21 60 9 80 4 Treated 40 24 42.00 ± 0.62 60 8 80 3.5 G. Muratore et al. / Food Chemi Fig. 1. Drying kinetics of untreated and treated cherry tomatoes. the maturation of the fresh tomatoes (Arias, Lee, Logendra, & Janes, 2000). The results agree with literature data regarding a convection drying system at 95 �C, obtained by Shi et al. (1999). Yeatman (1969) observed that the b�L�/a� ratio gave a high lin- ear correlation with the visual colour scores of processed tomatoes. The colour of treated semi-dry cherry tomatoes appeared more comparable with the colour characteristics of the fresh test. Hue values range from 180� (pure green colour) to 0� (pure red colour). In fresh tomatoes, the hue is deeper than in treated toma- toes, according to previous work (Arias et al., 2000). 3.3. Carotenoids, ascorbic acid and 5-hydroxymethylfurfural Table 3 shows the content of b-carotene, lycopene, ascorbic acid and HMF in the fresh tomato and in the untreated and treated semi-dry products. The fresh cherry tomato contains a high quan- tity of lycopene (99.8 mg/100 g d.m.) and b-carotene (38.0 mg/ 100 g d.m.). In untreated semi-dry samples the highest value of lycopene was found in the dehydrated sample at 80 �C (76.4 mg/ 100 g d.m.), while the lowest value was found at 40 �C (58.5 mg/ 100 g d.m.), confirming that in these samples lycopene was dam- aged by the length of the drying process. b-Carotene in the untreated samples followed the same trend described above. Most protection was achieved at 80 �C (34.8 mg/100 g d.m.), while the highest loss was at 40 �C (28.6 mg/100 g d.m.). b-Carotene was found to be more stable in comparison with lycopene and it decreased by up to 25.9 mg/ 100 g d.m. in the untreated product dried at 60 �C. In treated samples, lycopene and b-carotene contents were pre- served at low temperature with long process time (40 �C for 24 h) while for other temperatures this effect was less apparent or lack- ing. The b-carotene was minimum after drying at 60 �C, with losses ranging from 28% to 32% in treated and untreated tomatoes, respectively. Ascorbic acid loss was clearly temperature-dependent, as it in- creased with increasing dehydration temperature. The maximum losses were observed in samples dried at 80 �C, which showed a content of 112.7 and 178.5 mg/100 g d.m. in untreated and treated samples, respectively, highlighting the greater stability of ascorbic acid in the former samples, proving treatment was effective. The formation of HMF in semi-dry cherry tomatoes is lower than that reported in the literature for fully dried tomatoes, as was expected (Zanoni, Peri, Nani, & Lavelli, 1999); the highest con- centrations were found in samples dried at the highest tempera- ture (1.8 and 1.7 mg/100 g d.m. for untreated and treated, respectively), while the lowest values were observed at 40 �C (1.1 and 1.2 mg/100 g d.m). A high tomato consumption plays a protective role in inhibiting the propagation of radical chain reactions due to the carotenoid constituents, particularly lycopene and b-carotene, and also a vari- ety of natural antioxidants such as ascorbic acid and polyphenols (Lavelli & Giovanelli, 2003; Re, Bramley, & Rice-Evans, 2002). Food processing is generally believed to be responsible for a depletion of naturally occurring antioxidants. Carotenoids are light and temper- ature-sensitive, so high temperature, long processing time, light and oxygen have been shown to have effects on their degradation. Carotenoids and ascorbic acid decrease has been observed by Shi et al. (1999), Lavelli, Hippeli, Peri, and Elstner (1999) in the conven- tional air drying of tomatoes. Pre-treatment effectiveness is strictly linked to dipping solution components, as reported by Baloch, Khan, and Baloch (1997). The lower decrease of nutritional components in the treated samples can be explained by the protective role of sodium chloride and cit- stry 111 (2008) 887–891 889 ric acid. In fact the products undergo more rapid water loss in the presence of sodium chloride reducing the dehydration time, while citric acid provides secondary antioxidant activity. g/10 9.8 a 8.5 e 6.5 d 6.4 b 4.4 b 8.7 e 0.4 c . aci chlo ± 0 ± 0 ± 0 ± 0 ± 0 ± 0 ± 1 . em HMF is commonly associated with sugar thermal damage. It is a thermal damage marker for processed foods and an index of im- proper storage conditions, its level being close to zero in fresh foods (Babsky, Toribio, & Lozano, 1986). The HMF level is a useful Table 3 Mean contents of b-carotene, lycopene, ascorbic acid and 5-hydroxymethylfurfural Sample T (�C) b-Carotene Lycopene mg/Kg mg/100 g d.m. mg/Kg m Fresh – 31.0 ± 1.18 38.0 a 81.3 ± 2.28 9 Untreated 40 112.7 ± 0.01 28.6 cd 230.5 ± 2.78 5 60 101.8 ± 0.22 25.9 e 260.9 ± 4.70 6 80 135.6 ± 0.14 34.8 b 297.7 ± 0.14 7 Treated 40 167.3 ± 0.00 *38.5 a 290.8 ± 0.12 *7 60 109.4 ± 0.20 *27.4 cd 234.7 ± 0.29 *5 80 118.1 ± 0.20 *30.4 c 273.1 ± 0.83 *7 Means in columns followed by different letter are significantly different at P 6 0.05 * Values of treated samples were corrected considering the presence of salts (citric solution (42.00/39.16 = 1.07). Table 2 CIE colour parameters in fresh, untreated and in treated (dipping solutions of sodium Sample T (�C) L� a� b� Fresh – 22.33 ± 0.56 7.67 ± 0.19 20.53 Untreated 40 33.75 ± 1.18 22.48 ± 0.79 20.04 60 35.11 ± 1.05 22.80 ± 0.68 22.89 80 36.98 ± 0.92 26.54 ± 0.93 22.12 Treated 40 36.65 ± 1.03 18.92 ± 0.53 17.84 60 39.10 ± 1.64 19.60 ± 0.82 22.37 80 37.36 ± 1.57 21.99 ± 0.92 25.48 Means in columns followed by different letter are significantly different at P 6 0.05 890 G. Muratore et al. / Food Ch parameter for evaluating the technological history of food prod- ucts, like honey, fruit juices, etc. The formation of HMF involves hexoses through acid-catalyzed dehydration and cyclisation. The first step of the reaction consists of a structural hexose change into an intermediate 1,2-endiolic form, which rapidly eliminates water (Belitz & Grosch, 1999). The formation of HMF through the dehy- dration and cyclisation of hexoses, besides low pH values and heat supply, is enhanced by low water activity values (Muratore, Licc- iardello, Restuccia, Puglisi, & Giudici, 2006); therefore, the reaction is stimulated at the later stages of dehydration. HMF is also a major product of the Maillard reaction; however, considering the small concentrations of free aminic groups compared to sugar concentra- tion and low pH of tomato (Maillard reaction is favoured by high pH values), this pathway to HMF formation in dehydrated cherry tomatoes can be neglected. The small quantities and little difference of HMF content in trea