Influence of process variables on colour changes, carotenoids retention and cellular tissue alteration of cherry tomato during osmotic dehydration

Journal of Food Composition and Analysis 22 (2009) 285–294

Original Article

Influence of process variables on colour changes, carotenoids retention andcellular tissue alteration of cherry tomato during osmotic dehydration

A. Heredia, I. Peinado, C. Barrera, A. Andres Grau *

Institute of Food Engineering for Development, Polytechnic University of Valencia, Camino de Vera s/n, 46022 Valencia, Spain

A R T I C L E I N F O

Article history:

Received 2 September 2008

Received in revised form 10 November 2008

Accepted 19 November 2008

Keywords:

Lycopene

b-Carotene

Ternary solutions

Microscopy

Tomato

Colour

Food analysis

Food composition

A B S T R A C T

Osmotic dehydration is an appropriate technique for preserving nutritional components that are

naturally present in different vegetables. In order to quantitatively evaluate changes induced by osmotic

treatment in CIEL*a*b* colorimetric parameters and lycopene and b-carotene content, cherry tomato in

halves (L. esculentum var. cerasiforme cv. Cocktail) were osmotically treated by immersion in different

solutions (a 20% w/w, NaCl solution, a 55 Brix sucrose solution and a ternary solution (10% NaCl and

27.5% sucrose)) at 30, 40 and 50 8C for 24 h. The alteration suffered by the cellular tissue was also

analysed by means of microscopic observations. The obtained results showed a general increase in a* and

b* coordinates resulting from the concentration of the liquid phase and a decrease in lightness as a

consequence of the enhancement in sample opacity. Regarding carotenoids content, an increase in

lycopene and b-carotene was observed in samples osmotically dehydrated at moderate temperatures

(30 8C and 40 8C) with the solutions that include sucrose on its composition. In addition, microscopic

observations revealed a direct relationship between the integrity of the cellular matrix and the

preservation or even synthesis of lycopene and b-carotene.

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1. Introduction

Over the past few years, consumers have increasinglydemanded food products providing both good sensorial qualityand specific nutritional properties. In this sense, a great effort hasbeen made in food technology to adequately process particularconsumer requirements.

Lycopene is a natural antioxidant that belongs to thecarotenoids family such as b-carotene. However, whereasnumerous scientific studies have been focused mainly on b-carotene and have provided a wide knowledge about nutritionalvalue of this compound, the interest on lycopene health benefits isrelatively recent. Lycopene, which has up to twice the antioxidantactivity of b-carotene, has consistently been associated with theprevention of cardiovascular disease and different types of cancer(breast, colon and prostate) (Gerster, 1997; Giovannucci, 1999;Bramley, 2000). In addition to this property, lycopene has also beensuggested to induce cell-to-cell communications and modulationof the hormonal and the immune system (Rao and Agarwal, 1999).

Processing and storage of tomato products have promotedseveral research activities (Nguyen and Schwartz, 1998; Aneseet al., 1999; Abushita et al., 2000; Shi and Le Maguer, 2000; Zanoni

* Corresponding author.

E-mail address: [email protected] (A.A. Grau).

0889-1575/$ – see front matter � 2009 Elsevier Inc. All rights reserved.

doi:10.1016/j.jfca.2008.11.018

et al., 2000), in which growing attention has been paid to lycopenedegradation as affected by processing variables (high temperature,long processing time, and light or oxygen exposure). Most of theabove-mentioned studies reported a decrease in lycopene contentduring processing in which high temperatures (especially over70 8C) were applied. Nevertheless, recent studies suggested thatthermal processing can enhance the nutritional value of tomatoesby increasing total antioxidant activity (Dewanto et al., 2002;Chang et al., 2006). This fact could be related to the release oflycopene by disrupting cell walls or hydrolyzing lycopenederivatives (Thompson et al., 2000). A general agreement on thebest conditions for lycopene preservation can be found in thescientific data reporting that lycopene remains relatively constantat low process temperatures, inert atmosphere, limited lightexposure and antioxidants addition (citric acid, ascorbic acid,sodium pyrophosphate, etc.). Among the different processingtechniques, the osmotic dehydration presents clear advantages forpreserving lycopene due to the low temperatures implied in theprocess as well as the protective effect of the surrounding osmoticsolution to limit oxygen exposure. However, not many studies canbe found on the potential use of osmotic dehydration for limitinglycopene changes. Shi et al. (1999) suggested that osmoticdehydration completely avoided oxidation damage in comparisonto conventional air drying and vacuum-air drying in which bothoxidation and isomerisation occurred. Tonon et al. (2007) reportedthat the total carotenoids content was retained after 6 h of osmotic

A. Heredia et al. / Journal of Food Composition and Analysis 22 (2009) 285–294286

dehydration with ternary solutions. Nevertheless, any of theseboth articles neither studied the effect of a wide range of osmoticvariables (temperature, processing time, composition of theosmotic solution) on this pigment nor tomato tissue possiblealterations as a result of the mass transfer phenomena. In fact, thecharacteristics of the cellular matrix in which lycopene isdistributed affect both its bioavailability and its stability (Stahland Sies, 1992). The crystalline nature of lycopene in raw tomatomay account in part for its apparently low absorption efficiencyfrom the tomato plant matrix (Garrett et al., 2000). Thebioavailability of both lycopene and b-carotene from tomatoproducts has been shown to increase with heat and/or homo-genization, processes that break down plant cell walls, allowingthe carotenoids release. Although trans isomers of lycopene aregenerally stable in the plant matrix, once liberated they aresusceptible to heat-induced isomerisation to cis isomers, whichmay be more readily absorbed by the intestine (Nguyen andSchwartz, 1998). Therefore, it is also important to analyse thechanges suffered by the cell tissue during the processing.

Besides its health benefits, lycopene is the main colouringmatter responsible of the characteristic deep-red colour of tomato,consequently, it should be interesting to establish a relationshipbetween colour parameters and lycopene content in order to beable to estimate lycopene content by means of a faster,inexpensive, and reliable method. In this sense, some previousstudies (D’Souza et al., 1992; Shi et al., 1999; Thompson et al.,2000; Raffo et al., 2006), have achieved highly linear regression (R2close to 1) between lycopene content and the CIEL*a*b* chromaticcoordinates (especially with the a*/b* ratio) obtained fromreflectance readings on tomato.

In the present study, research was carried out to study the effectof some process variables (temperature, processing time andosmotic solution composition) on both colour and carotenoids(lycopene and b-carotene) changes during the osmotic dehydra-tion of cherry tomato halves. Additionally, microscopic observa-tions of fresh and osmodehydrated tomato tissue were conductedin order to analyze the effect of structural changes on carotenoidsdistribution.

2. Materials and methods

2.1. Raw material

Fresh cherry tomatoes (Lycopersicon esculentum var. cerasi-forme cv. Cocktail), always purchased from the same supplier andcultivated under the same conditions, were sorted for colour(bright red), size (diameter 22–28 mm) and absence of physicaldamage. Then, selected samples were gently rinsed with tap waterand cut into halves. The skin was not removed because most of thelycopene is located here, where concentration can be up to fivetimes higher than concentration in the tomato flesh (Al-Wandawiet al., 1985; D’Souza et al., 1992). Therefore, water and solutesdiffusion during osmotic treatment was assumed to take place onlythrough the cross section, since the thick epicuticular waxy layerspresent on tomatoes skin have a high resistance to mass transfer(Shi et al., 1997).

2.2. Osmotic solutions

In order to evaluate the effect that the composition of theosmotic medium exerts on the colour and the carotenoids contentof tomato halves undergoing osmotic dehydration, three differentaqueous solutions were employed: a 20% w/w sodium chloridesolution, a 55 Brix sucrose solution and a ternary solution (1:1)made of 27.5% w/w of sucrose and 10% w/w of sodium chloride. Thecomposition of these solutions was chosen according to their

closeness to the solubility limit of the solutes contained (in the caseof the binary solutions) and in order to evaluate the possiblesynergic effect between salt and sucrose.

2.3. Experimental methodology

Tomato halves were placed in a plastic basket divided into fivecompartments and immersed for 24 h in a plastic vessel containingthe osmotic solution. In all cases, an initial fruit to osmotic solutionratio of 1/20 w/w was employed to prevent undesirable dilution ofthe medium by water removal from tomato samples, which wouldlead to a faster decrease in the mass transfer driving force as theprocess progresses. With the same purpose, constant mechanicalstirring (80 rpm) was applied to the osmotic solution along thedifferent experiments. In order to avoid excessive fruit degradationand cooking, mild temperatures (30 8C, 40 8C or 50 8C) wereemployed and kept constant along the osmotic treatment bymeans of a thermostatic bath. The lycopene oxidation associatedwith long exposure to light was also prevented by keeping thesamples in darkness during their processing. At different pre-determined times (0, 30, 60, 90, 150, 270, 390, 900 and 1440 min),15 samples (halves of cherry tomato) were removed from theosmotic solution, gently drained with absorbent paper and dividedinto three lots to determine their colour and their lycopene and b-carotene contents in triplicate. Mass change was also evaluated intriplicate by weighing three individual samples perfectly identifiedwith coloured threads. Microscopic observations were alsoperformed in fresh samples and in those removed after 30, 120,390 and 1440 min.

2.4. Analytical determinations

All the analytical determinations carried out in this workrequired a previous homogenization of the samples.

Instrumental measurements of colour were conducted at roomtemperature in a Minolta spectrophotometer (model CM-3600d)by placing the tomato puree in a 15 mm thick and transparentplastic cell and by using a black plate as the background tostandardize the measurements. Visible absorption spectrum wasrecorded between 380 and 770 nm by reflectance to obtaintristimulus values of CIEL*a*b*, using illuminant D65 and standardobserver (108 visual field) as references. The coordinate a* takespositive values for reddish colours and negative values for thegreenish ones, while b* takes positive values for yellowish coloursand negative values for the bluish ones. L* is an approximatemeasure of lightness, which is the property that allows any colourto be regarded as equivalent to a member of the grey scale,between black (L* = 100) and white (L* = 0).

Previously, samples were measured with both black and whitecalibration tiles in order to study the possible translucency of thesamples. Since the same spectrum was obtained with the black andwhite tiles, the opacity of the tomato samples was confirmed, andonly data corresponding to the black tile were analysed.

Both lycopene and b-carotene content was spectrophotome-trically determined on hexane extracts by using a PerkinElmer UV–visible emission spectrophotometer (mod. Lamdba 25). As describedby Porter and Anderson (1967), an amount of 0.1 g of tomato pureewas accurately weighed and mixed with 4 mL of absolute ethanoland 3 mL of hexane (99% pure). After approximately 1 h underhorizontal agitation at 150 rpm in darkness, exactly 1 mL ofdeionised Milli-Q water was added to the mixture to allow theseparation of the two phases. Measurements were immediatelyperformed on a 0.5 mL aliquot taken from the upper phase between300 and 600 nm. Samples containing purified lycopene (99% pure) orb-carotene (95% pure) dissolved in hexane (99% pure) in concen-trations ranging from 0 to 10 mg/L were also analysed in order to

A. Heredia et al. / Journal of Food Composition and Analysis 22 (2009) 285–294 287

find the wavelength of maximum absorbance for each carotenoid. Inall analyses, absolute hexane was used as blank.

By procedure mentioned before, these wavelengths were 503for lycopene and 478 nm for b-carotene. The lycopene andb-carotene content of cherry tomato samples were calculated asfollows [Eqs. (I and II)] using the absorbance values mentioned.

mgLYC

100 g¼ A503 �MLYC � V

m � ELYC� 100 (I)

mgb-CAR

100 g¼½A478 � ðA503 � 0:9285Þ� �Mb-CAR � V

m � Eb-CAR� 100 (II)

where mgLYC/100 g and mgCAR/100 g are mg of lycopene orb-carotene/100 g of tomato; Al is the absorbance of the sampleat a certain wavelength; MLYC and Mb-CAR are the molecular weightsof lycopene (537 g/mol) and b-carotene (533.85 g/mol), respec-tively; V is the volume of the hexane layer in the extracted sample(2.7 mL); m is the analysed tomato mass; ELYC and Eb-CAR are theextinction coefficients of lycopene (172 M�1 cm�1) and b-carotene(139 mM�1) in hexane, respectively (Zscheille and Porter, 1947).

2.5. Microscopic observations

Carotenoid distribution within the cells and cellular changesinduced by osmotic dehydration were evaluated with a lightmicroscope (DM LM, Leica Microsystems) equipped with a CCDcamera (Leica ICC A) which was connected to a computer providingimage capture and manipulation software (Leica IM500 ImageManager). In order to make the results more comparable, tissue

Fig. 1. Evolution of the lightness (L*) of cherry toma

samples were obtained from the section placed in parallel 2 mmbelow the tomato halves’ interphase.

2.6. Statistical analysis

Statistical analysis of variance (simple ANOVA) was performedusing Statgraphics Plus 5.1 in order to verify if the difference onlycopene and b-carotene content between batches of cherrytomato purchased during different seasons was statisticallysignificant. Moreover, statistical analysis of variance (multifactorANOVA) was employed to estimate the possible significance of theeffect of the process variables (temperature and osmotic solutioncomposition) on both lycopene and b-carotene concentrationsalong the process.

3. Results and discussion

3.1. Influence of process variables on cherry tomato colour

Figs. 1–3 show the effect of the temperature and the processtime on the changes of CIEL*a*b* coordinates undergone in cherrytomato halves during the osmotic treatment. As it can be observed,changes in these parameters occurred more rapidly at thebeginning of the process (before 150 min.), when kinetics ofwater loss and solutes gain was reported to be faster (Heredia andAndres, 2008).

Regarding lightness (Fig. 1), it generally decreased as theprocess progressed and as the sugar content and the temperatureof the osmotic solution increased. This reduction in L* value couldbe attributed to the increase in samples opacity mainly resultingfrom the shrinkage of their structure due to the water lost and the

to halves during different osmotic treatments.

Fig. 2. Evolution of the coordinate a* of cherry tomato halves during different osmotic treatments.

A. Heredia et al. / Journal of Food Composition and Analysis 22 (2009) 285–294288

solutes gained during the osmotic treatment (Contreras et al.,2008). As an exception, the clarity of the samples remainedconstant or increased in treatments carried out with the 20% saltsolution at 30 8C and 40 8C.

The results obtained showed an increase of the chromaticcoordinates a* and b* as dehydration progressed (Figs. 2 and 3),reaching a more or less constant value after 390 min ofdehydration. By this processing time, the liquid phase of thesamples and the osmotic solution has been reported to be close tothe compositional equilibrium (Heredia and Andres, 2008). Inaddition, the increase of coordinate b* was higher than thatexperimented by coordinate a*. This increase of a* and b* can beattributed to the concentration of the liquid phase and thepigments present in the cellular tissue as a consequence of theosmotic dehydration.

Concerning the effect of the processing temperature oncoordinates a* and b*, it was dependent on the composition ofthe osmotic solution employed. In general, changes in a* and b*increased with the processing temperature in those treatmentscarried out with the osmotic solutions that include sucrose in itscomposition. On the contrary, changes in a* and b* were observedto be minimum in samples obtained by osmotic dehydration at50 8C with the 20% salt solution.

3.2. Influence of osmotic process variables on lycopene and

b-carotene contents

The simple statistical analyses of variance of lycopene withinthe different batches of fresh cherry tomato showed significantdifferences due to seasonality (Fig. 4). Batches employed in thisstudy from November to February (autumn–winter) exhibited

significant lower lycopene content than those employed from Mayto July (spring–summer). Regarding b-carotene content, an equaltrade as lycopene was obtained. These differences in carotenoidsfrom tomato fruits agreed with those observed by other authors.Raffo et al. (2006) proved that carotenes content in tomatoes var.‘‘Pomodoro di Pachino’’ varied from 8.35 to 15.12 mg/100 g,depending on harvesting period. Moreover, Dumas et al. (2003),who studied the lycopene content of twenty-four tomato varietiesharvested over two consecutive years in the south of Italy, reportedcarotenes content between 3.4 and 15 mg/100 g and between 4.5and 16.3 mg/100 g, for the first and the second year, respectively.

Figs. 5 and 6 show the effect of the temperature and theprocessing time on lycopene and b-carotene contents, respec-tively. Both residual lycopene or b-carotene were calculated as theratio between mg of each carotenoid remaining in the samplesafter the osmotic treatment and mg of the same carotenoid presentin fresh tomato of the corresponding batch since lycopene and b-carotene contents in different fresh cherry tomato batches werevariable as mentioned above. For these calculations, data notprovided about mass loss resulting from water outflow from thetomato tissue to the osmotic solution and soluble solids inflowfrom the osmotic solution to the tomato tissue were required(Heredia and Andres, 2008). These data allowed expressing themass fraction of each carotenoid present in treated samples pergram of fresh tomato.

Based on the evolution of carotenoids along the osmotictreatment, the effect of processing variables on b-carotene andlycopene contents was evaluated at short (90 min), intermediate(390 min) and long (1440 min) characteristic processing times.During the initial period of the process (until 90 min), an increasein the lycopene content was registered when the 55 Brix sucrose

Fig. 3. Evolution of the coordinate b* of cherry tomato halves during different osmotic treatments.

A. Heredia et al. / Journal of Food Composition and Analysis 22 (2009) 285–294 289

solution and the ternary solution were employed at 30 8C and40 8C. However, a decrease in lycopene content was observed at50 8C. This effect could be attributed to the fact that 30 8C and 40 8Care within the optimal range of temperatures for the synthesis oflycopene, which is from 12 8C to 37 8C (Shi et al., 2002; Lopez et al.,2003). In addition, a synthesis of lycopene like other phytochem-icals might be attributed to a response to osmotic stress (Torreset al., 2007). As explained by Giuliano et al. (1993), the activation oflycopene biosynthetic pathway could be due to up-regulation of

Fig. 4. Average and 95% LSD intervals for lycopene (a) and b-caroten

the genes encoding the enzymes responsible for lycopeneproduction. Nevertheless future research in this area would benecessary to investigate this aspect and to ascertain if a synthesisof carotenoids may occur during osmotic drying.

Regarding the osmotic solution composition, the use of a 20%salt solution resulted in a decrease of lycopene even at 30 8C.Possibly salt diffusing quickly through the tomato tissue mightinduce a great deterioration of the cellular matrix, thus resulting ina loss of the protection of tomato cells against external damage

e (b) content (mg/100 g) of each batch of fresh cherry tomato.

Fig. 5. Evolution of residual lycopene (ratio between lycopene content after the osmotic treatment and lycopene content in the raw material) in cherry tomato samples

dehydrated under different osmotic conditions.

Table 1Lycopene content (mg Lycopene/100 g of product) at 0, 90, 390 and 1440 min of

osmotic dehydration.

Osmotic

conditions

Time (minutes)

0 90 390 1440

20% NaCl 30 8C 6.1 (0.5) 6.1 (0.8) 6.5 (1.3) 8.0 (0.4)

20% NaCl 40 8C 10 (2) 10.4 (0.5) 14.947 (0.104) 6.0 (0.5)

20% NaCl 50 8C 6.3 (0.3) 7.0 (0.7) 10.1 (0.3) 9.5 (0.7)

55 Brix 30 8C 4.8 (0.9) 8.65 (0.03) 9.35 (0.14) 11.0 (0.3)

55 Brix 40 8C 6.1 (0.6) 8.3 (0.4) 10.8 (0.8) 6.1 (1.3)

55 Brix 50 8C 5.2 (0.5) 7.7 (0.4) 6.3 (0.5) 3.0 (0.3)

(1:1) 30 8C 6.6 (0.9) 9.12 (0.03) 9.5 (0.9) 12.4 (0.4)

(1:1) 40 8C 4.2 (0.2) 6.7 (0.4) 11.40 (0.02) 5.4 (0.8)

(1:1) 50 8C 4.5 (0.4) 7.1 (0.7) 6.4 (0.2) 5.5 (0.4)

(sd) standard deviation.

A. Heredia et al. / Journal of Food Composition and Analysis 22 (2009) 285–294290

(Gartner et al., 1997; Perkins-Veazie and Collins, 2004). Theseresults differed from the increase reported when osmotic solutioncontained sucrose (55 Brix and (1:1)). The effect of some sugars likeglucose as precursors in the synthesis of carotenoids has beenreported (Purcell, etc). This fact, combined with the protectiveeffect attributed to the surrounded osmotic solution, reduces theoxidation of lycopene in the tomato tissue matrix in comparisonwith the biodegradation taking place during other dehydrationtreatments in which samples are directly in contact with the air(Shi et al., 1999; Goula and Adamopoulos, 2005).

Focusing on the evolution of b-carotene during the osmoticdehydration, a decrease was observed in osmodehydrated cherrytomato with 20% salt solution, and an increase of b-carotenecontent (close to 20%) when osmotic dehydration was carried outwith the ternary solution (1:1). This result could suggest acombined effect of both solutes on the synthesis of carotenoids.

During the intermediate dehydration period (from 90 to390 min), the tendency on lycopene and b-carotene evolutionwas similar to that reported to the first period; however between390 and 1440 min of processing time, losses were registered forboth antioxidants increasing with temperature, salt content of theosmotic solution and processing time.

Despite the reduction in carotenoids content reported undercertain conditions, it is important to mention that, as aconsequence of osmotic dehydration a concentration of pigmentstakes place. Therefore, the intake of lycopene and b-carotene in100 g of partially osmodehydrated cherry tomato halves would behigher than the ingestion of these components provided by 100 gof fresh tomato (Tables 1 and 2). In particular, cherry tomato

samples dehydrated with the binary sucrose solution or theternary solution at 30 8C and 40 8C for 90 or 390 min containedalmost twice lycopene and b-carotene contents of fresh tomatoes(referred to 100 g of product at time t). In terms of bioactivity, itwould be interesting to perform complementary analysis in orderto distinguish between lycopene isomers (Shi et al., 1999; Goulaand Adamopoulos, 2005; Qiu et al., 2006). As previous studieshave confirmed, the isomerisation from trans to cis-forms ispromoted during thermal processing (Wilberg and Rodriguez-Amaya, 1995; Stahl and Sies, 1996; Nguyen and Schwartz, 1998;Shi et al., 1999).

The statistical analysis of variance with a 95% of confidentiallevel (multifactor ANOVA) was carried out with the aim of

Fig. 6. Evolution of residual b-carotene (ratio between b-carotene content after the osmotic treatment and b-carotene content in the raw material) in cherry tomato samples

dehydrated under different osmotic conditions.

A. Heredia et al. / Journal of Food Composition and Analysis 22 (2009) 285–294 291

establishing if the processing variables considered in this studypresented a significant influence on b-carotene and lycopenechanges after 90, 390 and 1440 min of osmotic dehydration. The F-ratio obtained from the multifactor ANOVA shows whether avariable contributes significantly to the variance of an analysedproperty. The higher the F-ratio value, the higher the significanceof the variable (temperature or osmotic solution) on the analysedcomponent. Table 3 shows F-ratio values of each variable and theirinteraction for lycopene and b-carotene contents after 90, 390 and1440 min of osmotic treatment. As it can be deduced, the osmoticsolution was the variable that affected to a greater extent bothantioxidants at first step of the process (90 min.); while thetemperature effect resulted more relevant at 390 and 1440 min. In

Table 2b-carotene content (mg b-carotene/100 g of product) at 0, 90, 390 and 1440 min of

osmotic dehydration.

Osmotic conditions Time (minutes)

0 90 390 1440

20% NaCl 30 8C 1.82 (0.14) 1.00 (0.13) 1.16 (0.13) 1.24 (0.05)

20% NaCl 40 8C 1.48 (0.06) 1.50 (0.02) 1.7 (0.3) 1.18 (0.09)

20% NaCl 50 8C 1.07 (0.07) 1.36 (0.03) 1.72 (0.05) 1.74 (0.05)

55 Brix 30 8C 0.78 (0.08) 1.04 (0.07) 1.46 (0.12) 1.83 (0.09)

55 Brix 40 8C 0.734 (0.009) 1.00 (0.03) 1.21 (0.04) 1.49 (0.07)

55 Brix 50 8C 0.70 (0.06) 1.18 (0.05) 1.55 (0.07) 1.14 (0.13)

(1:1) 30 8C 1.1 (0.2) 1.47 (0.12) 1.91 (0.03) 2.2 (0.2)

(1:1) 40 8C 0.78 (0.13) 1.49 (0.04) 2.5 (0.5) 1.7 (0.2)

(1:1) 50 8C 1.06 (0.13) 1.520 (0.006) 1.91 (0.14) 1.3 (0.3)

(sd) standard deviation.

all cases except lycopene content at 90 min, the interactiontemperature-osmotic solution was statistically significant (p-value � 0.001), especially for b-carotene.

3.3. Microscopic observations

As has been mentioned previously, the effect of the processingvariables (time, temperature and composition of the osmoticsolution) on pigments distribution (including lycopene) within thecellular tissue of tomato halves submitted to osmotic dehydrationwas evaluated by means of microscopic observations. Resultsobtained from microscopic analysis of raw cherry tomatoparenchyma tissue showed quite large and separated sphericalto oval cells with well-defined cell walls (Fig. 7). As it was typical inmature plant cells, a single and central vacuole was observed totake up most of the room in the cell (more than 80%). Orange to redgranules (chromoplasts) located at the cytoplasm confirmedcarotenoids (basically lycopene and b-carotene) synthesis fromstored starch and chlorophyll, which was also indicative of anadvanced ripeness degree. Different raw fruits tested showedcellular size to decrease close to the skin and carotenoids contentto decrease as approaching the tomato core. For that reason, allsamples analysed were taken from a layer placed in parallel 2 mmunder the surface contacting the osmotic solution.

As previously mentioned, osmotic treatment of cherry tomatoflesh caused important changes on its microscopic structure. Cellsbecame deformed, elongated with cell walls, and plasmamembrane folded and separated from the cell wall as osmosisprogressed. These phenomena occur more quickly as the

Table 3F-ratio values obtained from factorial ANOVA analysis for b-carotene and lycopene contents. The factors for the analysis were temperature (T), osmotic solution (OS) and their

interaction.

Principal effects FR

90 min 390 min 1440 min

Lycopene b-Carotene Lycopene b-Carotene Lycopene b-Carotene

T 9.62 ** 32.58 *** 32.37 *** 22.54 *** 22.89 *** 6.98 **

OS 29.54 *** 120.25 *** 2.57 NS 41.45 *** 1.66 NS 3.28 NS

Interactions T � OS 0.97 NS 24.38 *** 11.36 *** 23.90 *** 9.36 *** 25.85 ***

NS: non-statistical differences (p � 0.05).** p < 0.01.*** p < 0.001.

Fig. 7. Microscopic observations of fresh tomato pulp (�10 (a); �20 (b)).

A. Heredia et al. / Journal of Food Composition and Analysis 22 (2009) 285–294292

temperature and the salt content of the osmotic solution increased(Tonon et al., 2007) (Figs. 8 and 9). These results were in agreementwith those obtained from lycopene and b-carotene quantificationin fresh and processed samples. After a certain time (around390 min), protoplast relaxed and adopted a spherical shape, thusreducing the excess of energy associated to the cell matrixcontraction (Barat et al., 1998). No noticeable differences could beappreciated after 390 min between samples processed with thesame osmotic solution but at different temperature (Figs. 8 and 9).In all these cases, great compacting of the cell structure anddisorganization of the protoplast content were observed. As aresult of this breaking down of plasma membranes and cell walls,

Fig. 8. Microscopic observations of tomato pulp dehydrated at dif

carotenoids were spread out all over the cytoplasm and evenreleased outside the cell instead of gathering all together at alimited space inside the protoplast, as stated in raw samples. Thisphysical disruption of the cell structure observed in processedtomato products compared to fresh tomatoes has been reported toimprove lycopene bioavailability by making lycopene moreaccessible and enhancing its cis-isomerisation (Stahl and Sies,1996; Shi and Le Maguer, 2000; Riso et al., 2004; Schieber andCarle, 2005). On the contrary, lycopene has been proved to be moresusceptible to chemical changes and to decompose rapidly whenbrought into contact with other cellular components or exposed tolight, oxygen, heat, etc. (Gartner et al., 1997; Perkins-Veazie and

ferent times under different osmotic solutions at 40 8C (�10).

Fig. 9. Microscopic observations of tomato pulp dehydrated at different times with the ternary solution (1:1) at 30 and 50 8C (�20).

A. Heredia et al. / Journal of Food Composition and Analysis 22 (2009) 285–294 293

Collins, 2004), as it happens after plant tissue disorganization andcellular compartments damage.

With reference to the composition of the osmotic solutionemployed, the lowest reduction of the cellular volume observed insamples immersed in the 55 Brix sucrose solutions confirmed thesucrose ability to preserve cellular integrity or the salt ability todisrupt cellular structure. As it is shown in Figs. 8 and 9,plasmolysis resulting from the osmotic treatment was still notevident after 390 min in samples processed with the binarysucrose solution; while when salt was used to carry outdehydration, plasmolysis progressed more rapidly.

4. Conclusions

This study showed that osmotic treatment carried out with 55Brix or ternary osmotic solution (10% of NaCl and 27.5%, w/w) at30 8C and 40 8C could be a useful technique with the aim ofpreserving and even increasing lycopene and b-carotene contentsand therefore, the nutritional quality of processed cherrytomatoes. In addition, microscopic observations confirmed theability of sucrose to preserve cellular integrity, which is directlyrelated to the preservation and even synthesis of carotenoidsduring osmotic dehydration. Nevertheless, it is important to pointout that cellular disruption could also modify the bioavailability oflycopene and induce cis-isomerisation, being necessary for thedetermination of the isomers of lycopene. Unlike the relationshipreported in previous scientific studies between the colour and thelycopene content (D’Souza et al., 1992; Shi et al., 1999; Thompsonet al., 2000; Raffo et al., 2006), no direct correlation was foundbetween them in this research work. Therefore, colour changeswere mainly due to liquid phase composition and shrinkageinduced by the treatment; while lycopene content and itsbioactivity more related to structural modifications (plasmolysisphenomenon, shrinkage and carotenes distribution).

Acknowledgement

Authors would like to thank Direccion General de Investigaciondel Ministerio de Ciencia y Tecnologıa (AGL2003-00753) for thefinancial support given to this investigation.

References

Abushita, A.A., Daood, H.G., Biacs, P.A., 2000. Change in carotenoids and antioxidantvitamins in tomato as a function of varietal and technological factors. Journal ofAgricultural and Food Chemistry 48 (6), 2075–2081.

Al-Wandawi, H., Abdul-Rahman, M., Al-Shaikhly, K., 1985. Tomato processing wasteas essential raw material source. Journal of Agricultural and Food Chemistry 33,804–807.

Anese, M., Manzocco, L., Nicoli, M.C., Lerici, C.R., 1999. Antioxidant properties oftomato juice as affected by heating. Journal of the Science of Food and Agri-culture 79, 750–754.

Barat, J.M., Chiralt, A., Fito, P., 1998. Equilibrium in cellular food osmotic solutionsystems as related to structure. Journal of Food Science 63 (5), 836–840.

Bramley, P.M., 2000. Is lycopene beneficial to human health? Phytochemistry 54,233–236.

Contreras, C., Martın-Esparza, M.E., Chiralt, A., Martınez-Navarrete, N., 2008. Influ-ence of microwave application on convective drying: effects on drying kineticsand optical and mechanical properties of apple and strawberry. Journal of FoodEngineering 88 (1), 55–64.

Chang, C.H., Lin, H.Y., Chang, C.Y., Liu, Y.C., 2006. Comparisons on the antioxidantproperties of fresh, freeze-dried and hot-air-dried tomatoes. Journal of FoodEngineering 77 (3), 478–485.

Dewanto, V., Wu, X., Adom, K.K., Liu, R.H., 2002. Thermal processing enhances thenutritional value of tomatoes by increasing total antioxidant activity. Journal ofAgricultural and Food Chemistry 50, 3010–3014.

D’Souza, M.C., Singha, S., Ingle, M., 1992. Lycopene content of tomato fruit can beestimated from chromaticity values. HortScience 27, 465–466.

Dumas, Y., Dadomo, M., Di Lucca, G., Grolier, P., 2003. Effects of environmentalfactors and agricultural techniques on antioxidant content of tomatoes. Journalof the Science of Food and Agriculture 83, 369–382.

Garrett, D.A., Failla, M.L., Sarama, R.J., 2000. Estimation of carotenoid bioavailabilityfrom fresh stir-fried vegetables using an in vitro digestion/Caco-2 cell culturemodel. Journal of Nutrition and Biochemistry 11, 574–580.

Gartner, C., Stahl, W., Sies, H., 1997. Lycopene is more bioavailable from tomatopaste than from fresh tomatoes. American Journal of Clinical Nutrition 66 (1),116–122.

Gerster, H., 1997. The potential role of lycopene for human health. Journal of theAmerican College of Nutrition 16, 109–126.

Giovannucci, E., 1999. Tomatoes, tomato-based products, lycopene, and cancer:review of the epidemiological literature. Journal of the National Cancer Institute91, 317–331.

Giuliano, G., Bartley, G.E., Scolnik, P.A., 1993. Regulation of carotenoids biosynthesisduring tomato development. Plant Cell 5, 379–387.

Goula, A.M., Adamopoulos, K.G., 2005. Stability of lycopene during spray drying oftomato pulp. Lebensmittel-Wissenschaft und Technologie 38, 479–487.

Heredia, A., Andres, A., 2008. Mathematical equations to predict mass fluxes andcompositional changes during osmotic dehydration of cherry tomato halves.Drying technology: an international journal 26 (7), 873–883.

Lopez, A., Gomez, P., Artes-Calero, F., 2003. Use of a* and b* colour parameters toassess the effect of some growth regulators on carotenoid biosynthesis duringpostharvest tomato ripening. International Society for Horticultural Science,Acta 599 .

Nguyen, M., Schwartz, S., 1998. Lycopene stability during food processing.Proceedings of the Society for Experimental Biology and Medicine 218,101–105.

Perkins-Veazie, P., Collins, J.K., 2004. Flesh quality and lycopene stability offresh-cut watermelon. Postharvest Biology and Technology 31 (2), 159–166.

Porter, J.W., Anderson, D.G., 1967. Biosynthesis of carotenoids. Annual Review ofPlant Physiology 18, 197–228.

Purcell, A.E., Guy, A., Thompson Jr., 1961. Glucose as a carbon source for carotenesynthesis in tomatoes. Archives of Biochemistry and Biophysics 93 (2), 231–237.

Qiu, W., Jiang, H., Wang, H., Gao, Y., 2006. Effect of high hydrostatic pressure onlycopene stability. Food Chemistry 97, 516–523.

A. Heredia et al. / Journal of Food Composition and Analysis 22 (2009) 285–294294

Raffo, A., La Malfa, G., Fogliano, V., Maiani, G., Quaglia, G., 2006. Seasonal variationsin antioxidants components of cherry tomatoes (Lycopersicon esculentum cv.Naomi F1). Journal of Food Composition and Analysis 19, 11–19.

Rao, A.V., Agarwal, S., 1999. Role of lycopene as antioxidant carotenoid inthe prevention of chronic diseases: a review. Nutrition Research 19 (2),305–323.

Riso, P., Brusamolino, A., Scalfi, L., Porrini, M., 2004. Bioavailability of carotenoidsfrom spinach and tomatoes. Nutrition, Metabolism and Cardiovascular Diseases14 (3), 150–156.

Schieber, A., Carle, R., 2005. Occurrence of carotenoid cis-isomers in food: techno-logical, analytical, and nutritional implications. Trends in Food Science andTechnology 16 (9), 416–422.

Shi, J., Le Maguer, M., Bryan, M., 2002. Chapter 4: Lycopene from Tomatoes. In:Functional Foods Biochemical and Processing Aspects, Volume (II), CRC Press.

Shi, J., Le Maguer, M., 2000. Lycopene in tomatoes: chemical and physical propier-ties affected by food processing. Critical Reviews in Food Science and Chemistry40, 1–42.

Shi, J., Le Maguer, M., Kakuda, Y., Lipaty, A., 1999. Lycopene degradation andisomerisation in tomato dehydration. Food Research International 32 (1),15–21.

Shi, J., Le Maguer, M., Wang, S., Lipaty, A., 1997. Application of osmotic treatment intomato processing: effect of skin treatments on mass transfer in osmoticdehydration of tomatoes. Food Research International 30 (9), 669–674.

Stahl, W., Sies, H., 1996. Lycopene: a biologically important carotenoid for humans?Archives of Biochemistry and Biophysics 336 (1), 1–9.

Stahl, W., Sies, H., 1992. Uptake of lycopene and its geometrical isomers is greaterfrom heat-processed than from unprocessed tomato juice in humans. Journal ofNutrition 122, 2161–2166.

Thompson, K.A., Marshall, M.R., Sims, C.A., Wei, C.I., Sargent, S.A., Scott, J.W., 2000.Cultivar, maturity and heat treatment on lycopene content in tomatoes. FoodChemistry 65, 791–795.

Tonon, R.V., Baroni, A.F., Hubinger, M.D., 2007. Osmotic dehydration of tomato internary solutions: Influence of process variables on mass transfer kinetics andan evaluation of the retention of carotenoids. Journal of Food Engineering 82 (4),509–517.

Torres, J.D., Talens, P., Carot, J.M., Chiralt, A., Escriche, I., 2007. Volatile profile ofmango (Mangifera indica L.), as affected by osmotic dehydration. Food Chem-istry 101 (1), 219–228.

Wilberg, V.C., Rodriguez-Amaya, B.D., 1995. HPLC quantitation of major carotenoidsof fresh and processed guava, mango and papaya. Lebensmittel-Wissenschaftund Technologie 28, 474–480.

Zanoni, B., Pagliarini, E., Foschino, R., 2000. Study of the stability of dried tomatohalves during shelf-life to minimise oxidative damage. Journal of the Science ofFood and Agriculture 80, 2203–2208.

Zscheille, F., Porter, J., 1947. Analytical methods for carotenes of Lycopersiconspecies and strains. Analytical Chemistry 19, 47–51.