Variation in antioxidant components of tomatoduring vine and post-harvest ripeningGabriella Giovanelli,* Vera Lavelli, Claudio Peri, Simona NobiliDISTAM, Dept of Food Science and Technology and Microbiology, University of Milan, via Celoria 2-20133 Milan, Italy

Abstract: The variation in the antioxidant content (lycopene, b-carotene, ascorbic acid and total

phenolics) was evaluated on two tomato genotypes during vine and post-harvest ripening. Tomatoes

were sampled and analysed at seven ripening stages according to the colour value. The data indicate

that ripening conditions affected both the antioxidant accumulation kinetics and the ®nal content,

which was higher in post-harvest-ripened fruits. In particular, lycopene mainly accumulated in the

very last period of ripening and its content was not linearly related to colour changes. Antioxidant

accumulation and other ripening indexes were not signi®cantly different in the two tomato genotypes.

# 1999 Society of Chemical Industry

Keywords: tomato; ripening; carotenoids; ascorbic acid; total phenolics

INTRODUCTIONRecent epidemiological studies have shown that high

consumption of tomato is consistently correlated with

a reduced risk of some types of cancer1±3 and may

account for a low incidence of ischaemic heart

disease.4 The defensive role has been attributed to

the carotenoid constituents, particularly lycopene and

b-carotene, that accumulate in plasma and tissues in

relation to tomato intake.5 These components may

have a role in vivo by inhibiting reactive oxygen

species-mediated reactions, which have been asso-

ciated with a number of human diseases. In vitrostudies evidenced that carotenoids are very effective

singlet oxygen quenchers6 and can act as free radical

scavengers.3,7 In addition, carotenoids have an im-

portant biological role7 in the induction of cell±cell

communication and growth control. The interest in

the carotenoid content of tomato is documented by a

number of studies.8

In addition to carotenoids, tomato contains a variety

of natural antioxidants, including ascorbic acid and

phenolic compounds. The ascorbic acid content of

tomato provides a signi®cant contribution to dietary

intake.8 Information on phenolic compounds is mainly

a result of the studies of Herrmann,9 Fleuriet and

Macheix10 and Hertog et al.11 Few studies have

considered the tocopherol content.12,13

According to Hart and Scott,14 the antioxidant

content of tomato mostly depends on both genetic and

environmental factors and the ripening stage. Ripen-

ing of tomato has been widely studied with the main

objective to extend the fruit shelf-life. Genetic strategy

involved both genotype selection and development of

transgenic plants with improved agronomic and

industrial characteristics.15 Post-harvest physiology

studies have dealt with the effect of modi®ed and

controlled atmospheres and low temperatures.16±18

These studies have mainly focused on tomato con-

sistency, colour and shelf-life, while information about

variations in the antioxidant content is poor or

indirect. This work presents a study on the kinetics

of antioxidant accumulation in two different tomato

genotypes during vine and post-harvest ripening.

MATERIALS AND METHODSTomato fruitSamples of Lycopersicon esculentum cv Moneymaker

were grown in a greenhouse at the Dipartimento di

Chimica e Biotecnologia Agraria of the University of

Pisa (Italy). Two genotypes (Normal Red and

Crimson) were selected for this investigation. Genetic

studies indicated that the ogc gene, which is present in

Crimson genotypes, enhanced lycopene content but

reduced b-carotene content.19

Fruit ripening and samplingVine-ripened fruits at seven different ripening stages

(from mature-green to full red) were selected from a

single harvesting batch of tomatoes according to a

scale of skin colour (a* /b*) values ranging from�ÿ0.5

to �2.5.

For post-harvest ripening experiments, mature-

green tomatoes were picked, washed with 125mglÿ1

chlorine water and allowed to ripen with a daylight/

dark cycle in a well-ventilated room at 20°C.

Tomatoes were sampled at different ripening stages,

corresponding to a* /b* values similar to those for vine-

Journal of the Science of Food and Agriculture J Sci Food Agric 79:1583±1588 (1999)

* Correspondence to: Gabriella Giovanelli, DISTAM, Dept of Food Science and Technology and Microbiology, University of Milan, via Celoria2 - 20133 Milan, Italy(Received 22 October 1998; revised version received 6 April 1999; accepted 22 April 1999)

# 1999 Society of Chemical Industry. J Sci Food Agric 0022±5142/99/$17.50 1583

ripened samples. Under both ripening conditions,

each sample was made up of three to ®ve fruits, with a

skin a* /b* value differing by no more than 0.1units.

Sampling was stopped after 16 days, when tomatoes

were beginning to become soft and to wrinkle.

Preliminary treatments of fruitAfter sampling, fruits were sliced, deprived of paren-

chyma and seeds, frozen with liquid nitrogen and

stored at ÿ18°C. Before analyses, tomato samples

were partially thawed and homogenised with an Omni-

Mixer (17106 Survall Dupont Instruments) at mod-

erate speed for 2min.

Analytical methodsColour, pH, titratable acidity, carotenoids, ascorbic

acid and polyphenols were determined on the homo-

genate. Soluble solids and sugars were determined on

the clear solution obtained by Whatman No 4 ®ltration

of the homogenate.

All data were expressed on fresh weight basis. The

moisture content varied from 91.0 to 93.9 with no

trend during ripening.

ColourColour was measured with a tristimulus Minolta

Chromameter (mod CR-210), calibrated with a white

standard (Y =94.0; x =0.3141; y =0.321). Hunter's

L* , a* , and b* values were obtained, and colour was

expressed as a* /b* value. The a* /b* value is the ratio of

red-to-green component of colour and represents the

colour index which better relates to colour variation

during tomato ripening.20 This parameter has also

been related to lycopene accumulation in tomatoes.21

Colour was measured on whole fruit skin in order to

select fruits of uniform colour to be subjected to

analyses. It was then determined again on the sample

obtained from homogenisation of three to ®ve fruits.

This is the value which is referred to in graphs, kinetic

equations and comments in this paper.

Moisture contentThe moisture content was determined by gravimetry.

About 5.0g of sample was dried in a vacuum oven at

70°C for 12±14h. Determinations were carried out in

quadruplicate.

Titratable acidityTitratable acidity was determined using a pH meter

(PHM62 Standard Radiometer). The homogenate

was diluted with water (1:1v/v), and the mixture was

titrated to pH 8.1 with 0.10M NaOH. Determinations

were carried out in duplicate. Results were expressed

as citric acid.

Brix degreeThe Brix degree (°Bx) was determined in duplicate on

the ®ltered homogenate by an Atago DBX 55

Refractometer. This parameter, which is commonly

used in the tomato industry, is an index of soluble

solids concentration in the fruit and is expressed as g

saccharose per 100ml.

Reducing sugars (glucose and fructose)Glucose and fructose were determined in duplicate on

the ®ltered homogenate by an enzymatic method (D-

glucose D-fructose enzymatic kit, Boehringer Italia).

Results were expressed as total reducing sugars.

CarotenoidsCarotenoids were determined by HPLC. The HPLC

equipment consisted of an L7100 Merck Hitachi

pump, an L7400 Merck Hitachi UV detector and a

Merck Hitachi integrator. A Vydac 201 TP 54 C18

Column (25cm, 5mm), equipped with a C18 pre-

column, was used. Carotenoids were eluted with

methanol:tetrahydrofuran (95:5v/v) at 1.0ml minÿ1

¯ow rate at room temperature under isocratic condi-

tions.

Extraction was performed using the method re-

ported by Riso and Porrini,22 modi®ed as follows: 5g

of sample was extracted directly with 25ml tetra-

hydrofuran stabilised by addition of 0.1% butylated

hydroxytoluene (2,6-di-tert-butyl-p-cresol) (BHT).

After extraction and drying, the residue was dissolved

in petroleum ether (stabilised by addition of 0.1%

BHT), dried by nitrogen stream and kept under

nitrogen in the dark atÿ18°C prior to HPLC analysis.

b-Carotene and lycopene were identi®ed and quanti-

®ed by calibration curves built with pure standard

compounds (Sigma Chemical Company, Italy). Ex-

tractions were carried out in duplicate.

Ascorbic acidAscorbic acid was determined by HPLC according to

Mannino and Pagliarini.23 Teng of homogenate was

diluted with distilled water to 50g and homogenised

by Ultra-Turrax for 30s. Sample solutions were

®ltered (0.45mm), and 20ml was injected. Each

determination was carried out in duplicate.

Total phenolicsTotal phenolics were extracted, puri®ed by C18 Sep-

Pak cartridge (Waters, Milford, USA) separation, and

determined by the Folin±Ciocalteu reaction as re-

ported by Di Stefano and Cravero.24 Both extraction

and analysis were carried out in duplicate. Data were

expressed as chlorogenic acid.

RESULTS AND DISCUSSIONIt is worth noting that, in this work, the a* /b* value for

tomato skin was used as a reference parameter for

tomato sampling. This is an essential requisite for

studies on tomato carotenoids. In the absence of this

reference, literature data cannot be compared as a

result of individual variability of both fruits and

ripening conditions. All analytical data in the graphs

reported below are referred to the same a* /b* par-

ameter, determined on the homogenates relative to

1584 J Sci Food Agric 79:1583±1588 (1999)

G Giovanelli et al

each taking. The a* /b* ratio represents a simple,

signi®cant ripening index. Because of widely variable

metabolism of individual fruits and great dependence

of ripening on climatic conditions, both on the plant

and after harvesting, it would be pointless to report

data as a function of time. Analytical data for sugars,

extract and acids do not provide a signi®cant reference

to carotenoid synthesis either, as the following discus-

sion demonstrates.

Figure 1 shows a* /b* increase as a function of time

for post-harvest ripening experiments. The data show

that the a* /b* value increased almost linearly during 12

days (from an initial value of about ÿ0.5 to a ®nal

value of about 2.0), then the curve tended to level off.

It would be pointless to draw a similar graph for vine-

ripened tomatoes because the ripening kinetics varies

considerably for each fruit according to both its

position on the plant and exposure to sunlight.

Figures 2 and 3 show variations in the lycopene and

b-carotene content as a function of the a* /b* value.

Although lycopene concentration was one order of

magnitude higher than that of b-carotene, a similar

trend was observed for variations in the two com-

pounds as a function of the colour index. At the

breaker stage the a* /b* value was either null or

negative (prevalence of green colour), and carotenoid

content was insigni®cant. In vine-ripened tomatoes

lycopene and b-carotene concentrations progressively

increased linearly with increasing the ripening index.

Conversely, in post-harvest-ripened tomatoes lyco-

pene and b-carotene formation followed an exponen-

tial trend. Carotenoid formation was very slow up to

an a* /b* value of about 1, then it became faster,

resulting in an exponential relationship between

carotenoid synthesis and colour variation. When the

a* /b* value was above 2.0, lycopene and b-carotene

accumulation was much higher in post-harvest-

ripened than in vine-ripened tomatoes. The carote-

noid content of the former was almost twice that of the

latter when the a* /b* value was higher than 2.5.

The following unexpected practical considerations

can be drawn from the above results:

(1) Ripening degree and conditions had a greater

effect on carotenoid formation than genetic

differences between the two tomato genotypes

investigated.

(2) Carotenoid synthesis occurred by different kinetics

depending on whether vine-ripened or post-

harvest-ripened tomatoes were considered. What-

ever physiological signi®cance this behaviour may

have, practical data are of great interest: adequate

post-harvest storage can result in increased lyco-

pene content of tomato.

(3) Although instrumental determination of red

colour and evaluation of a* /b* index are the most

sensitive and signi®cant indicators for fruit matur-

ity, they did not show a direct, unequivocal

correlation with the lycopene content. The same

a* /b* value can correspond to lycopene contents

differing by 100%. These data are in agreement

with those of Koskitalo and Ormrod,25 who found

Figure 1. a* /b* changes in normal red (^) and Crimson (&) tomatoesduring post-harvest ripening.

Figure 2. Variations in lycopene content versus a* /b* in vine-ripened (^)and post-harvest-ripened (&) normal red tomatoes and in vine-ripened (^)and post-harvest-ripened (&) Crimson tomatoes.

Figure 3. Variations in b-carotene content versus a* /b* in vine-ripened (^)and post-harvest-ripened (&) normal red tomatoes and in vine-ripened (^)and post-harvest-ripened (&) Crimson tomatoes.

J Sci Food Agric 79:1583±1588 (1999) 1585

Antioxidant components of tomato during ripening

small changes in Hunter's colour values and ratios

when lycopene concentrations exceeded about

40mgkgÿ1.

Experimental data on lycopene synthesis vs a* /b*value were processed by non-linear regression using

the power equation y =a�bxc, which ®tted experi-

mental data with great precision (r2 values >0.9).

Equations were further corrected by replacing coef®-

cient b with a constant value (calculated as the arith-

metical mean of all b values) to enhance signi®cance of

coef®cient c. Since determination coef®cients r2 were

still very good, comparison of the four curves could be

made on the basis of the exponent value. All equations

and relevant determination coef®cients are shown in

Table 1. The higher exponent value in equations

relating to post-harvest ripening indicates that the rate

of increase in lycopene content was higher in these

samples. These data are in agreement with those of

D'Souza et al,21 who found a linear relationship

between a* /b* and lycopene concentration in various

tomato genotypes. Their study, however, only con-

sidered a* /b* values ranging from 0 to nearly 1.

Our ®ndings on b-carotene synthesis are in dis-

agreement with those of Koskitalo and Ormrod,25 who

showed that b-carotene synthesis stopped after tomato

colour had changed from orange into red. In our

experiments continuous b-carotene synthesis was

observed on both tomato genotypes under both

ripening conditions for a longer time than that usually

considered in tomato ripening studies.

Ascorbic acid variations during ripening are shown

in Fig 4. The data show that the two ripening

conditions gave opposite patterns of variation. In

post-harvest-ripened tomatoes, ascorbic acid showed

an initial decrease followed by a considerable increase

in the last stages (upward concave curve), while in

vine-ripened tomatoes, ascorbic acid accumulated

during the ®rst stages and then decreased (downward

concave curve). Similar behaviour had already been

observed by Abushita et al.13 Further data on ascorbic

acid content of tomato indicate that vine-grown

tomatoes contain more ascorbic acid than post-

harvest-ripened tomatoes.26±28 However, in the ab-

sence of an indication concerning the ripening degree

of tomato, it is not possible to make a comparison

between the above data and our data.

Regarding polyphenols (Fig 5), different trends

were detected under different ripening conditions. It

can be observed that the total phenolic content was

higher in post-harvest-ripened samples. No signi®cant

differences in phenolics were found in the two tomato

genotypes.

Little is known about phenolic synthesis and its role

in tomato, and available data are limited to vine ripen-

ing. Senter et al29 observed that phenolic concentra-

tion and localisation in tomato varied during ripening.

Hydroxycinnamic acid content decreased as the fruit

ripened, while 3-caffeoylquinic acid was synthesised in

mature tomato pulp. According to Hunt and Baker,30

Table 1. Relationship between lycopene content (mgkgÿ1) and a* /b* value during vine and post-harvest ripening of normal red and Crimsontomatoes

Lycopene=a�b (a* /b* )c (r2) Lycopene=a�16 (a* /b* )c (r2)

Vine ripening:

Normal red Lycopene=0.67�21.6 (a* /b* )1.36 (0.99) Lycopene=4.09�16 (a* /b* )1.61 (0.98)

Crimson Lycopene=5.5�14.6 (a* /b* )1.64 (0.95) Lycopene=4.49�16 (a* /b* )1.58 (0.95)

Post-harvest ripening:

Normal red Lycopene=ÿ4.1�18.0 (a* /b* )2.03 (0.91) Lycopene=ÿ2.36�16 (a* /b* )2.14 (0.91)

Crimson Lycopene=ÿ0.51�9.6 (a* /b* )2.67 (0.99) Lycopene=ÿ5.47�16 (a* /b* )2.18 (0.99)

Figure 4. Variations in ascorbic acid content versus a* /b* in vine-ripened(^) and post-harvest-ripened (&) normal red tomatoes and in vine-ripened(^) and post-harvest-ripened (&) Crimson tomatoes.

Figure 5. Variations in total phenolics content versus a* /b* in vine-ripened(^) and post-harvest-ripened (&) normal red tomatoes and in vine-ripened(^) and post-harvest-ripened (&) Crimson tomatoes.

1586 J Sci Food Agric 79:1583±1588 (1999)

G Giovanelli et al

¯avonoid content increased during ripening, and

synthesis was favoured by light. Recent studies carried

out on two tomato genotypes31 demonstrated that

chlorogenic acid concentration declined during ripen-

ing from the mature green to the red stage, while rutin

and p-coumaric-rutin levels remained substantially

unchanged.

°Bx, reducing sugars and titratable acidity were also

evaluated. The results are reported in Figs 6 and 7.

The two tomato genotypes had similar behaviour, and

slight differences may be ascribed to ripening condi-

tions. In particular, soluble solids accumulation (ie

°Bx, reducing sugars and titratable acidity) was higher

in vine-grown tomatoes, as reported by other

authors.32 This may be of great importance for tomato

sensory characteristics.

CONCLUSIONSThe study of antioxidant synthesis in tomato (lyco-

pene, b-carotene, ascorbic acid and total phenolics)

evidenced a considerable carotenoid accumulation

during both vine and post-harvest ripening experi-

ments. Such an accumulation continued throughout

the ripening process, even when other signi®cant

composition parameters remained substantially un-

changed.

A ®rst observation is that no saturation effect was

observed on antioxidant accumulation when this was

Figure 6. Variations in soluble solids (°Bx, *), reducing sugars (gkgÿ1, &) and titratable acidity (% citric acid, ~) versus a* /b* in vine-ripened and post-harvest-ripened normal red tomatoes.

Figure 7. Variations in soluble solids (°Bx, *), reducing sugars (gkgÿ1, &) and titratable acidity (% citric acid, ~) versus a* /b* in vine-ripened and post-harvest-ripened Crimson tomatoes.

J Sci Food Agric 79:1583±1588 (1999) 1587

Antioxidant components of tomato during ripening

related to colour changes (a* /b* value). Lycopene

synthesis showed the highest increase during ripening.

A second signi®cant observation is that carotenoid

accumulation during post-harvest ripening followed

an exponential rate up to high concentration values in

the very last period of ripening before over-ripening

symptoms (softening, water and turgor losses) became

evident. At the end of the experiments, the lycopene

and b-carotene concentration in post-harvest-ripened

tomatoes was almost twice the value reached in vine-

ripened tomatoes having the same colour (a* /b*)

index. In addition, it should be considered that post-

harvest-ripened tomatoes also showed a higher ascor-

bic acid and phenolic compound content at the end of

the experiments. This suggests that post-harvest-

ripened tomatoes are richer in antioxidants than

vine-ripened tomatoes. The physiological reasons for

this behaviour are unknown, which, however, is of

practical interest in view of the increasing interest in

antioxidants, especially lycopene.

Under the experimental conditions applied, the

in¯uence of the genetic factor appears to be insigni-

®cant as compared with the importance of the

phenomena described. It may be concluded that the

use of genetics should aim at producing tomatoes with

a long shelf-life in order to obtain high carotenoid

accumulation during prolonged storage.

ACKNOWLEDGEMENTSResearch-Supported by National Research Council

CNR of Italy

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