THE PHYSIOLOGY AND NUTRITION OF TOMATO SLICES AS...

================================= Pangaribuan, D.H. and D. Irving. 2006. The Physiology and Nutrition of Tomato Slices as Affected by Fruit Maturity and Storage Temperature. Jurnal Agrista, Vol 10 (3):142 – 151.

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THE PHYSIOLOGY AND NUTRITION OF TOMATO SLICES AS AFFECTED BY FRUIT MATURITY

AND STORAGE TEMPERATURE

Darwin H. Pangaribuan1 and Donald Irving2

1Jurusan Budidaya Pertanian Fakultas Pertanian Unila Jl. S. Brojonegoro 1 Bandar Lampung, 35145 Indonesia

2 School of Agronomy and Horticulture The University of Queensland Gatton Queensland, 4343 Australia

ABSTRAK

_______________________________________________________________________

FISIOLOGI DAN NUTRISI IRISAN TOMAT AKIBAT PENGARUH KEMATANGAN BUAH DAN SUHU SIMPAN. Penelitian ini bertujuan mengevaluasi pengaruh kematangan buah tomat dan suhu simpan terhadap ciri fisiologis dan kandungan nutrisi irisan buah tomat yaitu produksi etilen, laju respirasi, kebocoran elektrolit serta kandungan asam askorbik dan likopen. Penelitian yang menggunakan tomat cv. ‘Revolution’ ini dilaksanakan di Laboratorium Pascapanen Hortikultura milik ‘School of Agronomy and Horticulture’ The University of Queensland, Australia.. Perlakuan terdiri atas 4 tingkat kematangan buah yaitu hijau-kuning (‘turning’), oranye (‘pink’), merah muda (‘light-red’) dan merah (‘red’) dan 3 tingkat suhu simpan yaitu suhu 0 °C, 5 °C dan 10 °C. Buah tomat dikerat dengan alat ‘slicing machine’. Percobaan menggunakan rancangan acak lengkap dengan 5 ulangan. Hasil penelitian menunjukkan bahwa irisan tomat dari buah hijau-kuning menunjukkan laju produksi etilen dan tingkat respirasi yang lebih tinggi, kebocoran elektrolit yang lebih rendah, kandungan asam askobik dan likopen yang lebih rendah daripada irisan tomat dari buah berwarna merah. Irisan tomat yang disimpan pada suhu 0 °C menghasilkan laju produksi etilen dan tingkat respirasi yang lebih rendah, kebocoran elektrolit yang lebih rendah, kandungan asam askorbik yang lebih tinggi, kandungan likopene yang lebih rendah daripada irisan tomat yang disimpan pada suhu 10 °C.

Kata kunci: tomat, tingkat kematangan buah, suhu simpan, etilen, respirasi, nutrisi ________________________________________________________________________


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INTRODUCTION

Fresh-cut products remain biologically and physiologically active, as the tissues are

living and respiring (Reyes, 1996). The main problems with fresh-cut products are two-

fold. Firstly, fresh-cut products are highly perishable because mechanical processes such

as cutting, slicing, shredding, and trimming disrupt cellular structures (Rolle and Chism,

1987; Watada et al., 1996). Secondly, mechanical wounding results in increased

production of ethylene and respiration rates (Watada et al., 1996). In addition, the

cellular breakdown leads to undesirable enzymatic reactions, leakage of ions and other

cellular components, and consequently storage life is often reduced (Burns, 1995; Luna-

Guzman et al., 1999). If all these changes cannot be properly controlled, they can lead to

rapid senescence and deterioration of the product.

The ripening of climacteric fruits such as the tomato is stimulated by ethylene. Dramatic

physiological changes occur in tomato fruit during ripening, and those events are

associated with changes in ethylene production, respiratory and enzyme activity,

including cell wall and membrane-associated proteins. The capability to control tomato

ripening by modulating ethylene responses could extend the storage life of tomatoes.

The commercial value of ready-to-eat tomatoes is dependent on maintenance of quality

during storage. Although tomatoes continue to ripen during storage (Artes et al., 1999;

Mencarelli and Saltveit, 1988), commercial manufacture of tomato slices is challenging

because the tomato fruits must first be ripened, processed, and then stored until consumed

(Gorny et al., 1998). The quality of fresh tomato slices are affected by a number of


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factors such as cultivar, growing conditions, fruit maturity, postharvest handling and

storage temperature (Kader et al., 1977; Madhavi and Salunkhe, 1998). Among these

factors, fruit maturity and storage temperature are the focus of this study.

The experiment reported in this paper examines the postharvest physiology of tomato

slices in relation to maturity of the fruit and storage temperature. Physiological aspects

that characterise slice quality including ethylene production, respiration rate, electrolyte

leakage, ascorbic acid and lycopene were measured.

MATERIALS AND METHODS

Plant materials Fruits of tomato cv. ‘Revolution’ were harvested from a commercial field. Medium-sized

fruits were chosen with a mean fresh weight of 150.0 ± 14.6 g, and equatorial and

longitudinal dimensions of 68.7 ± 1.6 mm and 65.4 ± 2.4 mm, respectively. The four

stages of maturity were characterised by colour (hue angle, h°) (Cantwell and Kasmire,

2002) and firmness (Newtons, N) as ‘turning’ (h° 80-100, 21 ± 0.9 N), ‘pink’ (h° 63-77,

18 ± 0.8 N), ‘light-red’ (h° 55-65, 15 ± 0.6 N), and ‘red’ (h° 46-54, 12 ± 0.5 N).

Slice preparation

Experiment was conducted in the Postharvest Laboratory the University of Queensland,

Australia. A total of 5 slices (each 7 mm-thick) were cut parallel to the equatorial region

fruit with a commercial slicing machine. To ensure uniformity only equatorial slices


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were taken, and the upper stem-end and lower blossom-end slices were discarded. The

five equatorial slices from each fruit were considered as one replicate and were arranged

within containers as vertical stacks. Each plastic container (high density polyethylene

with length: 16.5 cm, width: 10.5 cm, depth: 6.5 cm) was capped with a lid perforated

with 2 holes (10 mm-diameters). The holes were packed with clean cotton wool to assist

in maintaining sterility, and to enable adequate ventilation of the atmosphere inside (Wu

and Abbott, 2002). Each containers containing two layers of absorbent paper on the

bottom to prevent juice accumulation (Gil et al., 2002). All containers were held in

storage rooms at 0, 5 or 10 °C with 95% relative humidity.

Assessments and experimental design For ethylene determination, samples were injected into a gas chromatograph (Shimadzu

model GC-8A) fitted with a flame ionisation detector. Temperatures of the injector port,

column and detector were 120, 90, and 120 °C, respectively. The 900 mm-long and 5

mm internal-diameter glass column was packed with activated alumina mesh size 80/100.

The Shimadzu CRGA Chromatopac integrator output was calibrated using an ethylene

standard gas (0.09 ± 0.02 µL L–1, BOC Gases β-grade) and the balance gas was nitrogen.

The carrier gas (1 kg cm-2 pressure) was high purity nitrogen (BOC Gases). Oxygen (0.3

kg cm-2) was supplied as medical grade air, and hydrogen (0.45 kg cm-2) was high purity

grade, both from BOC Gases.

Ethylene production rate on a fresh weight basis was calculated as follows:

Ethylene production (nmol g -1 h-1) =


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∆ C2H4 × wt(g) fresh

vol(L) space head×

t(h)1

× Ctemp273K

273K°+

× 22.41000

where:

∆ C2H4 = ethylene concentration in sample – background (µL L–1)

t = incubation time

For CO2 analyses, headspace samples were injected into a gas chromatograph (Shimadzu

model GC-8A) fitted with a thermal conductivity detector. Temperatures of the injector

port, column and detector were 30, 35, and 30 °C, respectively. The 1.5 m-long and 1.8

mm-internal diameter glass column was packed with activated alumina mesh size 80/100.

The gas chromatograph signal was recorded using a Shimadzu CRGA Chromatopac

integrator calibrated with a CO2 standard of 0.575% (v/v) in nitrogen (BOC Gases β-

grade). The carrier gas (1 kg cm-2 pressure) was high purity helium (BOC Gases).

The rate of carbon dioxide production was used to indicate the respiration rate. The

respiration rate on a fresh weight basis was calculated using the following equation:

Respiration rate (µmol g-1 h -1) =

∆ CO2 × 104 × wt(g) fresh

vol(L) space head × t(h)1 ×

Ctemp273K273K

°+ ×

22.41

where:

∆ CO2 = CO2 in sample – CO2 in background (% v/v).

t = incubation time


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Electrolyte leakage rate was determined from conductivity measurements according to

the procedure of King and Ludford (1983) and Hong et al. (2000). Four sections of

pericarp discs (about 6 mm diameter) were excised from each slice and combined. The

discs were weighed (about 2 g) and washed three times in distilled water and placed in

beakers containing 30 ml 0.4 M mannitol solution. In an initial experiment it was found

that conductivity of the bathing solution did not increase appreciably with incubation for

up to 6 h. The discs were held at 30 °C for 6 hours and then 20 mL of solution was taken

and initial electrical conductivity readings were taken using a conductance meter

(Activon Model 301, Conductivity Meter, Australia). The beakers were swirled for 10 s

before the electrolyte measurements were taken. The discs and bathing solutions were

then frozen at –20 °C for 24 hours and then thawed. Final conductivity readings were

taken and electrolyte leakage (%) was calculated (McCollum and McDonald, 1991):

Electrolyte leakage (%) = 100 tyconductivi Finalty conductivi Initial

×

Ascorbic acid concentrations were determined using High Performance Liquid

Chromatography (HPLC, LC-10 AD Liquid Chromatograph, Shimadzu, Japan) according

to Rizzolo et al. (1984). Approximately 20 g of slices stored at -80°C were thawed and

homogenised with a homogenizer (Janke & Kunkel IKA, Ultra Tunax T25) at 13 500

rpm for 2 minutes at room temperature. Ten gram of homogenate was weighed and

mixed with 25 ml of 6% (w/v) metaphosphoric acid. The solution was centrifuged (P

Selecta, Centronic, Spain) for 20 min at 6 000 rpm (2500 x g). The extract was


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transferred into a 100 ml volumetric flask after filtration through Whatman No. 1 filter

paper. The residue from the filtration was extracted with metaphosphoric acid once more

and the second extract was combined with the first. The mixture was filtered through

Whatman No. 1 filter paper and the filtrate was diluted to 100 ml with 6% (w/v)

metaphosphoric acid. An aliquot of the acid extract was then filtered through a Millipore

filter (Millex HA) prior to injection of 10 µL into the HPLC (SIL-10AXL, Shimadzu,

Japan). The ascorbic acid was separated on a column of Luna 5µ C18 (Phenomenex,

USA) with length 150 mm x diameter 4.6 mm, equipped with a guard column C18 5µ.

The mobile phase was 0.2 N orthophosphoric acid, the flow rate was 0.8 mL/min, and the

detection wavelength was 254 nm. L (+) ascorbic acid (0.01 mg/mL) (Merck) was used

as the external standard for quantification. To determine recovery of the procedure, a

known amount of pure ascorbic acid standard (i.e. 2 x the amount found normally) was

added to disc samples and then the extraction and chromatographic procedures were

applied to samples with and without standard ascorbic acid, in duplicate. The recovery

was 96 %, indicating complete extraction. Ascorbic acid concentration on a fresh weight

basis was calculated:

Ascorbic acid (mg /100 g) =

sampleg g 100

g1000mg 1

100L1000

L1g0.01

sample of Area standard of Area

××××µ

µµµ

Lycopene analyses were performed according to Beerh and Siddappa (1959), Adsule and

Dan (1979), and Hakim et al. (2000). Pigments were measured by homogenizing ca. 3 g

of frozen pericarp tissue with a homogenizer (Janke & Kunkel IKA, Ultra Tunax, T25) at

13 500 rpm in 10 ml of acetone in a centrifuge tube at room temperature. The tubes used


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were covered with aluminium foil to prevent light-induced lycopene oxidation. The

tubes were shaken on a shaker (B.Braun, Melsungen AG, Germany) for 15 min at 150

cycles/min and then centrifuged (P Selecta, Centronic, Spain) at 6000 rpm (2500 x g) for

10 minutes at room temperature. The supernatant was decanted and adjusted to 15 ml

with acetone. Lycopene concentrations were determined from the absorbance at 503 nm

in an acetone extract using a spectrophotometer (Pharmacia LKB, Ultrospec III, Japan).

This wavelength is best suited for tomato lycopene because the influence of carotenoids

is negligible (Beerh and Siddappa, 1959). Lycopene content was calculated using the

formula developed by Fish et al. (2002) using the molecular extinction coefficient of 17.2

x 104 mol cm-1 (Beerh and Siddappa, 1959; Mencarelli and Saltveit, 1988) and was

expressed on a fresh weight basis:

Lycopene (µg g-1) =

mL10L 1

cmΜ1017.2A

34503 ×

×× tissuekg mg 10

×tissuekg

mL 10.0×

tissuekg 0.0312 A ×

= 503

tissueg 31.2A 503 ×=

The experiment was laid out in a completely randomised design. The factors were 4

levels of fruit maturity (‘turning’, ‘pink’, ‘light-red’, ‘red’), and 3 levels of storage

temperature (0, 5 and 10 °C). Each treatment was replicated 5-fold. Experimental

assessments were made on days 1, 4, 7, and 10 after slicing. In the following graphs,

where maturity is the main factor, data from all temperatures are combined. Where

temperature is the main factor, all maturities are combined.


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RESULTS

The rates of ethylene production by slices decreased (P<0.001) with time in storage. The

decrease in ethylene during the first 4 days was quite rapid especially for ‘turning’ and

‘pink’ stages (Fig. 1A). After day 4, rates remained relatively stable until day 10. Slices

held at 10 °C had significantly higher (P<0.001) rates of ethylene production, but storage

at 0 or 5 °C greatly reduced the rates (Fig. 1B). There was a decline in ethylene

production from day 1 to day 4, then the rates of ethylene production stabilised

throughout the rest of the storage period, except at 10 °C after day 7.

Storage time (days)

1 4 7 10

Eth

ylen

e pr

odu

ctio

n (n

mol

g-1

h-1

)

0.0

0.1

0.2

0.3

0.4Turning Pink Light-red Red

(A)

Storage time (days)

1 4 7 10

Eth

ylen

e pr

odu

ctio

n (n

mol

g-1

h-1

)

0.0

0.1

0.2

0.3

0.410 oC 5 oC 0 oC

(B)

Figure 1 Changes in ethylene production of slices from fruit of different stages of maturity (A) and storage temperatures (B) during storage. Vertical bars represent LSD 0.05.


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Respiration rates by slices also decreased (P<0.001) with time in storage. On the first

day, the slices obtained from the ‘turning’ and ‘pink’ stages had the highest rates of

respiration (Fig. 2A), whilst slices obtained from ‘red’ maturity fruit had the lowest rates.

After 4 days, the respiration rates of slices from ‘turning’, ‘pink’, ‘and light- red’ fruit

were not different. Respiration rates of the slices at 10 °C were always higher compared

with those at 0 and 5 °C (Fig. 2B). There was a gradual decline in respiration rate during

storage at 0 and 5 °C with a slight increase after 4 days of storage at 10 °C.

Storage time (days)

1 4 7 10

CO

2 pr

odu

ctio

n ( µ

mol

g-1

h-1

)

0.0

0.2

0.4

0.6

0.8Turning Pink Light-red Red

(A)

Storage time (days)

1 4 7 10

CO

2 pr

odu

ctio

n ( µ

mol

g-1

h-1

)

0.0

0.2

0.4

0.6

0.810 oC 5 oC 0 oC

(B)

Figure 2. Changes in respiration rate of slices from fruit of different stages of maturity (A) and storage temperatures (B) during storage. Vertical bars represent LSD 0.05.


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Over the 10 days storage period, electrolyte leakage gradually increased from all slices.

Slices obtained from ‘turning’ and ‘pink’ stages of maturity showed the least leakage up

to day 4. After day 4, ‘pink’ slices leaked as much as more electrolytes than either ‘light-

red’ or ‘red’ slices. Significant (P<0.001) but lesser increases in leakage occurred from

‘light-red’ and ‘red’ maturity stage slices (Fig. 3A). Electrolytes gradually leaked from

the tomato slices over the first 7 days of storage at 0, 5 and 10 °C (Fig. 3B). During the

period from 7 to 10 days of storage, electrolyte leakage was faster at 5 and 10 °C than at

0 °C.

Storage time (days)

1 4 7 10

Ele

ctro

lyte

Lea

kage

(%)

0.3

0.4

0.5

0.6

RedLight-redPinkTurning

(A)

Storage time (days)

1 4 7 10

Ele

ctro

lyte

leak

age

(%)

0.3

0.4

0.5

0.6

10 oC 5 oC 0 oC

(B)

Figure 3. Changes in electrolyte leakage of slices from fruit of different stages of maturity (A) and storage temperatures (B) during storage. Vertical bars indicate LSD 0.05.


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The ascorbic acid content of tomato slices at all maturity stages decreased (P<0.001)

during storage (Fig. 4A). Despite these changes, ‘red’ slices had the highest ascorbic

acid contents throughout storage. Overall, the slices from ‘turning’ maturity fruit lost

ascorbic acid slightly faster (5.4% per day) than slices from ‘red’ maturity fruit (3.9% per

day). Temperature did not affect ascorbic acid concentration during the first day of

storage. The ascorbic acid content of the slices at 0 °C was always higher than those at 5

and 10 °C (Fig. 4B). There was a steady decline in ascorbic acid content during storage

at all temperatures tested. Slices stored at 0 °C lost ascorbic acid content at a rate of

around 3.0% per day but those stored at 10 °C lost ascorbic acid at the rate of around

6.2% per day.

Storage time (days)

1 4 7 10

Asc

orbi

c ac

id (m

g (1

00 g

)-1)

6

8

10

12

14

16

18

20Red Light-red Pink Turning

(A)

Storage time (days)

1 4 7 10

Asc

orbi

c ac

id (m

g (1

00 g

)-1)

6

8

10

12

14

16

18

20 0 oC 5 oC10 oC

(B)

Figure 4. Changes in ascorbic acid on a fresh weight basis of slices from fruit of different stages maturity (A) and storage temperatures (B) during storage. Vertical bars represent LSD 0.05.


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As expected, lycopene content was significantly higher (P<0.001) in ‘red’ slices than in

‘turning’ slices (Fig. 5A). Lycopene in ‘red’ slices was relatively stable during storage,

whereas lycopene from ‘pink’, ‘turning’ and ‘light-red’ slices gradually increased.

Lycopene content was significantly higher (P<0.001) in slices stored at 10 °C than at

lower temperatures (Fig. 5B) after 4 days storage. Lycopene content in slices stored at 10

°C gradually increased whereas lycopene level in slices at 0 and 5 °C changed only

slightly during storage.

Storage time (days)

1 4 7 10

Lyco

pene

( µg

g-1)

6

7

8

9

RedLight-redPinkTurning

(A)

Storage time (days)

1 4 7 10

Lyco

pen

e ( µ

g g-1

)

6

7

8

9

10 oC 5 oC 0 oC

(B)

Figure 5. Changes in lycopene content on a fresh weight basis of slices from different stages of maturity (A) and storage temperatures (B) during storage. Vertical bars represent LSD 0.05.


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DISCUSSION

The beginning of intact tomato ripening is usually indicated by an increase in the

production of CO2 and ethylene (Grierson and Kader, 1986). After slicing, slices from

fruit at different stages of maturity produced different amounts of ethylene relative to

each other. The ‘turning’ stage slices produced much more ethylene than ‘red’ stage

slices. This may be because early maturity fruit and slices have greater potential for

ethylene production, which means more ACC synthase and more ACC oxidase capacities

than tomatoes at later stages of maturity (Abeles et al., 1992). These results indicate that

the more advanced the maturity, the lesser the rate of ethylene production. Respiration

patterns were similar to the ethylene patterns, in which the ‘turning’ tomato slices had

higher respiration rates than ‘red’ tomato slices. This could also be associated with

greater capacities for ethylene production from less mature fruit and slices.

Storage at 0 and 5 °C substantially decreased the rate of ethylene production during the

storage period. Madrid and Cantwell (1993) showed that storage of cantaloupe pieces at

0 - 2.5 °C completely suppressed wound-induced ethylene compared with higher storage

temperatures. Artes et al. (1999) also reported that low temperature storage of tomato

slices (2 oC) reduced wound-induced ethylene production. These effects are most likely

due to the enzymes responsible for ethylene formation (ACC oxidase and ACC synthase)

being sensitive to low temperatures (Lurie, 2002).

Storage at 0 and 5 °C substantially decreased the respiration rate of sliced tomatoes

during storage. Temperature is the most important environmental factor in the


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postharvest life of fresh produce because of its dramatic effect on rates of biological

reactions including respiration (Lurie, 2002). The Van't Hoff rule states that the

respiration rate of fresh fruits and vegetables generally increases two to three folds for

every 10 °C rise in temperature (Shewfelt, 1986).

Electrolyte leakage is generally considered to be an indirect measure of plant cell

membrane damage and integrity (King and Ludford, 1983; Marangoni et al., 1996). The

experimental results indicate that membrane permeability increased with advanced

maturity (Fig. 3A). This was also shown in intact tomatoes in studies by Autio and

Bramlage (1986). A rapid increase in electrolyte leakage might be due to the changes in

membrane fluidity by cutting-induced oxidative stress (Hong and Gross, 1998).

Therefore, the differences in electrolyte leakage at the different stages of maturity are

possibly associated with senescence, where slices from advanced maturity stages (‘light-

red’ and ‘red’) may be more susceptible to oxidative stress than those from early stages

(‘turning’ and ‘pink’). In the present experiment, the effect of storage temperature on

electrolyte leakage was not significant until day 7 of storage. Sharom et al. (1994)

reported the differences appeared after day 7 of storage in whole tomatoes stored for 20

days at 5 °C, as did Murata and Tatsumi (1979) with tomatoes stored at temperatures

between 2 and 12.5 °C. Kuo and Parkin (1989) reported that cucumbers did not show

any changes in electrolyte leakage during storage at 2 °C for 10 days. Some researchers

have used electrolyte leakage as a marker for chilling injury (Cote et al., 1993; Kader and

Ludford, 1983; Sharom et al., 1994).


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Recently, Hong and Gross (2000) demonstrated the development of chilling injury in

fresh-cut tomato slices during cold storage using tomato cvs. ‘Sunbeam’ and ‘Mountain

Pride’ at the ‘light-red’ and ‘red-ripe’ stages of maturity. They used water-soaked area as

an indicator that expressed the degree of chilling injury. They also found that ethylene

may inhibit development of chilling injury in tomato at ‘light-red’ and ‘red’ stages of

maturity. Gil et al. (2002) also observed the development of water-soaked areas during

their experiments using ripe fruits of tomato cv. ‘Durinta’. Generally, translucency of

water-soaked areas was not the main disorder observed in this current study. The only

exception was that the ‘red’ maturity slices often exhibited translucency. Gil et al. (2002)

reported that translucency developed more frequently in fruit from advanced ripening

stages. In an experiment using tomato cv. ‘Solarset’ at ‘turning’ maturity, Hakim et al.

(2000) did not report any symptoms of chilling injury in fresh-cut slices. Moreover,

Conesa et al. (2000) observed chilling injuries did not develop on slices of tomato cv.

‘Calibra’ when stored at 0 °C. The difference in cultivars in these studies may explain

the differences in sensitivity to chilling injury.

There is a need for ready-to-eat tomato slices that have sufficient storage life while

retaining nutritional value. Levels of vitamins make a significant contribution to

nutritional value of fresh tomato slices. Concentrations of ascorbic acid in tomato slices

are affected by fruit maturity. In this study, the slices from ‘red’ and ‘light-red’ stages of

development contained more ascorbic acid than earlier stages of development (‘turning’

and ‘pink’) (Fig. 5.9A). Shi et al. (1999) also reported that the ascorbic acid content of

greenhouse plum tomato var. ‘Heinz 9478’ increased during ripening. This trend is most


18

likely due to the tomatoes antioxidant function when the ripening cells absorb high

amounts of oxygen as a result of an increasing rate of cell respiration (Abushita et al.,

1997). In addition, antioxidant concentration increases inresponse to various oxidative

stress (Lee and Kader, 2000).

The current experiments have shown that higher temperatures promote a loss of ascorbic

acid content, which is in agreement with the results of Watada et al. (1987). Increasing

storage temperatures from 0 °C to 10 °C or 21 °C resulted in greater losses of ascorbic

acid levels in kale, cabbage, and snap beans (Ezell and Wilcox, 1959), and carotene in

kale, collards, and turnip greens (Ezell and Wilcox, 1962). These results suggest that

higher storage temperatures can lead to a significant decline in antioxidant constituents of

tomato, suggesting that free-radical accumulation is enhanced at higher storage

temperatures (Toivonen, 2003). This study also clearly showed that ascorbic acid content

during storage at all temperatures tested gradually declined during storage (Fig. 5.9B).

Ascorbic acid reduction after cutting or peeling was also reported by Chiesa et al. (2003)

who reported that ascorbic acid levels in fresh-cut lettuce decreased during 10 days of

storage at 4 °C with a strong decrease after 3 days of storage. Klein (1987) reported that

ascorbate can be degraded by light and oxygen to which sliced tissues are exposed.

Smirnoff (1996) explained that ascorbate loss in slices may be related to oxidation in

injured tissues. By the end of storage, Klieber and Franklin (2000) reported that fresh-cut

Chinese cabbage lost 13% of their ascorbic acid. These observations suggest that

preserving the integrity of slices during storage is important during storage of tomato


19

slices if the levels of ascorbic acid are to be held at similar levels to intact stored

tomatoes.

Increase in lycopene level is directly related to the stage of ripeness. It was found that

lycopene levels were higher in slices from more mature fruit (Fig. 10A). This finding is

consistent with the observation that ripe ‘red’ tomatoes contain higher levels of lycopene

than ‘mature-green’ tomatoes (Klein, 1987). Liu and Luh (1977) also reported that ‘red’

maturity fruit produced increased carotenoid concentrations when processed into tomato

paste. In the samples measured in this experiment, lycopene contents ranged from 6.5 –

8.7 µg g–1, values close to those reported by Hakim et al. (2000) at ‘pink’ maturity.

CONCLUSION

Results indicate that the more advanced the maturity, the lesser the rate of ethylene

production as well as the respiration rate. The ‘turning’ tomato slices had higher ethylene

production and respiration rates than ‘red’ tomato slices. Storage at 0 and 5 °C

substantially decreased the rate of ethylene production and respiration rate during the

storage period. The results indicate that membrane permeability increased with

advanced maturity. Over the 10 days storage period, electrolyte leakage gradually

increased from all slices. The slices from ‘red’ and ‘light-red’ stages of development

contained more ascorbic acid than earlier stages of development (‘turning’ and ‘pink’).

Higher temperatures promote a loss of ascorbic acid content and lycopene levels.

Lycopene levels were higher in slices from more mature fruit.


20

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