From Producer to Consumer: Greenhouse Tomato Quality As Affected

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From producer to consumer - greenhouse tomato quality as affected by variety, maturity stage at harvest, transport conditions and supermarket storage Michel Verheul, Rune Slimestad, and Irene Holta Tjøstheim J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/jf505450j • Publication Date (Web): 28 Apr 2015 Downloaded from http://pubs.acs.org on May 3, 2015

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Journal of Agricultural and Food Chemistry

From producer to consumer – greenhouse tomato quality as affected by variety, maturity stage at harvest, transport conditions and supermarket storage

Michèl J. Verheul*, Rune Slimestad and Irene Holta Tjøstheim Norwegian Institute for Agricultural and Environmental Research – Bioforsk Vest Særheim, Postvegen 213, N-4353 Klepp station, Norway *Corresponding author: Phone: +47-934-08-525; Fax: +47-5142-6744; E-mail: [email protected]

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ABSTRACT

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Possible causes for differences in quality traits at the time of buying were studied in two

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widely different red tomato types. Three maturity stages were harvested from commercial

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greenhouses and transferred immediately to controlled environments simulating different

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storage, transport and supermarket conditions. Results show significant differences in

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development of color, fruit firmness, contents of soluble solids (SSC), titratable acids (TTA),

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phenolics and carotenoids from harvest to sale, as related to postharvest conditions. Fruit

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firmness, SSC and TTA of vine ripened red cherry tomatoes was 30, 55 and 11% higher than

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for those harvested at breakers and ripened to red. Temperature, light, UVC-radiation or

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ethylene during four days transport affected tomato quality traits, and differences persisted

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during three weeks of supermarket storage. Ethylene exposure gave a 3.7-fold increase in

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lycopene content in cherry tomatoes, whereas UVC-hormesis revealed a 6-fold increase

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compared to control. Results can be used to update recommendations concerning optimal

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handling.

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KEYWORDS

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Lycopersicon esculentum Mill.; quality; on-vine ripening; post-harvest treatment; color;

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firmness; taste; soluble solid content; total acid content; carotenoids; flavonoids.

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INTRODUCTION

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Tomato fruit quality is usually understood as a combination of some or all of the following

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parameters: visual appearance, firmness and texture, dry matter content, organoleptic

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compounds, and health influencing compounds.1 Research on tomato fruit storage has mostly

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focused on shelf life in terms of appearance and firmness. 2 However, taste and health

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influencing compounds of fresh tomatoes are of high relevance from a consumer perspective.

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and firmness, while the frequency and magnitude of subsequent purchases depend largely on

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consumer assessment of eating quality. In the case of tomatoes, taste is mainly defined by the

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content of reducing sugars and organic acids. 4-6 Both sugars and acids contribute to the

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sweetness and to the overall aroma intensity. 7 Firmness is appreciated by Norwegian

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consumers who consider firmness and texture to be strongly related. 3

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Tomatoes together with processed products thereof are important parts of the traditional

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Mediterranean diet associated with low mortality of cardiovascular diseases.8 Lycopene, the

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main carotenoid in red tomato, has received special attention due to results from

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epidemiological studies as well as from cell culture and animal studies which suggest that

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lycopene may lower the risk of cancer and cardiovascular diseases.9 In addition, tomato is a

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valuable source of β-carotene, a pro vitamin A compound, which like lycopene is a strong

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lipophilic antioxidant. Due to the high consumption of tomato-based products worldwide,

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attention has also been given to other phytochemicals from this species. The flavonol rutin

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(quercetin 3-(6’’-rhamnosyl)-glucoside) together with chalconaringenin (a chalcone) was

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found at higher concentrations in fresh cherry tomatoes than lycopene. 10 Both compounds

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exhibit antiradical and antioxidant properties. Since rutin together with apiorutin (quercetin 3-

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(2’’apiosyl-6’’-rhamnosyl)-glucoside) 11 are hydrophilic compounds, they are supposed to

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work differently from the carotenoids. Chlorogenic acid (5’-caffeoyl quinic acid) is an

The initial decision to buy fruit and vegetables is usually made on the basis of appearance

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aromatic acid in fresh tomatoes which occurs together with isomeric compounds and other

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minor phenylpropanoids. Together these compounds may account for similar concentrations

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as rutin in fresh tomatoes. Due to the orto-catechol structure of chlorogenic acid it is supposed

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to have some of the same antioxidant functions as rutin.

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Early harvesting is common practice in order to obtain firmer fruit suitable for transport. In

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Norway, wholesalers demand fruits to be harvested at maturity stage ‘breakers’. A storage

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temperature of 10-13 oC in the dark is often chosen to guarantee a long shelf life. 12

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Wholesalers obtain firmer fruits suitable for long distance transport and a longer marketable

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period. This commercial practice was justified by Lin and Block. 13 Since newer varieties

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often have longer shelf life, this practice leads also to long time storage, up to three weeks, in

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the supermarket before red ripe tomatoes reach the consumer. 14 Little is known about effects

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of storage conditions on organoleptic and health influencing compounds of fresh tomatoes.

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Consumers complain about the lack of taste of tomatoes in numerous newspaper and

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magazine articles. 15 The number of tomato varieties and types grown in Norwegian

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greenhouses for fresh consumption has increased dramatically the last five years. All types

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and varieties are stored the same way, and it is not known whether different tomato varieties

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and types react differently to storage conditions.

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Variables like maturity stage at harvest and environmental conditions during transport and

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supermarket storage might be crucial for tomato quality. Earlier studies have shown that

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maturity stage at harvest may influence post-harvest quality. 1 Effects of growing conditions

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on tomato quality of different tomato cultivars were reviewed earlier. 16

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Post-harvest treatment with UVC radiation might increase tomato quality, while sunlight

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might decrease tomato quality. 17 Long distance transport in Norway often includes

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suboptimal storage conditions due to joint transport with other products that require low

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temperature (2-8 oC) or give off ethylene. Little is known about effects and possible

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aftereffects of transportation on tomato quality that reaches the consumer.

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We carried out an experiment to quantify the effects of 1) maturity stage at harvest and 2)

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environmental conditions during transport on tomato quality during simulated supermarket

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storage at 22oC. Two widely different tomato varieties were used. Storage at 22 oC was

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compared to standard storage conditions at 12 oC in the dark. Effects of post-harvest treatment

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with UV-C radiation were elucidated.

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MATERIALS AND METHODS

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Plant material

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Fully developed cherry tomatoes (Lycopersicon esculentum Mill. ‘Susanne’) and round

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tomatoes (Lycopersicon esculentum Mill. ‘Dometica’) at maturity stage ‘breakers’, ‘pink’ or

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‘red’ 18 were harvested from two commercial greenhouses in southwestern Norway (58o47’ N,

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5o41’E) at August 30 and September 8 in 2010 and stored at 12 oC (± 0.2 oC) in the dark at a

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relative humidity (RH) of 85% (± 3%). Only undamaged fruits were harvested and handled

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carefully to decrease possible effects on flavor perception. 15 Fruit age at harvest was

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respectively 40, 47 and 54 days after flowering for ‘Susanne’, and 50, 57 and 64 days after

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flowering for ‘Dometica’ for maturity stages breakers, pink and red. Fruit size was 17 ± 3 g

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for ‘Susanne’ and 80 ± 5 g for ‘Dometica’. Samples for analyses were taken at August 31 and

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September 3, 6, 14 and 20 from first harvest, and at September 9, 13, 16, 23 and 30 from

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second harvest. All treatments included three maturity stages and three replications. Each

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sample consisted of six fruits, giving a total number of 9720 fruits.

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Storage conditions

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Fruits from both cultivars and all three maturity stages were transferred randomly to 20 m3

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storage rooms with forced ventilation and different temperature and light conditions. In the

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time period from day 1 until day 4 after harvesting, different transport conditions were

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simulated. Conditions, selected after communication with Norwegian wholesalers, included

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different temperatures: 2, 8, 12, and 15 oC, all in the dark, or light conditions: exposure to

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light provided by fluorescent tubes (Osram L58W/21) with a light intensity of 150 µmol m-2 s-

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at fruit height while kept at a temperature of 12 oC, and exposure to ethylene (150 ppm) at a

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temperature of 2 oC in the dark. To elucidate effects of UV-C radiation, fruits were exposed to

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UV-C radiation provided by UV lamps (Osram HNS 15W OFR) with a light intensity of 350

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µmol m-2 s-1 to fruit during 15 or 90 seconds at 12 oC and thereafter kept at 12 oC in the dark.

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All treatments were kept at a relative humidity of 85% (± 3%). Temperature fluctuations in all

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storage rooms were kept within ± 0.2 oC.

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After simulated transportation during 96 hours (day 4), the fruits were transferred to a storage

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room with a temperature of 22 oC, a light intensity of 40 µmol m-2 s-1 at fruit height provided

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by fluorescent tubes (Osram L58W/21), and a relative humidity of 85% (± 3%) during 17

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days, thus simulating storage conditions measured in Norwegian supermarkets in August

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2010. As a control, fruits were kept in a storage room at 12 oC and 85% relative humidity in

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the dark. Fruits showing microbiological decay were excluded from the quality analysis.

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Chemicals

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Chalconaringenin (CN) and rutin were isolated from cherry tomatoes as described

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previously.10 All other chemicals were obtained from Sigma-Aldrich, Norway.

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Quality traits

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Color, firmness, soluble solid content (SSC) and total titratable acid (TTA) was measured

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following the methods of Mitcham and coworkers, 19 and the mean value from the

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measurements of four to six individual tomatoes was used to describe the quality of a sample.

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Tomato color was determined in accordance to a color sheet scaling from 1, which is

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equivalent to full green, to 12 which is fully red fruit. Colors 4, 8, 12 represents maturity

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stages ‘breakers’, ‘pink’ and ‘red’. 18 Firmness was measured on two opposite sides at

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maximum distance from the columella for each of four tomatoes by use of a durometer

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(Durofel, Agro-Technologies, France). Complete lack of firmness is given number 1, whereas

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100 means full firmness. Fruit firmness below 40 is considered to be non-saleable in a

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Norwegian supermarket. SSC was determined by the use of a digital PR-100α refractometer

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(Atago Co., Japan) of tomato juice at ambient temperature. Juice was pressed by hand,

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measured, and data were expressed as equivalent ºBrix (or %SSC). For the assessment of

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TTA, four to six tomatoes for each sample were chopped in a food processor until maximum

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homogenization was achieved. The sample was transferred to a 0.5 l plastic bag, sealed and

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stored at -20 °C until further analyses. Within two weeks about 5 g of each sample was

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thawed and mixed with about 20 mL deionized water, and titrated (Basic Titrini 794,

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Metrohm, Switzerland) against 0.1 M NaOH until end equivalence point at pH 8.5-8.9. Total

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acid was expressed as citric acid equivalents (mg CAE 100-1 g FW).

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HPLC-analyses

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HPLC-analyses were made on samples from the second harvest. A liquid chromatograph

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(Agilent 1100 system, Agilent Technologies) supplied with an autosampler and a photodiode

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array detector was used for the analysis of individual phenolics and carotenoids. Separation of

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phenolics was achieved by an Eclipse XDB-C8 (4.6 × 150 mm, 5 µm) column (Agilent

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Technologies), and the use of a binary solvent system consisting of (A) 0.05% TFA in water

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and (B) 0.05% TFA in acetonitrile. The gradient (B in A) was linear from 5% to 10% in 5

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min, from 10% to 25% for the next 5 min, from 25% to 85% in 6 min, from 85% to 5% in 2

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min, and finally recondition of the column by 5% in 2 min. The flow rate was 0.8 mL min-1,

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10 µL samples were injected on the column, and separation took place at 30 ºC. Flavonoids

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were detected at 370 nm, whereas aromatic acids were detected at 320 nm. Carotenoids were

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separated over the same column by use of the binary solvent system (A) methanol-

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acetonitrile-water-0.2 M TRIS-HCl (pH 7.4) (15:65:18:2 v/v) and (B) methanol-n-hexane

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(7:1) with the gradient (B in A) linear from 0% to 100% in 15 min, 100% isocratic in 10 min,

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linear from 100% to 0% in 3 min, and finally reconditioning of the column in 2 min. 20 Flow

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rate was 1.0 mL min-1, 20 µL samples were injected on the column, and separation took place

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at 30 ºC. Lycopene and β-carotene were detected at 450 nm. All HPLC samples were filtered

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through a 13 mm syringe filter (Whatman Nylon filter 0.45 µm, Sigma-Aldrich) prior to

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injection. Individual standard curves were used to quantify chalconaringenin, rutin,

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chlorogenic acid, lycopene and β-carotene. Quercetin 3-(2’’-apiosyl-6’’-rhamnosyl)-glucoside

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(apiorutin) was quantified as equivalent of rutin, whereas the phenolic compounds 1-3 (Figure

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7) exhibiting similar chromatographic and spectral properties as chlorogenic acid were

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quantified as equivalents of chlorogenic acid.

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Statistics

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Statistical analysis included two sampling dates at harvesting, three replications, two

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cultivars, three maturity stages, nine treatments (nine storage conditions during simulated

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transport and two storage conditions after transport) and five sampling dates after harvesting.

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For statistical analysis, mean values for six fruits were used. To evaluate effects of

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supermarket conditions, fruits kept from day 1-4 at 12 oC in the dark before transfer to 22 oC

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in the light were compared to fruits kept at 12 oC in the dark during 21 days. Effects of

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simulated transport conditions were evaluated after transfer to 22 oC in the light. Results were

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subjected to analysis of variance using the GLM procedure from the SAS statistical computer

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program (version 9.2). The SNK test was used to determinate significant differences between

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cultivars, maturity stages, storage conditions, transport conditions and days after harvesting at

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a level of significance of P

From Producer to Consumer: Greenhouse Tomato Quality As Affected

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