AJFAND

THE EFFECT OF PHYSICAL DAMAGE ON RESPIRATION,
CHEMICAL AND PHYSICAL PARAMETERS
IN TOMATO (Lycopersicon esclentum) FRUIT

ABSTRACT

Tomato fruits (Lycopersicon esculentum) (var. Carl J) harvested at mature green IV stage, were subjected to impact bruising under three treatments. The selected tomatoes were also of similar shape and size to avoid size and shape related variability. Treatment one was the control in which fruits were not dropped at all (no damage). For treatment two, the tomatoes were repeatedly dropped five times from a height of 30 cm onto a polyvinyl chloride chopping board. For treatment three, the drop conditions were similar to those of treatment two, except the dropping was repeated ten times. The drops were meant to simulate handling, road and vehicle conditions that the tomatoes are subjected to from the areas of production to market outlets.Respiration, compositional and physical changes were measured before damage (day 0 ) and thereafter every day, for seven days.Results indicate that impact bruising had significant (P<0.05) effects on the studied parameters. Treatment three in which fruits had been dropped ten times, had significantly lower levels of respiration than the other two treatments, while the control had the highest. In the case of titratable acidity, the fruits dropped ten times had significantly (p<0.05) higher levels than the fruits dropped five times and the control. The pH levels followed inverse trend to that of titratable acidity, as the two parameters have an inverse relationship. The level for soluble solids was observed to be highest in the control, and significantly (p<0.05) lower in fruits dropped five and ten times, with the latter having the lowest value. Ascorbic acid content was observed to be lowest in fruits dropped ten times and highest in the control. The level of chlorophyll was highest in fruits dropped ten times and significantly lower in the fruits dropped five times and the control, with the latter having the lowest values. The level of ripeness followed the reverse trend to that of chlorophyll as it was measured in terms of the attainment of red color. Decay was observed to be highest in fruits dropped ten times, and was significantly (p<0.05) lower in the fruits dropped five times and lowest in the control. Deteriorative changes in the above attributes lead to reduced eating quality of tomatoes. For best quality, tomatoes should be handled and transported under conditions that inflict minimum impact damage to them.

LES EFFETS DES DEGATS PHYSIQUES SUR LES PARAMETRES CHIMIQUES, PHYSIQUES ET DE RESPIRATION
DU FRUIT DE LA TOMATE (Lycopersicon esclentum)

Les fruits de la tomate (Lycopersicon esculentum) (var. Carl J) récoltés encore verts au stade IV de maturité ont été meurtris en subissant trois traitements différents. Les tomates sélectionnées sont de taille et de forme semblables en vue d'éviter toute variance liée à ces deux aspects. Le traitement N°1 représente le cas de contrôle dans lequel les fruits ne subissent aucune chute (aucun dégât). Pour le traitement N°2, on laisse tomber les tomates à cinq reprises à partir d'une hauteur de 30 cm sur une planche à hacher en chlorate de polyvinyle. Pour le traitement N° 3, les conditions de chute sont semblables à celles du traitement N°2, sauf que l'on fait tomber les tomates dix fois de suite. Ces chutes sont censées simuler les conditions de manutention, des routes et des véhicules auxquelles les tomates sont soumises depuis les lieux de production jusqu'aux points de vente.

Les changements physiques ainsi que les modifications de la respiration et de la composition physique sont mesurés avant les dégâts (jour 0) et ensuite chaque jour pendant sept jours.

Les résultats indiquent que l'endommagement par meurtrissure comporte des effets considérables (P<0,05) sur les paramètres étudiés. Le traitement N°3 au cours duquel les fruits sont chutés à dix reprises, a donné lieu à des niveaux de respiration considérablement plus faible que les deux autres traitements alors que le cas témoin a démontré un niveau élevé sur cet aspect. Dans le cas d'acidité titratable, les fruits qui sont tombés dix fois montrent des niveaux considérablement plus élevés (p<0,05) que les fruits qui ont chutés cinq fois et les fruits du cas témoin. Les niveaux de pH ont suivi une tendance opposée à celle de l'acidité titratable, étant donné que les deux paramètres ont une relation inverse. L'étude a révélé un niveau de solides solubles plus élevé dans l'échantillon de contrôle et considérablement plus bas (p<0,05) dans les fruits qui sont tombés à cinq et dix reprises, avec une valeur plus basse pour le dernier cas. Il a été observé une quantité d'acide ascorbique plus petite dans les fruits que l'on a fait tomber à dix reprises. Elle atteint des niveaux plus élevés dans le cas témoin. Le niveau de chlorophylle est plus élevé dans les fruits que l'on a fait tomber dix fois et il est considérablement plus bas dans les fruits que l'on a fait chuter à cinq reprises et dans ceux qui ont été maintenus sous contrôle. Les niveaux les moins élevés ont été observés dans le dernier cas. Le niveau de maturité a suivi la tendance inverse à celle de la chlorophylle, étant donné qu'il est mesuré en termes de réalisation de la couleur rouge. Un niveau plus élevé de pourriture a été observé dans les fruits que l'on a fait tomber à dix reprises (p<0,05). Il est considérablement plus faible dans les fruits que l'on a fait chuter cinq fois et au niveau le plus faible, dans le cas de contrôle.

Les changements de détérioration dans les facteurs repris ci-dessus ont conduit à réduire la qualité des tomates consommables. Afin de maintenir une meilleure qualité, les tomates devraient être traitées et transportées dans des conditions qui infligent un minimum d'impact endommageant celles-ci.

Mots-clés: respiration, acide ascorbique, acidité, chlorophylle

Tomato (Lycopersicon esculentum) is one of the most important fresh vegetable fruits cultivated and consumed in the world. In the

United States of America

, for example, the fruit is ranked number one in terms of contribution of vitamins and minerals to the diet [1]. The fruit may be utilized in different forms due to its pleasant flavor and nutritional value. Tomato is a climacteric fruit and therefore exhibits a sharp increase in ethylene production and respiration at the initiation of ripening [1, 2]. The stage of harvest of the fruit depends on marketing conditions with those meant for immediate consumption being harvested at pink to red stages while those requiring storage or meant for distant markets being harvested at mature green or breaker stages of maturity [3]. In the less developed economies, harvest at mature green to breaker stages is preferable as the tomatoes are more resistant to physical damage at those stages.

In the developing countries, it has been observed that a lot of tomatoes that reach the markets have suffered physical damage especially bruising. The physically damaged fruit are graded as of inferior quality and therefore fetch little income and majority are discarded if not purchased as soon as possible since they do not store for long.

Tomato production experiences high postharvest losses in developing countries, particularly when production exceeds the market demand. One of the major causes of these postharvest losses is physical damage especially bruising, mostly inflicted during transportation due to lack of proper packaging materials, poor transportation methods and poor roads.

Not much study has been done on the effect of physical damage of the tomato fruit on its quality. This study was therefore conducted to evaluate the effect of impact bruising on the respiration, physical and chemical parameters of tomato fruits.

Sound tomato fruits (variety Carl J, commonly known as Kamongo in

Kenya

) were harvested at mature green IV stage and brought to the Food Science and Postharvest Technology laboratory at Jomo Kenyatta University of Agriculture and Technology. Fruits were sorted for physical damage, size, level of ripeness and shape, cleaned in tap water, rinsed in chlorine solution with two hundred parts per million available chlorine and mopped dry. Those that had physical damage, or were over-mature and of uneven size and shape, were rejected. They were divided into three treatments. Treatment one was the control with no drops (no damage). Treatments two and three involved dropping tomatoes from a height of thirty centimeters onto a PVC chopping board five and ten times respectively. The height and the drop surface were felt to be the likely conditions that simulate transport conditions of tomato fruit in some developing countries. This is similar to the procedure used by other researchers [2]. Each treatment was divided into lots of eighteen fruits. Respiration and fruit compositional parameters were determined before the above treatments (zero day storage), and thereafter daily, for seven days. Each lot was placed in perforated polyethylene bags and stored at 20 ^oC. Tomatoes harvested at mature green stage, are expected to take about ten days to reach table ripeness at 20 ^oC, the period within which the experiment was expected to be carried out, hence the choice of that temperature [4]. The fruit dropped ten times, had rapid deterioration, hence the experiment was terminated after seven days. On day six, fruits were examined for ripeness and decay.

Respiration was measured daily, using the Shimadzu gas chromatograph 8A (Japan), with column temperature at 150 ^oC, programme rate 5 mm /min, current 100 mA, attenuation sixteen and recorder range switch of five times twenty [1]. For each measurement, two to three fruits were used from each lot.

Fruits were chopped into small pieces and homogenized in a blender at high speed for 1 minute. Total soluble solids were determined as degrees brix (^oB) from the extracted juice using hand refractometer (ATAGO N-1E,

Japan

), range zero to thirty-two degrees brix [5].

The homogenized tomato tissue used for total soluble solids was used to assay for pH. The pH meter, model HM-7E ,TOA Electronic LTD (

Japan

), was adjusted accordingly and thereafter pH determined.

A fruit sample of 100 g was homogenized with 100 ml of distilled water, in a blender at high speed for one minute. The homogenate was filtered and 10 ml of the filtrate titrated against 0.1M NaOH using three to five drops of phenolphthalein indicator. Total titratable acidity as citric acid was calculated according to Kirk and Sawyer [5].

Ascorbic acid was determined using 2, 6 – dichlorophenolindophenol titration method [6], with slight modification. A fruit sample of 5 g was homogenized with 10% trichloroacetic acid (TCA) solution using a pestle and mortar. The homogenate was transferred into 100-ml volumetric flask and the volume made to the mark using distilled water followed by thorough mixing. A volume of 10 ml of the filtrate was taken and titrated with indophenol solution to a pink color endpoint. Blank titration was done using 10% TCA and indophenol solutions to the same color end point. The ascorbic acid content was then calculated.

The extraction was carried out by acetone extraction procedure [1], with some modifications. A sample of 4 g of tomato tissue was ground in 16 ml of 80% cold acetone using a pestle and mortar. The homogenate was filtered and the residue re-washed with 80% acetone until it was colorless. The volume of homogenate was made to 50 ml using 80% cold acetone. Using 80% cold acetone as blank, an aliquot of the extract was taken and the absorbance at 645 and 663_nm measured using a Shimadzu Double-beam spectrophotometer (

Japan

), UV-180. The total chlorophyll was then calculated using the formula below.

The fruits used for determination of respiration were the same ones used for the measurements of the chemical parameters.

For the assessment of decay and ripeness, each treatment had eighteen fruits packaged in a perforated polyethylene bag and held under the same conditions as other fruits, until the sixth day when the assessment was done. The assessment was visual. The fruits were inspected for any signs of ripeness and decay, the numbers for each attribute recorded accordingly, and reported as percentages. Any fruit that had turned pink to red was considered ripe.

Data were analyzed statistically using Microsoft Excel for Windows computer package, version 5, 1985 – 1993 [7]. Analysis of variance was performed and mean separation among treatments was done using the t-Statistic at five- percent level of significance.

RESULTS

Physical changes

Visual observation carried out on day six of storage, showed that fruits which had been dropped ten times had significantly lower (p<0.05) and higher (p<0.05) levels of ripeness and decay respectively (Table 1). The control fruits ripened normally compared to those dropped, as indicated by the ripeness results (Table 1).

In this study, the tomato (var. Carl J) fruits dropped ten times showed a general reduction in respiration rate and failed to attain the climacteric peak (Figure 1). Fruits dropped five times on the other hand reached climacteric peak on day four of storage and their respiration rate was significantly higher (p<0.05) on days two and three, than the control fruits which reached climacteric peak on day six of storage (Figure 1). Therefore, dropping the fruits five times stimulated their respiration.

Total soluble solids generally decreased significantly (p<0.05) in tomato fruits with increasing impact bruising (Figure 2). In the fruits dropped ten times, total soluble solids remained almost constant with storage time. The control fruits had significantly higher total soluble solids than the other treatments, and the level increased with storage time (Figure 2).

Figure 2. Effect of impact bruising on the total soluble solids content of tomatoes (Carl J) stored at 20 °C.

The treatment in which the tomatoes were dropped ten times, had lower pH values than other treatments, remaining almost constant until the fourth day, when pH dropped further (Figure 3). Some researchers [3] have indicated that the pH of tomato fruit increases with ripening stage, and this was clearly observed in the control fruit (Figure 3).

Figure 3. Effect of impact bruising on the pH levels of tomatoes (Carl J) stored at 20 °C.

It was observed that the total titratable acidity of the fruits dropped ten times, remained almost constant and higher (p<0.05) than that for other treatments (Figure 4). The total titratable acidity for the control was lowest, followed by that of the treatment where the fruits had been dropped five times (Figure 4).

In this study, results indicated a general decrease in ascorbic acid content of the fruit with storage time. Impact bruising significantly reduced the vitamin content of tomato fruit as indicated in Figure 5. In the fruit dropped ten times, ascorbic acid content reduced by more than ninety percent from day four onwards, compared to the control (Figure 5). Those dropped five times had lower ascorbic acid content than the control (Figure 5).

Figure 5. Effect of impact bruising on the ascorbic acid content of tomatoes (Carl J) stored at 20 °C.

In the tomatoes studied, results indicated a significant (p<0.5) reduction in the chlorophyll content of the control and those fruit dropped five times, while that of the fruits dropped ten times remained almost constant (Figure 6). The fruits dropped 10 times failed to ripen, as they remained green the entire period of study.

Figure 6. Effect of impact bruising on the chlorophyll content of tomatoes (Carl J) stored at 20 °C.

Physical damage (impact bruising) significantly (p<0.05) reduced ability of the tomatoes to ripen and also increased their rate of decay (Table 1). Decay has been associated with spoilage micro-organisms, which could be alleviated by application of total quality management techniques on the tomatoes [8]. At the level of retail markets, decayed tomatoes are rejected by consumers, hence are discarded as a result of decay and failure to ripen [9]. This directly translates into financial loss and also compromises food security, besides affecting the final processed product quality [9]. This problem is much worse in countries where transportation and handling methods as well as road systems are poor, such that impact bruising of tomato fruits occurs.

Respiration

The effect of impact bruising on respiration rate of the studied tomato fruit was found to be different from what has been reported before (Figure 1). Some researchers [10] in their study on stimulation of ethylene and carbon dioxide production of mature green tomatoes by impact bruising, reported that respiration increased with impact bruising and the climacteric phase was reached on day two of storage. Although it is true that impact bruising stimulates respiration of tomato fruits [2, 10], these results indicate that excessive impact bruising may not necessarily stimulate respiration (Fig. 1). A point is reached whereby impact bruising beyond a certain limit may instead destroy the cells, causing cell death that may result in ceasing most of the metabolic activities [9, 11]. Tricarboxylic acid cycle and cytochrome system which are important aspects of respiration require intact membrane systems for their operation to ensure that the substrates are properly organized to lead to the desired reactions [12]. However, when the cells die the membranes disintegrate, hence the respiratory process cannot take place efficiently thus the observed decline in respiration. Besides, intact cell organelles are required for efficient respiratory process [12].

Total soluble solids

The control fruits had the highest total soluble solids, and the level increased with storage time (Figure 2). The increase in total soluble solids is mainly as a result of hydrolysis of starch into soluble sugars [1]. This starch hydrolysis is an enzymatic process. Death of the cells as earlier mentioned causes leakage of membranes which probably affects the enzyme-substrate interaction thus leading to reduced starch hydrolytic activity and consequently the reduced soluble solids content [12]

Impact bruising significantly (p<0.05) reduced the pH of the fruit. The fruits that were dropped ten times had pH lower other treatments. This low pH remained almost constant until the fourth day when it dropped further (Figure 3). Some researchers indicated that the pH of tomato fruit increases with ripening stage [3] and this was clearly observed in the control fruit (Figure 3). The pH has an inverse relationship to titratable acidity, and this was observed in this study (Figures 3 and 4). The safety and taste of processed tomato products is influenced by pH. An optimum pH value of 4.3 is recommended for these products[13].

Total titratable acidity

The total titratable acidity for the control was highest, followed by that of the treatment where the fruits had been dropped five times (Figure 4). A reduction in titratable acidity in tomato fruit during ripening has been reported by several researchers [1], and this has been attributed to the utilization of the organic acids in respiration. Since impact bruising reduced respiration (Figure 1), the organic acids present in the dropped fruit were not used as much in this activity, hence they had a higher total titratable acidity compared to the other treatments.

Bruising, other mechanical injuries and excessive trimming have been observed to lower ascorbic acid content during postharvest period [14]. These observations are in agreement with the results obtained in this study, whereby the fruits subjected to impact damage had significantly (p<0.05) less ascorbic acid than the control (Figure 5). Ascorbic acid is one of the most important nutrients contributed by the tomato fruit to the diets of most people [1, 14,15]. Some researchers [3], have indicated that ascorbic acid content of tomato fruit decreases with ripening from mature green to red stage of development. A general increase in ascorbic acid content with ripening of most varieties of tomatoes studied, was observed while the fruit is on the plant [14,15].

Loss of ascorbic acid indicates a shift in the oxidation status of the fruit. Ascorbic acid is a reducing agent. Disintegration of the cells probably brings together ascorbic acid and ascorbic acid oxidase thus oxidizing it which lead to its reduction. It is also possible that the cell disintegration resulted in the release of some oxidizing agents, which lead to further reduction of ascorbic acid [15].

Total chlorophyll of the fruits was used to monitor their colour change, which was in turn used as an indicator of ripening. During ripening the total chlorophyll content of tomato fruit decreases from mature green stage to the red stage [3].

In the tomatoes studied, results indicate a reduction in the chlorophyll content of the control and those fruits dropped five times, while that of the fruits dropped ten times remained almost constant (Figure 6). This indicates that these fruits failed to ripen as they remained green the entire period of study. These results corresponded to those of ripeness in which ripening reduced with impact bruising (Table 1). Chlorophyll degradation is usually due to the action of the enzyme chlorophyllase, enzymatic oxidation and photodegradation [12]. However, the bruised fruits remained green as most of the oxidation products from chlorophyll, are green except the very low molecular weight ones, which are colourless [12].

CONCLUSION

Impact bruising significantly slowed down ripening, reduced respiration and affected the chemical composition of tomato fruit. The effect appears to differ with the extent of damage such that beyond a certain point, the cells may be injured extensively, causing a reduction in metabolic activities.

Impact damage induced decay in the fruit and significantly reduced the total soluble solids, pH and ascorbic acid content while titratable acidity increased. These physical, chemical and physiological parameters are very important for the final eating quality of the fruit. Their shift from normal, indicate poor eating quality, hence a likely rejection by the consumers. In order to ensure superior table quality of fresh tomatoes and therefore maximum financial returns to both farmers and sellers of the fruit, physical damage should be avoided at all levels during transportation and handling.

ACKNOWLEDGMENT

We are grateful to JICA for sponsoring the study and the Department of Food Science and Postharvest Technology at JKUAT for providing the necessary facilities.

Table 1
Percentage ripeness and decay of tomato
(Var. Carl J) fruits after six days of storage

Treatment	% Ripe	% Decay
Control	58.8	0
5 Drops	33.3	27
10 drops	5	54.2

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