Short communication
Qualitative changes in pepino fruits following
preharvest applications of ethephon
S. Lopez
*, J.V. Maroto, A. San Bautista, B. Pascual, J. Alagarda
Departamento de ProduccioÂn Vegetal, Universidad Politecnica de Valencia, ETSIA Camino de Vera, 14, 46020 Valencia, Spain
Accepted 5 May 1999
Abstract
Ethephon sprayed directly onto pepino fruits (Solanum muricatumAit., Chilean clone CH8) at
1920 mg lÿ1
advanced colour changes and therefore earliness of the crop. Colour changes evaluated
with a HunterLab colorimeter occurred more quickly in ethephon-treated fruits in whicha*/b* ratio
changed soon after treatment and reached the highest values in treated fruits. Among four visually
classified maturity groups, differences in some qualitative parameters (a*,a*/b*, soluble solids,
taste and carbohydrate contents) were found, but not between control and treated fruits. There was no significant loss of flavour or other measured quality parameters in earlier-harvested
ethephon-treated fruit.#2000 Elsevier Science B.V. All rights reserved.
Keywords: Ripening; Fruit colour; Hunter parameters; Carbohydrate contents
1. Introduction
Ripening of pepino (Solanum muricatum Ait.) fruits is slow and lasts even longer when cultivated during short days and low temperatures in Mediterranean areas (Maroto and LoÂpez-Galarza, 1997). Pepino has been described as a climacteric fruit (Alonso and Arias, 1983; Arenas, 1992; Bertolami and CannistraÁ, 1995), but Heyes et al. (1994) indicated that it has to be considered as non-climacteric.
* Corresponding author. Tel.: +34-96-387-73-37; fax: +34-96-387-73-39. E-mail address:slopez@prv.upv.es (S. Lopez).
0304-4238/00/$ ± see front matter#2000 Elsevier Science B.V. All rights reserved.
Treating pepino fruits with ethephon either preharvest or postharvest advances colour change. In postharvest treatments, along with a change in colour, El-Zeftawi et al. (1988) indicated a reduction in firmness and an increase in juice and soluble solids content. After preharvest treatments, during two crop seasons we observed earlier ripening but no significant changes in soluble solids content (Maroto et al., 1995).
Although firmness, soluble solids and taste are important, colour is the most important index of maturity in pepino. Colour changes from green to yellow or orange colour, with purple stripes. Completely yellow or orange-yellow colour is demanded for market, although fruits have to be harvested earlier for handling purposes (Arenas, 1992).
In our previous experiments, ethephon-treated fruits seemed to be slightly less orange-yellow than controls and slightly less firm. The present study is a continuation of previous work on preharvest ethephon applications to pepino fruits. The aim of this work was to evaluate possible differences in some qualitative parameters between control and ethephon-treated fruits, and also determine if any change in colour was accompanied by changes in other qualitative parameters during ripening.
2. Materials and methods
Two experiments were conducted in a plastic greenhouse during 1994±1995 season. Pepino plantlets (Chilean clone CH8; oval, pointy and striped) were planted in a loamy soil on 28 September 1994, arranged in rows 1 m apart and width 0.4 m between plants. Plants were trained to three branches, pruning all lateral shoots. Flowers were sprayed with `Procarpil' (0.075% 4-chlorophenoxy-acetic acid0.25% (2-naphthyloxy)acetamide) to increase fruit set. Plants were fertigated with a total amount of 35 g mÿ2of soluble fertilizer (20 N-4.7 P-11 K) and microelements, raising the EC from 1.5 to 1.9 dS mÿ1
from planting to harvest. Irrigation frequency varied from 2 to 7 days/week, applying 4 l mÿ2per irrigation. Each experimental unit had 20 plants.
Experiment1. Three replications for treated and control plants were arranged in a randomized block design. On 22 May 1995, 180 fruits in both treated and control plants, at the pale green stage, were labelled and treated plants were sprayed with ethephon at 1920 mg lÿ1 directly on the fruits, according to our previous experiments (Maroto et al., 1995). In all labelled fruits, colour was measured every 4 days from treatment, using a Minolta CR-300 colorimeter, obtaining Hunter parametersL*, a* andb*. Four rings were marked on the non-striped areas to always measure the colour at the same point, acquiring only background colour. After each measurement, commercially ripe fruits (golden-yellow colour) were picked and yield and fruit weight were evaluated. Colour measurements were always taken from ripening fruits.
Experiment 2. This was conducted in the same way as experiment 1, using another three replications for treated and control plants. From treatment day, fruits graded visually at different stages of maturity (pale-green, creamish-green, creamish-yellow and golden-yellow), using a subjective visual scoring system based on patchiness, according to Heyes et al. (1994), were sampled every 4 days, and colour, fruit firmness, soluble solids content, taste, fresh weight (fw), dry weight (dw) and carbohydrate contents were determined. ParametersL*,a*andb*
were obtained with a Minolta CR-300 colorimeter. Fruit firmness was determined with an Effegi hand penetrometer using a 1.5 mm diameter needle. Soluble solids were measured using a hand colorimeter and taste scores (0 ± very bad; 10 ± very good) were obtained from a panel of 10 persons. Starch, sucrose and reducing sugars were determined according to McCready et al. (1950).
3. Results and discussion
Experiment 1. In this experiment ethephon caused earlier ripening. It was possible to harvest 50% of the crop 14 days after treatment from treated plants and after 22 days from the controls (Fig. 1). The ratioa*/b* in ethephon-treated fruits was higher than in control fruits throughout the experiment (Fig. 2). In treated fruits there was an increase in the values of the a*/b* ratio immediately after treatment, whereas in control fruits this increase began approximately 16 days after treatment. Also the absolute increase ina*/b* ratio was higher in the ethephon-treated fruits than in the control fruits. Therefore ethephon treatment promoted a rapid change in colour in pepino fruits allowing earlier harvest, which confirms our previous work (Maroto et al., 1995).
Fig. 1. Percentage of fruits harvested in control and ethephon-teated plants. Vertical bars indicate
Experiment2. The values of the different parameters measured for treated and control fruits within the four maturity groups are presented as an average for all sampling dates (Table 1). Only one statistically significant interaction between maturity groups and treatment was found, which was for firmness. Hunter parametersa*anda*/b*ratio increased during ripening and clearly separated the visually classified maturity groups, although differences in L* were not significant. An increase in soluble solids content was also observed, although the content in the creamish-yellow fruits did not differ from that of the golden-yellow or creamish-green fruits. Taste also increased with ripening. However, dw/ fw ratio was not significantly different in the four maturity groups. In control and treated fruits we detected a reduction in fruit firmness as fruits ripen with significant differences between all groups (Table 1). However, in ethephon-treated fruits differences in firmness between golden-yellow and creamish-yellow fruits were not statistically significant. Overall these results agree with those of El-Zeftawi et al. (1988) and Heyes et al. (1994), who reported increased soluble solids and flavour and reduced firmness throughout the change in colour of pepino fruits. Starch content was higher in pale-green group than in other groups. Reducing sugars significantly decreased with advancing maturity groups, from pale-green to golden-yellow. Sucrose content increased as fruit ripened, being significantly different for each group (Table 1). These findings coincide in part with those of Schaffer et al. (1989), who indicated that pepino could be classified as a sucrose accumulator such as sweet melon or citrus, showing a reduction in starch and reducing sugars, and an increase in sucrose during ripening.
Within the visually classified groups, no differences were detected between ethephon-treated fruits and controls in relation to colour indices, soluble solids content, dry/fresh weight ratio, taste, starch, sucrose or reducing sugars content.
Fig. 2. Average Hunter ratioa*/b*of the remaining fruits (not harvested) at each measuring date.
Vertical bars indicateSE.
Values of Hunter parameters firmness (f), soluble solids (ss), dry/fresh weight ratio, taste, starch, sucrose and reducing sugars for treated (Et) and control (C) fruits in four ripening stages of pepino fruits: golden-yelow (GY), creamish-yelow (CY), creamish-green (CG) and pale-green (PG)
Maturity groups Treat Hunter colour f(g) ss (8Brix) dw/fw Taste Carbohydrate content (%dw)
L a a/b Starch Sucrose Reducing sugars
GY Et 62.8 0.56 0.02 413 6.98 0.05 7.31 4.18 44.3 16.3
C 62.7 0.71 0.01 385 7.15 0.06 7.14 4.87 42.8 17.6
CY Et 62.8 ÿ3.55 ÿ0.13 441 7.10 0.06 5.06 5.03 36.8 18.5
C 62.9 ÿ3.32 ÿ0.12 438 6.52 0.06 5.70 5.14 34.9 19.9
CG Et 62.1 ÿ7.25 ÿ0.29 536 6.82 0.06 5.20 5.78 30.5 21.5
C 62.9 ÿ6.54 ÿ0.28 610 6.38 0.06 4.59 5.61 27.7 22.4
PG Et 61.1 ÿ9.85 ÿ0.48 682 6.07 0.06 ± 6.80 23.9 23.8
C 60.9 ÿ9.91 ÿ0.49 818 6.00 0.06 ± 8.03 21.6 24.4
Averages GY 62.7 0.63a 0.01a 399 7.07a 0.05 7.23 a 4.53b 43.6a 17.5d
CY 62.8 ÿ3.44b ÿ0.12b 439 6.80ab 0.06 5.38b 5.09b 35.9b 19.2c
CG 62.5 ÿ6.90c ÿ0.29c 573 6.60b 0.06 4.90c 5.70b 29.1c 22.0b
PG 62.0 ÿ9.89d ÿ0.49d 750 6.04c 0.06 ± 7.42a 22.8d 24.1a
Et 62.2 ÿ5.03 ÿ0.22 518 6.51 0.06 5.86 5.20 33.9 20.0
C 62.4 ÿ4.07 ÿ0.22 563 6.74 0.06 5.81 5.84 31.8 21.1
Grouptreat NS NS NS * NS NS NS NS NS NS
Means in columns followed by a same letter do not significantly differ atP0.01 using Newman±Keuls test.
NS: Non significant atP0.05.
*Significant at
P0.05.
S.
Lopez
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Scientia
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157±164
Table 2
Correlation coefficients between fruit firmness (f), soluble solids (ss), taste, Hunter parameters and dry/fresh weight ratio (dw/fw), starch, sucrose and
reducing sugars in ethephon and control (in brackets) fruits
f ss taste L a a/b dw/fw Starch Sucrose Reducing sugars
For firmness, no differences between ethephon and control were detected in golden-yellow or creamish-yellow groups, but in the creamish-green and pale-green groups firmness was higher in control than in ethephon-treated fruits. These results and those of the experiment 1 indicate that preharvest ethephon not only hastens maturity and earliness, but it also does not significantly modify any other qualitative characteristics of the fruit such as firmness, soluble solids content and taste, which also confirms our previous work (Maroto et al., 1995). As a consequence, ethephon treatments in temperate areas could be applied selectively to accelerate colour changes and therefore the harvest, without any modification in the qualitative parameters. This would both reduce the number of fruits during late winter±early spring cycles and avoid excessive exposure to sunlight and/or premature ripening during late spring±early summer crops.
Correlation coefficients between the different parameters measured (Table 2) indicated that in both treated and control fruits, firmness was negatively correlated with taste,a*anda*/b* ratio, and positively with starch and reducing sugars, but was negatively correlated with L* only for control fruits. Soluble solids were significantly correlated with taste, L*, starch, sucrose and reducing sugars only in control fruits, and with dw/fw ratio only in treated fruits. Taste was also correlated with a* and a*/b* ratio. The differences in correlations between taste and soluble solids in treated and control fruits could have occurred because pale-green fruits had relatively high values, and also possibly because, as reported by Pluda et al. (1993), high temperatures may affect fruit flavour of pepino fruits. This could be the case in this experiment in which treatments took place late in spring. Colour indices a* and a*/b* were correlated with the carbohydrate contents. Starch was also significantly correlated with sucrose and reducing sugars, and sucrose also with reducing sugars both in ethephon-treated and control fruits. In general, ethephon treatment did not greatly modify the correlations between qualitative parameters in pepino fruits.
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