Postharvest Biology and Technology

Postharvest Biology and Technology 7 (1996) 161-170

Ripening characteristics of purple passion fruit on and off the vine

Shinjiro Shiomi ‘**, Leonard S. Wamocho, Stephen G. Agong 2

Depatiment of Horticulture, Faculty of Agriculture, Jomo Kenyatta University of Agriculture and Technology, PO. Box 62000, Nairobi, Kenya

Accepted 7 April 1995

Abstract

The characteristics of purple passion fruit (Pussi’oru e&is Sims.), detached at intervals from the vine and ripened, were compared with fruit left attached until just before analysis. The objective was to determine the minimum time between anthesis and harvest that allowed the production of good-quality fruit. Analysis of the rates of increases in size and weight showed a single sigmoidal curve; while size reached a maximum at 20 days after flowering (DAF), fruit weight continued to increase gradually. The respiration rate of fruit left attached to the vine until just before measurement decreased gradually with time but without showing a climacteric peak; ethylene production increased sharply soon after 70 DAF, thereafter remaining constant. After successive detachment of fruit at or after 40 DAF, a respiratory peak was shown, the onset of which occurred quicker the longer the fruit had remained attached. The onset of the rise in ethylene also depended on the length of attachment and then increased rapidly. As fruit matured, soluble solids conte,nt steadily increased and reached maximum levels at 70 DAF while titratable acidity increased rapidly up to 60 DAF and then decreased up to 80 DAF. Changes in fruit color from green to purple was attained between 70 and 80 DAF and this corresponded with the commencement of autocatalytic ethylene production. The results indicate that purple passion fruit appear to attain physiological maturity at about 60 DAF and can be harvested with acceptable quality at about 70 DAF for commercial use.

Keywords: Purple passion fruit; Passiflora edulis Sims.; Fruit maturity; Postharvest ripening; Respiration rate; Ethylene production; Soluble solids content; Titratable acidity

* Corresponding author. Fax: +I31 (86) 254-0714. ’ Present address: Laboratory of Postharvest Horticulture, Faculty of Agriculture, Okayama University, l-l-l ‘Bushima-Naka, Okayama 700, Japan. 2 Present address: Institute of Crop Science and Plant Breeding (FAL), Bundesallee 50, Braunschweig, Germany.

0925.5214/96/$15.00 0 1996 Elsevier Science B.V. AI1 rights reserved. SSDI 0925-5214(95)00023-2

162 S. Shiomi et al. I Postharvest Biology and Technology 7 (1996) 161-170

1. Introduction

Purple passion fruit (Passiflora edulis Sims.), a native of Brazil, is widely grown in tropical and subtropical countries (Chandler, 1958; Pruthi, 1963; Purseglove, 1968; Chan, 1980). As consumers’ eating habits become more diversified worldwide, this fruit has been gaining popularity even in the temperate zones. In Kenya, out of the 16,260 tons of passion fruit produced in 1991, 620 tons of the fresh fruit were exported mainly to European countries (HCDA, 1991; Kenya Ministry of Agriculture, 1991). Passion fruit is a perennial vine, which produces fruit throughout the year in Kenya, although there is a seasonal fluctuation in production so that fruit with different maturities are available most of the time. The harvesting method generally employed is to allow the fruit to fall to the ground after ripening (Gachanja and Gurnah, 1978; GTZ, 1978; Chan, 1980), after which they are gathered, graded and marketed.

Pruthi (1963) reviewed the physiology, chemistry and technology of passion fruit and pointed out that there were no marked differences in the physico-chemical characteristics between partially- and fully-mature fruits except superior aroma in the ripe fruit. Lower proportions of juice, sugars, ascorbic acid and flavor in immature fruit were also reported. Chan (1980) recommended the harvest maturity of purple passion fruit as light to deep purple stage for immediate consumption, whereas only the light purple stage is desirable for distant transport. Akamine et al. (1957) reported that purple passion fruit exhibits a typical climacteric respiratory pattern and a considerable amount of ethylene production. Exogenous ethylene treatment stimulates ripening of the fruit harvested at a mature-green stage with similar qualities as vine-ripened fruit (Arjona and Matta, 1991).

Other than the above, there is a dearth of information on purple passion fruit including morphological and physiological changes during fruit growth, maturation, ripening and storage even in countries where the fruit is popular and grown commercially. Therefore, we investigated the basic ripening characteristics of the fruit on and off the vine in an attempt to determine the minimum time between anthesis and harvest that allows the production of good-quality fruit.

2. Materials and methods

Plant materials Purple passion fruit (Passiflum edulis Sims.) were obtained from one-year-old

vines grown at the experimental farm of Jomo Kenyatta University of Agriculture and Technology, whose location is latitude 1”5’S, longitude 37”E and altitude 1525 m above sea level. Normal cultural practices for the area were followed for pruning, training, irrigation, fertilization, and pesticide application. Mean temperatures are more or less constant at 20°C throughout the year with annual rainfall of about 800 mm, so cultivation takes place in a semi-arid region. Fruit were all harvested from the vine at five or ten days intervals of ages from 5 to 90 days after flowering (DAF) on a single date, 12th February, 1992. Weight, length and diameter of fruit, skin color, soluble solids content, titratable acidity, and rates of carbon dioxide

S. Shiomi et al. IPostharvest Biology and Technology 7 (1996) 161-170 163

(respiration) and ethylene production were determined on the same day of harvest, which was defined as the characteristics of fruit development and ripening on the vine (Biale and Young, 1981; Inaba and Nakamura, 1981). Fruit for soluble solids content and titratable acidity were picked immediately prior to measurement. Rates of respiration and ethylene production during development were assayed for the fruit which were harvested and stored at 25°C for 2 h before being used. Some fruit were harvested from the vine at various stages of maturity, including 90 DAF fruit, and ripened at 25°C (RH 40-70%) in perforated polyethylene bags to determine the ripening characteristics off the tree. The experiment was terminated when growth of any microorganisms was visible on the harvested fruit.

Determination of carbon dioxide and ethylene Once every two days, one fruit was enclosed in a plastic jar with a capacity of 1440

ml, except for five-day fruit where three fruit were used. After the jars were sealed for 1 h at 25°C 1 ml of the head space gas from each of the jars was withdrawn and injected into gas chromatographs each equipped with a thermal conductivity detector or a flame ionization detector for the determination of carbon dioxide and ethylene concentrations, respectively.

Parameters in @it quality Each fruit was cut into halves and the juice was expressed by squeezing the pulp

using two-layered cotton gauze. Soluble solids content was determined with a hand refractometer (Atago Nl) as “Brix (= % sucrose). Titratable acidity was determined by titration with 0.1 N NaOH and was expressed as citric acid, the main organic acid in passion fruit (Pruthi, 1963; Chan, 1980). Color changes were scored according to the color index set up for this study as follows: 0 = all green; 1 = turning from green to purple; 2 = a quarter of the skin surface is purple; 3 = a half of the surface is purple; 4 = three quarters of the surface is purple; and 5 = full purple.

3. Results and discussion

Fruit growth Figure 1 shows the changes in size of purple passion fruit based on weight gain

and increases in length and diameter during development. There was a rapid and parallel increase in the fruit diameter and length during the early stages reaching full size at 20 DAF, which may be a specific pattern of growth in passion fruit. Fruit weight also increased rapidly up to 20 DAF and then more gradually towards maturation. Since juice began to form around the seeds only after 30 DAF, the second increase in weight might have been due to its accumulation. After 90 DAF, fruit were fully ripe and many of them had become detached. Similar results have previously been reported regarding fruit detachment by purple passion fruit by Gachanja and Gurnah (1978).

164 S. Shiomi et al. IPostharvest Biology and Technology 7 (1996) 161-170

Days after flowering

Fig. 1. Changes in weight, diameter and length of purple passion fruit during development. Bars are GE of the mean of ten fruit and the absence of an error bar indicates that it was smaller than the symbol.

Respiration and ethylene production Respiration rate was high in young fruit with a rapid decline to 10 DAF followed

by only a slight decrease towards 80 DAF (Fig. 2). Ethylene production was high in young fruit followed by almost no production up to 70 DAF. Mature fruit produced much ethylene but showed no increase in respiration and the repeated experiments conducted in different seasons had the same tendency (data not shown). Passion fruit has been classified among climacteric fruits which have distinguishing features of increased respiration and ethylene production rates during ripening and a response to exogenously applied ethylene (Biale and Young, 1981). In this study, however, purple passion fruit showed no respiratory climacteric on the vine in spite of a substantial amount of ethylene production. Generally, distinctions between climacteric and non-climacteric fruits have been examined in harvested fruit. Indeed, detached fruit at and after 40 DAF showed marked respiratory climacteric patterns (Fig. 3) with large amounts of ethylene production (Fig. 4). Younger fruit, that is before 40 DAF, did not show increases in respiration and ethylene production rates after harvest (data not shown). Ethylene production by detached fruit began earlier as the fruit aged progressively on the tree (Fig. 4), although fruit younger than 40 DAF did not show any significant levels of ethylene production. Similar results with more immediate commencement of ethylene in the later harvested fruit have been reported in avocado (Eaks, 1980) and Japanese apricot (Inaba and Nakamura, 1981) fruits. Ethylene production by the detached fruit was lo- to 20-fold greater than that by on-the-vine fruit and much higher than the quantity reported previously (Akamine et al., 1957; Sjaifullah and Lizada, 1985).

S. Shiomi et al. /Postharvest Biology and Technology 7 (1996) 161-170 165

1200

1000

i

800

600

400

200

0 0

-- carbon dioxide

ethylene

20 40 60 80 100

Days after flowering

Fig. 2. Rates of carbon dioxide and ethylene production in purple passion fruit during development.

Bars for carbon dioxide are &SE of the mean of three fruit and the absence of an error bar indicates

that it was smaller than the symbol. Values for ethylene represent the mean of three fruit.

40 DAF

60 DAF

70 DAF

--*-- 90 DAF

100 I I I 1

0 10 20 30 40

Days after harvest

Fig. 3. Changes in respiration rate of purple passion fruit harvested at different stages of maturity and

ripened at 25°C. Bars are ME of the mean of three fruit and the absence of an error bar indicates

that it was smaller than the symbol.

These differences in ethylene production between the fruit on and off the vine may be involved in the absence of respiratory climacteric on the vine. Sfakiotakis and Dilley (1973), Miccolis and Saltveit (1991), Saltveit (1993) and Shellie and

166 S. Shiomi et al. /Postharvest Biology and Technology 7 (1996) 161-170

1200

-o- 40DAF

- SODAF

--+-- 60 DAF

--+-- 70 DAf

--o- 80 DAF

--*-- 90 DAF

10 20 30

Days after harvest

Fig. 4. Ethylene production in purple passion fruit harvested at different stages of maturity and ripened at 25°C. Each value shows the mean of three fruit.

Saltveit (1993) observed a similar phenomenon in apples, melon cultivars, tomatoes and muskmelons, respectively, suggesting an inhibition of respiratory climacteric in fruits attached to the plant.

Soluble solids and acidity On the vine, fruit juice began to accumulate after 30 DAF and its color

changed from yellow to orange after about 60 DAF with specific aroma as fruit matured. Soluble solids content in the juice increased steadily from 20 DAF toward maturation (15-17%), whereas titratable acidity reached a peak at 60 DAF (5.9 g 100 ml-’ juice) followed by a rapid decrease (Fig. 5), indicating that the eating quality of the fruit improved after 60 DAF. Soluble solids content in the juice tended to decrease during postharvest ripening (Fig. 6), though temporal increases after picking were observed in the fruit harvested at and after 60 DAF which were similar to the trend during ripening on the vine. There was no significant difference in the rate of decrease in soluble solids content between 70-day fruit and older. Titratable acidity decreased steadily during ripening off the vine except in fruit harvested at 40 DAF, where there was an increase during the early period of storage (Fig. 7), as if they were following an on-vine development pattern (Fig. 5). A similar pattern of change in organic acids was reported during development of grapes (Ulrich, 1970) and during storage of Japanese apricot (Inaba and Nakamura, 1981).

Color development The fruit skin color remained green up to 70 DAF on the vine, after which

there was a rapid change, reaching a color index of 4 at 90 DAF (Fig. 5). In detached fruit, color developed to purple in SO- and go-day fruit to cover more

S. Shiomi et al. /Postharvest Biology and Technology 7 (1996) 161- I70 167

20

15

10

5

0

I t A A A

I 20 40 60 80 loo0

Days after flowering

Fig. 5. Changes in soluble solid content measured as “Brix (= % sucrose), titratable acidity and color

index of purple passion fruit during development. Fruit were picked immediately prior to analysis. Bars

are &SE of the mean of three fruit and the absence of an error bar indicates that it was smaller than

the symbol.

‘“I----- --O- 40 DAF

--+-- 60 DAF

--+-- 70DAF

----o-- BODAF

---x--- 9ODAF

10 20

Days after harvest

30

Fig. 6. Change in soluble solid content of purple passion fruit harvested at different stages of maturity

and ripened at 25°C. Bars are &SE of the mean of three fruit and the absence of an error bar indicates

that it was smaller than the symbol.

than 75% of the fruit surface, but this did not occur in fruit harvested at and before 70 DAF (data not shown). Arjona and Matta (1991) reported that the fruit in which color development was less than 75% of the fruit surface were

168 S. Shiomi et al. I Postharvest Biology and Technology 7 (1996) 161-170

6 N-c_& -o- 40DAF

60 DAF

70 DAF

80 DAF

90 DAF

0 10 20 30

Days after harvest

Fig. 7. Change in titratable acidity of purple passion fruit harvested at different stages of maturity and

ripened at 25°C. Bars are &SE of the mean of three fruit and the absence of an error bar indicates

that it was smaller than the symbol.

unacceptable by consumers. This may suggest that skin color in purple passion fruit is not directly related to ethylene production, considering that fruit younger than 80 DAF produced large amounts of ethylene during postharvest ripening but showed inadequate color development.

Weight loss during storage Fig. 8 shows weight loss during storage at 25°C in purple passion fruit harvested

at different stages of maturity. At all stages of maturity, there was a linear increase in weight loss with increase in storage time which is consistent with previous observations by Pruthi (1963). Younger fruit exhibited higher weight loss, probably due to higher metabolic rate and incomplete and soft rind tissue as well as higher surface area/volume ratio. However, the fruit harvested at and after 20 DAF showed almost the same extent of weight loss. Since purple passion fruit lose weight fast and shrivel under ordinary storage conditions, a practical way of controlling weight loss should be investigated in order to prevent rapid deterioration of the fruit. Based on the degree of shrivelling and growth of microorganisms on the fruit, the shelf life of 60- and 70-day fruit at 25°C was a few days longer than that of 80- and 90-day fruit (Figs. 6 and 7).

Currently in Kenya, purple passion fruit are used for fresh export and juice processing. For fresh export, top-quality fruit with full purple color and no blemishes are selected, while lower-grade fruit are sold locally for either juice processing or fresh consumption. Fruit for juice processing are usually kept at room temperature for a while prior to processing to allow decrease in acidity during which time the fruit start shrivelling. In both cases, it has been recommended that fruit should not

S. Shiomi et al. IPosthawest Biology and Technology 7 (1996) 161-170 169

E w 0

s .&?

3

50 ,

--- 5 DAF --a--_

1ODAF

- 20DAF

-- 40DAF

- 60 DAF

--*--- 70DAF

90 DAF

1

0 10 20 30 40

Days after harvest

Fig. 8. Weight loss in purple passion fruit during storage at 25°C. Bars are &SE of the mean of ten

fruit and the absence of an error bar indicates that it was smaller than the symbol.

be plucked from the vine, but fruit that drop naturally should be collected (that is about 80-90 DAF), in order to avoid inflicting wounds on the fruit, which may provide avenues for microbial infection (GTZ, 1978). Ripe fruit are easily bruised, thereby affecting their appearance and quality, resulting in reduced percentage of top-quality fruit for export. From the observations made in this study, i.e. increases in ethylene production and purple color, and decrease in titratable acidity, metabolic changes towards maturation and ripening might have occurred in purple passion fruit from 60 DAF on the tree. In the postharvest ripening, fruit harvested at 70 DAF (mature green stage) showed almost similar features to those of older fruits such as 80- and 90-day fruit. If color can develop normally after exogenous ethylene treatment as suggested by Arjona and Matta (1991), and the wounds caused by plucking fruit from the vine can be avoided by using proper tools or by careful handling, it should be possible to harvest purple passion fruit at mature green or turning stage. This is much earlier than the usual harvest maturity, but providing the fruit are not blemished by dropping, would give a good-quality product for export, and with a longer shelf life for distant marketing.

Acknowledgements

This work was funded and supported by Japan International Cooperation Agency (JICA). The authors wish to thank and acknowledge Prof. R. Nakamura, Prof. A. Inaba, Dr. Y. Kubo and Dr. EM. Mathooko from Okayama University, for generous assistance in writing and editing this manuscript.

170 S. Shiomi et al. IPosthamest Biology and Technology 7 (1996) 161-170

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