the effect of ripening stage on fruit quality after storage of yellow pitaya

Postharvest Biology and Technology 15 (1999) 99–105

The effect of ripening stage on fruit quality after storage ofyellow pitaya

Avinoam Nerd a,*, Yosef Mizrahi a,b

a The Institutes for Applied Research, Ben-Gurion Uni6ersity of the Nege6, P.O. Box 653,Beer-She6a 84105, Israelb Department of Life Science, Ben-Gurion Uni6ersity of the Nege6, P.O. Box 653,Beer-She6a 84105, Israel

Received 4 August 1998; accepted 14 October 1998

Abstract

Some physicochemical properties and flavour quality were determined in yellow pitaya (Selenicereus megalanthus)fruits harvested either at the beginning of ripening (colour break), or when they reached good eating quality(advanced colour stage), and then stored for up to 4 weeks at either 10 or 20°C. Colour-break fruits stored at 10°Cripened only after being transferred to 20°C. During ripening such fruits attained the physical properties of fruitsripened on the plant, but they contained significantly lower concentrations of soluble sugars and acidity, and had aninferior taste. Fruits harvested at the advanced colour stage and stored at 10 or at 20°C were also inferior to thoseof freshly-harvested fruits with respect to soluble sugars and acidity as well as taste quality, but their physicalproperties changed only slightly during storage. In both groups of fruit water was translocated from the peel to thepulp during storage. The lower weight loss, higher soluble sugar concentrations, and lower susceptibility to pathogensof advanced colour fruits as compared with colour-break fruits, suggest that the former stage is the correct one forharvest. © 1999 Elsevier Science B.V. All rights reserved.

Keywords: Selenicereus megalanthus ; Postharvest; Ripening; Water partition

1. Introduction

Yellow pitaya (Selenicereus megalanthus (Scum.ex Vaupel), Cactaceae) is a new orchard croporiginating in the northern part of South America(Cacioppo, 1990; Mizrahi et al., 1997) and is

cultivated in Colombia and Israel. The fruit is amedium-sized oblong berry with a yellow peelbearing tubercles and thorns that are shed duringripening. The pulp is white and delicate and con-tains numerous small digestible black seeds (Nerdand Mizrahi, 1997).

Yellow pitaya fruit is nonclimacteric and hasthe best quality when picked close to the fullcolour stage (Nerd and Mizrahi, 1998). However,

* Corresponding author. Tel.: +972-7-6461966; fax: +972-7-6472984; e-mail: [email protected].

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A. Nerd, Y. Mizrahi / Posthar6est Biology and Technology 15 (1999) 99–105100

little is known about the optimal harvest stage forprolonged storage. The fruits reach their final sizeat the beginning of ripening. During ripening,starch accumulated before the colour break isdegraded to soluble sugars (Nerd and Mizrahi,1998). Therefore, we assumed that the fruits couldbe harvested for marketing at an early ripeningstage. However, it is not known whether suchfruits will ripen properly during or after storage.

With the objective of determining the timing forcommercial harvesting and the post-harvest be-haviour of the fruits we examined a number ofphysicochemical properties and the flavour offruits harvested either at colour break or close tofull colour, and stored at two differenttemperatures.

2. Materials and methods

2.1. Plant material

Fruits for the study were obtained from a com-mercial Colombian clone of yellow pitaya (Weiss

et al., 1994), grown in a greenhouse located inBeer-Sheva, northern Israeli Negev Desert. Fruits(180–210 g) at two ripening stages defined byNerd and Mizrahi (1998) i.e. the beginning ofripening (colour break) and when reaching goodeating quality (advanced colour stage), were har-vested at the end of February 1998. About 90fruits of each group were randomly distributed intwo dark chambers at either 2091.5 or 1091.2°C, both chambers having 60–70% relativehumidity. The fruits were sampled for analysiswhen fresh and after 1, 2, 3, and 4 weeks ofstorage using six fruits at each sampling date. Inaddition the fruits harvested at colour break andstored at 10°C were transferred at the end ofweeks 2, 3 and 4 to 20°C and analysed when mostof the peel had become yellow. Fruits infected byfungus were removed from the chambers and theirnumber was recorded.

2.2. Fruit analysis

Six fruits of each treatment were analysed at

Fig. 1. Changes in peel colour grade (A), weight loss (B), and percentage of the total FW constituents by the peel (C) and pulp (D)in yellow pitaya fruits during storage. The fruits were harvested at either the colour break (CB) or the advanced colour stage (AC)and stored at either 10 or 20°C°. Values are means9S.E. (n=6).

A. Nerd, Y. Mizrahi / Posthar6est Biology and Technology 15 (1999) 99–105 101

Fig. 2. Percent water (FW basis) in the peel (A) and pulp (B) of yellow pitaya fruits during storage at 10 or 20°C. For a descriptionof the experiment and abbreviations see the caption to Fig. 1.

each sampling date. Peel colour was assessed visu-ally on a scale of 1–5 (Nerd and Mizrahi, 1998):1, bright green; 2, base of the fruit turned yellow(grades 1 and 2 were designated as colour break);3, yellow area extending to the middle of the fruit;4, most of the fruit is yellow (tips of the tuberclesremaining green); and 5, fully yellow. The peeland pulp were separated and weighed. A sampleof each tissue was oven-dried at 70°C for thedetermination of water content. The soluble solidsconcentration (SSC) was measured with a refrac-tometer (PR-100, Atago, Japan) in sap pressedfrom the pulp. To measure acid concentration, 10g of fresh pulp was macerated in distilled waterand titrated with 0.025 N NaOH to pH 8. Theconcentrations of total soluble sugars, starch, andmucilage were determined in 50-mg samples ofground dry pulp. Soluble sugars were extractedwith 3×6 ml 80% ethanol. After each extraction,the sample was centrifuged at 4000×g for 15 minand the supernatants pooled. Total soluble sugarsin the supernatant were measured by the phenol–sulfuric acid method (Dubois et al., 1956) withglucose as the standard. For starch determination,the pellet was digested with amyloglucosidase(Haissig and Dickson, 1979), and the soluble sug-ars were measured by the phenol–sulfuric acidmethod. For the mucilage determination theresidue remaining after digestion of starch wasstirred with 10 ml of 35% perchlorate for 1 h at

50°C. The sample was centrifuged, and the totalsoluble sugars measured in the supernatant by thephenol–sulfuric acid method.

2.3. Sensory e6aluation

Ten panelists assessed the flavour of the fruiton the selected sampling dates. A ten-point hedo-nic scale was used with 1 indicating extreme dis-

Table 1Changes in water content (% of initial) in fruits picked ateither colour break or at advanced colour stage after 4 weeksof storage at 10 or 20°Ca

Component Change in water content (%)

Harvested at colour Harvested at ad-vanced colourbreak

20°C10°C 20°C 10°C

Whole fruit −13.7−13.8 −21.6 −9.1−21.8−14.9−36.1Peel −22.3

+14.5 +5.8 +8.1+8.4Pulp

a At harvest, an average fruit (200 g) contained 129.2 g ofwater in the peel and 44.6 g of water in the pulp at thecolour-break stage and 89.8 g water in the peel and 82.2 gwater in the pulp at the advanced colour stage. The amount ofwater and changes in water content were calculated from thedata presented in Figs. 1 and 2.


Fig. 3. Concentration of titratable acidity (FW basis) in thepulp of yellow pitaya fruits during storage at 10 or 20°C. Fora description of the experiment and abbreviations see captionto Fig. 1.

3. Results and discussion

The colour grades of fruits harvested at thecolour break and at the advanced colour stagewere 1.390.2 and 3.790.1, respectively. Thechange in peel colour was small for both fruittypes at 10°C, while it was pronounced at 20°Cfor colour-break fruits (Fig. 1A). During storage,the fruits lost weight, the loss being greater in thefruits harvested at the colour break than at theadvanced colour stage (Fig. 1B). Weight loss wasmaximal in the colour-break fruits stored at 20°C(23.0%) and minimal in the advanced colour fruitsstored at 10°C (8.8%). The peel content (% ofwhole fruit FW) decreased during storage in par-allel to yellow colour development (Fig. 1C). Thepulp content showed an opposite trend to that ofthe peel, i.e. its percentage increased with yellow-ing (Fig. 1D).

The water percentage of the peel tended todecrease during storage, the change being influ-enced mainly by temperature (Fig. 2A). Regard-less of the storage temperature the waterpercentage of the pulp of the colour-break fruits

like and 10 indicating strong liking. The tests werecarried out under room conditions. At each test,two or three samples of pulp, each obtained fromsix fruits, were evaluated. One of the samples wasalways from fresh fruits harvested at the optimalripening stage (colour grade 4), while the otherswere stored fruits.

Fig. 4. Percent (FW basis) of SSC (A), total soluble sugars (B), starch (C) and mucilage (D) in the pulp of yellow pitaya fruits duringstorage at 10 or 20°C. For a description of the experiment and abbreviations see the caption to Fig. 1.


Table 2Flavour grading during storage of fruits harvested at eithercolour break or advanced colour and stored at either 10 or20°Ca

Taste grade of fruits stored at:Days of storage

10°C 20°C

Colour break14 6.3 acNDb

6.6 a21 ND28 4.2 bND

Advanced colour7.1 a7 7.3 a

6.7 ab 6.3 ab1421 6.3 ab6.7 ab

6.0 b 6.0 b28

a Flavour was assessed according to a 10-point hedonicscale, with 1 indicating extreme dislike and 10 indicating astrong liking. Values are means for ten tasters. Taste grades offruit freshly harvested at the colour break and at the advancedcolour stage were 3.590.3 and 8.190.5 respectively.

b ND=not determined.c Mean separation within column by Duncan’s multiple

range test, PB0.05.

and remained relatively unchanged during storage(Fig. 4A). The concentration of soluble sugarswas 2.2% of pulp FW in the fruits harvested atthe colour break and 4% higher in those harvestedat the advanced colour stage (Fig. 4B). The sugarcontent of the colour-break fruits slightly in-creased at the beginning of the storage period andthen decreased to the initial level. In the advancedcolour fruits, the sugars decreased during the first2 weeks of storage (faster at 20°C), reachingabout 60% of the initial value at the end of 4weeks. Starch, which was present in a significantamount only in fruits harvested at the colourbreak (5.6% of pulp FW), was degraded duringstorage, the degradation being faster at 20°C (Fig.4C). The rapid decline in starch at the beginningof storage may account for the small rise insoluble sugars, unlike the trend in fruits attachedto the plant where the decrease is accompanied byan equivalent increase in soluble sugars (Nerd andMizrahi, 1998). Sugar utilization by respirationduring ripening (Tucker, 1993) and a lack ofadditional source of assimilates, as in attachedfruits, may explain this difference. Mucilage,which is a mucopolysaccharide often found incactus fruits and stems (Roth, 1977; Ting, 1995),is also present in the pulp of yellow pitaya fruit.The mucilage content decreased during ripeningon the plant as well as in storage (Fig. 4D). Thehigh content of mucilage at the early ripeningstages causes the fruit at these stages to be verysticky and unappealing to many people.

Fruits picked at the colour break and stored for2, 3, or 4 weeks at 10°C reached colour grade 4only 11, 12, and 15 days, respectively, after theywere transferred to 20°C. Regardless of the stor-age duration, the fruits of the three groups atcolour grade 4 did not differ significantly (PB0.05) in their characteristics. The weight loss ofthe whole fruits was 14.891.1% and the peelcontent 53.192.3%. The concentrations (FW ba-sis) of various pulp constituents were: titratableacidity 12.691.6 mmol H+ kg−1, SSC and solu-ble sugars 16.591.5 and 2.5 90.1%, respectively,starch was negligible, and mucilage 1.190.05%.

It is noteworthy that the concentration of solu-ble sugars in yellow pitaya fruit is not close toSSC concentration, as found in many fruits, but

increased significantly, while it remained almostconstant in the advanced colour fruits (Fig. 2B).The data presented in Fig. 1B–D and in Fig. 2enabled us to calculate the water balance of thepeel and the pulp during storage (Table 1). Fruitsof all treatment groups lost water from the peel,while accumulating water in the pulp. The waterloss from the whole fruit was similar to the fruitweight loss (Fig. 1B). Since the detached fruit hadno external source of water, it is clear that thewater was translocated from the peel to the pulpduring storage. In view of the greater water lossfrom the colour-break fruits than from the ad-vanced colour fruits at both temperatures, we mayassume that evaporation was reduced as ripeningproceeded. A similar trend has also been reportedfor cactus pear (Opuntia ficus-indica) fruits duringstorage (Cantwell, 1995).

The titratable acidity was higher in the colour-break fruits than in advanced colour fruits andwas reduced in both groups of fruit during stor-age, reaching a value of about 50% of that atharvest at the end of 4 weeks (Fig. 3). The SSC atharvest was high in both groups of fruit (19–20%)


rather much lower. Some of the difference may berelated to the fact that soluble sugars were mea-sured in samples of pulp which contains non-solu-ble constituents such as seeds (about 5% of pulpFW, unpublished data), while SSC was deter-mined in the pulp sap. It is assumed that mucilageor other soluble constituents contribute to therelatively high values of SSC.

The flavour of the colour-break fruits improvedduring storage, but it never reached the grade ofthe advanced colour fruits, freshly harvested orheld in storage for several days (Table 2). Theflavour grade of the advanced colour fruits tendedto decrease during storage, becoming comparableto that of the colour-break fruits after 4 weeks instorage. The time that the colour-break fruitswere kept at 10°C did not affect their flavourquality significantly (PB0.05) after they ripenedat 20°C, the mean flavour grade being 5.890.5.Linear regression analysis indicated a significantpositive correlation (P=0.01) between the flavourand both soluble sugars (R=0.748) and acidity(R=0.719).

The fruits from the longer storage periods (3and 4 weeks) were firm and visually acceptable,but some fruits suffered from fungal infections atthe base of the fruit. The colour-break fruits weremore susceptible to infection than the advancedcolour fruits. After 4 weeks of storage, thesummed percentage of infected fruits was 17.1 and22.2 for the colour-break fruit stored at 10 and at20°C, respectively and only about 14% for theadvanced colour fruits regardless of the storagetemperature. Fungal infection has also been re-ported for cactus pear and red pitaya (Hylocereusundatus) fruits (Barbeau, 1990; Cantwell, 1995).Cactus pear fruits are therefore cut with a piece ofstem tissue, which when dry prevents fungus in-fection. However, the means to prevent such aninfection in yellow pitaya have yet to bedeveloped.

4. Conclusions

The fruits of the yellow pitaya harvested andstored at the colour-break stage (beginning of

ripening) achieved the physical properties of fruitsripened on the plant, but their soluble sugars andacidity levels were significantly lower, leading toan inferior taste. The fruits harvested at an ad-vanced colour stage (good eating quality) im-proved in storage in terms of the peel colour andthe pulp/peel ratio, but the levels of soluble sugarsand acidity as well as taste quality were reducedduring storage. The lower weight loss of the ad-vanced colour fruits as compared with that of thecolour-break fruits, their higher sugar content andtheir lower susceptibility to pathogens, suggestthat this is the suitable ripening stage for harvestfor both local as well as distant markets. Storageof the advanced colour fruits at 10°C attenuatedboth weight loss and the decline in the tastecomponents, acidity and soluble sugars.

Acknowledgements

The authors would like to thank the FleischerFoundation and the Israel Ministry of Agricul-ture, for partial support, Dorot Imber for editingthe manuscript, and Nira Taub for excellent tech-nical assistance.

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the effect of ripening stage on fruit quality after storage of yellow pitaya

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