Ripening and postharvest behaviour of fruits of two hylocereus species (cactaceae)

Box653, Beer-She 6a84105, Israel Received 10 February 1999; accepted 26 May 1999 Abstract Fruit growth and ripening, and the effect on fruit quality of various storage temperatures, were

Ripening and postharvest behaviour of fruits of two

Hylocereus species (Cactaceae)

aThe Institutes for Applied Research, Ben-Gurion Uni 6ersity of the Nege6, P.O Box653, Beer-She 6a84105, Israel

bDepartment of Life Science, Ben-Gurion Uni 6ersity of the Nege6, P.O Box653, Beer-She 6a84105, Israel

Received 10 February 1999; accepted 26 May 1999

Abstract

Fruit growth and ripening, and the effect on fruit quality of various storage temperatures, were studied with

Hylocereus undatus and Hylocereus polyrhizus plants growing in Beer-Sheva (Israeli Negev desert) under greenhouse

conditions Fruit growth was sigmoidal with a strong decline in growth rate after the onset of peel colour change The

first change in peel colour was recorded 24 – 25 days after anthesis in H undatus and 26 – 27 days in H polyrhizus In

both species, the peel turned fully red 4 – 5 days after the first colour change (mean temperature for the study period was 26.692.1°C) The slow growth phase was characterised by a decrease in the proportion of peel and concomitant increase in that of pulp, increase in the concentration of soluble solids and soluble sugars and a decline in firmness and the concentration of starch and mucilage The surge in acidity prior to colour change indicated the beginning of

the ripening processes For H polyrhizus, which has a red – violet pulp, the increase in pulp pigment paralleled the

development of peel colour Fruits were non-climacteric, and when harvested at close to full colour, they retained market quality for at least 2 weeks at 14°C or 1 week at 20°C Storage at 6°C is not recommended, because transfer from that temperature to room conditions caused fruits to lose their firmness and flavour rapidly © 1999 Elsevier Science B.V All rights reserved

Keywords:Hylocereus undatus; Hylocereus polyrhizus; Chemophysical changes; Gas production; Pitaya; Storage

1 Introduction

Several species of climbing cacti of the genus

Hylocereus have recently been developed as fruit

crops (Barbeau, 1990; Reyes-Ramos, 1995;

Mizrahi et al., 1997) The fruit of these species,

known as red pitaya in Latin America, is a medium – large berry bearing large green or red scales (Nerd and Mizrahi, 1997) The peel is usu-ally red, and the pulp varies from purple – red to white The pulp is delicate and juicy and contains numerous small soft seeds The plants are grown

in the open in tropical areas, but must be pro-tected from intense solar radiation and subfreez-ing temperatures when cultivated under subtropical conditions such those prevailing in Israel (Mizrahi et al., 1997; Raveh et al., 1997)

* Corresponding author Tel.: + 7-6461966; fax: +

972-7-6472984.

E-mail address: mizrahi@bgumail.bgu.ac.il (Y Mizrahi)

0925-5214/99/$ - see front matter © 1999 Elsevier Science B.V All rights reserved.

PII: S 0 9 2 5 - 5 2 1 4 ( 9 9 ) 0 0 0 3 5 - 6

Fruits of cultivated species of Hylocereus are

picked at various stages of peel colour

develop-ment, from first appearance to full colour

(Bar-beau, 1990; Reyes-Ramos, 1995) However little

research has been done on fruit development or

ripening and on the behaviour of the fruit during

or after storage Studies with yellow pitaya

(Se-lenicereus megalanthus), a related climbing cactus,

show that the duration of fruit development

de-pends on seasonal temperatures and that the

fruits reach the optimal flavour close to full

colour stage (Nerd and Mizrahi, 1998) This stage

is also the best time for harvest for short- or

long-distance markets (Nerd and Mizrahi, 1999)

With the objective of determining ripening

criteria for Hylocereus undatus and Hylocereus

polyrhizus, we examined flavour and a number of

physicochemical parameters during the last stage

of fruit development In addition, the effect of

storage temperature on fruit quality was

deter-mined for fruits harvested close to full colour

2 Materials and methods

2.1 Plant material and growth conditions

Studies were conducted in 1997 and 1998 in an

orchard of climbing cacti grown in a ventilated

greenhouse in Beer-Sheva (northern Israeli Negev

desert) The plants had been established from

cuttings in 1992 Clone B of H undatus (red peel

and white pulp) and clone C of H polyrhizus (red

peel and red – purple pulp; Weiss et al., 1994) were

used for the study Each clone sample consisted of

nine plants Spaces were 1.5 m within the row and

2.5 m between rows Plants were trained on a 1.5

m-high trellis system for support, and the soil was

a loamy loess Since these plants cannot grow in

Israel under full sunlight, about 50% shade was

provided by black net Average monthly

tempera-ture and relative humidity during the study

peri-ods (July – October 1997 and the same months in

1998) ranged from 25 to 30°C and 49 – 87% RH,

respectively Plants were drip-irrigated once a

week, to provide 5 l of water per plant in the

summer and 2.5 l in the winter Fertiliser

contain-ing 23% N, 3% P, 20% K at a concentration of 70

mg l− 1was applied with the irrigation water

Since both clones were self-incompatible (Weiss

et al., 1994), the nocturnal flowers, which stayed open for 1 night only, were hand cross-pollinated

in the night with pollen of the other species Pollinated flowers were tagged to allow calcula-tion of the number of days elapsed from anthesis

to various stages of fruit growth and development

2.2 Fruit growth and ripening

Length and mid-length diameter were measured with a caliper during fruit development in four fruits of each clone, set at the beginning of Au-gust 1997 Physicochemical parameters and flavour were determined in fruits of both clones set between mid-July and mid-August of the same year Fruits were harvested at random at 3 – 4-day intervals between 25 and 41 days after anthesis (DAA) for a total of six fruits per clone at each date At the first date the fruits were either green

or on the verge of first colour; 8 – 10 days before the last date they were all fully red

2.3 Storage

Fruits were picked in September 1998, either at first colour stage or 2 – 3 days after appearance of first colour (close to full colour) They were washed with tap water to remove the sugars ex-creted from the scales during fruit development, dried with tissue paper and distributed randomly among three dark chambers held at 691.6°C,

1491.4°C or 2091°C, and at 65–75% RH Sixty fruits of each species were stored at each tempera-ture Physicochemical parameters and flavour were examined once a week, until the appearance

of visible disorders such as scale wilting Fruits stored at 6°C were also analysed after 1 week of further storage at 20°C Five fruits were analysed

at each sampling date

2.4 Fruit analysis

Colour values of peel and pulp at the equator

of the fruit were determined with a Minolta Chroma Meter CR-200 (Ramsey, NJ) and ex-pressed as hue angles (McGuire, 1992) Fruit

firm-ness was determined at two opposite points on

the equator of each fruit with a penetrometer

(Faccini, Alfonsine, Italy) fitted with a 2.5-mm

plunger Peel and pulp were separated and

weighed, and a sample of each was weighed

both when fresh and after drying at 70°C for

determination of water content The

concentra-tion of red pigment in H polyrhizus pulp which

belongs to the betacyanin group (Forni et al.,

1992), was determined in 1g samples obtained

from the inner part of the pulp Tissue was

ho-mogenised in 80% ethanol and filtered through

Whatman paper no 41 The filtrate was mixed

with 0.1 M acetate buffer at pH 4.5, and

ab-sorbance determined at 538 nm (lmax) with a

Uvikon 810 spectrophotometer (Kontron,

Mi-lano, Italy) The concentration of pulp pigments

was expressed as betanin using A538 (1%) = 1120

(Forni et al., 1992) Acid concentration was

de-termined from 10 g of pulp macerated in

dis-tilled water and titrated with 0.05 M NaOH to

pH 8.0 Ascorbic acid concentration was

deter-mined in extracts of fresh pulp by titration with

2,6-dichloro-indophenol (AOAC, 1990) Soluble

solids concentration (SSC) was measured with a

refractometer (PR-100, Atago, Japan) in sap

pressed from the pulp The concentrations of

total soluble sugars, starch, and mucilage were

determined in dry samples of pulp according to

a procedure previously reported (Nerd and

Mizrahi, 1999) Flavour of fruits was assessed

by a panel of ten on a hedonic scale with 1

indicating extreme dislike and 10 indicating

strong liking

2.5 Ethylene and CO2 production rates

Fruits picked at first colour and 3 and 6 days

later (three per species at each date) were

weighed and then enclosed individually in jars

held at 20°C and under a light regime of 12 h

fluorescent light/12 h dark A continuous air

flow at approximately 5 ml min− 1 was passed

through the jar Ethylene and CO2

concentra-tions in the effluent air stream were analysed

with a gas chromatograph (Varian 3300,

Sugar-land, TX) once a day

3 Results and discussion

3.1 Fruit growth and ripening

In both H undatus and H polyrhizus, growth of

fruits attached to the vine exhibited a sigmoid pattern (Fig 1) Peel colour was developed during the last phase which was characterised by a slow growth rate First colour (area between the scales

turned faint red) appeared 24 – 25 DAA in H.

undatus and 26 – 27 DAA in H polyrhizus Fruits

of both species turned fully red 4 – 5 days after first colour Like the fruit dimensions, fruit fresh weight reached 80% of the final maximum weight, before appearance of first colour (Fig 2(A)) Significant increase in pulp content (percent of fruit fresh weight) occurred several days before, and throughout colour change (Fig 2(B)), while fruit firmness dropped to less than 1 kg cm− 2 in that time (Fig 2(C)) During the final stage, percentage

of water in the peel decreased (more markedly in

H undatus) while remaining almost constant in the

pulp (Fig 2(D)) Calculations based on data

Fig 1 Growth (length and diameter) during fruit development

on the vine in H undatus and H polyrhizus Values are

means9SE (n=4).

Fig 2 Whole fruit fresh weight (A), percentage of peel or pulp

in fruit by weight (B), firmness (C), and water percent (FW

basis) (D), during the last stage of fruit development in H.

undatus and H polyrhizus Values are means 9SE (n=6).

Fig 3 Colour changes in H undatus (red peel and white pulp) and H polyrhizus (red peel and red-violet pulp) during the last

stage of fruit development Values are means9SE (n=6).

of colour change was low in fruits of both species, ranging from 7.0 to 11.4 mg 100 g− 1fresh weight Changes in the concentration of soluble solids and

a number of non-structural carbohydrate compo-nents of the pulp occurred during fruit develop-ment Both soluble solids and soluble sugars concentrations increased significantly during colour development, reaching 16 – 17 and 8 – 9%, respectively, at full colour stage (Fig 5(A, B)) Since changes in the two parameters were highly correlated, SSC appears to be a reliable indicator for maturity in the investigated species The con-centrations of starch and mucilage decreased in relation to the accumulation of soluble sugars

presented in Fig 2 show that during the slow

growth period (25 – 41 DAA), pulp dry weight

increased significantly from 36 to 62 g in H.

undatus and from 21 to 48 g in H polyrhizus,

while peel dry weight (around 18 g in both species

at 25 DAA) decreased slightly by 4 g in that time

Hence the peel although accounting for a high

proportion of fruit weight 20 – 25 DAA, could not

have been an important source of assimilates to

the developing pulp which presumably received

assimilates from the stem

The decreasing values of the peel hue angle

during maturation (Fig 3) reflect development of

peel colour In H polyrhizus, which has a red –

vi-olet pulp, the development of peel colour was

accompanied by an increase in the content of

water-soluble pigment in the pulp (Fig 3) The

maximum concentration of pigment (expressed as

betanin) in fruits with fully red peel was 0.24 mg

g− 1 fresh weight Titratable acidity of pulp

showed a short-lived surge at the start of colour

change, followed by a decline later on to 30

mmol H+ kg− 1 in H undatus and 45 mmol

H+ kg− 1in H polyrhizus (equivalent to 0.22 and

0.32% citric acid, respectively; Fig 4) Ascorbic

acid concentration of the pulp during the period

Fig 4 Concentration of titratable acidity (FW basis) during

the last stage of fruit development in H undatus and H polyrhizus Values are means 9SE (n=6).

Fig 5 Concentration (FW basis) of soluble solids (SSC) (A),

soluble sugars (B), starch (C), and mucilage (D), during the

last stage of fruit development in H undatus and H.

polyrhizus Values are means9SE (n=6).

and SSC and soluble sugars were high The ratio

of percentage of soluble sugars to acidity (in terms

of citric acid) in such fruits was 40 in H.

undatus and 22 in H polyrhizus Thus for both

red pitayas, chemical changes during ripening, colour development and palatability were found

to coincide, as reported for the yellow pitaya S.

megalanthus (Nerd and Mizrahi, 1998) In the

cactus pear (Opuntia ficus indica), however,

opti-mum eating quality was reached at first colour stage (Nerd and Mizrahi, 1997)

3.2 Gas production

Production of ethylene and CO2 in fruits har-vested at various colour stages was low and did not peak during 6 days at 20°C The production rate of ethylene ranged from 0.025 to 0.091 ml

kg− 1 h− 1 and that of CO2 from 0.52 to 0.78 ml

kg− 1 h− 1 Hence H undatus and H polyrhizus

may be defined as non-climacteric, similar to other cactus fruit crops that have been

investi-gated, namely cactus pears (Opuntia species) and yellow pitaya (S megalanthus; Nerd and Mizrahi,

1997, 1998)

3.3 Storage

Fruits were picked close to full colour and examined at the end of 3 consecutive weeks in storage at different temperatures Distinct disor-ders were observed at the end of week 2 for fruits held at 20°C and at the end of week 3 for fruits held at 14°C Symptoms consisted of extreme softening, difficulty in separation of peel from the pulp, and wilting and browning of scales (these phenomena appeared usually together) The con-centration of soluble solids and soluble sugars remained fairly constant throughout storage at all the storage temperatures (Table 2) High storage temperatures resulted in lower fruit firmness, wa-ter content, acidity and flavour The two species responded to storage in a similar manner, though

fruits of H polyrhizus tended to maintain a higher

level of acidity at 14 and 20°C This higher acidity

may explain the higher preference rating of H.

polyrhizus recorded under these conditions Some

of the fruits stored at 6°C were transferred at

(Fig 5(C, D)) Maximal concentration of starch

was less than half that of the soluble sugars in

ripe fruit, and accumulation of soluble sugars

during ripening cannot be therefore attributed to

starch degradation alone The two species differed

with regard to timing of changes in chemical

constituents and other maturation parameters

which coincided with the timing of first colour

appearance

Organoleptic testing indicated that fruits were

most palatable 33 – 37 DAA (Table 1) At that

stage they had turned fully red, acidity was low

Table 1

Flavour rating of fruits of H undatus and H polyrhizus

harvested between 25 and 41 DAA a

DAA Flavour (rating)

3.3 c 3.7 c

29

5.7 b

41

a Flavour was assessed by a panel of ten according to a

hedonic scale with 1 indicating extreme dislike and 10

indicat-ing strong likindicat-ing.

bMean separation within column at P50.05 by Duncan’s

multiple range test.

Table 2

Effect of storage temperatures on fruit attributes in H undatus and H polyrhizusa

Storage Firmness Water loss SSC Soluble sugars Acidity mmol H + Flavour

(%)

Weeks

°C

H undatus

14.0 a 6.6 a

3

H polyrhizus

1

1

a Fruits were harvested close to full colour and analysed prior to appearance of distinct disorders such as extreme softening and scale wilting Values are means9SE (n=5).

bMean separation within column at P50.05 by Duncan’s multiple range test.

different times to 20°C and their attributes

exam-ined 1 week later (data not shown) Fruits

trans-ferred at the end of week 1 were similar to those

stored immediately after harvest for 1 week at 20°C

(Table 2) However fruits transferred to 20°C at the

end of week 2 or 3 at 6°C became soft (B0.3 kg

cm− 2), had high water loss (8 – 11%), low acidity

(B25 mol H+ kg− 1) and poor flavour (B2.5)

Fruits of H undatus developed chilling injury

symptoms such as wilting and darkening of the

scales and browning of the outer layer of the pulp

upon transfer to 20°C after 2 weeks at 6°C

To summarise, fruit harvested close to full colour

kept their visual acceptance, i.e marketing quality

for at least 3 weeks at 6°C, 2 weeks at 14°C or 1

week at 20°C Fruits stored at 6°C maintained their

eating quality (flavour) for a longer period but lost

quality rapidly when transferred to room

tempera-ture The effect of harvesting at an earlier ripening

stage (first colour) on fruit quality during or after

storage should be examined with a view to

extend-ing the shelf life of these pitayas

Acknowledgements

The authors thank the Fleischer Foundation and the Israel Ministry of Agriculture for a partial financial support, Dorot Imber for editing the manuscript and Josef Mouyal and Eyal Naus for their technical assistance

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