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Citation: Chen, S.-Y.; Islam, M.A.;
Johnson, J.B.; Xu, C.-Y.; Mazhar, M.S.;
Naiker, M. Comparative Analysis of
Shelf-Life, Antioxidant Activity, and
Phytochemical Contents of
Australian-Grown and Imported
Dragon Fruit under Ambient
Conditions. Horticulturae 2024,10,
1048. https://doi.org/10.3390/
horticulturae10101048
Received: 30 August 2024
Revised: 25 September 2024
Accepted: 28 September 2024
Published: 1 October 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
horticulturae
Article
Comparative Analysis of Shelf-Life, Antioxidant Activity, and
Phytochemical Contents of Australian-Grown and Imported
Dragon Fruit under Ambient Conditions
Si-Yuan Chen 1,* , Mohammad Aminul Islam 2,3 , Joel B. Johnson 4, Cheng-Yuan Xu 5,
Muhammad Sohail Mazhar 5,6 and Mani Naiker 1, *
1School of Health, Medical & Applied Sciences, CQ University Australia, Bruce Hwy,
North Rockhampton, QLD 4701, Australia
2School of Information and Communication Technology, Griffith University, Brisbane, QLD 4111, Australia;
mohammadaminul.islam@griffithuni.edu.au
3Department of Computer Science and Mathematics, Bangladesh Agricultural University,
Mymensingh 2202, Bangladesh
4Queensland Alliance for Agriculture and Food Innovation, The University of Queensland,
Brisbane, QLD 4072, Australia; joel.johnson@uq.edu.au
5Research Institute for Northern Agriculture, Charles Darwin University, Ellengowan Drive,
Brinkin, NT 0810, Australia; stephen.xu@cdu.edu.au (C.-Y.X.); muhammadsohail.mazhar@nt.gov.au (M.S.M.)
6Agriculture Branch, Department of Agriculture and Fisheries of the Northern Territory Government,
Darwin, NT 0828, Australia
*Correspondence: s.chen3@cqu.edu.au (S.-Y.C.); m.naiker@cqu.edu.au (M.N.)
Abstract: Dragon fruit (Hylocereus spp.), renowned for its aesthetic appeal and rich antioxidant
content, has gained global popularity due to its numerous health benefits. In Australia, despite grow-
ing commercial interest in cultivating dragon fruit, there is uncertainty for local growers stemming
from competition with imported varieties. Notably, there is a lack of comparative research on the
shelf-life, antioxidant activity, and phytochemical contents of Australian-grown versus imported
dragon fruit, which is crucial for enhancing market competitiveness and consumer perception. This
study compares the shelf-life, antioxidant activity, and phytochemical content of Australian-grown
and imported dragon fruits under ambient conditions, addressing the competitive challenges faced
by local growers. Freshly harvested white-flesh (Hylocereus undatus) and red-flesh (H. polyrhizus)
dragon fruit were sourced from Queensland and the Northern Territory and imported fruit were
sourced from an importer in Queensland. All fruit were assessed for key quality parameters in-
cluding peel color, firmness, weight loss, total soluble solids (TSS), pH, titratable acidity (TA), total
phenolic content (TPC), total flavonoid content (TFC), ferric reducing antioxidant power (FRAP),
cupric reducing antioxidant capacity (CUPRAC), total betalain content (TBC), and total anthocyanin
content (TAC). The results indicate that Australian-grown white dragon fruits exhibited average one
day longer shelf-life with less color degradation, better firmness retention, and less decline in weight
loss, TSS, and acidity compared to imported fruits. Australian-grown red dragon fruits showed
similar shelf-life compared to fruits from overseas. Antioxidant activities and phytochemicals were
consistently higher in Australian-grown fruits throughout their shelf-life. These findings indicate
that Australian-grown dragon fruits offer better physical quality and retain more nutritional value,
which could enhance their marketability.
Keywords: dragon fruit; white-flesh; red-flesh; Australian-grown; imported; shelf-life; ambient;
antioxidant activity; phytochemicals
1. Introduction
Pitaya, commonly known as dragon fruit, originates from several cactus species
within the Cactaceae family [
1
]. Although native to regions in Mexico and northern South
Horticulturae 2024,10, 1048. https://doi.org/10.3390/horticulturae10101048 https://www.mdpi.com/journal/horticulturae
Horticulturae 2024,10, 1048 2 of 30
America [
2
], its cultivation has extended significantly to tropical and subtropical areas,
including Vietnam, China, and Australia [
3
]. The optimal growth conditions for dragon fruit
include annual rainfall between 25 to 51 inches and the ability to withstand temperatures
up to 40
◦
C [
4
]. Dragon fruit, with its cactus-like adaptations, thrives in environments with
high light intensity and warm climates, as long as it receives sufficient water and is grown
in fertile soils [4].
Dragon fruit is a valuable source of antioxidant phytochemicals, which contribute
to various health benefits. Recent research on its bioactive properties has substantiated
these health-promoting effects, including its antioxidant capacity, antidiabetic, anticancer,
anti-inflammatory, antihyperlipidemic, and anti-obesity properties, as well as its hepato-
protective and prebiotic potential. The presence of polyphenols, betalains, carotenoids,
flavonoids, alkaloids, terpenoids, steroids, tannins, and saponins in dragon fruit plays a
significant role in mediating these beneficial effects [4].
Dragon fruit was introduced to Australia in the 1970s, and its cultivation has since
expanded to Queensland (QLD), the Northern Territory (NT), Western Australia (WA),
and New South Wales (NSW) [
5
]. By 2010, NT had become the principal cultivation
region, with approximately 35,000 planting sites (one planting site consists of around
three individual plants) and accounting for over 60% of the national production, which
is over 50,000 planting site in total [
6
]. Southeast Queensland has also experienced rapid
cultivation growth due to rising market demand.
Three primary species of dragon fruit can be identified by their skin and pulp colors:
Hylocereus undatus (white-flesh), H. polyrhizus (red-flesh), and H. megalanthus (yellow) [
7
].
Studies indicate that white- and red-flesh varieties are predominantly grown in Australia,
with H. undatus being the major cultivar in the NT and H. polyrhizus yielding significant
production in QLD [6] (Figure 1).
Horticulturae 2024, 10, x FOR PEER REVIEW 2 of 31
1. Introduction
Pitaya, commonly known as dragon fruit, originates from several cactus species
within the Cactaceae family [1]. Although native to regions in Mexico and northern South
America [2], its cultivation has extended significantly to tropical and subtropical areas,
including Vietnam, China, and Australia [3]. The optimal growth conditions for dragon
fruit include annual rainfall between 25 to 51 inches and the ability to withstand temper-
atures up to 40 °C [4]. Dragon fruit, with its cactus-like adaptations, thrives in environ-
ments with high light intensity and warm climates, as long as it receives sufficient water
and is grown in fertile soils [4].
Dragon fruit is a valuable source of antioxidant phytochemicals, which contribute to
various health benefits. Recent research on its bioactive properties has substantiated these
health-promoting effects, including its antioxidant capacity, antidiabetic, anticancer, anti-
inflammatory, antihyperlipidemic, and anti-obesity properties, as well as its hepato-pro-
tective and prebiotic potential. The presence of polyphenols, betalains, carotenoids, flavo-
noids, alkaloids, terpenoids, steroids, tannins, and saponins in dragon fruit plays a signif-
icant role in mediating these beneficial effects [4].
Dragon fruit was introduced to Australia in the 1970s, and its cultivation has since
expanded to Queensland (QLD), the Northern Territory (NT), Western Australia (WA),
and New South Wales (NSW) [5]. By 2010, NT had become the principal cultivation region,
with approximately 35,000 planting sites (one planting site consists of around three indi-
vidual plants) and accounting for over 60% of the national production, which is over
50,000 planting site in total [6]. Southeast Queensland has also experienced rapid cultiva-
tion growth due to rising market demand.
Three primary species of dragon fruit can be identified by their skin and pulp colors:
Hylocereus undatus (white-flesh), H. polyrhizus (red-flesh), and H. megalanthus (yellow) [7].
Studies indicate that white- and red-flesh varieties are predominantly grown in Australia,
with H. undatus being the major cultivar in the NT and H. polyrhizus yielding significant
production in QLD [6] (Figure 1).
Figure 1. Current dragon fruit cultivation regions in Australia [8].
Figure 1. Current dragon fruit cultivation regions in Australia [8].
Recent research, such as the study by Chen [
9
], has explored the phytochemical profile
of Australian-grown dragon fruit, identifying key compounds like polyphenols, flavonoids,
and betalains that contribute to its antioxidant capacity. There is a notable lack of research
on the quality of Australian-grown dragon fruits, particularly regarding their shelf-life and
antioxidant capacity. Despite the increasing commercial interest in dragon fruit cultivation
Horticulturae 2024,10, 1048 3 of 30
in Australia, owing to its low maintenance and high nutritional value, the future remains
uncertain for Australian growers [
10
]. The market’s opening to imports (mainly Asian
countries such as Vietnam, Philippines, and Malaysia) in 2017 has introduced substantial
price competition, posing challenges for domestic growers who face higher cultivation,
transportation, and operational costs, especially in remote areas [
11
]. This competition
has adversely impacted business confidence and constrained the expansion of the local
dragon fruit industry. Furthermore, there is a notable lack of research on the quality of
Australian-grown dragon fruits, particularly regarding their shelf-life and antioxidant
capacity. Addressing these research gaps would not only elevate the value and appeal
of local produced dragon fruits but also contribute to the global understanding of their
nutritional benefits.
This study assessed the current offerings of the Australian dragon fruit market and
aimed to highlight the possible competitive advantages of Australian-grown over the
imported dragon fruits regarding on their quality and antioxidant characteristics during
shelf-life. Results of this research are expected to enhance consumer perceptions, strengthen
the market position of the Australian-grown dragon fruit, potentially assist with establish-
ing industry standards tailored to the local-grown dragon fruit, and, most importantly,
support the domestic growers for future growth of the Australian grown fruit.
2. Materials and Methods
2.1. Samples
The Australian-grown white-and red-flesh dragon fruits were freshly received from
two farms in Humpty Doo, NT and four farms in Sunshine Coast, QLD, based on growers’
harvesting experience and fruit availability. Imported samples (originally from Vietnam)
were collected from JE Tipper, a wholesaler based in Brisbane, QLD. After washing with
tap water and air drying, the samples were stored in air ventilated baskets under ambient
conditions (see Section 2.3 for details) for further analysis.
2.2. Chemicals and Reagents
All the chemicals, reagents and standards were analytical grade purchased from
ChemSupply Australia Pty Ltd. (Gillman, Australia). All dilutions and preparation of
aqueous solutions are made using deionized water, unless otherwise specified. Solutions
were stored at 4 ◦C in the refrigerator until they were used.
2.3. Shelf-Life
The shelf-life evaluation was conducted through a controlled storage experiment,
where uniformed size dragon fruit samples without physical damage were selected and
stored in corrugated fiberboard boxes (6 fruits in each) under ambient temperature and hu-
midity conditions monitored by Tapo T310 (Table 1). Regular assessments were performed
at predetermined intervals (every second day) to track changes in selected parameters
throughout the storage period. In detail, the shelf-life of Australian-grown and overseas
dragon fruits were determined by counting the number of days from the date of receipt
until samples were failed to meet the criteria of Class II fruit based on the Codex Alimenta-
rius Standard for dragon fruit CXS 237-2003 [
12
]. According to this standard, defects on the
appearance of the Class II fruits are less than 2 cm
2
of the total surface of the fruit [
12
]. The
collected data from two seasons were combined and statistically analyzed to identify trends
and significant differences in quality attributes. The overall shelf-life of Australian-grown
dragon fruit was calculated by averaging the results from QLD and NT in this study.
Factors such as peel color, firmness, weight loss, Brix, pH, and titratable acidity were
recorded, as they are crucial for assessing overall quality and marketability of dragon fruit.
Individual analyses were conducted the day after samples receipt, except for fruits
from the NT, which were tested on the fourth day due to extended transportation time.
For peel color and firmness, three samples were randomly chosen for each designated
shelf-life point to ensure a representative assessment of the entire batch of fruit. Triplicate
Horticulturae 2024,10, 1048 4 of 30
measurements were taken for each sample to ensure comprehensive coverage of each fruit.
After measuring color and firmness, the three samples were blended to create a homoge-
neous juice mixture. This blended juice was then utilized to test the remaining analytical
parameters, with all tests conducted in triplicate to ensure reliability and consistency of
the results.
Table 1. Temperature and humidity conditions during shelf-life evaluation.
Origin Temperature Range (◦C) Humidity Range (%)
First season
QLD 20.4–24.7 54–82
NT 22.3–25.6 63–89
Overseas 20.2–23.8 55–80
Second season
QLD 20.5–24.6 50–82
Overseas 20.0–24.0 54–78
QLD: Queensland; NT: Northern Territory.
2.3.1. Peel Color
For determining the color of the dragon fruit peel, hyperspectral images were captured
using a Hyperspectral Camera Specim IQ manufactured by Specim, Spectral Imaging LTD.,
Oulu, Finland. Subsequently, a determination program was developed using PyCharm CE
codes (version 2023.3.1) to calculate the color value of a randomly selected circular area on
the dragon fruit peel (Figure 2). Following the partial least squares regression (PLSR) color
index model well-developed by Wanitchang et al. [
13
], the color value in this experiment
was computed as the logarithm of the reflectance ratio at 681 nm and 551 nm, specifically
represented as log(R
681
/R
551
). To eliminate potential background effects, a white reference
pad was utilized during the color measurement process. Triplicate measurements were
taken for each sample to ensure a representative assessment of the whole fruit.
Figure 2. Color measurement process. (a) Hyperspectral image captured by hyperspectral camera;
(b) Result window of PyCharm CE color determination program. The rectangular area helps in
calibration using the white reference, while the circle indicates the region of interest on the dragon
fruit as described in Section 2.3.1.
2.3.2. Firmness
Firmness measurements of the dragon fruit were performed using an EZ SX Texture
Analyzer (Shimadzu, Australia) coupled with a 5 mm diameter indentation elasticity jig.
The firmness was presented as the maximum force for breaking the peel. The penetration
point was selected at the center of the peel. Triplicate measurements were taken for each
sample to ensure a representative assessment of the whole fruit.
Horticulturae 2024,10, 1048 5 of 30
2.3.3. Weight Loss (%)
Weight loss was measured by subtracting the current weight from the initial weight of
the sample and expressed as a percentage. This is calculated using the formula:
Weight Loss (%)=W1−W2
W1
×100
where:
W1= Initial weight of the sample (g)
W2= Current weight of the sample (g)
2.3.4. Total Soluble Solids (TSS), pH and Titratable Acidity
Total soluble solids were measured using a refractometer (PAL-1, ATAGO), and pH
was measured with a pH meter (Orion Star™ A211 Benchtop pH Meter, Thermo Fisher
Scientific, Australia).
Titratable acidity was determined using a modified AOAC method [
14
]. A total of
10 g of homogenized juice mixture was mixed thoroughly with 50 mL deionized water. The
resulting mixture was then titrated against 0.1 N sodium hydroxide until the pH reached
8.2, as monitored by the pH meter. The result was calculated as malic acid equivalent
(MAE) using the formula:
Titratable Acidity (%)=N×V×M
m×100
where:
N = Normality of NaOH
V = Volume of NaOH is used (mL)
M = Molecular weight of malic acid (134.0874 g/mol)
m = Weight of the sample (g)
2.4. Antioxidant and Phytochemical Assays
2.4.1. Extraction
A modified version of the aqueous-methanolic extraction technique developed by
Johnson et al. [
15
] was employed. In this approach, one gram of pre-homogenized dragon
fruit pulp juice (obtained as described in Section 2.3) was carefully weighed and placed
into a 50 mL centrifuge tube. For the extraction of total betalain and anthocyanin content,
10 mL of a 90% methanol solution (acidified with 0.1% hydrochloric, v/v)) was added. For
total phenolic content (TPC), total flavonoids, ferric reducing antioxidant power (FRAP)
and cupric reducing antioxidant capacity (CUPRAC) analyses, 10 mL of a 90% aqueous
methanol solution was used. The tube was then vigorously mixed using a vortex mixer
and placed on a platform shaker at 200 rpm for 15 min in darkness at room temperature.
Following this, the mixture was centrifuged at 3000 rpm for 6 min (Thermo Scientific
Heraeus Megafuge 16). The supernatant was filtered through Whatman qualitative filter
paper (Grade 1, 90 mm diameter with 11
µ
m pore size), and the resulting filtrate was
collected and stored (in fridge at −4◦C) for further analysis.
2.4.2. Measurement of Phytochemical Contents and Antioxidant Activity
Total phenolic content was determined by a Folin–Ciocalteu (FC) assay developed
by Johnson et al. [
16
]. An aliquot of methanolic extract (400
µ
L) was combined with
2 mL of a 10-fold diluted FC reagent and then subjected to a 10 min incubation period
in darkness at room temperature. Subsequently, 2 mL of sodium carbonate (7.5%, w/v)
was added to the mixture, followed by an additional 30 min incubation at 40
◦
C. After the
incubation, a portion of the resulting solution was transferred to a cuvette for absorbance
measurement at 760 nm using a UV-Vis spectrophotometer (Genesys 10S UV-Vis, Thermo
Scientific, Adelaide, Australia). Milli-Q water was used to blank the instrument and gallic
Horticulturae 2024,10, 1048 6 of 30
acid (0–100 ppm) was utilized as the calibration standard, and the results were presented
as milligrams of gallic acid equivalents (GAE) per 100 g of fresh weight of the sample (mg
GAE/100 g FW).
Total flavonoid content was measured by modifying an aluminum chloride colori-
metric assay developed by Chen et al. [
9
]. An aliquot the methanolic extract (400
µ
L) was
combined with 400
µ
L of methanolic aluminum chloride solution (10%) and 600
µ
L of
aqueous sodium acetate solution (1 M), followed by a 30 min incubation at room tempera-
ture. The resulting mixture was then transferred to a cuvette for absorbance measurement
at 415 nm using a UV-Vis spectrophotometer (Genesys 10S UV-Vis, Thermo Scientific,
Australia). Milli-Q water was used to blank the instrument and quercetin (0–20 ppm) was
used as the standard, and the results were reported as milligrams of quercetin equivalents
(QE) per 100 g of fresh weight of the sample (mg QE/100 g FW).
The FRAP assay was conducted in accordance with a modified protocol as originally
devised by Johnson et al. [
17
]. An aliquot of the dragon fruit methanolic extract (100
µ
L) was
first combined with 3 mL of FRAP solution consisting of 300 mM aqueous sodium acetate at
pH 3.56, 20 mM ferric chloride, and 10 mM TPTZ (2,4,6-tri(2-pyridyl)-s-triazine), combined
in a 10:1:1 ratio. The resulting mixture was then incubated at 37
◦
C for 4 min. After incuba-
tion, a portion of the mixture was transferred to a cuvette for absorbance measurement at
593 nm using a UV-Vis spectrophotometer (Genesys 10S UV-Vis, Thermo Scientific, Aus-
tralia). Milli-Q water was used to blank the instrument and trolox (0–100 ppm) was used as
calibration standard, and the results were expressed as milligrams Trolox equivalents (TE)
per 100 g of fresh weight of the sample (mg TE/100 g FW).
The CUPRAC assay was conducted following a modified methodology developed
by Johnson et al. [
17
]. An aliquot of the dragon fruit methanolic extract (100
µ
L) was
combined with 1 mL of a 10 mM aqueous copper (II) chloride, 1 mL of 1 M ammonium
acetate, 1 mL of a 7.5 mM neocuproine solution, and 1 mL of distilled water. This mixture
was then incubated at 50
◦
C in darkness for 30 min. Subsequently, the absorbance of the
mixture was measured utilizing a UV-Vis spectrophotometer (Genesys 10S UV-Vis, Thermo
Scientific, Australia) at 450 nm. Milli-Q water was used to blank the instrument and trolox
(0–400 ppm) was used as calibration standard and the results were expressed as milligrams
of Trolox equivalents (TE) per 100 g of fresh weight of the sample (mg TE/100 g FW)
The method for the determination of TBC was modified from Zitha et al. [
18
]. Total
betalain content (TBC) was the sum up of betacyanin and betaxanthin contents in the
dragon fruit pulp. Milli-Q water was used to blank the instrument and an aliquot of the
methanolic extract (2 mL) was transferred to a cuvette for absorbance reading using a
UV-Vis spectrophotometer (Genesys 10S UV-Vis, Thermo Scientific, Australia) at 538 nm
for betacyanin and 483 nm for betaxanthin. The results were computed using the following
formulas and reported as milligrams per 100 g of fresh weight of the sample (
mg/100 g FW
)
Betacyanin mg·100g−1=A1×DF ×M1×V×1000
η1×W×L×100
Betaxanthin mg·100g−1=A2×DF ×M2×V×1000
η2×W×L×10 ×100
where:
A1= Absorbance at 538 nm
A2= Absorbance at 483 nm
DF = Dilution Factor (if necessary)
M1= Molecular Weight of Betanin (550 g/mol)
M2= Molecular Weight of Indicaxanthin (308 g/mol)
V = Volume of the Extract (L)
η1= Molar Extinction Coefficient of Betanin (60,000 L/mol·cm)
η2= Molar Extinction Coefficient of Indicaxanthin (48,000 L/mol·cm)
W = Sample Mass (g)
L = Path Length (1 cm)
Horticulturae 2024,10, 1048 7 of 30
The TAC was determined utilizing a modified protocol derived from the work of Zitha
et al. [
18
]. In this method, milli-Q water was used to blank the instrument and 2 mL of
acidified methanolic extract was transferred to a cuvette for absorbance reading using a UV-
Vis spectrophotometer (Genesys 10S UV-Vis, Thermo Scientific, Australia) at 535 nm. The
results were computed using the following formula and reported as milligrams of cyanidin-
3-glucoside equivalents (CGE) per 100 g of fresh weight of the sample (mg CGE/100 g FW).
Total Anthocyanin Content mg·100g−1=A×DF ×M×V×1000
W×ε×L×100
where:
A = Absorbance at 535 nm
DF = Dilution Factor
M = Molecular weight of cyanidin–3–glucoside (449.2 g/mol)
V = Volume of sample extraction (L)
W = Weight of the sample (g)
ε= Molar Absorptivity (26,900 L/mol)
L = Path Length (1 cm)
2.5. Statistical Analysis
All analysis and tests were conducted in triplicates for each sample, with results
expressed as mean
±
standard deviation (SD, n= 3) on a fresh weight (FW) basis. Statis-
tical analysis was performed using SPSS (version 29.0.1). One-way analysis of variance
(ANOVA) was used to evaluate the effects of storage days and sample regions or varieties
on shelf-life quality parameters (color, firmness, weight loss, TSS, pH, and TA), antioxidant
activities (FRAP and CUPRAC) and phytochemical measurements (TPC, TFC, TBC, and
TAC). Tukey’s Honestly Significant Difference (HSD) test was applied to analyze variations
among varieties/regions concerning shelf-life parameters, antioxidant activities, and phy-
tochemical contents. Pearson’s correlation coefficients were calculated to assess significant
correlations (p< 0.05; two-tailed) among shelf-life quality parameters antioxidant activities
and phytochemical contents.
3. Results and Discussion
3.1. Fruit Quality during Shelf-Life
The quality changes during the shelf-life of dragon fruit in this study encompass the
analysis of color, firmness, weight loss, total soluble solids (TSS), pH, and titratable acidity
(TA) throughout the storage period. The Results and Discussion Section focuses specifically
on the differences between different regions. This approach was taken because several
previous studies have already compared the fruit quality during shelf-life of white- and
red-flesh varieties, revealing that the red-flesh variety has typically shorter shelf-life and
exhibits higher a* values and lower L* values for color, lower firmness, greater weight loss,
higher TSS, and lower TA compared to the white-flesh variety [
19
–
21
]. Similar trends in
these shelf-life parameters were also observed in this study. The detailed results for these
parameters are shown in Table A1 in Appendix A.
3.1.1. Color
Color originates from the natural pigments present in fruits and vegetables, many of
which undergo transformation as the plant progresses through stages of maturation and
ripening [
22
]. It is also a critical quality attribute in fruits, significantly influencing consumer
choices and preferences. Measuring the color of fruits serves as an indirect indicator of
other quality attributes due to its simplicity, operation speed, and strong correlation with
other physicochemical properties [
23
]. In this study, the color index log (R
681
/R
551
) value
serves as a quantitative measure that correlates with the color of the dragon fruit peel. A
higher value corresponds to a less red peel, while a lower value suggests more intense red
coloration. The color development of dragon fruit during shelf-life is shown in Figure 3.
Horticulturae 2024,10, 1048 8 of 30
Horticulturae 2024, 10, x FOR PEER REVIEW 8 of 31
and exhibits higher a* values and lower L* values for color, lower firmness, greater weight
loss, higher TSS, and lower TA compared to the white-flesh variety [19–21]. Similar trends
in these shelf-life parameters were also observed in this study. The detailed results for
these parameters are shown in Table A1 in Appendix A.
3.1.1. Color
Color originates from the natural pigments present in fruits and vegetables, many of
which undergo transformation as the plant progresses through stages of maturation and
ripening [22]. It is also a critical quality aribute in fruits, significantly influencing con-
sumer choices and preferences. Measuring the color of fruits serves as an indirect indicator
of other quality aributes due to its simplicity, operation speed, and strong correlation
with other physicochemical properties [23]. In this study, the color index log (R
681
/R
551
)
value serves as a quantitative measure that correlates with the color of the dragon fruit
peel. A higher value corresponds to a less red peel, while a lower value suggests more
intense red coloration. The color development of dragon fruit during shelf-life is shown
in Figure 3.
Figure 3. Development of peel color in dragon fruit during shelf-life under ambient conditions. (a)
White-flesh dragon fruit peel color development during shelf-life; (b) red-flesh dragon fruit peel
color development during shelf-life. QLDW, Queensland-grown white-flesh dragon fruit; NTW:
Northern Territory-grown white-flesh dragon fruit; OverseasW, overseas-grown white-flesh dragon
fruit; QLDR, Queensland-grown red-flesh dragon fruit; OverseasR, overseas-grown red-flesh
dragon fruit.
It is reported that the intensity of the red color of the peel progressively diminished
as senescence begins in dragon fruit [24]. In this study, the overall trend of peel color de-
velopment in dragon fruit observed using a hyperspectral camera showed similar results
to those reported by Lata et al. [21] using a colorimeter with decreases in L* and a* value
(indicating decreases in the red pigment and lightness of the dragon fruit peel). For white-
flesh dragon fruit, NTW exhibited the most stable red coloration during its shelf-life (rang-
ing from 0.76 ± 0.06 to 0.91 ± 0.03), followed by OverseasW (from 0.74 ± 0.14 to 0.95 ± 0.17).
QLDW had the least red coloration intensity throughout its shelf-life, starting at 0.86 ±
0.10 on day 2 and reaching 1.00 ± 0.05 on day 10. For red-flesh dragon fruit, QLDR showed
more intensive red coloration than OverseasR during its shelf-life, with values increasing
from 0.50 ± 0.13 on day 2 to 0.83 ± 0.09 on day 8, whereas OverseasR started at 0.73 ± 0.05
and ended at 0.97 ± 0.10 on day 8. According to this study, for the white-flesh variety,
fruits from NT may appear more appealing to consumers four days after harvest when
stored under ambient conditions, followed by the overseas-grown and QLD-grown fruits.
Figure 3. Development of peel color in dragon fruit during shelf-life under ambient conditions.
(a) White-flesh dragon fruit peel color development during shelf-life; (b) red-flesh dragon fruit
peel color development during shelf-life. QLDW, Queensland-grown white-flesh dragon fruit;
NTW: Northern Territory-grown white-flesh dragon fruit; OverseasW, overseas-grown white-flesh
dragon fruit; QLDR, Queensland-grown red-flesh dragon fruit; OverseasR, overseas-grown red-flesh
dragon fruit.
It is reported that the intensity of the red color of the peel progressively diminished
as senescence begins in dragon fruit [
24
]. In this study, the overall trend of peel color
development in dragon fruit observed using a hyperspectral camera showed similar results
to those reported by Lata et al. [
21
] using a colorimeter with decreases in L* and a* value
(indicating decreases in the red pigment and lightness of the dragon fruit peel). For
white-flesh dragon fruit, NTW exhibited the most stable red coloration during its shelf-life
(ranging from 0.76
±
0.06 to 0.91
±
0.03), followed by OverseasW (from 0.74
±
0.14 to
0.95
±
0.17). QLDW had the least red coloration intensity throughout its shelf-life, starting
at 0.86
±
0.10 on day 2 and reaching 1.00
±
0.05 on day 10. For red-flesh dragon fruit,
QLDR showed more intensive red coloration than OverseasR during its shelf-life, with
values increasing from 0.50
±
0.13 on day 2 to 0.83
±
0.09 on day 8, whereas OverseasR
started at 0.73
±
0.05 and ended at 0.97
±
0.10 on day 8. According to this study, for the
white-flesh variety, fruits from NT may appear more appealing to consumers four days
after harvest when stored under ambient conditions, followed by the overseas-grown
and QLD-grown fruits. Conversely, QLD-grown red-flesh dragon fruit may appear more
appealing to consumers than the overseas variety throughout the entire shelf-life when
stored under ambient conditions.
Betalain is the primary pigment responsible for the red coloration of the dragon fruit
peel [
25
]. The storage of dragon fruit under ambient conditions leads to the degradation
of this pigment, resulting in discoloration and browning, primarily due to its sensitivity
to light and temperature variations [
26
]. This phenomenon of color degradation under
ambient storage has also been observed in other fruits, such as banana [
27
], mandarin [
28
],
and pomegranate [29].
3.1.2. Firmness
Firmness is a critical quality parameter in shelf-life evaluation. In fruits and vegetables,
it is not only related to textural and freshness of the fresh produce, but structural integrity
affected by enzymatic activity, moisture loss, cell wall degradation, etc. [
30
] These processes
will soften the product, leading to poor consumer perception and reduced marketability [
31
].
The evaluation of changes in firmness of both Australian-grown and the imported dragon
fruit during shelf-life stored under ambient conditions were conducted (Figure 4).
Horticulturae 2024,10, 1048 9 of 30
Horticulturae 2024, 10, x FOR PEER REVIEW 9 of 31
Conversely, QLD-grown red-flesh dragon fruit may appear more appealing to consumers
than the overseas variety throughout the entire shelf-life when stored under ambient con-
ditions.
Betalain is the primary pigment responsible for the red coloration of the dragon fruit
peel [25]. The storage of dragon fruit under ambient conditions leads to the degradation
of this pigment, resulting in discoloration and browning, primarily due to its sensitivity
to light and temperature variations [26]. This phenomenon of color degradation under
ambient storage has also been observed in other fruits, such as banana [27], mandarin [28],
and pomegranate [29].
3.1.2. Firmness
Firmness is a critical quality parameter in shelf-life evaluation. In fruits and vegeta-
bles, it is not only related to textural and freshness of the fresh produce, but structural
integrity affected by enzymatic activity, moisture loss, cell wall degradation, etc. [30]
These processes will soften the product, leading to poor consumer perception and reduced
marketability [31]. The evaluation of changes in firmness of both Australian-grown and
the imported dragon fruit during shelf-life stored under ambient conditions were con-
ducted (Figure 4).
Figure 4. Changes in the firmness of dragon fruit stored under ambient conditions during its shelf-
life. (a) Changes in the firmness of white-flesh dragon fruit during shelf-life; (b) changes in the firm-
ness of red-flesh dragon fruit during shelf-life. QLDW, Queensland-grown white-flesh dragon fruit;
NTW: Northern Territory-grown white-flesh dragon fruit; OverseasW, overseas-grown white-flesh
dragon fruit; QLDR, Queensland-grown red-flesh dragon fruit; OverseasR, overseas-grown red-
flesh dragon fruit.
An overall descending trend in firmness was observed across all groups. For the
white-flesh dragon fruits, OverseasW exhibited the highest firmness throughout its shelf-
life, starting at 16.45 ± 3.44 N
Max
on day 2 and decreasing to 13.46 ± 1.09 N
Max
on day 8. This
was followed by NTW, which ranged from 12.69 ± 1.95 N
Max
on day 4 to 11.26 ± 0.51 N
Max
on day 8, and QLDW, which started at 11.34 ± 2.26 N
Max
on day 2 and dropped to 8.54 ±
1.76 N
Max
on day 10. Similarly, imported red-flesh dragon fruit maintained higher firmness
than QLD-grown throughout its shelf-life, with values ranging from 13.99 ± 1.09 N
Max
to
10.89 ± 0.89 N
Max
and from 9.78 ± 1.27 N
Max
to 8.35 ± 1.06 N
Max
, respectively. These results
surpass those reported by Lata et al. [21] for fruit stored under similar conditions in India,
where white-flesh fruit firmness ranged from 10.20 N on day 2 to 8.73 N on day 7, and
red-flesh fruit firmness ranged from 7.55 N on day 2 and 5.10 N on day 7. Similar decreases
Figure 4. Changes in the firmness of dragon fruit stored under ambient conditions during its shelf-
life. (a) Changes in the firmness of white-flesh dragon fruit during shelf-life; (b) changes in the
firmness of red-flesh dragon fruit during shelf-life. QLDW, Queensland-grown white-flesh dragon
fruit; NTW: Northern Territory-grown white-flesh dragon fruit; OverseasW, overseas-grown white-
flesh dragon fruit; QLDR, Queensland-grown red-flesh dragon fruit; OverseasR, overseas-grown
red-flesh dragon fruit.
An overall descending trend in firmness was observed across all groups. For the
white-flesh dragon fruits, OverseasW exhibited the highest firmness throughout its shelf-
life, starting at 16.45
±
3.44 N
Max
on day 2 and decreasing to 13.46
±
1.09 N
Max
on
day 8. This was followed by NTW, which ranged from 12.69
±
1.95 N
Max
on day 4 to
11.26 ±0.51 NMax
on day 8, and QLDW, which started at 11.34
±
2.26 N
Max
on day 2 and
dropped to
8.54 ±1.76 NMax
on day 10. Similarly, imported red-flesh dragon fruit main-
tained higher firmness than QLD-grown throughout its shelf-life, with values ranging from
13.99 ±1.09 NMax
to
10.89 ±0.89 NMax
and from 9.78
±
1.27 N
Max
to
8.35 ±1.06 NMax
,
respectively. These results surpass those reported by Lata et al. [
21
] for fruit stored under
similar conditions in India, where white-flesh fruit firmness ranged from 10.20 N on day 2
to 8.73 N on day 7, and red-flesh fruit firmness ranged from 7.55 N on day 2 and 5.10 N on
day 7. Similar decreases for fruits stored under ambient conditions have also been observed
in mango [32] and lemon [33].
The values of firmness serve as critical insights into the freshness, quality, and mar-
ketability of fruits. A higher value often indicates that the structural integrity of the fruit is
maintained, which correlates with lower enzymatic activity and less cell wall degradation,
thereby reduced the potential of spoilage [
31
]. High value is also associated with a reduced
risk of mechanical damage during handling and transportation [
34
]. For both white- and
red-flesh dragon fruits, the imported fruits may retain better structural integrity than the
Australian-grown fruits, resulting in less enzymatic activity and a reduced potential for
spoilage and mechanical damage during handling.
The firmness of both imported white- and red-flesh dragon fruits experienced a more
rapid decrease throughout shelf-life compared to the Australian-grown fruit. This may
be because the overseas fruits were transported under refrigerated conditions to prevent
quality loss during long-distance transportation. The suppressed enzymatic activities in
fruits under refrigerated conditions can be accelerated when the fruits are removed to
ambient conditions, resulting in a rapid decrease in firmness [35].
The higher firmness values of imported dragon fruit compared to Australian-grown
dragon fruit are likely because the overseas growers often harvest fruits earlier. Firmness
of dragon fruit tends to be higher at earlier maturity stage [
36
] and the structural integrity
of dragon fruit is preserved during long periods of transportation and storage [
37
]. Unlike
Horticulturae 2024,10, 1048 10 of 30
dragon fruits from the overseas, Australian-grown dragon fruits are often harvested at
a later maturity stage to maximize the marketability for local consumers, focusing on
appearance, taste, and overall quality.
3.1.3. Weight Loss
Weight loss is a critical parameter in evaluating the shelf-life of fresh produce, signifi-
cantly affecting overall quality. Since fruits are typically sold by weight, substantial weight
loss during shelf-life can lead to reduced marketability [
38
]. The weight loss in Australian-
grown and imported dragon fruits during shelf-life is shown in Figure 5, indicating a
general increasing trend across all groups. Imported fruits exhibited the highest weight loss
throughout shelf-life for both white- and red-flesh varieties, starting at
2.36 ±0.84%
on day
4 and increasing to 6.27
±
1.52% on day 8 for white-flesh fruits, and from 2.71
±
1.03% on
day 4 to 7.31
±
1.32% on day 8 for red-flesh fruits. Queensland-grown (QLD) white-flesh
fruits demonstrated higher weight loss than Northern Territory-grown (NT) white-flesh
fruits throughout the shelf-life, ranging from 1.33
±
0.42% (day 4) to 4.01
±
0.84% (day
10) and from 1.19
±
0.17% (day 6) to 2.41
±
0.28% (day 8), respectively. The QLD-grown
red-flesh variety showed weight loss from 2.71
±
1.03% on day 4 to 5.70
±
1.88% on day 8.
These findings are consistent with similar research on Indian-grown dragon fruit conducted
by Lata et al. [21].
Horticulturae 2024, 10, x FOR PEER REVIEW 11 of 31
Figure 5. Weight loss of dragon fruit during shelf-life stored under ambient conditions. (a) Weight
loss of white-flesh dragon fruit during shelf-life; (b) weight loss of red-flesh dragon fruit during
shelf-life. QLDW, Queensland-grown white-flesh dragon fruit; NTW: Northern Territory-grown
white-flesh dragon fruit; OverseasW, overseas-grown white-flesh dragon fruit; QLDR, Queensland-
grown red-flesh dragon fruit; OverseasR, overseas-grown red-flesh dragon fruit.
Weight loss primarily reflects the moisture loss of fresh produce during respiration
and transpiration [38]. This water loss causes significant reductions in cell turgor pressure,
leading to decreased firmness and a shriveled appearance [37]. Dehydration not only con-
centrates nutrients such as sugars but also increases oxidative stress, which can result in
the decline of essential nutrients, including vitamins and volatile compounds responsible
for odor and flavor [39]. Additionally, moisture loss can impact the activity of enzymes
like polyphenol oxidase (PPO), which may oxidize phenolic compounds, thereby reduc-
ing their antioxidant capacities [39]. Other enzymes, such as pectinase [40] and beta-glu-
cosidase [41], play a pivotal role in the hydrolysis and degradation of polysaccharides and
other cellular components during dehydration. Consequently, higher weight loss
throughout the shelf-life suggests that imported white- and red-flesh dragon fruits may
experience accelerated deterioration and shortened shelf-life under ambient conditions
compared to Australian-grown fruits. Higher weight loss also implies that imported fruits
are exposed to greater oxidative stress, potentially reducing their visual quality and nu-
tritional value.
3.1.4. TSS (°Brix)
The total soluble solids (TSS) content is an indicator of the concentration of the solu-
ble solids (mainly sugar contents) in fruit juice, serving as indicator of sugar content, in
other words, sweetness [39]. Changes of TSS in Australian-grown and imported dragon
fruit during shelf-life under ambient conditions are shown in Figure 6.
Figure 5. Weight loss of dragon fruit during shelf-life stored under ambient conditions. (a) Weight
loss of white-flesh dragon fruit during shelf-life; (b) weight loss of red-flesh dragon fruit during
shelf-life. QLDW, Queensland-grown white-flesh dragon fruit; NTW: Northern Territory-grown
white-flesh dragon fruit; OverseasW, overseas-grown white-flesh dragon fruit; QLDR, Queensland-
grown red-flesh dragon fruit; OverseasR, overseas-grown red-flesh dragon fruit.
Weight loss primarily reflects the moisture loss of fresh produce during respiration
and transpiration [
38
]. This water loss causes significant reductions in cell turgor pressure,
leading to decreased firmness and a shriveled appearance [
37
]. Dehydration not only
concentrates nutrients such as sugars but also increases oxidative stress, which can result in
the decline of essential nutrients, including vitamins and volatile compounds responsible
for odor and flavor [
39
]. Additionally, moisture loss can impact the activity of enzymes like
polyphenol oxidase (PPO), which may oxidize phenolic compounds, thereby reducing their
antioxidant capacities [
39
]. Other enzymes, such as pectinase [
40
] and beta-glucosidase [
41
],
play a pivotal role in the hydrolysis and degradation of polysaccharides and other cellular
components during dehydration. Consequently, higher weight loss throughout the shelf-
life suggests that imported white- and red-flesh dragon fruits may experience accelerated
deterioration and shortened shelf-life under ambient conditions compared to Australian-
Horticulturae 2024,10, 1048 11 of 30
grown fruits. Higher weight loss also implies that imported fruits are exposed to greater
oxidative stress, potentially reducing their visual quality and nutritional value.
3.1.4. TSS (◦Brix)
The total soluble solids (TSS) content is an indicator of the concentration of the soluble
solids (mainly sugar contents) in fruit juice, serving as indicator of sugar content, in other
words, sweetness [
39
]. Changes of TSS in Australian-grown and imported dragon fruit
during shelf-life under ambient conditions are shown in Figure 6.
Horticulturae 2024, 10, x FOR PEER REVIEW 12 of 31
Figure 6. Changes in the total soluble solids (TSS) of dragon fruit stored under ambient conditions
during its shelf-life. (a) Changes in the TSS of white-flesh dragon fruit during shelf-life; (b) changes
in the TSS of red-flesh dragon fruit during shelf-life. QLDW, Queensland-grown white-flesh dragon
fruit; NTW: Northern Territory-grown white-flesh dragon fruit; OverseasW, overseas-grown white-
flesh dragon fruit; QLDR, Queensland-grown red-flesh dragon fruit; OverseasR, overseas-grown
red-flesh dragon fruit.
Figure 6 shows the changes in total soluble solids (TSS) of Australian-grown and im-
ported dragon fruit over the course of their shelf-life when stored at ambient temperature.
A slow decreasing trend was observed across all groups. This reduction in TSS under am-
bient storage conditions has been observed in other fruits, such as strawberries [42], pa-
payas [43], and peaches [44]. Throughout the shelf-life, both imported white- and red-
flesh dragon fruits exhibited lower TSS values compared to Australian-grown fruits. For
white-flesh fruits, the TSS started at 13.92 ± 0.57% on day 2 and decreased to 13.13 ± 0.59%
on day 8, while red-flesh fruits began at 14.92 ± 1.22% on day 2 and dropped to 14.17 ±
1.50% on day 8. Among the Australian-grown white-flesh dragon fruits, those grown in
Queensland (QLD) showed higher TSS throughout the shelf-life, ranging from 14.43 ±
0.83% on day 2 to 13.11 ± 1.22% on day 10. Northern Territory (NT)-grown white-flesh
dragon fruits ranged from 14.37 ± 0.29% on day 4 to 13.13 ± 0.35% on day 8. For QLD-
grown red-flesh varieties, the TSS started at 14.92 ± 1.22% on day 2 and dropped to 14.17
± 1.50% on day 8. These findings are consistent with similar research on Indian-grown
dragon fruit conducted by Lata et al. [21]. The results from this study indicate that Aus-
tralian-grown dragon fruits maintain a higher sweetness level compared to imported
dragon fruits throughout their shelf-life under ambient conditions.
3.1.5. pH
Monitoring pH is essential in evaluating the shelf-life of fresh produce, as it is closely
related to the growth of bacteria, yeast, and mold [39]. Additionally, pH serves as an indi-
cator of the stability of health-promoting nutrients and pigments, such as betacyanin [45].
Figure 7 illustrates the pH changes in Australian-grown and imported dragon fruits dur-
ing shelf-life under ambient conditions. An overall increasing trend was observed across
all groups. Throughout the shelf-life, both imported white- and red-flesh dragon fruits
exhibited lower pH values compared to Australian-grown fruits. For white-flesh fruits,
the pH began at 4.42 ± 0.03 on day 2 and rose to 5.09 ± 0.06 by day 8, while red-flesh fruits
started at 4.86 ± 0.02 on day 2 and increased to 5.53 ± 0.02 by day 8. Among the Australian-
grown white-flesh dragon fruits, those cultivated in Queensland (QLD) maintained higher
pH levels throughout the shelf-life, ranging from 4.56 ± 0.22 on day 2 to 5.45 ± 0.19 by day
10, whereas Northern Territory (NT)-grown fruits ranged from 4.61 ± 0.12 on day 4 to 5.19
Figure 6. Changes in the total soluble solids (TSS) of dragon fruit stored under ambient conditions
during its shelf-life. (a) Changes in the TSS of white-flesh dragon fruit during shelf-life; (b) changes
in the TSS of red-flesh dragon fruit during shelf-life. QLDW, Queensland-grown white-flesh dragon
fruit; NTW: Northern Territory-grown white-flesh dragon fruit; OverseasW, overseas-grown white-
flesh dragon fruit; QLDR, Queensland-grown red-flesh dragon fruit; OverseasR, overseas-grown
red-flesh dragon fruit.
Figure 6shows the changes in total soluble solids (TSS) of Australian-grown and im-
ported dragon fruit over the course of their shelf-life when stored at ambient temperature. A
slow decreasing trend was observed across all groups. This reduction in TSS under ambient
storage conditions has been observed in other fruits, such as strawberries [
42
], papayas [
43
],
and peaches [
44
]. Throughout the shelf-life, both imported white- and red-flesh dragon
fruits exhibited lower TSS values compared to Australian-grown fruits. For white-flesh
fruits, the TSS started at 13.92
±
0.57% on day 2 and decreased to
13.13 ±0.59%
on day 8,
while red-flesh fruits began at 14.92
±
1.22% on day 2 and dropped to
14.17 ±1.50%
on
day 8. Among the Australian-grown white-flesh dragon fruits, those grown in Queensland
(QLD) showed higher TSS throughout the shelf-life, ranging from 14.43
±
0.83% on day 2 to
13.11
±
1.22% on day 10. Northern Territory (NT)-grown white-flesh dragon fruits ranged
from 14.37
±
0.29% on day 4 to 13.13
±
0.35% on day 8. For QLD-grown red-flesh varieties,
the TSS started at 14.92
±
1.22% on day 2 and dropped to 14.17
±
1.50% on day 8. These
findings are consistent with similar research on Indian-grown dragon fruit conducted by
Lata et al. [
21
]. The results from this study indicate that Australian-grown dragon fruits
maintain a higher sweetness level compared to imported dragon fruits throughout their
shelf-life under ambient conditions.
3.1.5. pH
Monitoring pH is essential in evaluating the shelf-life of fresh produce, as it is closely
related to the growth of bacteria, yeast, and mold [
39
]. Additionally, pH serves as an indi-
cator of the stability of health-promoting nutrients and pigments, such as betacyanin [
45
].
Figure 7illustrates the pH changes in Australian-grown and imported dragon fruits during
Horticulturae 2024,10, 1048 12 of 30
shelf-life under ambient conditions. An overall increasing trend was observed across all
groups. Throughout the shelf-life, both imported white- and red-flesh dragon fruits exhib-
ited lower pH values compared to Australian-grown fruits. For white-flesh fruits, the pH
began at 4.42
±
0.03 on day 2 and rose to 5.09
±
0.06 by day 8, while red-flesh fruits started
at 4.86
±
0.02 on day 2 and increased to 5.53
±
0.02 by day 8. Among the Australian-grown
white-flesh dragon fruits, those cultivated in Queensland (QLD) maintained higher pH
levels throughout the shelf-life, ranging from 4.56
±
0.22 on day 2 to 5.45
±
0.19 by day
10, whereas Northern Territory (NT)-grown fruits ranged from 4.61
±
0.12 on day 4 to
5.19
±
0.06 by day 8. For QLD-grown red-flesh varieties, the pH started at 4.86
±
0.02
on day 2 and increased to 5.53
±
0.02 by day 8. The results from this study suggest that
imported dragon fruits have a reduced capacity to maintain their nutritional levels and
are more susceptible to spoilage when stored under ambient conditions. These results are
consistent with similar research on Indian-grown dragon fruit conducted by Lata et al. [
21
].
A similar increasing trend of pH has also been reported in other fruits such as litchi [
46
]
and mango [47].
Horticulturae 2024, 10, x FOR PEER REVIEW 13 of 31
± 0.06 by day 8. For QLD-grown red-flesh varieties, the pH started at 4.86 ± 0.02 on day 2
and increased to 5.53 ± 0.02 by day 8. The results from this study suggest that imported
dragon fruits have a reduced capacity to maintain their nutritional levels and are more
susceptible to spoilage when stored under ambient conditions. These results are consistent
with similar research on Indian-grown dragon fruit conducted by Lata et al. [21]. A similar
increasing trend of pH has also been reported in other fruits such as litchi [46] and mango
[47].
Several processes occur within fruits during storage that contribute to a rise in pH.
Under ambient storage conditions, enzymatic activity increases, and enzymes including
citrate synthase (CS) and malic enzyme (ME) [48] convert organic acid such as citric and
malic acid into sugars and other neutral compounds [49]. Additionally, the fruit respira-
tion process can also breaks acids into carbon dioxide and water, leading to a decrease in
acidity, and thus an increase in the pH [50].
Figure 7. Changes in the pH of dragon fruit stored under ambient conditions during its shelf-life.
(a) Changes in the pH of white-flesh dragon fruit during shelf-life; (b) changes in the pH of red-flesh
dragon fruit during shelf-life. QLDW, Queensland-grown white-flesh dragon fruit; NTW: Northern
Territory-grown white-flesh dragon fruit; OverseasW, overseas-grown white-flesh dragon fruit;
QLDR, Queensland-grown red-flesh dragon fruit; OverseasR, overseas-grown red-flesh dragon
fruit.
3.1.6. TA
Titratable acidity (TA) is crucial in evaluating the shelf-life of fruits, as higher acidity
levels can inhibit microbial growth, thereby reducing the risk of spoilage [51]. Changes in
TA in Australian-grown and imported dragon fruit during shelf-life under ambient con-
ditions are presented in Figure 8. An overall declining trend can be observed across all
groups, consistent with findings from similar studies on Indian-grown dragon fruit by
Lata et al. and other fruits such as plums [52], apples [53], and pears [54]. For white-flesh
dragon fruits, Queensland-grown (QLDW) started with a TA value of 0.62 ± 0.23% on day
2, declining to 0.24 ± 0.01% by day 10. In comparison, the imported white-flesh fruits
(OverseasW) began at 0.61 ± 0.02% on day 2 and decreased to 0.29 ± 0.01% by day 8. The
Northern Territory-grown white-flesh dragon fruits (NTW) showed TA values of 0.39 ±
0.02% on day 4, reducing to 0.30 ± 0.04% by day 8. For red-flesh dragon fruits, Queensland-
grown (QLDR) exhibited a decrease from 0.38 ± 0.13% on day 2 to 0.23 ± 0.07% by day 8,
whereas the imported red-flesh dragon fruits (OverseasR) started at 0.46 ± 0.01% on day
2 and declined to 0.19 ± 0.03% by day 8. Notably, Australian-grown dragon fruits main-
tained higher TA levels after day 4 compared to imported fruits, suggesting beer acidity
retention and potentially fresher taste.
Figure 7. Changes in the pH of dragon fruit stored under ambient conditions during its shelf-life.
(a) Changes in the pH of white-flesh dragon fruit during shelf-life; (b) changes in the pH of red-flesh
dragon fruit during shelf-life. QLDW, Queensland-grown white-flesh dragon fruit; NTW: Northern
Territory-grown white-flesh dragon fruit; OverseasW, overseas-grown white-flesh dragon fruit;
QLDR, Queensland-grown red-flesh dragon fruit; OverseasR, overseas-grown red-flesh dragon fruit.
Several processes occur within fruits during storage that contribute to a rise in pH.
Under ambient storage conditions, enzymatic activity increases, and enzymes including
citrate synthase (CS) and malic enzyme (ME) [
48
] convert organic acid such as citric and
malic acid into sugars and other neutral compounds [
49
]. Additionally, the fruit respiration
process can also breaks acids into carbon dioxide and water, leading to a decrease in acidity,
and thus an increase in the pH [50].
3.1.6. TA
Titratable acidity (TA) is crucial in evaluating the shelf-life of fruits, as higher acidity
levels can inhibit microbial growth, thereby reducing the risk of spoilage [
51
]. Changes
in TA in Australian-grown and imported dragon fruit during shelf-life under ambient
conditions are presented in Figure 8. An overall declining trend can be observed across
all groups, consistent with findings from similar studies on Indian-grown dragon fruit by
Lata et al. and other fruits such as plums [
52
], apples [
53
], and pears [
54
]. For white-flesh
dragon fruits, Queensland-grown (QLDW) started with a TA value of 0.62
±
0.23% on
day 2, declining to 0.24
±
0.01% by day 10. In comparison, the imported white-flesh
fruits (OverseasW) began at 0.61
±
0.02% on day 2 and decreased to 0.29
±
0.01% by day
Horticulturae 2024,10, 1048 13 of 30
8. The Northern Territory-grown white-flesh dragon fruits (NTW) showed TA values of
0.39 ±0.02%
on day 4, reducing to 0.30
±
0.04% by day 8. For red-flesh dragon fruits,
Queensland-grown (QLDR) exhibited a decrease from 0.38
±
0.13% on day 2 to
0.23 ±0.07%
by day 8, whereas the imported red-flesh dragon fruits (OverseasR) started at 0.46
±
0.01%
on day 2 and declined to 0.19
±
0.03% by day 8. Notably, Australian-grown dragon fruits
maintained higher TA levels after day 4 compared to imported fruits, suggesting better
acidity retention and potentially fresher taste.
Horticulturae 2024, 10, x FOR PEER REVIEW 14 of 31
Figure 8. Changes in the titratable acidity (TA) of dragon fruit stored under ambient conditions
during its shelf-life. (a) Changes in the TA of white-flesh dragon fruit during shelf-life; (b) changes
in the TA of red-flesh dragon fruit during shelf-life. QLDW, Queensland-grown white-flesh dragon
fruit; NTW: Northern Territory-grown white-flesh dragon fruit; OverseasW, overseas-grown white-
flesh dragon fruit; QLDR, Queensland-grown red-flesh dragon fruit; OverseasR, overseas-grown
red-flesh dragon fruit.
The initial higher TA in imported dragon fruits followed by a rapid decrease from
day 4 to day 6 is likely due to refrigerated transportation, which slows down metabolism
and enzymatic activities, resulting in lower organic acid consumption [55]. In contrast,
Australian-grown dragon fruits experienced relatively consistent ambient conditions
post-harvest, leading to a gradual decrease in TA. This temperature effect has also been
observed in other fruits such as aronia berry [56] and strawberry [57]. Similar to pH, the
mature stage of the dragon fruit also significantly impacts TA [58]. Zitha et al. reported
significant TA changes occurred in red-flesh dragon fruit, ranging from 1.28% to 0.20% of
malic acid from 28 to 42 days after anthesis [18].
3.1.7. Overall Shelf-Life
The shelf-life of dragon fruits was assessed by counting the number of days from the
receipt date until the samples no longer met the criteria for Class II fruit (see Section 2.3)
according to the Codex Alimentarius Standard for dragon fruit (CXS 237-2003). For white-
flesh dragon fruits, freshly received Australian-grown fruit has an average of 9 days of
shelf-life under ambient conditions, whereas freshly received imported fruit has an aver-
age of 8 days of shelf-life. For the red-flesh variety, the shelf-life is identical for both Aus-
tralian-grown and imported dragon fruit, at 8 days after being freshly harvested or re-
ceived. The slightly longer shelf-life observed in Australian-grown white-flesh dragon
fruit is likely caused by higher TSS and TA at the beginning and lower weight loss (see
Table A1) during storage (Table 2).
Table 2. Overall shelf-life of Australian-grown and imported dragon fruit stored under ambient
conditions.
Days after Being Freshly Received
White-flesh dragon fruit
Australian-grown 9
Imported 8
Red-flesh dragon fruit
Australian-grown 8
Figure 8. Changes in the titratable acidity (TA) of dragon fruit stored under ambient conditions
during its shelf-life. (a) Changes in the TA of white-flesh dragon fruit during shelf-life; (b) changes in
the TA of red-flesh dragon fruit during shelf-life. QLDW, Queensland-grown white-flesh dragon fruit;
NTW: Northern Territory-grown white-flesh dragon fruit; OverseasW, overseas-grown white-flesh
dragon fruit; QLDR, Queensland-grown red-flesh dragon fruit; OverseasR, overseas-grown red-flesh
dragon fruit.
The initial higher TA in imported dragon fruits followed by a rapid decrease from
day 4 to day 6 is likely due to refrigerated transportation, which slows down metabolism
and enzymatic activities, resulting in lower organic acid consumption [
55
]. In contrast,
Australian-grown dragon fruits experienced relatively consistent ambient conditions post-
harvest, leading to a gradual decrease in TA. This temperature effect has also been observed
in other fruits such as aronia berry [
56
] and strawberry [
57
]. Similar to pH, the mature
stage of the dragon fruit also significantly impacts TA [
58
]. Zitha et al. reported significant
TA changes occurred in red-flesh dragon fruit, ranging from 1.28% to 0.20% of malic acid
from 28 to 42 days after anthesis [18].
3.1.7. Overall Shelf-Life
The shelf-life of dragon fruits was assessed by counting the number of days from the
receipt date until the samples no longer met the criteria for Class II fruit (see Section 2.3)
according to the Codex Alimentarius Standard for dragon fruit (CXS 237-2003). For white-
flesh dragon fruits, freshly received Australian-grown fruit has an average of 9 days of
shelf-life under ambient conditions, whereas freshly received imported fruit has an average
of 8 days of shelf-life. For the red-flesh variety, the shelf-life is identical for both Australian-
grown and imported dragon fruit, at 8 days after being freshly harvested or received. The
slightly longer shelf-life observed in Australian-grown white-flesh dragon fruit is likely
caused by higher TSS and TA at the beginning and lower weight loss (see Table A1) during
storage (Table 2).
Horticulturae 2024,10, 1048 14 of 30
Table 2. Overall shelf-life of Australian-grown and imported dragon fruit stored under ambient
conditions.
Days after Being Freshly Received
White-flesh dragon fruit
Australian-grown 9
Imported 8
Red-flesh dragon fruit
Australian-grown 8
Imported 8
Recent studies have explored various postharvest techniques to extend the shelf-life
of dragon fruit, encompassing physical, chemical, and biological preservation methods.
Lau et al. reported that white-flesh dragon fruit treated with hot water at 55
◦
C for 15 min
and subsequently bagged in sealed, hole-free polyethylene plastic bags maintained their
physical appearance significantly better and exhibited a much lower incidence of disease
infestation for up to 21 days in chilled storage, compared to those stored under similar
conditions without heat treatment [
59
]. Wu et al. applied blue light to red-flesh dragon
fruit and found that this treatment slowed down the decrease in total soluble solids (TSS),
titratable acidity (TA), and antioxidant activities during storage [
60
]. Calcium chloride
treatment has been reported by Awang et al. [
61
] and Ghani et al. [
62
] as an efficient chemical
approach to prolong the shelf-life of red-flesh dragon fruit. This treatment significantly
increased the firmness and slow down the decline in pH, TSS, and TA of the fruit during
storage. Chitosan coating has been utilized for decay prevention in postharvest fruits and
vegetables. Prashanth et al. [
63
] indicated that in dragon fruit treated with 4% chitosan
coating, the trends of weight loss, firmness, TSS and TA were significantly slowed down,
demonstrating decay inhibition capacity. Biological approaches, such as plant essential
oil treatment, have also been investigated. Chaemsanit et al. [
64
] reported that applying
700
µ
L/L of peppermint oil on coconut shell granular activated carbon inhibited 100% of
decay mold and fungi during storage at 25
◦
C. These techniques can be recommended
for postharvest handling of dragon fruit in Australia to enhance competitiveness with
imported dragon fruits.
3.2. Antioxidant Activities
Dragon fruit is known for its rich antioxidant contents, which plays a critical role
in protecting cells from oxidative stress and free radical-induced damage [
65
]. These
antioxidants are associated with numerous health benefits such as anti-inflammatory, anti-
cancer, and anti-obesity properties [
25
]. In this study, the analysis of antioxidant activities
during shelf-life of dragon fruits includes measurements of total phenolic content (TPC),
total flavonoid content (TFC), ferric reducing antioxidant power (FRAP), cupric reducing
antioxidant capacity (CUPRAC), total betalain content (TBC, applicable to red-flesh fruits
only), and total anthocyanin content (TAC, applicable to red-flesh fruits only). Detailed
data for these analyses are provided in Tables A2 and A3 in Appendix A. It is worth noting
that different concentration level of antioxidative compounds presented in dragon fruits
depends on the cultivar and factors affecting cultivation and harvest, such as soil, climate
conditions, irrigation, fertilization, etc. [66–70].
3.2.1. Results
The bar graph in Figure 9illustrates the total phenolic content (TPC), total flavonoid
content (TFC), ferric reducing antioxidant power (FRAP), cupric reducing antioxidant
capacity (CUPRAC), total betalain content (TBC), and total anthocyanin content (TAC) in
Australian-grown and imported dragon fruits throughout their shelf-life under ambient
conditions. An overall decline trend can be observed across all groups. This decreasing
trend matches with previous similar study on Indian-grown dragon fruit reported by Lata
et al. [21].
Horticulturae 2024,10, 1048 15 of 30
The total phenolic content (TPC) in Australian-grown and imported dragon fruits through-
out their shelf-life under ambient conditions is exhibited in Figure 9a. Queensland-grown
white-flesh dragon fruits (QLDW) started with a TPC of
168.94 ±5.86 mg GAE/100 g FW
on
day 2, decreasing to 132.84
±
8.74 mg GAE/100 g FW by day 10. Northern Territory-
grown white-flesh (NTW) fruits had a TPC of 164.95
±
1.66 mg GAE/100 g FW on day
4, reducing to 143.71
±
1.23 mg GAE/100 g FW by day 8. There is no significant differ-
ence (p> 0.05) in TPC between QLDW and NTW across shelf-life. In contrast, the im-
ported white-flesh dragon fruits (OverseasW) began at
150.25 ±0.72 mg GAE/100 g FW
on day 2 and dropped to 121.31
±
1.03 mg GAE/100 g FW by day 8. For the red-flesh
varieties, Queensland-grown (QLDR) fruits exhibited the highest TPC values, starting at
303.70 ±10.44 mg GAE/100 g FW
on day 2 and slightly decreasing to 285.44
±
7.48 mg
GAE/100 g FW by day 8. The imported red-flesh fruits (OverseasR) started at 273.98
±
6.41 mg
GAE/100 g FW on day 2 and decreased to 255.04
±
4.38 mg GAE/100 g FW by day 8. Ob-
servation of this study indicates that red-flesh dragon fruit has higher TPC than white-flesh
fruit, which is identical to the similar study on Indian-grown dragon fruit study conducted
by Lata et al. [
21
]. Overall, the data suggests that Australian-grown dragon fruits maintain
higher TPC levels throughout their shelf-life compared to imported fruits. This indicates
better retention of antioxidant properties and potentially higher nutritional quality. In
addition, Zakaria et al. [
71
] reported a TPC value of 11.47
±
0.01 mg GAE/100 g FW in
white-flesh and 20.50
±
0.02 mg GAE/100 g FW in red-flesh dragon fruit from Malaysia,
indicating Australian-grown dragon fruits have higher concentration level of total phe-
nolics. According to study conducted by Arivalagan et al. [
72
], dragon fruits from India
also exhibited lower TPC results, with 24.8
±
0.9 mg GAE/100 g FW in white-flesh and
48.3 ±3.9 mg GAE/100 g FW in the red-flesh dragon fruit.
Horticulturae 2024, 10, x FOR PEER REVIEW 17 of 31
started with a FRAP value of 163.19 ± 6.61 mg TE/100 g FW on day 2, which decreased to
128.81 ± 4.80 mg TE/100 g FW by day 10. Comparatively, the imported white-flesh dragon
fruits (OverseasW) began at 145.37 ± 1.23 mg TE/100 g FW on day 2 and dropped to 123.32
± 1.35 mg TE/100 g FW by day 8, consistently showing lower FRAP values than QLDW.
Northern T