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Postharvest physiology of Corchorus olitorius baby leaf growing with different nutrient solutions

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The storage at 4°C in darkness of Corchorus olitorius L. baby leaf as a ready-to-eat (RTE) vegetable has been studied for the first time. C. olitorius was cultivated in a floating system with different nutrient solutions: standard (NS100%) or halved (NS50%). Several quality factors of this produce were evaluated during season (spring, summer, autumn) considering treatments and days of storage in order to understand the interactions. During storage, sucrose, total and reducing sugars, nitrate, phenolic compounds, anthocyanins, chlorophylls, and carotenoids were measured. Results showed that chlorophylls decreased by 20–30% for both treatments and the changes were statistically different during spring. Carotenoid content did not change until the end of the storage and values ranged from 0.60 g kg⁻¹ to 0.75 g kg⁻¹ fresh weight depending on the season. Phenols and anthocyanins decreased within 10 days: −40% of phenols and −50% of anthocyanins, respectively. No interaction between nutrient solutions and storage behaviour was reported. Thus, C. olitorius resulted to be a good source of nutraceutical compounds and it is able to maintain these components during storage. Moreover, the public interest in regards to nutritional and healthy food is rapidly increasing, promoting the discovery of new vegetables, like C. olitorius, for RTE commercialisation.
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Postharvest physiology of Corchorus olitorius baby
leaf growing with different nutrient solutions
Andrea Giro & Antonio Ferrante
To cite this article: Andrea Giro & Antonio Ferrante (2017): Postharvest physiology of Corchorus
olitorius baby leaf growing with different nutrient solutions, The Journal of Horticultural Science and
Biotechnology, DOI: 10.1080/14620316.2017.1382313
To link to this article: http://dx.doi.org/10.1080/14620316.2017.1382313
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Postharvest physiology of Corchorus olitorius baby leaf growing with different
nutrient solutions
Andrea Giro and Antonio Ferrante
Department of Agricultural and Environmental Sciences - Production, Landscape, Agro-energy, Università degli Studi di Milano, Milano,
Italy
ABSTRACT
The storage at 4°C in darkness of Corchorus olitorius L. baby leaf as a ready-to-eat (RTE)
vegetable has been studied for the first time. C. olitorius was cultivated in a floating system
with different nutrient solutions: standard (NS100%) or halved (NS50%). Several quality
factors of this produce were evaluated during season (spring, summer, autumn) considering
treatments and days of storage in order to understand the interactions. During storage,
sucrose, total and reducing sugars, nitrate, phenolic compounds, anthocyanins, chlorophylls,
and carotenoids were measured. Results showed that chlorophylls decreased by 2030% for
both treatments and the changes were statistically different during spring. Carotenoid con-
tent did not change until the end of the storage and values ranged from 0.60 g kg
1
to 0.75 g
kg
1
fresh weight depending on the season. Phenols and anthocyanins decreased within
10 days: 40% of phenols and 50% of anthocyanins, respectively. No interaction between
nutrient solutions and storage behaviour was reported. Thus, C. olitorius resulted to be a good
source of nutraceutical compounds and it is able to maintain these components during
storage. Moreover, the public interest in regards to nutritional and healthy food is rapidly
increasing, promoting the discovery of new vegetables, like C. olitorius, for RTE
commercialisation.
ARTICLE HISTORY
Accepted 14 September 2017
KEYWORDS
RTE salad; phenol content;
storage; ethnic vegetable;
African vegetable
Introduction
Corchorus olitorius is considered a traditional leafy
vegetable by the FAO in many developing countries.
The increase of public interest in nutritional and
healthy food has been rapidly increasing worldwide
(Cawley et al., 2015). Therefore, the identification of
new, potentially high-quality leafy vegetables has been
promoted by fresh cut industries, which are involved in
the processing and commercialisation of ready-to-eat
food. The C. olitorius, commonly known as jute or Jews
mallow, is grown as a leafy vegetable in tropical and
sub-tropical areas of Africa and Asia (Tanmoy et al.,
2015). It is cultivated for its potential benefits for
human health, given its high levels of nutritional com-
ponents such as phenols and carotenoids (Yan, Wang,
Chen, Zhuang, & Wang, 2013). It is also an important
source of amino acids, such as methionine (Freiberger
et al., 1998). Moreover, the jute leaves are excellent
sources of vitamin C, minerals, and sugars (Ogunlesi
et al., 2010). Innovative storage facilities are applied to
minimally process leafy vegetables, because of their
plant tissuesphysiological characteristics. These char-
acteristics are specific for each vegetable, requiring par-
ticular technologies for storage (Medina, Tudela,Marín,
Allende, & Gil, 2012). Preventing the diminishing of
quality parameters and the degradation of nutrient con-
tent is always a priority for the food industry and for
consumers (Tulio, Ose, Chachin, & Ueda, 2002).
However, consumers are prone to evaluating the fresh-
ness and taste of vegetables rather than their nutritional
content, although for a potential functional food like C.
olitorius, the retained nutrient content is a key factor.
Greenness, for example, is one of the first visual para-
meters evaluated by the consumer during the purchas-
ing of leafy vegetables, so much so that, the visual
appearance is considered the most important quality
index for commercialisation in supermarkets (Roura,
Davidovich, & Valle, 2000). However, health-oriented
consumers prefer to buy ready-to-eat (RTE) vegetables
as a source of phytochemicals and antioxidant com-
pounds, which can prevent stress-related diseases
(Cocetta, Baldassarre, Spinardi, & Ferrante, 2014). The
floating system technique allows for the control of the
nutrient supply and mineral content within the leaves.
Moreover, during storage, nutrients and bioactive com-
pounds might be affected by agronomic aspects
(Scuderi et al., 2011), as reported by Fallovo,
Rouphael, Rea, Battistelli, and Colla (2009). In fact,
nutrient solutions influenced several quality compo-
nents such as minerals, nitrates and chlorophyll
CONTACT Andrea Giro andrea.giro@unimi.it
Supplemental data for this article can be accessed here.
THE JOURNAL OF HORTICULTURAL SCIENCE AND BIOTECHNOLOGY, 2017
https://doi.org/10.1080/14620316.2017.1382313
© 2017 The Journal of Horticultural Science & Biotechnology Trust
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content. The aim of this work is to evaluate the post-
harvest performance of C. olitorius as baby leaf produce
for the fresh cut industry grown in two nutrient solu-
tions with different concentrations of nutrients. The
interaction between growing nutrient solutions and
the quality retained during storage has been studied
and characterised. This work seeks to evaluate if the
reduction of mineral concentrations in the nutrient
solution could influence the quality of the produce at
harvest and during storage. The cultivations have been
carried out in different seasons, in order to verify if the
results were consistent all year around.
Materials and methods
Plant material and growing system
An Egyptian accession of Jute (Corchorus olitorius
L.)wasgrownineighthydroponicfloatingsystem
modules. Seeds were directly sown on panels con-
taining perlite. Three cultivation cycles were per-
formed: two during spring and summer (from
March 2014 to April 2014 and from May 2014 to
June 2014) and one during autumn (from October
2014 to November 2014) in the greenhouse of the
University of Milan. Solar radiation and tempera-
ture were recorded throughout the entirety of the
growingcycles(suppl.Figures1and2).Inorderto
create a small floating system module, the panels
(20 x 15 cm) were placed on 12 L tanks (25 x 15 x
35 cm) after germination. Four modules of each
type of nutrient solution were used. The nutrient
solutions compared were: standard (NS100%) and
halved (NS50%) nutrient solutions. The macronu-
trients in the NS100% were expressed in mM (N-
NO
3
12; N-NH
4
3.8, P 2.8, K 3.8, Ca 3.5, Mg 1.4),
while in the NS50% the concentrations were
halved. The micronutrients expressed in µM (4.2
B, 2.1 Cu, 12 Mn, 1.4 Mo, 3.8 Zn) were the same in
both nutrient solutions. The quality of the jute
leaves was evaluated during 10 d of storage (0, 1,
3, 7, and 10 d) in a cold room at 4°C in dark
conditions. Forty g of C. olitorius leaves were
enclosed in plastic boxes and sampling was per-
formed in quadruplicates during their shelf-life.
Each day of sampling corresponded to one box
for both of the nutrient solutions.
Nitrate determinations
About 1 g of fresh, fully expanded young leaves was
ground in 5 mL of distilled water. The extracts were
centrifuged at 10,000 gfor 5 minutes. After centrifu-
gation, supernatant was collected for the colorimetric
determinations. Four biological replications were
analysed for each biochemical assay.
Nitrate content was determined in leaves using a
salicylic acid method (Cataldo, Maroon, Schrader&
Youngs, 1975). Twenty µL of samples were collected
and 80 µL (5% weight/volume) of salicylic acid in
concentrated sulphuric acid were added. After the
reaction, 3 mL of NaOH 1.5 N were added. Samples
were cooled at room temperature (25°C) for 15 min-
utes and then they were read at 410 nm using a
spectrophotometer (Evaluation 300 BB Thermo).
Nitrate concentrations were calculated using a cali-
bration standard curve.
Chlorophylls and carotenoids determination
Total chlorophylls and carotenoids were determined
using the spectrophotometer method. Three leaf disks
(5 mm diameter) from three different leaves were
randomly sampled, avoiding vascular tissue, and
5 mL of methanol (99.9%) was added to the disks
for the extraction. Samples were incubated in a dark
room at 4°C for 24 h, then the samples were read at
470, 652 and 665 nm. The chlorophyll and carotenoid
concentrations were determined using Lichtenthalers
formulas (1987).
Sucrose, reducing and total sugars determination
For the determination of sucrose, about 1 g of fresh
leaves was extracted by homogenisation in a mortar
with 5 mL of distilled water. The samples were centri-
fuged at 10,000 g for 5 min. The sucrose assay was
performed by mixing 0.2 mL of crude extract with
0.2 mL of 2 M NaOH and incubated in a water bath at
100°C for 10 min, then 1.5 mL hot resorcinol buffer
(containing 30% hydrochloric acid, 1.2 mM resorcinol,
4.1 mM thiourea 1.5 M acetic acid) was added to sam-
ples and incubated in a water bath at 80°C for another
10 min. After cooling at room temperature, the optical
density was determined spectrophotometrically at
500 nm, using a sucrose standard curve (0, 0.5, 1, 1.5
and 2 mM) (Rorem, Walker, & McCready, 1960).
The reducing sugar analysis was performed using
0.2 mL of crude extract that was added to 0.2 mL of
a solution containing 62.6 mM dinitrosalicylic acid
(DNS) and 1.52 M potassium sodium tartrate. The
reaction mixture was heated at 100°C for 5 min,
then 1.5 mL of distilled water was added and absor-
bance readings were taken at 530 nm. The reducing
sugars were expressed as glucose equivalent using a
glucose standard curve (0, 1, 2, 3 and 4 mM)
(Miller, 1959).
The total sugars were determined spectrophotome-
trically following the anthrone method (Yemm &
Willis, 1954) with slight modifications: the anthrone
reagent (10.3 mM) was prepared dissolving anthrone
in ice-cold 95%H
2
SO
4
. The reagent was left to stand for
3040 min before use, 0.5 mL leaf extract was placed on
2A. GIRO AND A. FERRANTE
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top of 2.5 mL of anthrone reagent incubated in ice for
5 min and then vortexed vigorously. The reactions were
heated to 95°C for 10 min and left to cool in ice.
Readings were performed at 620 nm. The calibration
curve was carried out using a glucose solution.
Phenolic compounds and anthocyanins
determination
Phenols were spectrophotometrically determined in
fresh samples following two different approaches: the
direct measure of the methanolic extract absorbance
at 320 nm (phenolic index) and the Folin-Ciocalteu
method (Lamuela-Raventos, 1999). Phenolic index
was expressed as ABS
320nm
g
1
, while total phenols
were measured using the Folin-Ciocalteu method and
expressed as g kg
1
gallic acid equivalent (GAE).
For the anthocyanins determination, samples of
frozen tissue (3050 mg) were ground in a pre-chilled
mortar and extracted into methanolic HCl (1%).
Samples were then incubated overnight at 4°C in
the dark. Samples were determined spectrophotome-
trically at 535 nm using Evaluation 300 BB Thermo
and quartz UV light cuvette. The concentration was
expressed in cyanidin-3-glucoside equivalents using
direct absorption (Klein & Hagen, 1961).
Statistical analyses
The data reported were ± standard errors of the mean
(SEM). The data were subjected to two-way ANOVA
analysis and differences between treatments were
determined using Bonferronis post-test (P < 0.05).
Results
Nitrate and total sugars content
Among the various quality parameters, nitrates and
sugars are particularly important because they can
have positive and negative effects on human health.
In our study, nitrates were significantly different from
plants grown in the different nutrient solutions in
spring (Figure 1(a)), while no differences were
observed in the summer and autumn cycles
(Figure 1(c)). At harvest, nitrate concentration in
leaves of plants grown in spring was on average
19% lower in NS50% (4.2 g kg
1
) compared to
NS100% (5.2 g kg
1
). During storage, nitrate concen-
tration did not change in the leaves harvested in
spring (Figure 1(a)), while it declined after
410 days in the experiments performed with leaves
harvested in summer (Figure 1(b)). In autumn,
nitrate reduction was found after 10 days only in
Figure 1. Storage behaviour at 4°C of leaf nitrate (a, b, c) and total sugars (d, e, f). Content of Corchorus olitorius plants grown
during spring (a, d), summer (b, e) and autumn (c, f) on either full (circles) or half strength (squares) nutrient solutions and
stored at 4°C for up to 10 d. Given are ± standard error of the mean (n = 4). Asterisks indicate significant differences between
means obtained for plants grown on the two nutrients (P < 0.05 = *, P < 0.01 = **; P < 0.001 = ***). Different letters indicate
statistical differences between different days of storage.
THE JOURNAL OF HORTICULTURAL SCIENCE AND BIOTECHNOLOGY 3
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the leaves of plants grown with NS50% nutrient solu-
tion (Figure 1(c)). During storage, nitrate content
results were statistically different between samples
harvested from the two nutrient solutions over the
course of 7 days.
Total sugars in C. olitorius leaves grown with
NS100% in spring showed statistical differences from
NS50% at harvest and during the first day of storage,
with values that ranged from 12 g kg
1
to 9 g kg
1
,in
NS100% and NS50%, respectively (Figure 1(d)). In
summer and autumn, the harvested leaves did not
show significant differences between the two nutrient
solutions. Total sugars measured at harvest among
seasons and between nutrient solutions ranged from
16.7 g kg
1
to 8.5 g kg
1
(Figure 1(df)). In all storage
experiments, the total sugars declined, starting from
the first or fourth day of storage (Figure 1(df)).
Sucrose and reducing sugar content
At harvest, the sucrose content was statistically dif-
ferent only in the summer and spring cycles, with
1.2 g kg
1
in leaves harvested from NS100%
(+44.3%), and 0.7 g kg
1
in leaves harvested from
NS50%. During storage, sucrose content declined
after 4 days in leaves harvested from NS100%
(Figure 2(b)) and in leaves harvested in autumn
from NS50% treatment stored for 10 days (Figure 2
(c)). There was no significant difference regarding the
reducing sugars between the two nutrient solutions at
harvest and during storage in all seasons. Although
there was no interaction overall, there is a percentage
of chance of random interactions that may be
observed in these experimental conditions, therefore
no significant interaction was considered.
During postharvest, the reducing sugars decreased
in all storage experiments. In leaves obtained from the
spring cultivation, there was a 10% reduction of redu-
cing sugars, passing from 4.0 g kg
1
at harvest to 3.6 g
kg
1
after 10 days of storage. In summer, the highest
reduction was observed in NS100% treatment with
89.2% (Figure 2(e)). In autumn, however, the highest
reduction of 62% was found in leaves harvested from
NS50% with values of 3.2 g kg
1
at harvest and 1.2 g
kg
1
at the end of storage (Figure 2(f)).
Phenols content and anthocyanin
Phenolic compounds were not significantly influ-
enced by nutrient solutions and they decreased
during shelf-life. Considering the high percentage
of chance of random interaction between storage
Figure 2. Storage behaviour at 4°C of leaf sucrose (a, b, c) and reducing sugars (d, e, f). Content of Corchorus olitorius plants
grown during spring (a, d), summer (b, e) and autumn (c, f) on either full (circles) or half strength (squares) nutrient solutions
and stored at 4°C for up to 10 d. Given are ± standard error of the mean (n = 4). Asterisks indicate significant differences
between means obtained for plants grown on the two nutrients (P < 0.05 = *, P < 0.01 = **; P < 0.001 = ***). Different letters
indicate statistical differences between different days of storage.
4A. GIRO AND A. FERRANTE
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time and nutrient solutions, no interaction was
observed overall.
Phenol content decreased from harvest, but it did
not decrease in a linear way. High losses in phenolic
content arose from 1 d to 4 d as occurred for the
reducing sugars. Jute grown in the NS100% treatment
in the spring cycle reduced its phenolic content from
2.2 g kg
1
to 2.1 g kg
1
with a 5.6% reduction and in
the NS50% treatment, phenolic content decreased
from 1 d to 4 d, from 2.7 g kg
1
to 2.1g kg
1
with a
21.8% loss. However, C. olitorius leaves grown in the
NS100% treatment and harvested in the summer
cycle lost their phenols between 4 d and 7 d, and
passed from 1.0 g kg
1
to 0.7g kg
1
, with a 27.7% loss.
During summer, C. olitorius leaves harvested from
NS50% maintained the same trend observed during
spring, in fact, the higher losses were found between
1 d and 4 d with a loss percentage of 37.7%. Leaves
harvested from the NS50% treatment reduced the
phenols from 1.7 g kg
1
to 1.0 g kg
1
.C. olitorius
harvested from both NS50% and NS100% did not
show significant differences during autumn at harvest
as well as during shelf-life (Table 1). Anthocyanin
content showed a similar trend during shelf-life in
all seasons. During spring and summer, in jute har-
vested from NS50%, the anthocyanin significantly
increased (Table 2). Within NS50% leaves cultivated
in autumn, anthocyanin decreased significantly dur-
ing shelf-life. In spring and summer leaves, anthocya-
nin did not show any significant reduction during the
entire storage experiment. However, their values dur-
ing shelf-life suggested a slow reduction trend start-
ing after 1 d. The critical decrease point occurred
between 1 d and 4 d, in fact, an anticipated
Table 1. Storage behaviour at 4°C of phenols expressed as gallic acid equivalent (GAE) g kg
1
in Corchorus olitorius grown in a
floating system with full nutrient solution (NS100%) and reduced (NS50%) in three different seasons: spring, summer and
autumn.
harvest 1 d 4 d 7 d 10 d
Spring
NS100% 2.2 ± 0.34 2.2 ± 0.39 2.1 ± 0.24 2.2 ± 0.97 2.1 ± 0.17
NS50% 2.6 ± 0.19 2.7 ± 0.21 2.1 ± 0.26 2.3 ± 0.13 2.0 ± 0.17
Diff. treatments ns ns ns ns ns
Interaction Interaction accounts for 7.75% of the total variance. F = 0.75, Dfn = 4, Dfd = 30, P value = 0.56
The interaction is not considered significant.
Summer
NS100% 1.4 ± 0.23 1.2 ± 0.19 1.3 ± 0.27 1.0 ± 0.4 1.1 ± 0.16
NS50% 1.6 ± 0.35 1.7 ± 0.21 1.0 ± 0.22 0.7 ± 0.7 1.0 ± 0.15
Diff. treatments ns ns ns ns ns
Interaction Interaction accounts for 11.82% of the total variance. F = 1.48, Dfn = 4, Dfd = 30, P value = 0.23
The interaction is not considered significant.
Autumn
NS100% 0.8 ± 0.40 0.8 ± 0.03 0.6 ± 0.07 0.6 ± 0.050 0.7 ± 0.13
NS50% 0.8 ± 0.10 0.7 ± 0.13 0.6 ± 0.03 0.6 ± 0.13 0.7 ± 0.08
Diff. treatments ns ns ns ns ns
Interaction Interaction accounts for 0.92% of the total variance. F = 0.1, Dfn = 4, Dfd = 30, P value = 0.98
The interaction is not considered significant.
Values were standard error of the mean (n = 4). Data were subjected to two-way ANOVA analysis and differences between means were determined
using Bonferronis Post-test. Indicated significant statistical differences.
Table 2. Anthocyanin content (g kg
1
) expressed as cynidin-3-glucoside in Corchorus olitorius grown in a floating system with
full nutrient solution (NS100%) and reduced (NS50%). in three different seasons: spring, summer and autumn.
harvest 1 d 4 d 7 d 10 d
Spring
NS100% 0.4 ± 0.26a0.4 ± 0.26a0.4 ± 0.59a0.4 ± 0.19b0.4 ± 0.52a
NS50% 0.6 ± 0.51 0.6 ± 0.53 0.5 ± 0.53 0.4 ± 0.29 0.4 ± 0.47
Diff. treatments ** ** ns ns ns
Interaction Interaction accounts for 11.45.% of the total variance. F = 1.73, Dfn = 4, Dfd = 30,, P value = 0.16.
The interaction is not considered significant.
summer
NS100% 0.4 ± 0.50 0.4 ± 0.42 0.4 ± 0.49 0.4 ± 0.48 0.4 ± 0.80
NS50% 0.6 ± 0.17 0.6 ± 0.15 0.6 ± 0.33 0.5 ± 0.12 0.5 ± 0.69
Diff. treatments ** ** ns ns ns
Interaction Interaction accounts for 3.08% of the total variance. F = 0.34, Dfn = 4, Dfd = 30, P value = 0.84.
The interaction is not considered significant.
autumn
NS100% 0.1 ± 0.21a0.1 ± 0.23a0.1 ± 0.19a0.1 ± 0.09a0.9 ± 0.10b
NS50% 0.1 ± 0.22A0.1 ± 0.20A0.1 ± 1.3A0.9 ± 0.07B0.6 ± 0.07B
Diff. treatments ns ns ns ns ns
Interaction Interaction accounts for 2.33% of the total variance. F = 0.43, Dfn = 4, Dfd = 30, P value = 0.78.
The interaction is not considered significant.
Values were standard error of the mean (n = 4). Data were subjected to two-way ANOVA analysis and differences among means were determined using
Bonferronis Post-test. Indicated significant statistical differences for: P < 0.05 = *, P < 0.01 = **; P < 0.001 = ***. Asterisks indicate differences
between different NS treatments. Different letters indicate statistical differences between different days of storage.
THE JOURNAL OF HORTICULTURAL SCIENCE AND BIOTECHNOLOGY 5
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anthocyanin loss (15.8%) was observed (Table 2). On
the contrary, during spring, within NS100% jute
leaves, anthocyanins decreased rapidly after 4 days
of storage (Table 2). During summer, greater antho-
cyanins reduction was found between 1 d and 4 d
with 8.5% loss in leaves cultivated in NS50%, while
no significant loss of the anthocyanin content was
observed in leaves obtained from the NS100% treat-
ment during the entire shelf-life. During autumn,
anthocyanin content in leaves of jute plants grown
in NS100% and NS50% decreased with the same
trend during the entire shelf-life. Jute leaves grown
in NS50% showed higher reduction until 7 d of
storage with a 38% loss. NS100% showed anthocya-
nins decline later than 7 days until the end of storage
with a 31% loss.
Carotenoids and total chlorophyll content
Chlorophyll content was highly stable in C. olitorius
leaves during shelf-life. No difference was found
from harvest until the end of the storage period
(Table 3). Between NS100% and NS50% treatments,
the differences in chlorophyll content were observed
after 4 and 10 days of storage in samples harvested
in spring. Chlorophyll content at harvest ranged
from 3.2 g kg
1
for NS100% to 2.9 g kg
1
for
NS50%. During summer, chlorophyll content ran-
ged from 2.7 g kg
1
for NS100% to 2.8 g kg
1
for
NS50%. During autumn, the chlorophyll content
within the leaf during storage decreased after
7 days of storage by 51% for NS100%, while in
NS50% the chlorophyll loss was 17.7% after 7 days,
but the difference was not statistically different.
Total carotenoids were different between nutrient
solutions only in the autumn growing cycle, with
concentrations of 0.27 g kg
1
in NS100% and
0.18 g kg
1
in NS50% (Table 4). During storage, no
significant change was observed in the experiments
carried out in spring and summer. The only statis-
tical differences in the storage experiments were
found after 10 days in the leaves harvested from
both nutrient solutions.
Discussion
The nutraceutical components of fruits and vegeta-
bles are represented by several bioactive molecules
such as anthocyanins, carotenoids, phenols and vita-
mins. These compounds contribute to the antioxidant
potential of the produce. The concentrations of these
compounds vary among species and ethnic vegetable
varieties have higher concentrations of these bioactive
molecules (Afolayan & Jimoh, 2009; Giro & Ferrante,
2016). Besides these health-promoting compounds,
there are others such as nitrates, which must be
maintained lower than the EU regulation limits (EU
no. 1258/2011) because they may be dangerous for
human heath since they are correlated with gastro-
intestinal cancer induction (Knekt, Järvinen, Dich, &
Hakulinen, 1999; Santamaria, 2006). Therefore,
nitrate content is an important quality parameter
that has to be controlled in leafy vegetables. It is
well known that nitrate accumulation is inversely
correlated with the availability of solar radiation,
which is responsible for the activation of nitrate-
reductase, a key enzyme for nitrate assimilation in
plants (Cram, 1976). These findings explain the lower
nitrate concentrations during summer
(Supplementary file). Under low light intensity con-
ditions, nitrates and oxalate ions have an osmotic
regulatory function in the cell in substitution for
organic acids and sugars. Therefore, the nitrates are
accumulated in the leaf vacuole to counteract the low
Table 3. Chlorophyll (a + b) content (g kg
1
) storage behaviour at 4°C determined in leaves of Corchorus olitorius grown in a
floating system with a full nutrient solution (NS100%) and reduced by half (NS50%) in three different seasons: spring, summer
and autumn.
harvest 1 d 4 d 7 d 10 d
spring
NS100% 3.1 ± 0.16 3.2 ± 0.16 3.2 ± 0.16 2.6 ± 0.10 2.8 ± 0.06
NS50% 2.9 ± 0.30a2.5 ± 0.14a2.6 ± 0.28a2.4 ± 0.05a1.8 ± 0.07b
Diff. treatments ns ns * ns **
Interaction Interaction accounts for 10.12% of the total variance. F = 1.8, Dfn = 4, Dfd = 30, P = 0.15
The interaction is not considered significant.
summer
NS100% 2.7 ± 0.27 2.2 ± 0.39 2.5 ± 0.12 2.2 ± 0.04 2.2 ± 0.06
NS50% 2.8 ± 0.05 2.6 ± 0.13 2.3 ± 0.12 2.1 ± 0.05 2.3 ± 0.02
Diff. treatments ns ns ns ns ns
Interaction Interaction accounts for 5.20% of the total variance. F = 0.68, Dfn = 4, Dfd = 30, P = 0.65
The interaction is not considered significant.
autumn
NS100% 2.2 ± 0.27a2.2 ± 0.41a2.0 ± 0.27a1.0 ± 0.1b0.8 ± 0.34b
NS50% 1.5 ± 0.21 1.5 ± 0.28 1.2 ± 0.14 1.3 ± 0.02 1.0 ± 0.06
Diff. treatments ns ns ns ns ns
Interaction Interaction accounts for 12.08% of the total variance. F = 1.99, Dfn = 4, Dfd = 30, P = 0.12
The interaction is not considered significant.
Values were standard error of the mean (n = 4). Asterisks indicate differences between different NS treatments. Different letters indicate statistical
differences between different days of storage.
6A. GIRO AND A. FERRANTE
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sugar content due to lower photosynthetic activity
(Blom-Zandstra, 1989; Raven & Smith, 1976).
Nitrates are partially reduced during shelf-life or sto-
rage, but significant amounts remain stable within the
leaves. The stability of nitrates during postharvest is
due to the lack of electron flux from photosynthetic
machinery and low temperatures, which slow down
all enzyme activities (Evans, 1989).
Chlorophyll in leafy vegetables strongly depends
on nitrate content and light intensity (Kasim &
Kasim, 2012). However, nutrient solutions did not
influence chlorophyll content, indicating that both
contain enough nutrients for the adequate biosynth-
esis of these compounds. Carotenoid content also
followed the chlorophyll trend, because of the protec-
tion function of chlorophylls against photo-oxidation.
Carotenoids, in addition to phenols and anthocya-
nins, are considered to be important antioxidants
for the human diet (Martin, Zhang, Tonelli, &
Petroni, 2013). Carotenoids in C. olitorius leaves
were higher compared to other Mediterranean leafy
vegetables like rocket (0.08 g kg
1
) and dandelion
(0.07 g kg
1
) (Bianco, 1995; Giro & Ferrante, 2016).
During storage, carotenoids did not statistically
decrease in C. olitorius leaves in spring and summer,
guaranteeing a high concentration for the consumer.
Instead, greater reduction was observed in autumn
after 7 days of shelf-life: 10% for both nutrient
solutions. However, this aspect does not compromise
the quality for the consumers because the commer-
cialisation of leafy vegetables is limited to 7 days.
Sugar content in leaves depends on environmen-
tal conditions rather than nutrient solutions (Fallovo
et al., 2009). After harvest, sugar content within
leaves represents the substrate for respiration and
the maintenance of basal metabolism. Sugar avail-
ability affects the storability and the shelf-life of
produce (Kays & Paull, 2004). In fact, during sto-
rage, sugar reduction is influenced by storage tem-
perature, which affects the respiration rate of the
produce (Brecht, 1995; Mbong, Ampofo-Asiama,
Hertog, Geeraerd, & Nicolai, 2017; Paull, 1999).
The high content of total sugars within C. olitorius
leaves represents a good energetic reserve, which can
be used for quality retaining during storage.
However, the sucrose content in C. olitorius leaves,
if compared with other varieties of baby leaf, such as
lettuce, is retained. In lettuce baby leaf, the sucrose
content greatly declined after 5 days of storage at 5°
C (Spinardi & Ferrante, 2012). Reducing sugars
decreased after 4 days of storage. In fact, unlike
sucrose, reducing sugars are metabolic sugars, pri-
marily used as a substrate for cell respiration.
Moreover, reducing sugars and sucrose content
were less influenced by nutrient solutions and sto-
rage conditions. These results can be explained, con-
sidering that total sugars during postharvest can be
hydrolysed in simple sugars maintaining reducing
sugars and sucrose stable. Sugars have important
nutritional functions for human health, not only as
energetic compounds but also as a probiotic for
human gut microbiota (Goh & Klaenhammer,
2015).During spring, significant differences between
nutrients solutions were measured at harvest within
1 day for total sugars. The significant differences can
be explained considering the higher light availability
and optimal growing temperature conditions during
springtime. In both NS100% and NS50%, nitrates
did not change during shelf-life. Significant differ-
ences were found among seasons according to dif-
ferent light intensities (Fallovo et al., 2009). Total
phenols and anthocyanins did not show high varia-
bility during postharvest. The main changes can be
due to the seasonseffect on the phenolic
Table 4. Carotenoid content (g kg
1
) storage behaviour at 4°C determined in leaves of Corchorus olitorius grown in a floating
system with a full nutrient solution (NS100%) and reduced by half (NS50%) in three different seasons: spring, summer and
autumn.
harvest 1 d 4 d 7 d 10 d
spring
NS100% 0.60 ± 0.06 0.65 ± 0.03 0.66 ± 0.04 0.64 ± 0.017 0.73 ± 0.23
NS50% 0.65 ± 0.03 0.64 ± 0.02 0.60 ± 0.03 0.58 ± 0.03 0.54 ± 0.02
Diff. treatments ns ns ns ns ns
Interaction Interaction accounts for 1.04% of the total variance. F = 0.11, Dfn = 4, Dfd = 30, P = 0.097
The interaction is considered significant.
summer
NS100% 0.72 ± 0.07 0.76 ± 0.03 0.69 ± 0.09 0.64 ± 0.01 0.65 ± 0.03
NS50% 0.75 ± 0.01a0.75 ± 0.02a0.67 ± 0.01a0.60 ± 0.00b0.60 ± 0.03b
Diff. treatments ns ns ns ns ns
Interaction Interaction accounts for 2.93% of the total variance. F = 0.41, Dfn = 4, Dfd = 30, P = 0.79
The interaction is considered significant.
autumn
NS100% 0.27 ± 0.04 0.27 ± 0.05 0.31 ± 0.04 0.15 ± 0.03 0.09 ± 0.05
NS50% 0.18 ± 0.04a0.31 ± 0.05a0.19 ± 0.02a0.18 ± 0.00a 0.08 ± 0.11b
Diff. treatments ns ns ns ns ns
Interaction Interaction accounts for 4.25% of the total variance. F = 0.70, Dfn = 4, Dfd = 30, P = 0.59
The interaction is considered significant.
Values were standard error of the mean (n = 4). Asterisks indicate differences between different NS treatments. Different letters indicate statistical
differences between different days of storage.
THE JOURNAL OF HORTICULTURAL SCIENCE AND BIOTECHNOLOGY 7
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metabolism (Samuolienė, Sirtautas, Brazaitytė,&
Duchovskis, 2012). The phenols content might also
be correlated to nitrogen availability and to pheny-
lalanine ammonia-lyase activity (Kováčik & Bačkor,
2007). In fact, when theres low nitrogen availability,
the plants activate the phenylalanine ammonia-lyase
enzyme to obtain nitrogen, removing the amine
group from the phenylalanine (Creasy & Zucker,
1974). This is a futile cycle that is transiently acti-
vated by plants to cope with nitrogen deficiency.
This can explain the lower anthocyanin concentra-
tion in the leaves of C. olitorius grown in NS100%.
Conclusion
Our results demonstrated that halved NS did not
negatively affect postharvest performance of this
crop. Therefore, the reduced nutrient solution can
be advised for the reduction of fertiliser input during
cultivation and allow the re-use of the nutrient solu-
tion for multiple cycles. The storage at 4°C preserved
the most important quality factors such as chloro-
phyll, carotenoid and sucrose. We can conclude that
C. olitorius baby leaf maintained high-quality charac-
teristics during shelf-life, in particular, antioxidant
compounds. This leafy vegetable can be effectively
suggested as a new ready-to-eat vegetable for the
fresh cut industry, providing high nutraceutical com-
ponents to the consumer. Moreover, the halved solu-
tion raised secondary metabolite contents such as
anthocyanin and phenols, suggesting that a sub-opti-
mal use of nitrogen supply can promote the accumu-
lation of these compounds and reduce nitrate losses
at the same time without consequence in postharvest
behaviour. However, further physiological studies
should be carried out considering the positive
responses of C. olitorius to a sub-optimal use of
nitrogen supply.
Disclosure statement
No potential conflict of interest was reported by the
authors.
ORCID
Andrea Giro http://orcid.org/0000-0003-2253-097X
Antonio Ferrante http://orcid.org/0000-0001-7781-9784
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... In the Middle East and North Africa, the species Corchorus olitorius L. (n = 24), known by the common name of molokhia, is consumed as a leafy vegetable, fresh or dry, accompanying soups or as part of traditional dishes of Arab and African culture [19][20][21][22]. It has a high nutritional value as source of essential amino acids, such as methionine [23]; however, it has important nutraceutical properties, containing high concentrations of β-carotene, riboflavin, ascorbic acid, folic acid, iron, tocopherols, and phenolic compounds [24]. Given the presence of these antioxidant metabolites, its use has been associated with the prevention of chronic diseases such as cancer, diabetes, hypertension, and heart disease [24][25][26]. ...
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