Qualidade pós-colheita de pomelos (Citrus paradisi Macf.) produzidos em
plantações iniciais no estado do Ceará, Brasil
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Introduction
Brazil is a leading world citrus producer. However, traditionally citrus
production has focused primarily on the production of fruit for processing,
mostly juices, rather than on producing good quality table fruits. In recent
years, the grapefruit (Citrus paradise Macf.) has received much attention
because of its nutritional and antioxidant properties. Besides ascorbic acid,
grapefruit also contains abundant flavonoids, which are reported to be the
important part of active ingredients. Recently, reporters are focusing on the
newly discovered beneficial effects of the grapefruit juice on human health,
such as protection against high blood pressure or cholesterol increase (WU;
GUAN; YE, 2007), as well as already well known benefits such as antioxidant and
anticarcinogenic (KAWAII et al., 1999). Ceará state, located in the northeast
Brazil, has been gaining attention as a significant emerging fruit producer in
the country. Fruit crops cultivated elsewhere in the country now are heavily
produced, placing Ceará state among the greatest fruit producers and exporters
in Brazil. Citrus, including grapefruit, traditionally cultivated in the south,
mostly São Paulo State, is on the list of recently planted fruit crops in
Limoeiro do Norte county, north state. To be considered as high quality for the
fresh market, however, grapefruit should meet some quality standards such as
color intensity, size, shape, peel thickness, smoothness, and a minimal soluble
solids/acid ratio threshold for good flavor (ARPAIA; KADER, 2000) at harvest,
as well as after storage. External color might be a concern in areas where
fruit reaches internal maturity while the peel is still green. In this case it
becomes necessary the development of the customary yellow to orange color
through a process called degreening. Besides, favorable climate conditions, it
is known that rootstock has a significant effect on fruit quality at the time
of harvest (MCCOLLUM; BOWMAN, 2002). Thus, it becomes fundamental that a study
be carried out to access quality of locally grown grapefruits at harvest and
after storage.
This work aimed at evaluating postharvest quality of locally grown 'Star Ruby'
and 'Ruby Red' grapefruits ('Star Ruby' grafted on 'Swingle' citrumelo (Citrus
paradise x Poncirus trifoliata) rootstock, 'Ruby Red' grafted on 'Swingle'
citrumelo (Citrus paradise x Poncirus trifoliata) or 'Rangpur' lime (Citrus
limonia) rootstock.
Material and methods
Plant material
Fruits from 'Star Ruby' grapefruit grafted on 'Swingle' citrumelo rootstock
(SR/SC), 'Ruby Red' grapefruit grafted on 'Swingle' citrumelo (RR/SC) or
'Rangpur' lime rootstock (RR/RL) were harvested in August, 2009, from a well-
managed orchard located at Taboleiro de Russas, Limoeiro do Norte County (5º13'
S, 37º54' E), Ceará state, and transported by road to The Laboratory of Food
Quality and Control, Universidade Federal do Ceará, located in Fortaleza.
Sample preparation and condition of storage
Upon arrival, fruit were sorted out for stage of maturity (more than 2/3 of
fruit showing yellow color), shape, size, freedom from defects and sunburn.
Fruit were washed with water at room temperature, air-dried, and divided into
two sets. The first set was composed of 30 fruit, being 10 fruit per grafted
variety and was reserved for non destructive analyses such as mass loss and
external color. For that, each fruit was numbered and individually analyzed at
harvest and every period of three days up to 15 days of storage. The second set
was composed of 36 fruit, being 12 fruit per grafted variety and was reserved
for destructive analyses such as internal quality, including fruit diameter,
thickness of the peel, pulp color, juice content, soluble solids, titratable
acidity, pH, and ascorbic acid. For that, fruit were analyzed at harvest and
after fifteen days of storage. Both set of fruit were stored at ambient
condition (22 ± 2 ºC, 60 ± 5% RH).
Quality assessment
Cumulative mass loss (%) was determined by weighting each numbered fruit during
storage and then calculating mass loss in relation to fruit mass at harvest.
Peel and pulp color were determined using a Minolta Chroma Meter (Minolta
Corporation Instrument Systems). L, a*, b* values were scored from opposite
sides of the fruit and results expressed as L, chroma and hue angle (MCGUIRE,
1992). Juice was extracted with an automated squeezer with a rotating red.
Juice content (%) was calculated by weighting fruit juice and dividing it by
fruit mass. Soluble solids (SS) (Brix) were determined in juice samples with a
digital refractometer (0-45 Brix) (Palette 100, Atago, Co., Ltd). Acidity (mg
citric acid/100g juice) was determined by titration with 0.1N NaOH, end point
pH 8.2; pH was measured with a pHmeter directly in the juice. Ascorbic acid
followed methodology reported by Hernádez, Lobo and González (2006).
Statistics
Data from the first set of fruits were analyzed using an entirely randomized
model, with ten replications, in a split plot array. The main plot was composed
by the combination variety and rootstock ('Star Ruby' grapefruit grafted on
'Swingle' citrumelo rootstock (SR/SC), 'Ruby Red' grapefruit grafted on
'Swingle' citrumelo (RR/SC) or 'Rangpur' lime rootstock (RR/RL)), while the
subplot included 5 durations (0; 3; 6; 9; 12, and 15 days). All data were
subjected to analysis of variance (SISVAR 4.3). Tukey´s test (P < 0.05) was
used to compare treatments classification when F values were significant for
main effects.
Results and discussion
Fruit Internal Quality
Fruits from the two varieties, regardless of rootstock, were elliptical in
shape, showing smooth and healthy peel, with fruit diameter varying from 107 to
129 mm and weighting from 450 to 770 g. Peel thickness from all fruits fell
into the range of 0.6 to 0.8 mm. These average weight values are higher than
those reported by Lederman et al. (2005) for six grapefruit varieties ('M.
Foster', 'Star Ruby', 'Rio Red', 'Red Blusa', 'Triumph', and 'Marsh F.
Nucelar') produced under irrigation in a semi-arid area located in Pernambuco
State, a neighboring state in the northeastern region in Brazil. Fruit weight
and average diameter, reported above, fall within the diameter range for large
grapefruits produced in Corsega, France (PAILLY; TISON; AMOUROUX, 2004).
Fruits presented brilliant, vivid crimson pulp color for the two varieties,
regardless of rootstock, as indicated by the average values of luminosity,
chroma, and hue angle, 45; 32 and 27, respectively.
RR/SC fruit soluble solids averaged 9.33 and was significantly higher than
those of RR/NL fruits (7.5 Brix) or SS/SC fruits (7.5 Brix) (TAB._1). Overall,
soluble solids did not differ from harvest to the end of storage for the two
varieties grafted on the three rootstocks (p < 0.05). These SS values are
within the range of SS reported by Patil et al. (2004) for late harvested 'Rio
Red' grapefruits. Stability of soluble solids of grapefruit during storage
(PAILLY; TISON; AMOUROUX, 2004; PATIL; VANAMALA; HALLMAN, 2004), as well as the
effect of rootstock on fruit quality, including soluble solids and postharvest
behavior (MCCOLLUM; BOWMAN, 2002), are well documented.
Average values of titratable acidity varied from 0.65 to 1.09 mg citric acid/
100g juice at harvest and from 0.71 to 1.38 mg citric acid/100g juice after 15
days of room temperature storage (TAB._1). This pulp quality parameter was
influenced by rootstock, as fruits grown on RR/RL produced significantly higher
acidity than fruits grown on RR/SC (p < 0.05). The average values reported
above are close to that of 'Flame' grapefruit (1.3 mg citric acid/100g juice)
grafted on different rootstocks and produced in Bahia State (FLORI, 2008). pH
values averaged 3.83; 3.67, and 3.08; for MRL, DSSC, and MSC, which, in turn,
was significantly lower than the first two values (p < 0.05) (TAB._1).
The results of SS/TA ratio were converse to those of TA, since SS values at
harvest were similar to those measured at the end of storage (TAB._2). SS/TA
ratio average values were 6.3 for SR/SC fruits, 7.8 for RR/SC fruits, and 12
for RR/RL fruits, which is above the minimal value recommended for good flavor
(ARPAIA; KADER, 2002). Those values are also higher than the average value
reported for 'Star Ruby' (5.26) and 'Red Blush' grapefruits (5.67) produced in
Pernambuco State (LEDERMAN et al., 2005).
SR/SC fruits presented a higher amount of vitamin C, 59 mg ascorbic acid/100g
juice, than RR/SC fruits, 56 mg ascorbic acid/100g juice, and RR/RL fruits, 53
mg ascorbic acid/100g juice (TAB._2). These means, however, did not differ
statistically. The average values of ascorbic acid of locally grown grape
fruits are higher than those reported for orange juice, 36 mg ascorbic acid/
100g juice (WU; GUAN; YE, 2007) and 'Rio Red' grapefruit, 20 mg ascorbic acid/
100g juice (PATIL; VANAMALA; HALLMAN, 2004). Even though no significant
differences were observed from harvest to the end of storage in this study, the
contents of ascorbic acid after 15 days of storage were slightly higher than
those observed at harvest. Higher content of ascorbic acid after 35 days of
storage was observed for late harvested 'Rio Red' grapefruits (PATIL; VANAMALA;
HALLMAN, 2004). Considering the benefits brought by ascorbic acid intakes on
human health the maintenance of this acid during storage comes as a great
advantage for stored grapefruits, as compared with fruits presenting high
losses of that acid during storage.
Commercially acceptable juice content was observed for the two grapefruit
varieties, and the rootstock did not seem to affect juice content of 'Ruby Red'
fruits (TAB._2). That value was superior to the 36% yielded by 'Star Ruby'
grapefruit grown in Corsega, France (PAILLY; TISON; AMOUROUX, 2005).
Cumulative mass loss did not differ among rootstocks (p = 0.7495) and increased
linearly with storage time (p = 0.00), reaching about 12% of the initial value
at the end of storage (FIG._1). Singh and Reddy (2006) reported a loss of about
20% of initial mass in 'Nagpur Mandarin' orange stored for 18 days at ambient
condition (28 °C and 58% RH), while Alferez et al. (2010) observed a mass loss
of as low as 3% in 'Marsh' grapefruit stored at 20 °C and 95% RH. Discrepancy
among results might have been caused by storage conditions, such as relative
humidity and temperature which may play a direct role on the magnitude of the
loss. Pailly, Tison and Amouroux (2002) associated mass loss, among other
factors, to fruit diameter, in a way that the smaller the fruit diameter the
higher the mass loss.
Luminosity of the peel was affected by treatments (p = 0.031) and storage
periods (p = 0.00), although independently. Overall, luminosity of the peel
decreased over the course of storage following a linear equation, and this
decrease was strongly influenced by storage durations (R2 = 0.928) (FIG._2).
SR/SC fruits presented luminosity averaging 56.2, which was significantly
higher than that found for 'Ruby Red' fruits, 54.5 and 55.6 for RR/RL and RR/SC
fruits, respectively. Suggesting that brightness of the peel of 'Ruby Red'
fruits may be influenced by rootstock (TAB._3). Conversely to brightness, 'Ruby
Red' fruits were significantly yellower, with a pinkish blush, while 'Star
Ruby' fruits presented a lesser intense yellow color, as indicated by hue angle
values (TAB._3).
Similarly to luminosity, hue angle of the peel was affected by treatments (p =
0.002) and storage periods (p = 0.00) independently (FIG._3). Taken as a whole,
hue angle values increased from 58.8º to 60º after six days of storage to
decrease thereafter to 56o at the end of storage, indicating the loss of any
remaining shade of green.
Chromaticity of the peel was also affected by treatments (p = 0.008) and
storage periods (p = 0.00) independently (FIG._4). The pattern of change in
chroma values indicates that peel color became less vivid, as chroma decreased
from harvest to the end of storage (TAB._3). Corroborating with the results
above, 'Ruby Red' fruits, especially RR/RL fruits, presented the highest values
of chroma, confirming the vivacity of the yellowish peel (TAB._3).
Conclusions
1. Grapefruits from initial plantings in Ceará state, Brazil, present excellent
internal quality, comparable to fruit produced in traditional grapefruit
producing areas of the Country;
2. Fruit from 'Ruby Red' grapefruit grafted on 'Rangpur' lime rootstock stand
out for presenting high equilibrium between SS and acidity, consequently, best
flavour;
3. It may be stated that grapefruits produced in Ceará State, Brazil, does not
need to undergo degreening process.
Acknowledgements
The authors thank Banco do Nordeste do Brasil (BNB) and Fundacão Cearense de
Apoio ao Desenvolvimento Cientifico e Tecnológico (FUNCAP), for financial
support, FRUTACOR, for the gift of the fruit, and Anne Mary Gillen, for
proofreading the manuscript.
