J. Appl. Hort., 2(2):79-83, July-December, 2000
Effect of CaCl2 sprays, heat, and combined CaCl2-heat treatments
on the quality of apples (Malus domestica Borkh.)
R. Drisa, R. Niskanen
a
and El Assi N.b*
a
Department of Applied Biology, Horticulture, P.O. Box 27, FIN-00014 University of Helsinki, Finland b University of
Jordan, College of Agriculture, Department of Horticulture and Plant Protection, P.O. Box 13367, Amman 11942,
Jordan* Corresponding author. E-mail address: najibasi@ju.edu.jo
Abstract
‘Lobo’ apple fruits were subjected to preharvest CaCl2 spraying treatment, pre-storage heat treatment, and combined CaCl2+heat
treatment and were held at 2oC and 90-95% R.H. for six months. Respiration and ethylene production rates were monitored, soluble
solids, juice pH, firmness, total dry matter and macronutrient (P, K, Ca, Mg, and N) contents were determined. Additionally, physiological
disorders incidence and pathological disease occurrence were recorded. The respiration and ethylene production rates slightly decreased
in heat-treated apples and increased in CaCl2-treated apples. CaCl2 treatment did not increase fruit firmness or Ca concentration.
Combined CaCl2+heat treatment and heat treatment increased the pH. At the beginning of storage the firmness of heat and CaCl2+
heat-treated fruits was lower, but more than that of the control fruits at the end of storage period. After 6 months of storage, least
disorder and disease symptoms were observed in the CaCl2+heat treatment.
Key words: Apples, Malus domestica Borkh., calcium, macronutrients, ethylene, firmness, respiration, soluble solids
Introduction
The use of pre-, or post-harvest chemical treatments is becoming
more restricted due to consumer preference for chemical-free food,
and the increasing resistance of many microorganisms to commonly
used chemicals. Calcium is associated with regulation of the
ripening process and storage behaviour of apples (Marcelle, 1990).
Many physiological storage disorders such as bitter pit and
senescence breakdown are due to the low calcium concentration
in apple flesh (Shear, 1974; Ferguson, 1984, Dris and Niskanen,
1998). Maintenance of relatively high calcium content in fruit
tissues results in slower ripening and softening as well as reduced
respiration and ethylene production rates (Bangerth et al., 1972;
Faust and Shear, 1972; Lieberman and Wang, 1982). Pre-harvest
calcium spraying treatments on apples have been reported to reduce
the incidence of physiological storage disorders (Vang-Petersen,
1981; Raese et al., 1990; Peryea, 1991). Pre-storage heat treatment
of apples has been shown to have beneficial effects on fruit quality
during storage by delaying ripening and reducing ethylene
production rate (Burg, 1962; Porritt and Lidster, 1978; Klein and
Lurie, 1990). Limited research on the preharvest calcium spraying
treatments has been done on apples grown in Finland (Dris and
Niskanen, 1997; 1998), and pre-storage heat-treatment on apples
has not been studied so far. Our objective was to study the effect of
preharvest CaCl2 spray, pre-storage heat-treatments and combined
CaCl2 and heat treatments on storage life of ‘Lobo’ apple fruits
grown in the Åland Islands district.
Materials and methods
Twelve-year old ‘Lobo’ apple trees with A2 type rootstock grown
commercially in two separate orchards in the district of the Åland
Islands (56-61°N, 19-20°E) were used in this study. Two plots of
5 trees/ plot/orchard were chosen to conduct the present study.
One plot/orchard was treated by foliar spraying with CaCl2 solution
(Ca 1.3 g/l) six times during fruit development with a two-week
interval, and the other plot was left untreated. CaCl2 sprays started
in mid June (after fruit set) and ended early September (3 weeks
before harvest).
A total of 720 fruits were hand harvested on the third of October
from the two orchards (designated ‘Lobo’1 and ‘Lobo’2), washed
with water, air dried at ambient temperature, and transported on
the same day to the laboratory. Fruits from untreated control (180
fruits) and CaCl2-treated plots (180 fruits) from each orchard were
then divided further into 2 subgroups of 90 fruits each. One
untreated and one CaCl2-treated subgroups were subjected to prestorage heat treatment in specific heat chambers at 38 oC for 4
days as described by Klein and Lurie (1990). Relative humidity
was supplied by placing water trays on the floor of the heat chambers
and maintained at 50% with the available equipment. Accordingly,
the following four treatments were carried out on the fruits (90 in
each treatment) from the two orchards: CaCl2-treated; heat-treated;
CaCl2+ heat–treated; and untreated control-treatment. All fruits
were stored for six months at 2oC and R.H. 90-95%.
The assessment of quality characteristics and nutrient analysis were
carried out at the beginning of the storage period and consequently
after 1, 3 and 6 months storage, and the respiration (CO2 evolution)
and ethylene production rates were monitored for 101 days.
Measurements on fruits from the two orchards were taken
separately, averaged, and then considered as replicates, except for
the respiration and ethylene production rates determination.
For monitoring respiration and ethylene production rates, two sound
and uniformly sized apple fruits with two replicates for each
treatment were weighed and placed in one-liter jars in the cold
storage room at 2oC. Prior to taking gas samples, each jar was
tightly closed with metal lid for 12 to 14 h, gas samples were drawn
with a syringe through the rubber septum in the lid, then jars were
uncovered. A 5 ml gas sample was injected into a gas
80
Journal of Applied Horticulture
chromatograph (model HP 5890 Series II) equipped with a
Porapak Q column for CO2 and a flame ionization detector for
ethylene. Measurements were repeated 7 to 8 times during
storage for ‘Lobo’ 1 and ‘Lobo’ 2 fruits from the first and second
orchard, respectively.
rates up to the 66th day of storage (Fig. 3 and 4). Similarly, CaCl2treated apple fruits showed slight increase in ethylene production
rate up to the 66th day of storage (Fig. 4). Noticeably, a sharp
increase in ethylene production rate was observed after 24 days
in the CaCl2-treated apple fruits followed by a steady sharp
Six apple fruits were randomly chosen for the textural test. The
diameter (cm) of individual fruit was measured with sliding
callipers, and firmness (kg) was determined by a penetrometer
(The Instron Universal Testing Instruments, Instron TMM 100,
Instron Ltd, England). The fruit was compressed for a distance
of 1 cm (speed 10 cm min-1) with a 5.0 cm in diameter measuring
device, and the force exerted was recorded.
For measuring the total soluble solids (TSS) and pH, two apple
fruits were cut transversally and pressed with a small juice
extractor. The concentration of soluble solids was measured by
a refractometer (model Abbe-3L Bausch & Lomb). The pH of
the juice was measured using a pH-meter (Model PHM 83).
The incidence of physiological storage disorders such as
senescence breakdown, low temperature breakdown and water
core etc., and diseases such as blue mould rot, brown rot etc.
were evaluated. The affected fruits were calculated as a
percentage of the total.
Data was subjected to Analysis of Variance (ANOVA) with
SAS General Linear Program Model procedure (SAS Institute,
1989). The mean separation was done by the Least Significant
Difference (LSD) method at the 0.05 level.
350
µlC2H4(kg/hr)
300
250
200
150
100
50
Fig. 3
0
4
18
24
58
66
72
95
101
58
66
72
95
101
400
350
300
µlC2H4(kg/hr)
For the nutrient analysis, seeds and stems of six apple fruits
were removed with an apple borer (diameter 20 mm) after which
the fruits were cut with a vegetable-slicing machine (Hobart
VS 9A). The slices were frozen at -20°C, and then freeze-dried
for 12-16 h and vacuum packed in laminate bags. The percentage
of dry matter in fruit flesh was determined by weighing apple
slices before and after drying. Fruit samples were pulverized
and the concentration of dry matter was determined by drying
the pulverized samples (2 g) at 105°C for 1.5 h. Nitrogen was
determined by the Kjeldahl method (Tecator Digestion System
20, 1015 Digester and Kjeltec Auto 1030-analyzer, Tecator Ltd,
Höganäs, Sweden). Fruit samples were ashed at 475°C and the
ash was dissolved in 0.5 M HCl. Phosphorus in the ash extracts
was determined by the ammonium vanadate method (Jackson,
1958), potassium by flame photometry, and calcium and
magnesium by atomic absorption spectrophotometry (AAS).
250
200
Results and discussion
Whole-fruit respiration, measured by CO2 production rate,
fluctuated during storage between 0.5 to 7.0 mg-1 kg-1 hr -1 (Fig. 1
and 2). Even though the values showed slight to no significant
differences among treatments, a slight decrease was noticed in the
respiration rate of heat-treated apple fruits compared to the other
treatments (Fig. 1). On the contrary, CaCl2-treated apple fruits
showed a slight increase in their respiration rates (Fig. 1 and 2).
The pronounced effect on apple fruits by the reduction of the
respiration and ethylene production rate is in agreement with Klein
and Lurie (1990) who observed that respiration rate of ‘Anna’ and
‘Granny Smith’ apple fruits declined after heat treatment and
remained lower than that of the control fruits. Ethylene production
rate followed a similar trend as described above, where the heattreated apple fruits from both orchards exhibited slightly lower
150
100
50
0
Fig. 4
4
Control
18
24
Days in storage
CaCl 2
Heat
CaCl2+Heat
Leagends
CO2 production rate (mg-1 kg-1 h-1)of Control, CaCl2-treated, Heattreated, and CaCl2 +Heat treated ‘Lobo’1 (Fig. 1) and ‘Lobo’2
(Fig. 2) apple fruit during storage at 2oC.
C2H4 production rate (µl kg-1 h-1) of Control, CaCl2-treated, Heattreated, and CaCl2 +Heat treated ‘Lobo’1 (Fig. 3) and ‘Labo’2
(Fig. 4) apple fruit during storage at 2oC.
CaCl2 sprays, heat, and combined CaCl2-heat treatments on quality of apples
decline until the last measurement (Fig 4). Cultivar ‘Lobo’
showed a similar trend as ‘Anna’ apples (Klein and Lurie, 1990)
in respect to ethylene production rate, which virtually ceased
during heat treatment and after the treatment remained at a lower
level than that in the control fruits. However, regardless of the
type of the treatment, the rates of respiration and ethylene
production were relatively low, which is in agreement with results
obtained in fruit held at low temperature (Kader, 1992).
Table 1. Effect of preharvest CaCl2, pre-storage heat, and CaCl2 +
heat treatments on apple fruit texture (firmness/diameter- kg-1.cm-1)
and dry matter (expressed as a percentage of fresh weight) during
storage at 2oC for six months
Parameter/1
Storage period (months)
Treatment
Texture
Control
CaCl2
Heat
CaCl2+ Heat
Dry Matter
Control
CaCl2
Heat
CaCl2+ Heat
0
1
3
6
15.9 a2
14.3 ab
12.1 bcd
11.3 cd
13.7 abc
11.5 bcd
10.4 de
10.6 de
7.0 fg
6.3 gh
7.9 efg
9.9 def
3.7 h
3.7 h
11.6 bcd
9.2 defg
14.5 ab
15.5 a
15.6 a
14.5 ab
13.8 abc
13.2 abc
14.4 ab
14.5 ab
13.7 abc
11.8 c
13.5 abc
13.3 abc
12.9 bc
12.1 bc
13.7 abc
14.4 ab
Table 2. Effect of preharvest CaCl2 sprays, pre-storage heat, and
CaCl2 + heat treatments on apple fruit pH, TSS%, during storage
at 2oC for six months*
Parameter/1
Storage period (months)
Treatment
0
1
3
6
pH
Control
3.3 g2
3.2 g
3.8 de
4.1 bc
CaCl2
3.4 fg
3.4 fg
3.7 ef
4.3 abc
Heat
3.5 efg
3.4 fg
3.7 ef
4.5 a
CaCl2+ Heat
3.7 ef
3.7 ef
4.0 cd
4.4 ab
TSS%
Control
10.4 ab
9.5 b
10.7 ab
10.8 ab
CaCl2
9.8 ab
10.7 ab
10.4 ab
10.1 ab
Heat
10.7 ab
10.7 ab
10.8 ab
10.3 ab
CaCl2+ Heat
11.0 a
10.3 ab
10.9 ab
10.7 ab
1Each parameter is considered separately.
2Values for the corresponding parameter followed by the same letter
(s) are not significantlydifferent at the 0.05 level by the LSD method.
A steady decrease in apple weight was observed with time
progression with no significant differences among the values
obtained in all treatments (data not shown). The control and
CaCl2-treated fruits exhibited considerable decrease in firmness
values with time progression in storage (Table 1). Approximately
75% reduction was recorded in the firmness values for control
and CaCl2-treated fruits. A decrease in firmness was also noticed
in CaCl2+Heat-treated fruits, but it was gradual and minimal
compared to the first two treatments (Table 1).
This is in agreement with Davenport and Peryea (1990) and
Peryea (1991) who observed that fruit firmness was not affected
by calcium treatment. This could be due to the inadequate Ca
distribution within the fruit tissues resulting in an insufficient
81
amount of Ca to exert an effect on firmness. However, our results
contradict those obtained by Peryea (1991) where a slight
increase in fruit firmness by frequent calcium treatments was
observed. In the heat-treated fruits a pronounced decrease in
firmness was observed up to the 3rd month, but a noticeable
recovery in firmness values was observed in fruits after 6 months
of storage (Table 1), which could be due to the inhibition of cell
wall-degrading enzymes (Liu, 1978; Porritt and Lidster, 1978;
Klein and Lurie, 1990).
A steady decrease in the dry matter values obtained for all
treatments with time progression in storage . However, significant
difference between the initial and the final dry matter values
was detected only in the CaCl2-treated fruits (Table 1).
An increase in the pH values was noticed with time progression
mainly after the 3rd and 6th months of storage with significant
differences among the values obtained in all treatments (Table 2).
As compared to the control, the combined CaCl2+ heat treatment
increased the pH after 0 to 1 month storage and heat treatment
after 6 months (Table 2). The percentage of the TSS showed
fluctuations with no significant differences among the values (Table
2). Similar results of lower juice acidity and unaffected SSC were
previously reported (Klein and Lurie, 1990).
Table 3. Disorder incidence and disease occurrence in the control,
preharvest CaCl2, pre-storage heat, and CaCl2 + heat-treated apple
fruits during storage at 2 oC for six months
Parameter/1
Storage period (months)
Treatment
0
1
3
6
Disorders
Control
0.01c2
0.0 c
2.5 c
52.5 ab
CaCl2
0.0 c
0.0 c
5.0 c
60.0 a
Heat
0.0 c
0.0 c
0.0 c
62.5 a
CaCl2+ Heat
0.0 c
0.0 c
0.0 c
42.5 b
Diseases
Control
0.0 d
0.0 d
0.0 d
35.0 a
CaCl2
0.0 d
0.0 d
0.0 d
7.5 ab
Heat
0.0 d
0.0 d
15.0 bcd
35.0 a
CaCl2+ Heat
0.0 d
0.0 d
10.0 cd
17.5 bc
1Each parameter is considered separately.
2Values for the corresponding parameter followed by the same letter
(s) are not significantlydifferent at the 0.05 level by the LSD method.
The combined CaCl2-heat treatment was effective in reducing
the physiological disorders occurrence among all treatments
(Table 3). Development of some physiological storage disorders
have been reported to be reduced by heat treatment. Brooks and
Harley (1934) effectively controlled soft scald in ‘Jonathan’
apples by heating at 35-40°C for 8 to 24 h. Heat treatment at
38°C for 4 to 6 days almost eliminated breakdown, core browning
and decay of ‘Spartan’ apples and the incidence of physiological
storage disorders in ‘Golden Delicious’ (Porritt and Lidster,
1978). In our study, neither heat treatment nor CaCl2 treatment
was effective in decreasing physiological storage disorders
incidence in apples. It is possible that such a result obtained in
our experiments may be due to inadequate Ca distribution within
the fruit tissue. Also early disease symptoms were detected after
the 3rd month in the heat and CaCl2+heat treatments (Table 3).
After 6 months of storage, the least disease symptoms were
82
Journal of Applied Horticulture
observed in the CaCl2+ heat treatment (Table 3). However,
CaCl2 treatment was relatively effective in reducing the disease
occurrence (Table 3). There were only few significant
differences in fruit nutrient concentrations between treatments
and during storage period (Table 4 and 5).
Heat treatment could be effective in prolonging the storability of
apple fruits provided that high relative humidity (over 90%)
was maintained during heat treatment. The influence of heat
treatment might differ depending on apple cultivars (Mignani
et al., 1994).
Table 4. Effect of preharvest CaCl2, pre-storage heat, and CaCl2 +
heat treatments on phosphorus and potassium (expressed as mg1. kg-1. fw-1) in apple fruits held at 2oC for six months.
Parameter/1
Storage period (months)
Treatment
0
1
3
6
Phosphorus
Control
107.2 a2 122.3 a
121.2 a
109.6 a
CaCl2
117.7 a
84.5 a
101.4 a
103.6 a
Heat
111.4 a
109.0 a
99.1 a
119.1 a
CaCl2+ Heat
111.6 a
105.6 a
106.9 a
119.6 a
Potassium
Control
1171.0d 1218.0 d
1723.0 a
1169.0 d
CaCl2
1301.0 bcd 1039.0 d
1482.0 bcd 1083.0 d
Heat
1255.0 cd 1253.0 cd 1708.0 abc 1179.0 d
CaCl2+ Heat 1235.0 d 1956.0 a
1711.0 abc 1267.0 bcd
Accordingly, our results indicate that preharvest CaCl2 treatment
was not successful in achieving the expected results, neither
was the heat treatment for such a long-term storage.
Nevertheless, these treatments can be recommended only for a
three-month storage period, but not for longer. The combined
treatment of CaCl2+ heat resulted in maintaining firmness to
some extent, decreasing the physiological and pathological
disorders, provide evidence that it might be the best of the three
treatment applied.
Table 5. Effect of preharvest CaCl2, pre-storage heat, and CaCl2 +
heat treatments on calcium and nitrogen contents (expressed as
mg-1. kg-1.fw-1) in apple fruits held at 2oC for six months.
Parameter/1
Storage period (months)
Treatment
0
1
3
6
Calcium
Control
55.3 bc2 47.4 c
68.4 bc
66.7 bc
CaCl2
81.8 b
65.4 bc
68.5 bc
80.0 b
Heat
80.0 b
118.2 a
65.1 bc
57.0 bc
CaCl2+ Heat
54.8 bc
63.6 bc
84.2 b
64.9 bc
Nitrogen
Control
427 ab
458 ab
447 ab
432 ab
CaCl2
540 a
418 ab
444 ab
541 a
Heat
833 ab
448 ab
374 ab
462 ab
CaCl2+ Heat
350 b
460 ab
456 ab
556 a
1 Each parameter is considered separately.
2 Values for the corresponding parameter followed by the same letter
(s) are not significantly different at the 0.05 level by the LSD method.
Calcium treatment has been reported to often increase Ca
concentration in apples (Vang-Petersen, 1981; Raese, 1989;
Raese et al., 1990). In our experiments, preharvest CaCl2
treatment did not increase the Ca level in apple flesh, rather
decreased it. This could be explained by the results of Davenport
and Peryea (1990), who considered that foliar application of
Ca might fail to penetrate into the fruits and the small amount
of Ca absorbed from foliar sprays could be analytically masked
by background Ca levels in the whole fruit samples. In the study
of Davenport and Peryea (1990), no effect of preharvest CaCl2
treatments was found on fruit mineral composition or other
quality characteristics, and on the incidence of physiological
storage disorders. In our experiments, CaCl2 treatment did not
significantly affect the P, K, Ca, Mg, and N levels in apple fruits.
However, in addition to the increased fruit N level in a previous
experiment, also P and K were found to increase in Ca-treated
fruits (Dris and Niskanen, 1997; Dris et al., 1999).
Acknowledgments
We express our gratitude to the Ministry of Agriculture and
Forestry, the Government of the Åland Islands and Kemira Agro
Ltd Horti for financial support.
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