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CHAPTER 3
CALCIUM: AN INDISPENSABLE
ELEMENT EFFECTING POSTHARVEST
LIFE OF FRUITS AND VEGETABLES
VIJAY YADAV TOKALA1 and B. V. C. MAHAJAN2*
1Curtin Horticulture Research Laboratory, School of Molecular and
Life Sciences, Curtin University, Perth, WA, Australia
2Punjab Horticultural Postharvest Technology Centre, Punjab
Agricultural University, Ludhiana, Punjab, India
*Corresponding author. E-mail: mahajanbvc@gmail.com
ABSTRACT
Calcium is essential macronutrient involved in numerous biochemical and
physiological processes in the plants. It acts as intracellular messenger and
is responsible for maintaining the plant cell wall integrity. These properties
instigate significant impact on the postharvest fruit quality, ripening, senes-
cence, decay, and physiological disorders. Pre- and postharvest application
of calcium has reportedly reduced incidence of different disorders, main-
tained quality and extended postharvest life in horticulture produce. In the
present chapter an attempt is made to provide an overview about different
aspects of calcium application, mechanism of action and its impacts on the
postharvest life of the fruits and vegetables.
3.1 INTRODUCTION
Fruits and vegetables have an important role in the human diet and their
consumption helps to lower the risk of chronic diseases and to maintain a
healthy weight (McGuire, 2011). During recent decades, the global demand
for year-round availability of fruits and vegetables has increased, which
60 Emerging Postharvest Treatment of Fruits and Vegetables
may be ascribed to the change in dietary habits, increase in health aware-
ness, taste preferences, and the lifestyle of present-day consumers (Yuk et
al., 2006; Pollack, 2001). The continuous increase in population would also
increase the global demand for food, but on the other hand, the growing
competition for land, water, and energy, coupled with overexploitation of
natural resources, will affect our ability to produce food (Godfray et al.,
2010). Prevention of postharvest losses is increasingly cited as a means to
effectively contribute to available food supplies making it a prime goal to
develop technology to reduce their losses (Kitinoja et al., 2011). Many studies
provide indications that postharvest losses are substantial. It is commonly
cited that one-third of the world’s agricultural produce is lost before reaching
to consumers (Gustavsson et al., 2011). Fruits and vegetables are compara-
tively more perishable due to their high moisture content and these losses
vary greatly among developing countries (Lipinski et al., 2005). The magni-
tude of losses in fruits and vegetables due to pathological or physiological
factors is estimated at about 25–30%, which is because of lack of awareness
about appropriate postharvest handling and nonavailability of adequate post-
harvest infrastructure at the farm and/or market level (Sharma et al., 2009).
Therefore, efficient postharvest techniques have become an absolute neces-
sity as it not only reduces the monetary loss estimated at millions per year
but also minimizes wastage of labour, energy, and inputs invested in their
production. The shelf-life extension of any fruit and vegetable is prerequi-
site for minimizing the postharvest losses. Many techniques are available
in the literature to extend the storage life of produce; however, the calcium
application has a significant impact on the shelf-life of fruit and vegeta-
bles. Different benefits of calcium application have been discussed by many
workers, namely, delay in ageing or ripening, reduction in postharvest decay,
increase in the nutritional value, and control of different physiological disor-
ders. The aim of this chapter is to give an in-depth detail about the calcium
applications for enhancing storage life and quality improvement of different
horticultural crops.
3.2 IMPORTANCE OF CALCIUM
Calcium is an essential plant nutrient closely related to quality and firmness
of fruits (Sams, 1999) as the divalent cation (Ca2+) is required for various
structural roles in the cell wall and membranes. It acts as a counter-cation for
inorganic and organic anions in the vacuole, and an intracellular messenger in
the cytosol (Marschner, 1995). Earlier studies regarding the effect of calcium
Calcium: An Indispensable Element Effecting Postharvest 61
on fruit and vegetable quality were majorly concerned with its association
with physiological disorders (DeLong, 1936). Calcium has received consid-
erable attention in recent years because of its desirable effects in delaying
senescence and controlling physiological disorders in fruits and vegetables.
For fruits and vegetables to function and adapt efficiently to different envi-
ronmental conditions, their cells must communicate with one another. It is
becoming increasingly evident that calcium ions are important as intracel-
lular messengers in plants. Changes in cell-wall structure, membrane perme-
ability, and enzyme activation are known to influence various aspects of
cell physiology. Since the discovery of calmodulin, it has become clear that
the calcium messages are often relayed by this ubiquitous calcium-binding
protein (Cheung, 1980; Poovaiah, 1985). Calcium ions (Ca2+) are used in the
synthesis of new cell walls, particularly the middle lamellae that separate
newly divided cells. Calcium is also used in the mitotic spindle during cell
division. It is required for the normal functioning of plant membranes and
has been implicated as a secondary messenger for various plant responses to
both environmental and hormonal signals (Sanders et al., 1999). In its func-
tion as a secondary messenger, calcium may bind to calmodulin, a protein
found in the cytosol of plant cells. The calmodulin–calcium complex regu-
lates many metabolic processes.
Studies on leaf senescence (Poovaiah and Leopold, 1973; Ferguson, 1984)
and fruit ripening (Tingwa and Young, 1974; Poovaiah, 1979; Suwwan and
Poovaiah, 1978) have indicated that the rate of senescence often depends
on the calcium status of the tissue and that by increasing calcium levels,
various parameters of senescence such as respiration (Faust and Shear,
1972; Bangerth et al., 1972), protein, and chlorophyll content (Poovaiah
andLeopold,1973),and membrane uidity (Paliyath et al., 1984)can be
altered. It is a well-known fact that calcium plays an important role in main-
taining the quality of the fruits and vegetables (Shear, 1975; Bangerth, 1979;
Hopngerand Poovaiah, 1979;Artecaet al.,1980; Collier andTheodore,
1982; Huber,1983). Calcium deciencyisrare in nature, but thereexists
possibility in soils with low base saturation or high acidic depositions due
to chemical fertilizer abuse (McLauhglin and Wimmer, 1999). Many physi-
ologicaldisordersaictingfruitsandvegetablesareknowntoberelatedto
the calcium content of the tissue (Shear, 1975). White and Broadley (2003)
mentioned that the deciency symptoms can occur in dierent parts of
the plant, namely, (1) in young expanding leaves, such as in “tip burn” of
leafy vegetables; (2) in enclosed tissues, such as in “brown heart” of leafy
vegetables or “black heart” of celery; or (3) in tissues fed principally by the
62 Emerging Postharvest Treatment of Fruits and Vegetables
phloem rather than the xylem, such as in “blossom-end rot” of watermelon,
bell pepper, and tomato fruit, “bitter pit” in apples, and “empty pods” in
peanuts.They havespecied thatthese disorders occuras calciumcannot
be mobilized from older tissues and redistributed via the phloem, because
of which the developing tissues have to depend on the immediate supply of
calcium in the xylem, which is in turn dependent on transpiration. Disorders
such as “cracking” in tomato, cherry, and apple fruit occur in tissues lacking
sucientcalcium uponhypoosmoticshock (followingincreased humidity
or rainfall after a long dry spell), presumably as a result of structural weak-
nesses in cell walls.
TABLE 3.1 Disorders Due to Calcium Deficiency.
Crop Disorders References
Apple Bitter Pit Simons (1962) and Ferguson and Watkins (1989)
Cracking Shear (1971)
Internal breakdown Bramlage and Shipway (1967)
Tomato Blossom-end Rot Saure (2001)
Cracking Bangerth (1973) and Dickson and McCollum (1964)
Lettuce Tip Burn Collier and Theodore (1982)
Celery Blackheart Takatori et al. (1961)
Cherry Cracking Bullock (1952) and Bangerth (1973)
Prune Cracking Cline and Tehrani (1973)
Pears Cork spot Woodbridge (1971) and Mason and Welsh (1970)
Black end Woodbridge (1971)
Carrot Cavity spot Guba et al. (1961) and Maynard et al. (1963)
Leaf tip burn Tibbitts and Palzkill (1979)
Mango Spongy tissue
(Alphonso)
Wainwright and Burbage (1989)
Strawberry Leaf tip burn Tibbitts and Palzkill (1979)
Increasing the calcium normally decreases the incidence of the disor-
ders. Calcium disorders are troublesome and may occur during both storage
and shipping, thus making fruits unusable after they arrive at the market.
Calcium chloride can also act upon the quality of processed foods by acting
as a darkening inhibitor and eective method for the prevention of after-
cooking darkening of potato french-fries (Mazza and Qi, 1991). Calcium
deciencyiscommoninhorticulturalcrops,butthedeciencyisrarelydue
totheinsucientcalciuminthesoil(Naradisorn,2013).Thedisordersthat
Calcium: An Indispensable Element Effecting Postharvest 63
result from inadequate calcium in fruit may be due to a poor calcium distri-
bution rather than low calcium uptake, as in the same plant, the calcium
content in the leaves is often higher than that of the fruit (Conway et al.,
1994a).Similarly,calciumcontentwassignicantlyhigherintheleaftissues
whencomparedto petioles, whichhadsignicantlymore calcium than in
fruit tissue (Dunn, 2003).
Calcium is essential for structure and function of cell walls and
membranes. There are three types of evidence for the role of calcium in
membranes. First, under calcium-decient conditions, there is a profound
deterioration of membranes (Marinos, 1962). Second, calcium alters the
actual architecture of membranes; its introduction into natural (Paliyath
et al., 1984) or articial membranes of phospholipids (Gary-Bobo, 1970)
results in an enormous change in uidity and water permeability.Third,
calcium can powerfully alter an array of physiological activities which are
specicallyassociatedwiththemembranefunction,forexample,itcanturn
on the active transport of some ions through membranes (Hanson, 1983).
Calcium plays a special role in maintaining the cell-wall structure in fruits
and other storage organs by interacting with the pectic acid in the cell walls
to form calcium pectate. Thus, fruits treated with calcium promote mainte-
nance of the cell-wall structure and membrane integrity by increasing the
calcium content of the tissues (Scott and Wills, 1975; Poovaiah et al., 1978;
Paliyath et al., 1984; Drake and Spayd, 1983). High calcium-containing
tubers are less susceptible to decay (McGuire and Kelman, 1983, 1986) and
consequently could be stored for longer period of time. Increase in calcium
concentration in the tubers lowers the incidence of the internal defects and
maintains its quality (Kleinhenz et al., 1999).
3.3 PHYSIOLOGY OF ACTION
Calcium-related physiological disorders that occur in a wide range of vege-
tables and fruits are usually associated with loss of membrane integrity with
resultant loss of cell compartmentalization and ultimately cell death in their
tissues (Christiansen and Foy, 1979; Poovaiah, 1979). Sufficient Ca2+ is
known to be important for maintaining normal cell-wall structure, thereby
reducing the incidence of internal breakdown disorders in horticulture crops
(Conway et al., 1992). Maintenance of firmness and resistance to softening
resulting from the application of calcium have been attributed to the stabi-
lization of membrane systems and formation of calcium pectates, which
increase the rigidity of the middle portion and cell wall of the fruit (Grant et
64 Emerging Postharvest Treatment of Fruits and Vegetables
al., 1973; Jackman and Stanley, 1995). The role of calcium in maintaining
firmness has been associated with plant disease resistance (Naradisorn,
2013). It is suggested that calcium application to fruits can either enhance
the resistance of fruit to postharvest pathogens or reduce susceptibility to
postharvest diseases and disorders. Additionally, calcium may also cause
a reduction of pathogen conidia germination and germ-tube elongation by
limiting nutrients available to pathogens on the fruit surface (Moline, 1994).
During ripening, major changes take place in the pectin-rich middle-
lamella region of cells where calcium ions have a role in linking adjacent
acidic pectin polymers (Seymour et al., 1993). Under normal conditions, as
fruit mature, there is increased availability of nutrients for pathogens on the
surface of the fruit. However, calcium may enhance the resistance of fruit to
pathogens by interacting with cell-wall components. Postharvest pathogens
produce pectolytic enzymes, which cause softening of host tissues (Conway
et al., 1994b). Lara et al. (2004) suggested that improved resistance to fungal
attack in calcium-treated fruit was associated with the preservation of cell-
wall and middle-lamella structure. Calcium ions bind tightly to the pectins in
the cell walls and produce cationic bridges between pectic acids, or between
pectic acids and other acidic polysaccharides. These bridges make the cell
walls less accessible to the action of pectolytic enzymes (Moline, 1994;
Conway et al., 1994b).
Apart from the structural and functional role of calcium in plant cell walls
and membranes, it is also as important as an intracellular “second messenger”
(Zocchi and Mignani, 1995). Calcium ions are commonly involved as intra-
cellular messengers in the transduction by plants of a wide range of biotic
stimuli including signals from pathogenic and symbiotic fungi (Kang et al.,
2006; Vandelle et al., 2006; Yamniuk and Vogel, 2004; Navazio et al., 2007;
Gressel et al., 2002; Uhm et al., 2003; Hu et al., 2002). The defense responses
such as increased accumulation and excretion of phytoalexins, calloses, etc.,
which act against pathogens were produced on an application of calcium
saltsinonion(Dmitrievetal.,1996;Dyachoketal.,1997),sunower,and
grape (Dmitriev et al., 2003; Poinssot et al., 2003).
3.4 CHEMICALS USED
Calcium, as its chloride salt, has great potential in delaying ripening/aging,
extending postharvest shelf-life, improving nutritional value by increasing
calcium content, maintaining fruit firmness and quality (Lau et al., 1983;
Mason et al., 1975; Conway et al., 1992; Ferguson, 2001), and also helping in
Calcium: An Indispensable Element Effecting Postharvest 65
reducing the incidence of different physiological disorders, namely, internal
breakdown, scald, and water core (Yuen, 1994). Calcium chloride (CaCl2) is
natural, inexpensive, edible, and has been approved by the FDA (Food and
Drug Administration) for postharvest use. Foliar spray effects of calcium
chloride, calcium phosphate, and polyphenolic acid chelate of calcium
were compared in “Mclntosh” apple fruits with the aim to increase calcium
uptake into fruits without causing phytotoxicity to find that both calcium
chloride and calcium chelates sprays increased fruit calcium concentrations
and reduced senescence breakdown, while calcium phosphate sprays did not
increase fruit calcium concentrations but increased phosphorus concentra-
tion, which was not associated with reduced breakdown (Bramlage et al.,
1985).
Ferguson(2001)pointsoutthatthoughcalciumnitrateisalsoaneective
source of calcium, its use can cause russet problems later during fruit devel-
opment. Subbaiah and Perumal (1990) used dierent sources of calcium,
namely, calcium oxide, calcium chloride, and calcium sulfate, and found that
calcium chloride sprays had a better impact in improving quality and shelf-
lifeoftomatoes.Subbiah(1994)reportedthatcalciumchloridehasaneec-
tiverole in increasing rmness of the tomato fruits,whilermnessindex
was lowered by the increase in the levels of added nitrogen; hence, calcium
nitratemaynotbeadesirablecalciumsourceforenhancingthermnessof
the fruit. Hong and Lee (1999) also reported that calcium chloride treatments
aremoreeectiveinenhancingthequalityoftomatofruitswhencompared
to calcium nitrate. Singh et al. (1993) reported that two consecutive sprays of
calcium nitrate (1% or 2% Ca2+) or calcium chloride (0.6% or 1.2% Ca2+) at
20 and 10 days before harvest on “Dashehari” mango trees improved storage
life of fruit while retaining its quality. It was further reported that 0.6% Ca2+
calcium chloride proved to be the most favorable treatment.
Sprays of 200 ppm Ca2+ chelated with carboxylic acids (Calhard®) once
a week at the rate of 200 L per 100 m2 markedly increased strawberry fruit
rmnessalongwithcalciumandascorbicacidcontentsinthefruit(Conway,
1982). Naradisorn (2013) has reported that some fruits are particularly sensi-
tive to damage by chloride and the calcium sulfate (CaSO4) could be a poten-
tial alternative, as it also improves the soil structure and has been associated
with an improved root health. Postharvest treatment with calcium lactate was
suggested as a potential alternative to calcium chloride for shelf-life exten-
sion of fresh-cut cantaloupe and treated fruits were approximately 25–33%
rmerthancutanduntreatedcantaloupesamples,withoutprovidingunde-
sirable bitterness (Luna-Guzmna and Barrett, 2000). Dipping of strawberry
66 Emerging Postharvest Treatment of Fruits and Vegetables
cultivars“Cardinaland“Sunriseincalciumlactateimprovedberryrm-
ness (Morris et al., 1985). Matchima (2013) found that dipping strawberry
cultivar“Selvaincalciumlactateat3000ppmCawaseectiveindelaying
botrytis rot development during 7 days of storage.
3.5 METHODOLOGY OF APPLICATION
Methods of postharvest calcium treatment of fruit vary, and it may include
dipping (Mootoo, 1991; Suhardi, 1992; Yeun, 1994), spraying (Sharples and
Johnson, 1976; Drake et al., 1979), reduced pressure infiltration (Tirmazi
and Wills, 1981; Yeun et al., 1993, 1994), and foliar application of calcium
chloride to delay ripening and retard mold development in strawberries
(Chéour et al., 1990, 1991) and raspberries (Montealegre and Valdes, 1993).
Postharvest dip in calcium chloride solutions is also combined with the
heat treatment. Heat allows the formation of COO− groups from the pectin
content of the fruits or vegetables with which Ca2+ ions can form salt-bridge
cross-links (Stanley et al., 1995). This makes the cell wall-less accessible to
the enzymes that cause softening. This practice controls ripening, softening,
and decay at the same time (Sams et al., 1993).
Calcium dips have been used as rming agents to extend postharvest
shelf-life of fruits and vegetables such as apples (Mir et al., 1993; Sams
et al., 1993), peaches (Postlmayr et al., 1956), pineapples (de Carvalho et
al., 1998; Goncalves et al., 2000), oranges (Boas et al., 1998), tomatoes
(Floros et al., 1992), sliced pears (Rosen and Kader, 1989), and sliced canta-
loupe (Luna-Guzman et al., 1999). Strawberries submerged in 1% calcium
chloride solution for 15 min at 25°C and stored at refrigerated conditions
showed enhanced shelf-life (Garcia et al., 1996; Rosen and Kader, 1989).
The calcium chloride pretreatment in combination with gum acacia, gelatin,
provedtobeaneectivemethodforthepreventionofafter-cookingdark-
ening of french-fries (Mazza and Qi, 1991).
Conway and Sams (1984) treated “Golden Delicious” apples for 2 min
with 0–12% CaCl2solutionsbydipping,vacuuminltration(4.83psi),and
pressureinltration(10psi)andfoundthatoutofallthetreatmentsdipping
was least eective in increasing the calcium concentration of the tissue,
while vacuum inltration was superior over dipping and pressure inltra-
tionmethodwasmosteective.Vacuuminltrationof4calciumchloride
hasshownasignicantriseinthequalityparameterofapplesovercontrol
and water application (Poovaiah, 1986). Hong and Lee (1999) have accom-
plished vacuum inltration by applying the desired volume of calcium
Calcium: An Indispensable Element Effecting Postharvest 67
chloride and calcium nitrate solutions in millilitres on the stem-scar, placing
fruit under 250 Torr (4.834 lb sq. in−1) for 10 s and slowly releasing the
vacuum, allowing the solution to enter the fruit. Combination of 1% calcium
chlorideand0.5oxygenproducesimmediatermnesseectontheslices
of pear and greater maintenance (Rosen and Kader, 1989). Shorter and Joyce
(1998)have vacuum (partial pressure) inltratedcalcium(4 g Ca2+ L−1 as
CaCl2)atreducedpressure levels(−33, −66,and−99kPa)andfoundthat
fruitsinltratedat−66and−99kPaexhibitedinjuries,whichincludedexac-
erbatedlenticelblackeningandanaerobico-odorandtasteevident atthe
end of shelf-life.
Applying supplementary calcium into soil has been suggested as the
most ecient way of increasing calcium in plant organs (Conway et al.,
1994b). However, research on strawberry indicated that calcium is unlikely
to be translocated from roots to fruit. Increasing calcium concentration in
soil through the application of calcium sulfate increased leaf calcium content
but not that of fruit (Dunn and Able, 2006). To increase calcium content in
fruit, it is recommended that calcium should be applied directly to the fruit
surface (Garcia et al., 1996).
3.6 CONCENTRATION OF CHEMICALS USED
In some apple varieties, namely, Granny Smith and Yellow Newtown,
a single postharvest dip of 60 s in 2% (for Yellow Newtown) or 3% (for
Granny Smith) calcium chloride solution in place of in-season sprays have
been effective. Time of dip and mixing of the solution need to be carefully
managed as longer exposures or a higher percent solution can lead to fruit
bum. Using steel or iron tank for dipping is not recommended as it can
contribute to fruit damage (Caprile, 2012). Treating carrot shreds, slices, and
sticks with 1% calcium chloride solution significantly improved the posthar-
vest quality and shelf-life (Izumi and Watada, 1994). Postharvest dip in 1%
calcium chloride solution at 25°C has been found to be the most effective
method to reduce decay percentage, increase the firmness, and shelf-life of
strawberries and pears (Rosen and Kader, 1989; Garcia et al., 1996; Mahajan
et al., 2008) (Fig. 3.1). One percent calcium chloride application at about
3 psi significantly extended the shelf-life and about 30% of the significant
commercial value of peaches (Wills and Mahendra, 1989; Mahajan and
Sharma, 2000). Application of 6% calcium chloride as a preharvest foliar
spray in mandarin showed a higher quality and increased storage life in
the harvested fruits (El-Hammady et al., 2000). Foliar application of 0.2%
68 Emerging Postharvest Treatment of Fruits and Vegetables
calcium chloride solution in tomatoes, during the fruit growth period consid-
erably improved the quality of produce, while postharvest application of 1
mL of 8% calcium chloride to mature-green tomato fruits through vacuum
infiltration method has enhanced the calcium content in the fruits (Subbiah
and Perumal, 1990; Hong and Lee, 1999). Subbiah (1994) further observed
that 0.5% calcium chloride spray significantly increased the firmness index
of tomato fruits, when compared with calcium nitrate. Matchima (2013)
found that dipping strawberry in calcium lactate at 3000 ppm was effective
in delaying botrytis rot development during 7 days of storage. Singh et al.
(1993) experimented by two consecutive sprays of calcium nitrate (1% or
2% Ca2+) or calcium chloride (0.6% or 1.2% Ca2+) at 20 and 10 days before
harvest on “Dashehari” mango trees and found that it enhanced storage life
while retaining its quality. They further reported that comparatively 0.6%
Ca2+ calcium chloride proved to be the most favorable, while 1.2% Ca2+
calcium chloride treatment caused scorching of the marginal and lamellar
portion of the leaves.
Thetemperatureofthecalciumchloride diphadasignicantinuence
onthermnessofthemelonslices,wheretreatmentsat60Cshowedbetter
results than the dip at 20°C and 40°C (Luna-Guzman et al., 1999). Poovaiah
(1986) reported that there was a higher increase in the ascorbic acid content
of Golden Delicious apple when 4 calcium chloride was vacuum-inl-
trated, in comparison to 2%. A single coating of potato pieces with a combi-
nation of 0.5% calcium chloride and 5% pectin and sodium alginate reduced
the oil content of the French fries by 40% and retained high moisture content
(Khalil, 1999).
3.7 STAGES OF APPLICATION
The difference in growing condition, environmental factors, and fruit devel-
opment can influence the amount of calcium uptake by fruits (Conway et al.,
1994b; Wojcik and Swiechowski, 1999). To increase calcium concentration,
foliar sprays should be conducted at the late fruit growth stages (Wojcik,
2001).
Preharvest calcium application may be considered as a cultural practice
for maintaining adequate calcium concentration in fruit. Calcium-containing
compounds have been applied as supplemental fertilizers in soil amendments
or foliar sprays. Calcium chloride (CaCl2) and calcium nitrate (Ca(NO3)2)
Calcium: An Indispensable Element Effecting Postharvest 69
are commonly used for foliar sprays (Bramlage et al., 1985). Application
of calcium nitrate through irrigation water reduced the severity of leaf grey
mould of tomato plants grown in perlite by 70% (Elad and Volpin, 1993).
Foliar application of calcium chloride to peach trees throughout the
growing season improves fruit quality and maintains the quality longer
than the nontreated fruits (Robson et al., 1989). Foliar application of
calcium chloride at 0–20 kg ha−1 between 3 and 9 days before harvest
led to increased quality and reduced disease incidence in strawberry fruit
(Chéour et al., 1990). “Delicious” and “Golden Delicious” apples from
trees sprayed with calcium chloride three to four times per year at the rates
of 3.60 g L−1 and 4.76 g L−1, respectively, had more fruit calcium concen-
trations in comparison to control trees (Raese and Drake, 1993). Prehar-
vest foliar sprays of calcium chloride in red dragon fruit have increased
fruit rmness and reduced severity ofpostharvestdiseases(Ghani et al.,
2010). Similarly, calcium chloride sprays at a rate of 1.5 kg ha−1 at every 5
daysintervalfrompetalfallstagehasimprovedfruitrmnessanddisease
resistance in strawberries (Wójcik and Lewandowski, 2003). A minimum
of three preharvest sprays in apples, applied at monthly intervals begin-
ning in May or June showed positive results in California. Dilute sprays
(300–400 gal ac−1) are most eective but good coverage of the fruit is
essential (calcium doesn’t move rapidly within the fruit or from leaf to
fruit. For more severe cases, shorter treatment intervals (every 2 weeks)
over the same 3-month period are recommended. There is also evidence
to indicate that the earlier treatment, beginning in May or even at one-
inchfruitsiemaybemoreeectiveinverysusceptiblevarieties(Caprile,
2012). A preharvest foliar spray of CaCl2 at anthesis not only increased the
absorption of calcium in leaves and fruits but also enhanced the yield and
shelf-life of tomato (Abbasi et al., 2013).
El-Hammady et al. (2000), when applied 4% and 6% calcium chloride
solutions to Mandarin trees at mature-green stage of fruits, found positive
results pertaining to physical and nutritional parameters of the fruits. Fruits,
whenvacuum-inltratedwithcalciumchloridesoonafterharvestandstored
at refrigerated conditions, showed a signicant increase in ascorbic acid
levels till 15 weeks of application (Poovaiah, 1986). The pretreatment of
potatoes with calcium chloride before processing in combination with gum
acacia,gelatinprovedtobeaneectivemethodforthepreventionofafter-
cooking darkening of french-fries (Mazza and Qi, 1991).
70 Emerging Postharvest Treatment of Fruits and Vegetables
3.8 EFFECTS OF CALCIUM APPLICATION
3.8.1 EFFECT ON QUALITY PARAMETERS
Increasing the concentration of Ca2+ by pressure infiltration has shown to
delay softening in the fruits (Mootoo, 1991; Suhardi, 1992; Yeun et al., 1993).
Similarly, maximizing calcium concentration, without incurring damage, can
reduce risk of disorders and help in maintaining firmness and other desirable
quality parameters in apple (Stow, 1993; Ferguson, 2001), avocado (Tingwa
and Young, 1974), litchi (Roychoudhury et al., 1992), raspberries (Eaves et
al., 1972), and tomato (Wills and Tirmazi, 1979). Postharvest application
of calcium chloride increased the flesh calcium concentration of cherries,
improved texture (firmness and bio-yield), and incidence of pitting resulting
from impact damage (Lidster et al., 1978; 1979). Calcium treatment main-
tained firmness in sliced strawberries even better than that in the case of
whole strawberries and this could be attributed to the availability of more
surface area for calcium chloride adsorption (Morris et al., 1985) (Table
3.2). Similarly, calcium chloride-treated carrot shreds had more calcium
concentration and firm texture, when compared to carrot slices and sticks
exposed to similar treatments (Izumi and Watada, 1994). In red dragon fruit,
preharvest calcium chloride sprays increased fruit firmness, but fruit quality
such as soluble solids and titratable acidity were not affected by the calcium
sprays (Ghani et al., 2010). Foliar application of calcium chloride at rates
of 0–20 kg ha−1 between 3 and 9 days before harvest increased the calcium
content of strawberry and also delayed fruit ripening, although there was
no effect observed on acidity, soluble solids and titratable acidity (Chéour
et al., 1990). Sprays of Ca2+ chelated with carboxylic acids (Calhard) once
a week increased strawberry fruit firmness and the force required to punc-
ture the skin of calcium-treated strawberries was greater than that of control
(Conway, 1982).
Mahajan and Sharma (2000) found that preharvest spray of 1% calcium
chloride not only improved quality parameters (size and totals sugars) but
also maintained the quality during extended storage life of peaches. It also
delayed maturity and improved storability of Mandarin oranges (Hsiung
and Iwahori, 1984; Schirra and Mulas, 1994) and mangoes (Tirmazi and
Wills, 1981; Mootoo, 1991; Yeun et al., 1993; Singh et al., 1993). Applica-
tion of 6% calcium chloride as a preharvest foliar spray in Mandarin oranges
showed comparatively higher values of ascorbic acid and also recorded less
Calcium: An Indispensable Element Effecting Postharvest 71
physiological loss in weight of fruits (El-Hammady et al., 2000). Calcium
chloridedipimprovedrmnessandcalciumcontentoffresh-cutmelonslices
while reducing the rate of change in metabolism. The respiration rate (CO2
production) and the ethylene production rate were reduced, which pertain to
increase in shelf-life of fresh-cut melon slices (Luna-Guzman et al., 1999),
apples (Ferguson, 1984), avocados (Tingwa and Young, 1974), and mangoes
(Mootoo, 1991; Van Eeden, 1992).
Calcium treatment also had a signicant eect on the organoleptic
acceptance of peaches where calcium-treated fruits not only rated superior
in appearance, aroma, avor, and texture after harvest but also continued
the overall acceptance greater than the control fruit even after 4 weeks of
storage (Robson et al., 1989). The use of calcium chloride may impart bitter-
nessor avordierenceswhich results fromresidual calcium chlorideon
the surface of the fruit (Morris et al., 1985).
FIGURE 3.1 Effect of calcium chloride on storage life and fruit quality of pear and plum.
Source: Adapted from Mahajan and Dhatt (2004); Mahajan et al. (2008).
TABLE 3.2 Effects of Calcium Application.
Fruit Effect References
Apple Retains fruit firmness
Increase fruit calcium content
Increase vitamin C content
Reduce postharvest decay
Reduce respiration and ethylene produc-
tion rates
Poovaiah (1986), Conway
and Sams (1984), and
Ferguson (1984)
72 Emerging Postharvest Treatment of Fruits and Vegetables
Fruit Effect References
Straw-
berry and
blueberry
Extends shelf-life
Slows down the rate of decay
Maintains firmness of the fruit for an
extended period
Garcia et al. (1996), Rosen
and Kader (1989), Morris et
al. (1985), and Hernandez-
Munoz et al. (2006)
Peach Improve quality
Extend shelf-life
Reduces brown rotting and disease index
Wills and Mahendra (1989),
Souza et al. (1999), Robson et
al. (1989), and Mahajan and
Sharma (2000)
Pear Maintains firmness and freshness of
sliced pears for an extended period
Rosen and Kader (1989)
Orange Extend shelf-life
Improve quality
Fewer disorders
Hsiung and Iwahori (1984),
Schirra and Mulas (1994),
and El-Hammady et al.
(2000)
Pineapple Reduce internal browning
Reduce phenolics and decay
Goncalves et al. (2000) and
de Carvalho et al. (1998)
Cantaloupe Improve firmness
Extend the shelf-life
Luna-Guzman et al. (1999)
Carrot Improve firmness
Extend shelf-life
Izumi and Watada (1994)
Tomato Improve firmness and quality
Increases shelf-life
Enhance lycopene and ascorbic acid
Subbiah and Perumal (1990),
Subbiah (1994), and Hong
and Lee (1999)
Potato Extend storage life
Reduces browning and decay
Improves the quality of processed prod-
ucts and reduces oil consumption
Walter et al. (1993), Klein-
henz et al. (1999), and Mazza
and Qi (1991)
3.8.2 EFFECT ON NUTRITIONAL AND BIOCHEMICAL STATUS
Ascorbic acid levels increased in the Golden Delicious apple fruits with
postharvest calcium chloride infiltration during storage at refrigerated condi-
tions. On the other hand, ascorbic acid levels showed a decreasing trend
under control with the increase in storage period (Poovaiah, 1986). The
ascorbic acid and lycopene levels in the tomato fruits increased considerably
TABLE 3.2 (Continued)
Calcium: An Indispensable Element Effecting Postharvest 73
with foliar application of 0.2% calcium chloride during fruit growth stage
(Subbaiah and Perumal, 1990). Strawberries dipped in calcium chloride and
stored at 25°C showed high levels of calcium content which decreased with
increase in storage temperature (Garcia et al., 1996). Sprays of Ca2+ chelated
with carboxylic acids (Calhard) once a week increased ascorbic acid and
calcium content (Conway, 1982).
Postharvest application of calcium reduced enzyme levels and increased
the levels of neutral sugar in peaches (Souza et al., 1999). Postharvest
calcium treatment reduced the phenolics (indicative of decaying) content
of the pineapples and showed extended shelf-life in comparison to control,
regardless of the storage temperature and duration of treatment, which may
be due to maintenance of the pectin substances in their cell walls due to
calcium absorption (de Carvalho et al., 1998; Goncalves et al., 2000).
3.8.3 EFFECT ON MICROBIAL GROWTH AND
PHYSIOLOGICAL DISORDERS
Conway and Sams (1984) have indicated that calcium-enriched tissue
develops resistance to fungal attack by stabilizing or strengthening cell
walls, thereby making them more resistant to harmful enzymes produced by
fungi, and it also delays ageing of fruits. Garcia et al. (1996) have demon-
strated that postharvest dip in calcium chloride reduced strawberry decay
significantly by improving fruit firmness. Brown rotting and disease index
was reduced to the significant percentage in peaches treated with calcium
chloride, in comparison to untreated peaches (Souza et al., 1999). The total
microbial count was substantially reduced when carrot shreds were treated
with 1% calcium chloride solution and increased resistance of tissues to
the bacterial infections rather than to a bacterial action (Izumi and Watada,
1994). In red dragon fruit, preharvest spray of calcium chloride reduced the
severity of anthracnose and brown-rot diseases (Ghani et al., 2010).
Foliar application of calcium chloride at 0–20 kg ha−1 between 3 and
9 days before has reduced grey mould (Botrytis cinerea) development
(Chouretal.,1990).Similarly,fruitatharvestwerermerandmoreresis-
tant to Botrytis fruit rot than those in the control when fruits were sprayed
with calcium chloride at a rate of 1.5 kg ha−1 spray at every 5 days interval
from petal fall stage (Wójcik and Lewandowski, 2003). Application of
calcium sulfate to strawberry plants showed less incidence of grey mould
than fruit harvested from plants that received no calcium for cultivars
“Aromas” and “Selva.” The shelf-life of “Aromas” and “Selva” increased
74 Emerging Postharvest Treatment of Fruits and Vegetables
by about 8% when plants received 500 ppm Ca in comparison with plants
that did not received calcium treatment. Elad and Volpin (1993) applied
calcium sulfate to soil before planting tomato seedlings and found that it
reduced the grey mould disease severity by 30–40%. Fruits harvested from
strawberry plants applied with calcium sulfate had a less incidence of grey
mould than untreated plants along with enhanced shelf-life (Matchima,
2013). Abbasi et al. (2013) reported that calcium chloride at anthesis
reduced occurrence of blossom-end rot, improved quality and shelf-life of
the tomato fruits (Table 3.1). Goncalves et al. (2000) reported that post-
harvest treatment of pineapple slices with calcium chloride retarded their
decay rate and internal browning of the fruit regardless of the temperature
and duration of the treatment.
3.9 NEGATIVE EFFECTS OF CALCIUM APPLICATION
The extent of positive responses of fruits to calcium application may
vary and can be limited (O’hare and Zauberman, 1992; Suhardi, 1992).
The fruit damage such as mesocarp discoloration in avocado (Yeun et al.,
1994) and lenticel spotting in mango (Tirmazi and Wills, 1981; O’Hare and
Zauberman, 1992) can occur at too high Ca2+ concentrations. However, a
major disadvantage of postharvest calcium treatments has been the inability
to predict potential injury (lenticel pitting and surface discoloration) to the
fruits (Conway et al., 1994c; Yeun, 1994). Application of calcium nitrate and
calcium chloride can cause phytotoxicity and even relatively low concentra-
tions of calcium chloride can produce serious foliar injury, while calcium
nitrate is more likely to produce fruit injury (Bramlage et al., 1985). Injury
probably is a phytotoxic response to too much calcium in the fruits (Conway
and Sams, 1985). At least part of the calcium-induced injury appears to be
due to salt stress since the severity of the injury increases with the concen-
tration (Sharples and Johnson, 1976) and decreases when fruit is rinsed of
the surface calcium immediately after calcium treatment (Scott and Wills,
1977). Calcium-induced injury to the apples can also be reduced, but not
eliminated, by storing fruits in high humidity (Lidster et al., 1977). In case
of mango, calcium-induced injury was reduced by packaging the fruit in
polymeric films that modified atmosphere and increased the humidity in the
air surrounding the fruit (Yeun et al., 1993).
Calcium: An Indispensable Element Effecting Postharvest 75
3.10 CONCLUSION
It is clearly established that calcium plays a wide and important role in pre-
and postharvest life of fruit and vegetables. The importance of calcium in
the nutrition of plants has long been recognized and application of calcium
early in plant development may be important for the later, but direct calcium
application to fruit may be more significant in the former. The pre- and post-
harvest factors could clearly influence the effect of calcium on shelf-life
extension, quality improvement, and control of decay of harvested produce.
KEYWORDS
•calcium
•postharvest
•shelf-life
•fruit quality
•decay control
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