Citrus species are major exports products of Egypt. The total cultivated area
for citrus fruits are 159,446,143 ha with total production estimated to 3,311,300
ton (FAO, 2010). The orange cultivation accounts 63%
of Egypts total citrus production. Three main varieties of oranges are
produced in Egypt: Navel, Valencia and Baladi. Washington Navel orange (Citrus
sinensis, L. Osbeck) is the most popular orange cultivar among other citrus
species in Egypt.
Green and blue moulds, caused by Penicillium digitatum (Pers.Fr.) Sacc.
and Penicillium italicum Wehmer, respectively, are the most significant
postharvest diseases of citrus in all production areas that like Spain, California
or Israel (Eckert and Eaks, 1989).
Both P. digitatum and P. italicum are severe wound pathogens
that can infect the fruit in the orchard, the packinghouse and during allocation
and marketing. They reproduce very quickly and their spores are ubiquitous in
the atmosphere and on fruit exterior and are simple distributed by air currents.
Therefore, the source of fungal inoculum in citrus orchards and packing houses
is virtually continuous during the season (Kanetis et
al., 2007). Citrus fruit can become soiled with conidia
of the two fungi that are loosened in handling of diseased fruit. The conidia
located in damage that laceration oil glands or penetrate into the albedo of
the peel usually bring irreversible infection within 48 h at 20-25°C (Eckert
and Eaks, 1989). The germination of conidia of both Penicillium species
inside rind wounds requires free water and nutrients (Plaza
et al., 2003; Lahlali et al., 2006;
Stange et al., 2002).
Postharvest diseases caused by Geotricum candidum (sour rot),
Penicillium digitatum (green mould) and P. italicum (blue mould)
are the very significant negative agents affecting in handling and marketing
of citrus fruits in Egypt (El-Mougy et al., 2008).
They cause dangerous problems to the harvested citrus fruits during handling,
transportation, exportation and the storage process. Although the use of chemical
fungicides gave satisfactory control against mould infection, the fungicide
residual can have a harmful effect on people and the environment.
Moreover, successive use of fungicides could lead to some fungal isolates to
develop a significant resistance to the applied fungicides. Therefore, alternative
fungicide treatments are needed for the management of postharvest diseases of
Qin et al. (2010) revealed that boron strongly
inhibited spore germination, germ tube elongation and mycelial spread of Botrytis
cinerea in the culture medium. Moreover, application of boron at 1% caused
the appearance of abnormal spores (disrupted) in some cases. Furthermore, boron
led to the leakage of cellular constituents (soluble proteins and carbohydrates)
from hyphae of B. cinerea. The quantities of boric acid and its sodium
salts applied as pesticides are modest compared to amounts used for the other
non-pesticidal purposes. Further, boric acid, borax and boron-containing salts
are ubiquitous in the environment. Boron occurs naturally in water, fruits,
forage crops and is an essential nutrient for plants as well as an essential
element for many organisms.
The mechanisms by which boron decreased gray mold decay, may be directly related
to the disruption effect of boron on cell membrane of the fungal pathogen that
resulted in the breakdown of the cell membrane and loss of cytoplasmic materials
from the hyphae. Exogenous application of boron was shown to alleviate the occurrence
of browning injuries in pears during controlled atmosphere storage (Xuan
et al., 2005). Nevertheless, little information is available concerning
the effect of boron for control of plant disease caused by microbial pathogens
and the physiological basis involved. The inhibition effect of P. expansum
may be related to the increased oxidative stress caused by boron through
suppressing the expression of antioxidant enzymes in the pathogen (Qin
et al., 2007).
Jojoba oil is commonly known as liquid wax, colorless and odorless with unique
physical and chemical properties. Also, jojoba oil can easily be hydrogenated
into a soft wax that can be used in candle wax, various kinds of polishes, coating
material for fruits and pills (Nagvi and Ting, 1990).
Abd El-Moneim and Abd El-Mageed (2006) revealed that
coating Washington Navel orange fruits with jojoba oil led to reduce fruit decay,
weight loss and increasing fruits storage life. As storage days progressed total
soluble sugar (TSS) increased, but the titratable acidity and ascorbic acid
contents decreased. Abd-Allah et al. (2012)
found that coating persimmon fruits with jojoba oil helped to delay ripening
and reduced weight loss and decay percentage.
The purpose of this study was to investigate the dipping affection boric acid
and/or jojoba oil on controlling postharvest diseases caused Penicillium
digitatum (green mould) and P. italicum (blue mould) to improve
fruit quality during marketing period.
MATERIALS AND METHODS
This investigation was carried out for two successive seasons (2011 and 2012)
to evaluate the effect of jojoba oil and boric acid as postharvest treatments
on the quality of Washington Navel orange fruits during marketing.
Isolation and identification: Penicillium digitatum (green mould)
and P. italicum (blue mould) were isolated from naturally infected Washington
Navel orange fruits after storage of several weeks. These isolates were the
most aggressive one in our collection and produced the largest lesions on inoculated
fruits. These fungi were purified and maintained on Potato Dextrose Agar (PDA)
and stored at 4°C, with periodic transfers through citrus fruits to maintain
its aggressiveness. Fruits were ready for examination under a stereoscopic binocular
microscope (6-50 X) for the presence of fungi and to study their habit characters.
When necessary the compound microscope was used for confirming the identification
after having examined the morphology of conidia and conidiophores (Singh
et al., 1991).
Effect of jojoba oil and/or boric acid on linear growth and dry weight of
fungi isolated from Washington Navel orange fruits:
||Linear growth: Jojoba oil and boric acid were tested
in vitro on the linear growth of the pathogenic fungi. Different concentrations
were added to 10 mL of sterilized PDA before solidification and then poured
in sterile Petri-dishes. After solidification, the plates were inoculated
with fungal disc (5 mm) in the center of the plate and incubated at 27±1°C.
Three plates for each particular treatment for each fungus were used as
replicates; three plates were prepared to serve as control for each fungus.
Linear growth was observed daily and diameter of fungal colonies were recorded
when plates of any treatment were filled with the fungal growth
||Dry weight: One hundred milliliter of liquid PD medium in 250 mL
Erlenmeyer flasks were amended with different concentrations of the tested
compounds after autoclaving. Each flask was inoculated using two discs of
0.6 mm in diameter of fungal culture, then incubated at 20°C±2
for 7 days. Control flasks contain no concentrations of these compounds.
Three replicates were used for each concentration. At the end of incubation
period, the mycelium was filtered off and washed several times with distilled
water, then dried in an oven at 80°C for 48 h till constant weight (El-Morsy,
In vitro experiments: Orange fruits were picked from12 year old
Washington Navel orange trees budded on Sour orange (Citrus aurantium)
rootstock grown in a private orchard at Aga city, Dakahlia, Governorate. At
both seasons, fruits were harvested at the first week of January which is the
optimum maturity stage. Selected fruits were directly transported to the laboratory
of post-harvest at Hort. Res. Inst. Mansoura, Egypt. Defective fruits were almost
equal in size and apparently insect and pathogen injury free. All fruits were
washed with tap water to remove the dust and foreign materials, then air-dried
and a quick sorting was done to research fruit for any defects. At the beginning
of the experiment, samples of 15 fruits were taken to determine the initial
fruits properties and then received the following treatments:
||Control (dipping fruits in tap water)
||Dipping fruits in boric acid (1.0)
||Dipping fruits in jojoba oil (0.1%)
||Dipping fruits in boric acid (1.0%)+jojoba oil (0.1%)
The fruits were left to dry and then packed in one layer inside ventilated
carton boxes each consists of 15 fruits. Nine boxes served for each treatment.
The total number of boxes were 36 for all treatments and then held at 18°C±1
with 75-80% relative humidity.
The fruits were periodically examined at 15 days intervals until the end of
the marketing period (45 day), to determine the following parameters:
||Disease infection: It was determined according to the following equation:
||Quality of washington Navel orange fruits:
||Loss in fruit weight: It was determined according to
the following equation:
||Decay: It was determined according to the following
||Total loss in fruit: It was determined according to
the following equation:
Total loss in fruit (%) = Loss weight%+decayed fruits weight%
||Peel thickness (mm): Rind thickness of each fruit was
measured by digital verneir caliper (Nawaz et al.,
||Juice percentage: It was obtained from the following
||Soluble solids content (SSC%): Soluble solids content
in fruit juice was measured using a Carl-Zeiss hand refractometer according
to AOAC (2005)
||Titratable acidity (TA%): It was determined in10 mL of fruit juice
by titrating with 0.1 N sodium hydroxide in the presence of phenolphthalein
as indicator and the results were expressed as a percentage of citric acid
according to AOAC (2005)
||Soluble solids content (SSC)/acid ratio%: This ratio was calculated
from the results recorded for fruit juice SSC and titratable acidity
||Ascorbic acid (mg 100-1 g fresh weight): Ascorbic acid
(vitamin C) was measured by the oxidation of ascorbic acid with 2, 6-dichlorophenol
endophenol dye and the results were expressed as mg 100-1 g fresh
weight according to Ranganna (1979)
||Ascorbic acid oxidase (AAO) unit/mg protein/min: The reaction mixture
consist of 0.1 mL enzyme extract and 2.9 mL ascorbic acid-phosphate buffer
(pH 5.6) prepared as 8.8 mg ascorbic acid dissolved in 300 mL phosphate
buffer. The oxidation of ascorbic acid was measured by changes in optical
density at 265 nm in 30 sec. intervals for 5 min. The unit of AAO activity
was defined as the amount of enzyme which decompose 1 mmol ascorbic acid
per minute at 25°C. Protein content of the extracts was determined according
to Bradford (1976) using bovine albumin serum as
Statistical analysis: Data of both seasons were analyzed using analysis
of variance (ANOVA) technique. Differences among treatment means were statistically
compared using the least significant differences test (LSD) at p = 0.05 using
the CoStat v6.4 program.
RESULTS AND DISCUSSION
The propose of this work was to estimate the effect of postharvest dipping
in boric acid and/or jojoba oil alone on fruits quality and decreasing decay
of Washington Navel orange during shelf life under ambient conditions at 18°C±1
with 75-80% relative humidity.
Linear growth and dry weight of fungi isolated from washington Navel orange:
Data in Table 1 show the effect of dipping with jojoba oil
and/or boric acid on linear growth and dry weight of P. digitatum and
P. itelicum isolated from Washington Navel orange fruits. It was also
noticed that the reduction in linear growth and dry weight were correlated to
the increase in compounds concentrations. Boric acid (1.0%)+jojoba oil (0.1%)
treatment were complete inhibition of the linear growth and dry weight of
P. digitatum and P. itelicum. This result is in agreement with the
finding of Latifa et al. (2011) on citrus who
reported complete inhibition of mycelia growth of P. itelicum which was
generally associated with complete inhibition of sporulation by organic acids
Data in Table 2 show the effect of dipping with jojoba oil
and/or boric acid on disease infection of Washington Navel orange fruits stored
for 45 days at room temperature. In both seasons, prolonging the marketing stage
resulted in decreased in disease infection with the increase in compounds concentrations.
Boric acid (1.0%)+jojoba oil (0.1%) treatment gave the maximum reduction in
disease infection caused by P. digitatum and P. itelicum (0.0%).
This result is in agreement with the finding (Troncoso-Rojas
and Tiznado-Hernandez, 2007) on fruits and vegetables by chemical alternatives
to conventional fungicides for postharvest disease control should be natural
or synthetic compounds with known and minimal toxicological effects on mammals
and the environment.
||Effect of jojoba oil and boric acid on linear growth (cm)
and dry weight (g) of fungi isolated from Washington Navel orange fruits
||Effect of jojoba oil and/or boric acid as postharvest treatments
on disease infection% of Washington Navel orange fruits stored for 45 days
at room temperature during 2011 and 2012 seasons
The origin of these alternatives includes classifications such as food additives
and substances listed as GRAS (Generally Regarded as Safe) by the United States
Food and Drug Administration, natural compounds obtained from plants, animals
or microorganisms including some volatiles and essential oils, phenolic compounds,
plant extracts, peptides, alkaloids, lectins, antibiotics, propolis, latex or
chitosan and other chemicals such as calcium polysulfide or ammonium molybdate.
Effect of jojoba oil and/or boric acid on orange fruits
Loss in fruit weight percentage: Citrus fruits lose water at low
relative humidifies after harvest are prone to stem-end rind breakdown, a physiological
injury that can predispose fruit to decay. Table 3 shows that
all dipping treatments with jojoba oil and/or boric acid significantly reduced
fruit weight loss than the control during both seasons under the study.
||Effect of jojoba oil and/or boric acid as postharvest treatments
on weight loss, decay and total loss of Washington Navel orange fruits stored
for 45 days at room temperature during 2011 and 2012 seasons
The prolongation of the marketing stage resulted in increased fruit weight
loss. However, control fruits lost 23.36 and 21.16% of their weight in the two
seasons, respectively. Fruits estimated to boric acid treatment caused 17.93%
in the first season and 14.53% in the second season weight loss, whereas jojoba
oil treatment caused 17.10% weight loss in the first season and 14.13 in the
second season. The most effective treatment in both seasons were that of boric
acid (1.0%)+jojoba oil (0.1%) which recorded fewer weight losses values13.53
and 11.13, respectively, than the other treatments used or the control.
The Application of jojoba-based waxes significantly reduced internal O2
levels and increased internal CO2 (Erkan et
al., 2005), since Abd El-Moniem et al. (2008)
found that jojoba treatment reduced weight loss percentage of mango fruits comparing
with the control. Additionally, Abd-Allah et al.
(2012) found that coating persimmon fruits with jojoba oil helped to delay
ripening and reduced weight loss and decay percentage.
Decay percentage: Concerning the decay percentage of orange fruit, developed
during marketing stage, Table 3 reveals that control fruits
became deplorable after 45 days which maintained 25.40 and 24.56% decayed fruits
in both seasons, respectively.
Boric acid (1.0%)+jojoba oil (0.1%) did not show any decayed fruit during 45
days in the first season and 30 days in the second season which causes only15.96%
decayed fruits after 45 days through shelf life.
Whereas, fruits dipping with jojoba oil alone recorded higher decay percentage
20.50 and 19.43% at two seasons than those dipping with boric acid alone (18.66
and 17.46%, respectively).
Decay was mentioned as one of the limiting factors for postharvest life of
citrus fruit because of removing the natural wax of citrus peel through the
handling in packinghouses (Huating, 2004).
Boron deficiency is known to alter cell wall structure, membrane integrity,
enzyme activity and a wide range of plant metabolites (Goldbach,
1997). Also, boron has been shown to be essential to the structure and function
of plant cell walls and membranes (ONeill et al.,
Wojcik et al. (1999) showed that boric acid
application to apple fruit play an important role in reduced the infection with
Botrytis cinerea and decreased fruit bitter pit, internal breakdown and
Gloeosporium-rot. This related to the disruption effect of boron on cell
membrane of the fungal pathogen that resulted in the breakdown of the cell membrane
and loss of cytoplasmic materials from the hyphae.
Rolshausen and Gubler (2005) demonstrated that boron
could be used for the control of disease in grapevine caused by the fungus Eutypa
lata. In addition, boron inhibited spore germination and mycelial growth
of B. cinerea, indicating that the effect of boron against gray mold
on table grapes may be directly related to its antifungal activity and has been
used extensively in agriculture for control of fungi, bacteria and many insects.
Treatment of grapes with boron offers an effective, economical and environmentally
safe management strategy to control B. cinerea, moreover, boron is an
essential plant micronutrient (Qin et al., 2010).
Total loss in fruit percentage: The total loss in weight which including
both loss in fruit weight and decayed fruits, are presented in Table
3. It is clear that the total loss in fruit was significantly increased
during marketing as storage period prolonged. Moreover, all the applied treatments
reduced the percent of total loss in fruit significantly than the control,yet
the percent were 48.76% and 45.72% after 45 days through shelf life at room
temperature in both seasons, respectively.
Moreover, boric acid (1.0%)+jojoba oil (0.1%) was more effective in reducing
the percent of total loss in fruits compared with single application of boric
acid or jojoba oil. The percent of total loss due to this treatment were about
13.53 and 27.09% after 45 days during marketing, respectively in both seasons.
In this respect, dipping fruits by boric acid was more effective in reducing
the total loss in orange offering about 36.59 and 31.99% compared with jojoba
oil presenting about 37.60 and 33.56% under 45 days of shelf life in both seasons
There are two major problems limit the long-term storage capability of citrus
fruits; the first is pathological breakdown that leading to decay; the second
is physiological breakdown, resulting in the appearance of the various rind
disorders (Porat et al., 2004). Abd
El-Moniem et al. (2008) studied the effect of different coating materials
and concluded that coating Washington Navel orange fruits with jojoba oil and
orange oil were the best in reducing decay and wet loss with increasing fruits
storage life. Hoa et al. (2002) treated mango
fruits with different coating treatments and found that, all coating treatments
reduced the respiratory rate and loss of firmness; also the changes in the acid
content were delayed in all coated mangoes.
Ahmed et al. (2007) concluded that, the first
utilization of trans jojoba oil (TJO) as Valencia orange fruit coating is promising
wax than the other investigated coating materials. It can be predicted that
TJO coatings resistance to gas exchange is strongly influenced its ability
either by blocking pores on the surface of the fruit or, acting as barriers
not only to gases migration to restrict respiration, but also to water vapor
transfer reducing transpiration and weight loss. So TJO wax can be used successfully
without any additives as coating product from natural source. It is substitute
or alternative to commercial wax used in handling citrus fruit for export, this
facilitate good quality up to 8 weeks which was enough period for sea or land
shipment for exported citrus fruit.
The mechanisms by which boron decreased gray mold decay of table grapes may
be directly related to the disruption effect of boron on cell membrane of the
fungal pathogen that resulted in the breakdown of the cell membrane and loss
of cytoplasmic materials from the hyphae (Qin et al.,
Soluble solids content (SSC): It is clear from Table 4
that the percent of SSC in fruit juice gradually increased as the storage period
advanced during shelf life. The increase in soluble solids content with prolongation
of storage period may probably be due to increased hydrolysis of polysaccharides
and concentration of juice due to dehydration. The data also disclose that,
boric acid at 1.0%+jojoba oil at 0.1% gave a somewhat increment in SSC% in fruit
juice (12.26 and 13.83%) than all treatments used or the control during shelf
life through both seasons. Since, all treatments used and the control produced
fruits with higher significant percent of SSC in fruit juice than those treated
with boric acid at 1.0% during the two seasons under the study. In this respect,
boric acid at 1.0% provided the lowest percent of SSC which were 11.83 and 12.66%
after 45 days through shelf life at room temperature in both seasons, respectively.
||Effect of jojoba oil and boric acid as postharvest treatments
on SSC, titratable acidity and SSC/acid ratio of Washington Navel orange
fruits stored for 45 days at room temperature during 2011 and 2012 seasons
Abd El-Motty et al. (2007) demonstrated that,
preharvest spraying with boric acid treatment at 0.25% after 50 days of storage
at 0°C significantly increased T.S.S.% and total sugars% of "Canino" apricot
fruit than all treatments used. The obtained results are in agreement with those
of Hassan et al. (2005) who reported that spraying
boric acid increased percentage of total soluble solids in "Canino" apricot.
Asgharzade et al. (2012) showed that spraying
boron as a pre-harvest treatment had significant effect on texture of apple
fruits and increased brix index about 9.18% as compare to control treatment.
Abd-Allah et al. (2012) showed that that coating
persimmon fruits with jojoba oil helped to delay ripening preserve fruit quality.
Also, total sugars were increased gradually with the increase of storage period.
However, it seems that sugar content was increased with decreasing jojoba concentration.
In this respect, it seems that jojoba oil is benefit natural product to conserve
persimmon fruits during cold storage.
Titratable acidity (TA): A gradual decrease in titratable acidity was
found in all treatments used from harvest until 45 days through shelf life at
room temperature in both seasons. Data from Table 4 demonstrate
that all treatments used reduced the percent of total acidity in fruit juice
than the control during both seasons. Control fruits retained higher significant
percent of TA than all treatments used attaining, 0.53 and 0.57% in both seasons,
respectively. Commonly, minimum percent of TA was found in fruit treated with
boric acid at 1.0%+jojoba oil at 0.1 attained 0.372% in the first season while,
boric acid alone gave the lowest percent (0.412%) in the second season, but
the variation was unpronounced.
The decrease in acidity with the storage period might be due to utilization
of organic acids in the respiration process. A gradual decrease in acidity has
also been reported by Jawandha et al. (2012).
Moreover, El Bulk et al. (1997) concluded that,
fruit will reach high levels of sugar, ascorbic acid, soluble solids and their
lowest level of acidity as they ripened.
SSC/acid ratio in fruit juice: Considering to SSC/acid ratio, data in
Table 4 reveal that the values of SSC/acid ratio were progressively
increased by the advance in storage period from harvest till 45 days during
shelf life at room temperature. The increment in SSC/acid ratio during the storage
period mainly due to the augmentation of SSC content with the reduction in total
acidity in fruit juice during the storage period.
With regard to the effect of these treatments on SSC/acid ratio, the data reveal
that, boric acid at 1.0%+jojoba oil at 0.1% produced a higher pronounced values
of SSC/acid ratio compare to all treatments used (32.95 and 32.08) during both
seasons, respectively. Whereas, control fruits reduced the content of SSC/acid
ratio pronouncedly through both seasons, since it presented 22.66 and 23.63%,
compared with boric acid or jojoba oil alone.
As SSC/acid ratio is a flavoring factor, so these results depicted that with
increase in the ratio there was a decrease in the acidity so with low SSC/acid
ratio, quality of fruit is poor and taste of fruit becomes watery and insipid.
In addition, the ratio is used to determine the fruit maturity standards, so
where the ratio is high, fruit will mature earlier. Zekri
(2000) reported that the higher the brix: acid ratio, the earlier is the
fruit maturity. Hansch and Mendel (2009) mentioned
that boron has a main role in many processes specially transport of sugars and
Abd-Allah et al. (2012) established that coating
persimmon fruits with jojoba oil helped to preserve fruit quality and increased
both flesh firmness and acid content.
Peel thickness: The thickness of peel is considered to be a character
of importance in many fruits. It was noticed that, peel thickness of Washington
Navel orange decreased with increasing storage period as shown in Table
5. The peel thickness was significantly higher with boric acid at 1.0% combined
with jojoba oil at 0.1% than other treatments. Appeared peel thickness of this
treatment was 3.10 and 3.86 mm after 45 days through shelf life at room temperature
in both seasons, respectively. Slight differences were noticed in the same period
with dipping fruits by boric acid alone in the first season recording 2.86 mm
and by jojoba oil in the second season sorting 3.33 mm. Meanwhile the decrease
in peel thickness was significantly with control fruits in the second season
that realized 2.96 mm after 45 days during shelf life at room temperature.
Some physiological, nutritional and functional properties of the fruits, like
the respiratory intensity, the sugar content and the antioxidant capacity, play
an indirect role in the enzymatic peeling because they affect the possibilities
of storage and the quality of the finished product (Pretel
et al., 2005). From the molecular point of view, pectin, cellulose
and hemicelluloses are responsible for the adherence of the skin to the fruit.
Therefore, both pectinases and cellulases are needed for the enzymatic peeling.
The cellulases are probably needed for the release of the pectinsin the albedo
and the pectinases contribute to the hydrolysis of the polysaccharides of the
cell wall (Ismail et al., 2005). However, the
adherence of the peel to the fruit and its thickness are different according
to the species or the citrus varieties and the design of the cuts, the vacuum
conditions, temperature and pH also affect the peeling (Pretel
et al., 2007).
||Effect of jojoba oil and/or boric acid as postharvest treatments
on peel thickness, juice volume, ascorbic acid and ascorbic acid oxidase
(AAO)of Washington Navel orange fruits stored for 45 days at room temperature
during 2011 and 2012 seasons
Juice volume: In many citrus, the juice content of fruits is estimated
to be higher with thinner the peels. The amount of juice present in a fruit
is considered to be one of the most important qualities in juicy fruits like
citrus wherever, only the juice comprises the human consumable part in the fruit.
Data in Table 5 indicated that the percent of juice volume
gradually decreased from harvest till 45 days as a storage period advanced during
shelf life. Boric acid 1.0%+jojoba oil 0.1% was more effective in reducing the
losses percent of juice volume of orange fruits significantly compared with
boric acid or jojoba oil each alone. The percent of juice volume due to this
treatment was about 80.90 and 88.83% after 45 days during marketing, respectively
in both seasons.
The maturity of fruit is assessed from the color, juice content, TSS and acidity
of the juice. Since, juice yield of the oranges increased during the first two
months of the storage then decreased during the rest of storage period (Erkan
et al., 2005).
Ascorbic acid: Data presented in Table 5 indicated
that, vitamin C contents of orange decreased gradually during shelf life. This
finding could be attributed to the conversion of ascorbic acid to dehydro ascorbic
acid and decreasing the active form of ascorbic (Hacisevki,
2009). The reduction in ascorbic acid at control fruits ranged in the first
season from 36.36-29.86 mg 100 g-1 fresh weight (about 17.90%) and
realized in the second one from 35.10 to 29.33 mg 100 g-1 fresh weight
(about 16.43% losses). This finding is correlated to the previously mentioned
about SSC/acid ratio, where these fruits recorded less fruit quality characters.
On contrary, the high pronounced ascorbic acid values were found with boric
acid (1.0%)+jojoba oil (0.1%), since the reduction in ascorbic acid content
in this treatment ranged from 36.36-34.16 mg (the percent of decline reached
6.04%) and from 35.10 to 31.36 mg (the percent of decline reached 10.62%), after
45days of shelf life at room temperature in both seasons, respectively. Ascorbic
acid is an important nutrient quality parameter and is very sensitive to degradation
due to its oxidation compared too there nutrients during food processing and
storage (Veltman et al., 2000). Ascorbic acid
is also involved in the cell cycle (Kerk and Feldman, 1995)
and in other important enzyme reactions in plant issues (i.e., ethylene biosynthesis).
Ascorbic acid oxidase (AAO): Ascorbic acid oxidase (AAO; EC 188.8.131.52.)
is a Cu-containing enzyme that catalyzes the oxidation of ascorbate to 2-dehydroascorbate
with the concomitant reduction of molecular oxygen to water (Ohkawa
et al., 1989). Also, AAO an enzyme in plant tissues that oxidizes
ascorbic acid to dehydro-ascorbic acid; it is only released when the plant wilts
or is cut.
From data presented in Table 5, AAO activity in fruit juice
of orange gradually increased during shelf life in both seasons. Moreover, all
the applied treatments reduced the activity of AAO in fruit significantly than
the control stored for 45 days at room temperature. Since, the percent in control
fruits were 0.63 and 0.58% after 45 days through shelf life at room temperature
in both seasons, respectively. Furthermore, boric acid 1.0%+jojoba oil 0.1%
was more effective in reducing the activity of AAO in orange fruits compared
with boric acid or jojoba oil each alone. The percent of AAO due to this treatment
was about 0.50 and 0.46% after 45 days during marketing, respectively, in both
The storage period had a more significant effect on the content of ascorbic
acid than the temperatures did. It has previously been reported that a loss
of ascorbic acid in citrus fruit is not caused by storage temperature (Rapisarda
et al., 2008) and that there was no loss of ascorbic acid during
storage of oranges at low temperature. The oxidation of ascorbic acid by mature
fruit would probably be due to one or more of the following agents, typical
AAO such as that found in green fruit, copper ions, polyphenoloxidase and/or
an atypical ascorbic acid oxidase.
Ascorbic acid oxidation leads to the destruction of vitamin C and the loss
of nutrition in foods. This browning is the spontaneous thermal decomposition
of ascorbic acid under both aerobic and anaerobic conditions. It was reported
that over 80% of the browning of dried apple during storage packed under vacuum
resulted from oxidative non-enzymatic reaction (Bolin and
In the presence of the enzyme, vitamin C is oxidized in the attendance of air
by copper to give hydrogen peroxide which destroys ascorbic acid. Ascorbic acid
oxidase is a copper containing enzyme which catalyzes the oxidation of ascorbic
acid to dehydro ascorbic acid and water. However, during extraction of fruit
juice, ascorbic acid oxidase activity increases (Hacisevki,
Blood oranges present suitable characteristics for preparation as ready-to-eat
products. During shelf-life, such produce could be susceptible to quality degradation
due to the action of some enzymes, among which polyphenol oxidase (PPO) and
ascorbate oxidase (AAO), considered as two markers of oxidation and reduction
of anthocyanins and ascorbic acid. PPO activity was very low, probably due to
the low pH of oranges; furthermore, it was noticed that the decrease of phenols
and anthocyanins content did not have a statistically significant relation with
PPO activity course during storage. Otherwise, AAO activity was very high and
correlated to the decrease of vitamin C content. Nevertheless, such decrease
did not exceed 20-30% of the initial ascorbic acid content (Ingallinera
et al., 2005).
It could be concluded that, the combination treatment of boric acid (1.0%)
plus jojoba oil (0.1%) was the most effective treatment in decreasing weight
losses, fruit decay, total loses in fruit, titratable acidity and ascorbic acid
oxidase, as well as linear growth, dry weight and disease infection percentage
of the tested pathogenic fungi. However, increasing soluble solids, SSC/acid
ratio, peel thickness, ascorbic acid content and juice percent is reported by