Abstract: A plastichouse experiment was carried out during the 2004/2005 season at Abu-Ghannam`s farm in Kreimeh in the northern Jordan Valley, to compare the effect of four fermented organic matter doses (1.5, 3.0, 4.5 and 6.0 kg m-2) with that of the conventional fertilizer and control treatments on strawberry cultivar Honor growth. Strawberries were used to study some postharvest parameters related to length of storage and fruit quality using two storage methods; normal cold storage (air storage) and Modified Atmosphere storage (MA). For this purpose, fruits were harvested in February, March and April and stored at 0 ° C and about 90-95% RH. A Randomized Complete Block Design (RCBD), with two factor factorial (6 treatments and 2 storage conditions) and three replicates (harvest dates), was used. At the end of the storage experiment the highest anthocyanin content was obtained under air storage conditions. Among the different treatments 4.5 kg OM m-2 treatment gave the highest anthocyanin content, while 1.5 kg OM m-2 treatment gave the lowest content. The interaction between the control and MA storage resulted in the lowest weight loss, while the highest weight loss was obtained by the interaction between conventional and air storage. MA storage prolonged berries storage life; the longest storage period was recorded for the 6 kg OM m-2 treatment and the lowest was recorded for the control treatment. Number of rotted fruits was highest in the MA compared to air storage. No effect of the treatments or interaction between the treatments was observed in respect to fruit rot incidence.
INTRODUCTION
Shelf life is the maximum periods after harvest with nearly 100% of the stored fruits are still marketable and it is cultivar dependent (Pelayo et al., 2003). Fruit shelf life during storage is an important feature from a producer’s and a distributor’s point of view, allowing the determination of risks arising from the loss of commercial value of fresh fruit in trade turnover (Radajewska and Borowiak, 2002). Strawberry is one of the most delicate and highly perishable fruits, being susceptible to mechanical injury, physiological deterioration, water loss, decay and has very short storage ability and postharvest shelf-life. Fruit quality characteristics are primarily influenced by preharvest crop management; the quality of the harvested produce can be at best maintained, but not improved after harvest (Perez et al., 1997; Manleitner et al., 2002; Ames et al., 2003). The berries are very fragile and susceptible to mechanical injury, their skin results in rapid loss of water in low humidity environments and strawberries have one of the highest respiration rates of all fresh commodities (Mitcham, 1996). Organically grown strawberries were firmer and more resistant to deterioration than the conventionally grown fruits, so postharvest losses of conventionally grown fruits were significantly higher than those of organically grown fruits (Cayuela et al., 1997).
Minimum maturity indices of strawberry included 2/3-3/4 fruit surface showing pink or red color, at this stage the berries are firmer than fully ripe fruits (Mitcham, 1996; Kader, 1999; Haffner, 2002). Strawberry can be stored at 0°C and 90 to 95% relative humidity (Mitcham, 1996; Krivorot and Dris, 2002) for up to 5-7 days if precooled after harvest (Rivera and Tong, 2004). Even under low temperature and high humidity conditions, storage life is usually only about 7 days (Perez et al., 1997), or 7-10 days according to the cultivar used, but storage period could be extended to 13-15 days if fruits are packaged in polyethylene (PE) bags (Krivorot and Dris, 2002).
Packaging material affects the quality and shelf life; packing in polyethylene bags decreased respiration, maintained quality, prolonged the shelf life (Krivorot and Dris, 2002). In addition packaging protects against mechanical damage and prevents moisture loss (Perez et al., 1997). However, non-perforated films significantly increased shelf life, improved fruit firmness and reduced weight loss and rot. Respiration rate and ethylene production increased under air storage conditions at 5°C as found by Pelayo et al. (2003). Morris et al. (1985) reported that as postharvest holding time and temperature increased the quality of strawberries decreased.
Anthocyanin synthesis continued in harvested fruit, particularly those stored in air, even at low storage temperature; after 2 weeks of storage, anthocyanin was increased by 18% (Holcroft and Kader, 1999). Fruit harvested at 50% red became fully red during storage and the anthocyanin concentration increased by 140, 50 and 30% in fruit harvested at 50% red, red and red + 24 h, respectively. But in another experiment conducted Manleitner et al. (2002) an opposite trend was found; they did not see any significant difference between different storage methods when referring to anthocyanin content, which was 40.7 mg/100 g before storage, 39 mg/100 g after storage in open containers and 39.4 mg/100 g after storage in covered containers with non-perforated films.
Rivera and Tong (2004) found that strawberry fruits may lose some color, shrivel and lose flavor, after few days of storage and berry shelf life can be extended by packing berries in containers coated with heat-shrink polyethylene film. Average weight loss in open trays was higher than packaged strawberries; Manleitner et al. (2002) found that average weight loss in open trays was 7.1% (1.78%/day), while in trays covered with perforated film weight loss was 1.33% (0.33%/day).
The major postharvest disease of strawberries is gray mold or ash mold rot, caused by the fungus Botrytis cinerea (Rivera and Tong, 2004), which is one of the most common and serious fruit rot diseases, found on both green and ripe strawberries (Ames et al., 2003; Kadir, 2003). It causes major losses which are associated with bruising and soft or leaky berries (Mitcham, 1996; Kivijarvi et al., 2002). Infections first occur on fruit tissue under the calyx, fruit infections appear as soft and light brown areas that increase rapidly under cool temperatures, wet conditions and high relative humidity (Sikora, 1996).
In Jordan, no research has been done regarding postharvest behaviour of organically produced strawberry fruits, in spite of good sources of organic matter especially animal manure and plant residues, which are available at very low costs.
This experiment aimed to compare between the effect of MA and air storage conditions on strawberry fruit quality grown using organic and conventional production systems.
MATERIALS AND METHODS
This study was conducted during the 2004/2005 season, in a plastichouse (9x56.5 m) in the northern Jordan Valley. The organic matter for this experiment was prepared, according to Preusch et al. (2004) recommendations. Soil solarization was applied to the soil of the experimental site from the 1st of August to the 15th of October, according to procedures outlined by Abu-Blan and Abu-Gharbieh (1994).
Field Treatments
The width of the plastichouse was divided into nine equal sections (1 m
each), while the length was divided into four equal sections (each 14 m long),
so each experimental unit (bed) represented 1x14 m (width by length) while the
remaining 0.5 m from the length was left at the entrance of the plastichouse.
The conventional planting was done according to the system applied in the farm
where the experiment was conducted, which included the use of pesticides and
inorganic fertilizers. However, in organic culture treatments, all types of
chemicals (pesticides and inorganic fertilizers) were excluded and the rates
of 1.5, 3, 4.5 and 6 kg fermented compost/m2 were spread and incorporated
into the beds. In addition to the conventional treatment and the four organic
treatments a control treatment (no organic and no inorganic fertilizers and
pesticides) was included in the study.
A Randomized Complete Block Design (RCBD), with four replicates per treatment was used. All data obtained were statistically analyzed by variance, according to the procedure outlined by Steel and Torrie (1980). The differences between means of the different treatments were compared by the Least Significant Difference (LSD) test using SAS and differences with probability value at p = 0.05 were considered significant.
Storage Treatments
In this experiment; strawberry fruits were stored at 0°C and about 90-95%
RH, under two storage conditions; Modified Atmosphere Packaging (MAP) or normal
cold storage conditions. It included 12 treatments as indicated in Table
1. Berries produced in the first experiment, were used in the storage experiment.
At the assigned date fruits were harvested and placed in a shady cool place
until being directly transferred to the cold room at the University of Jordan
campus. Fruits were cleaned from soil by hand and mixed. Only non diseased fruits
with suitable degree of ripeness and lack of any apparent damage and with clear
red color were used for this experiment which was repeated at three harvesting
dates (February, March and April, 2005). Each storage time; triplicate jars
were used for each replicate and then average readings were considered.
After that 420-470 g strawberry fruits were placed in a plastic jar (500 g capacity) and stored uncovered (air storage) or covered with shrink wrap (MAP). The shrink wrap (manufactured in Al-Nur Jordanian company for plastic industry, Amman-Jordan) is made from LLD-polyethylene resin, approved as pollution-free by FDA of US, it does not generate any harmful monomer or poisonous gas even at high temperature and it's heat resistance temperature is 120°C, while it's cold resistance temperature is -60°C.
| Table 1: | Storage experiment treatments |
| *MA: Modified Atmosphere | |
During storage air temperature and relative humidity were recorded by Hygrothermograph (TR di Turoni and C. Snc Hygrothermograph, Italy), humidity in the cold room was controlled by Humidifier (Ultrasonic Humidifier Cole-Parmer Inst. Co., Order No. U-37700-85, USA).
Parameters Measured
Each fruit jar was removed from the cold room, when fruits in it started
showing any wilting or any rot incidence, at each storage average readings were
recorded for the three jars per treatment.
Fruit Keeping Quality Anthocyanin
Before and at the end of each storage date; 3 to 4 fruits per plastic jar
and replicate were used for anthocyanin determination. Strawberry fruit color
was expressed as mg anthocyanin per 100 g fruit fresh weight, anthocyanin content
was estimated by pH-Differential Spectrophotometer method, absorbance was taken
by Spectrophotometer (Varian, Cary 100 Conc, CaryWin soft ware, Australia).
For anthocyanin estimation; fruits were grinded and homogenized through pestle
and mortar. Then a 10 g sample was placed in a plastic bottle, 100 mL of 1:
99 V/V (HCl: methanol) added to it and shacked for half an hour, then filtrated
through filter paper, two samples 5 mL each were placed in two volumetric flasks
(25 mL) and the volume for each flask, was completed with a different pH buffer
(pH 1 for sample 1 and pH 4.5 for sample 2). The absorbance was measured for
each of the samples at the wavelengths 510 and 700 nm. After that, the following
equation was applied:
Absorbance = (A 510 nm pH 1 – A 700 nm pH 1) – (A 510 nm pH 4.5 – A 700 nm pH 4.5)
Then total anthocyanins (% W/W) in the samples were calculated according to the following equation: % W/W = A/0LxMWxDFxV/Wtx100.
Where:
| A | = | Absorbance. |
| ε | = | Pelargonidin 3-Glucoside (PGD 3-GLU) coefficient = 22400. |
| L | = | Cell path length (usually 1 cm) |
| MW | = | Anthocyanin molecular weight = 433.2 |
| DF | = | Dilution factor. |
| V | = | Final volume (mL). |
| Wt | = | Sample weight (mg). |
Then the obtained values (g/100 g) were converted into mg anthocyanin/100 g fruit fresh weight by multiplying with 1000. Finally the results were expressed as milligrams of pelagonidin-3-glucoside per 100 g fruit fresh weight. According to the procedures used by Cheng and Breen (1991); Garzon and Wrolstand (2002); NSF International (2004).
Rot Incidence
Directly after the end of storage; the number of spoiled fruits in each
plastic jar was recorded.
Storage Period
Maximum storage period was estimated by counting the number of days from
the first day of storage until the end of the storage period, while the fruits
are still marketable.
Average Daily Weight Loss
It was estimated for each plastic jar, by dividing average weight loss during
the storage period, through the number of days in storage.
Experimental Design and Statistical Analysis
A Randomized Completely Block Design (RCRD), with two factor factorial (6
field treatments and 2 storage conditions) and three replications (three storage
dates) was used. All data obtained were statistically analyzed by variance according
to the procedure outlined by Steel and Torrie (1980), the differences between
means of the different treatments were compared by Least Significant Difference
(LSD) test using SAS. Then interactions between treatments were separated by
software MSstat. Statistical differences with probability values at p = 0.05
were considered significant.
RESULTS AND DISCUSSION
Anthocyanin Content
There were significant differences in anthocyanin content of strawberries
between MA and air storage. Maximum anthocyanin content (52.31 mg/100 g f. wt)
was found in the air storage treatment, while the lowest anthocyanin content
(42.86 mg/100g f. wt) was obtained by the MA storage treatment (Table
2). This means that air storage enhanced anthocyanin synthesis during storage
compared to MA storage, also anthocyanin content could be due to the relatively
high moisture loss from the air stored fruits compared to the MA stored fruits
which were protected against moisture loss (Perez et al., 1997), thus
resulting in concentrated anthocyanin content (which was measured on fruit fresh
weight basis) of the air stored fruits (Table 2). In addition,
oxygen (O2) availability in air storage could enhance anthocyanin
production, while shortage of O2 under MA conditions is supposed
to limit anthocyanin production.
Results of fruit anthocyanin content tested immediately at the beginning of the storage experiment (Table 3), showed that the 6 kg OM m-2 treatment gave the highest content (40.69 mg/100 g f. wt.), while the control treatment gave the lowest content (35.1 mg/100 g f. wt.). Comparing these results with results obtained at the end of storage; indicate an increase in anthocyanin content after storage in MA and in air storage. The percent of anthocyanin increase ranged from 15.97-24.12%. These results are in agreement with those obtained by Forney et al. (1998) and Pelayo et al. (2003) who found an increase in anthocyanin concentration during strawberry storage, due to continuous synthesis of this pigment especially in air storage. On the other hand results of the treatments with the storage type interactions did not show any significant effect on the fruit anthocyanin content, nevertheless the highest anthocyanin content (57.5 mg/100 g f. wt.) obtained by the 4.5 kg OM m-2 treatment under air storage conditions and the lowest (41.19 mg/100 g f. wt.) obtained by the 1.5 kg OM m-2 treatment under MA storage conditions (Table 5). These results indicate that anthocyanin synthesis during storage significantly affected by the field treatments and storage type treatments.
Weight Loss
The highest average daily weight loss (1.69%) was obtained in the air storage,
while the lowest weight loss (0.10%) was obtained in the modified atmosphere
storage (Table 2). Similar results were obtained by Krivorot
and Dris (2002) who found that weight loss of non-packaged berries was 2.0-4.0%
per day, which was higher than that of packaged fruits and packaging in polyethylene
bags resulted in only 0.05-0.63% weight loss per day, due to increased transpiration.
| Table 2: | Effects of storage method (MA or air), on anthocyanin content, weight loss, length of storage and number of rotted fruits of plastichouse grown strawberries irrespective of the treatments |
| *MA: Modified Atmosphere; ** Means within each column having different letter(s) are significantly different according to LSD at 5% level | |
| Table 3: | Effect of organic matter on fruit anthocyanin content at the beginning and at the end of storage and percent of anthocyanin change of plastichouse grown strawberries |
| * OM: Organic Matter; ** Means within each column having different letter(s) are significantly different according to LSD at 5% level; + Means the percent of increase in anthocyanin content | |
| Table 4: | Effect of organic matter on fruit weight loss, length of storage and number of rotted fruits of plastichouse grown strawberries |
| * OM: Organic Matter; ** Means within each column having different letter(s) are significantly different according to LSD at 5% level | |
| Table 5: | Interaction of field treatments (organic matter or chemical fertilizer) with storage type (MA or air) on fruit anthocyanin content, weight loss, length of storage and number of rotted fruits of plastichouse grown strawberries |
| + OM: Organic Matter; * MA: Modified Atmosphere; ** Means within each column having different letter(s) are significantly different according to LSD at 5% level | |
In addition packaging protected strawberries against mechanical damage and prevented moisture loss (Perez et al., 1997) and reduced weight losses (Manleitner et al., 2002).
On the other hand, the highest average daily weight loss (1.08%) was obtained by the conventional treatment without a significant difference from the control treatment, while the lowest weight loss (0.8%) was obtained by the 3 kg OM m-2 treatment (Table 4). All organic matter treatments had a significantly lower average daily weight loss compared to the conventional treatment. The control treatment had an intermediate weight loss when compared to the conventionally and organically produced fruits (Table 4). According to Cayuela et al. (1997) organically produced strawberries were firmer and more resistant to deterioration than conventionally grown fruits. Therefore, losses of conventionally grown fruits were significantly higher than those of organically grown fruits.
Table 5, showed that the highest average daily weight loss (2.05%) was obtained by the conventional treatment under air storage conditions, without being significantly different from fruits under air storage conditions of all other treatments. The lowest weight loss (0.09%) was obtained by fruits from the control treatment which were kept under MA conditions, without being significantly different from other fruits stored under MA conditions, irrespective of their origin. The high weight losses in the conventional treatment stored under air storage type could be due to two main reasons: 1. Fruit stored under air storage conditions had always higher weight losses compared to MA stored fruits. 2. The large fruit size of the conventionally produced fruits compared to the organically produced fruits or the control, caused higher moisture losses and more fruit respiration. On the other hand the low weight losses of the MA stored control fruits could be due to low moisture losses and low respiration rate under MA conditions, in addition to the small fruit surface area compared to fruit of other production systems.
Storage Duration
In the case of number of days in storage, there were significant differences
between the two types of storage (MA and air storage); the longest storage period
(16.46 days) was obtained by MA storage, while the shortest storage period (8.61
days) was obtained by air storage (Table 2). As a result,
it appears that MA increased the storage period of strawberries from 8 to about
17 days. These results are in line with findings of Krivorot and Dris (2002),
who found that storage life, is usually about 7-10 days according to the cultivar
used, but it could be extended to 13-15 days if fruits are packaged in polyethylene
(PE) bags. Furthermore the present results are within the range obtained by
different researchers; for example, Perez et al. (1997) reported the
storage life of strawberry fruits to be about 7 days, while Krivorot and Dris
(2002) found it to be between 7-10 days in air storage and 13-15 days for packaged
fruits. MA storage reduced weight loss (Manleitner et al., 2002) decreased
respiration and maintained quality of strawberries (Krivorot and Dris, 2002).
On the other hand, the increase in respiration under air storage conditions
resulted in reduced storage capability of strawberries (Pelayo et al.,
2003). On the other hand the control treatment lasted in storage for a significantly
shorter period when compared to all other treatments except the 1.5 kg OM m-2
and the conventional treatments (Table 4). There were no significant
differences in the interaction of the treatments and storage type in respect
to the number of days in storage (Table 5). The longest storage
(17 days) was obtained by the 6 kg OM m-2 treatment under MA storage
type. While the shortest storage period (≈ 8 days) was obtained by the
control treatment under air storage condition, which could be due to the air
storage conditions that did not maintain fruit quality. In addition these results
indicate that length of storage was only significantly affected by the both
treatment and storage type, while the interaction between both didn't affect
the length of strawberry fruit storage.
Number of rotted fruits
In the case of number of rotted fruits the significantly highest number
of fruits affected by rot (3.85 fruits/container) was found in the MA storage,
while the lowest number of rotted fruits (0.04 fruits/container) was found under
air storage conditions (Table 2). These results disagree with
those obtained by Krivorot and Dris (2002) who found that fruit decay was significantly
reduced by non-perforated films. The relatively high number of rotted fruits
under MA conditions could be due to the extended storage life by MA and to the
high relative humidity inside the containers, such conditions are known to stimulate
fungi growth. On the other hand the highest number of rotted fruits (2.39 fruits/container)
was observed in the control treatment and the lowest (1.5 fruits/container)
in the 3 kg OM m-2 (Table 4). No significant differences
in the number of rotted fruits, were observed as a result of the interaction
between storage type and treatment (Table 5), but the highest
number of rotted fruits (4.78 fruits/container) was obtained by the control
treatment under MA conditions and the lowest (0.0 fruits/container) was obtained
by control, 1.5, 3 and 6 kg OM m-2 treatments under air storage conditions.
So it seems that only the storage condition type had a significant effect on
the number of rotted fruits, while other treatments (treatments or the interaction
between the treatments and storage type) had no significant effect on the number
of the rotted fruits.
CONCLUSIONS
Anthocyanin synthesis was increased during storage; air storage gave the highest content, while modified atmosphere storage gave the lowest anthocyanin content. On the other hand the 4.5 kg OM m-2 treatment gave the highest fruit anthocyanin content during storage, while 1.5 kg OM m-2 treatment gave the lowest content. Organic matter treatments had significantly lower weight loss compared to the conventional treatment and modified atmosphere storage reduced weight loss compared to air storage. The interaction between the control and modified atmosphere storage produced the lowest weight loss, while the highest weight loss was obtained by the interaction between the conventional production and air storage. Modified atmosphere storage prolonged berries storage life, compared to air storage and the 6 kg OM m-2 treatment resulted in the longest storage period. Number of rotted fruits was highest in modified atmosphere storage compared to air storage. Further work should systematically investigate modified atmosphere packaging materials, with defined gas permeability to CO2, O2 and water vapor to guarantee optimal microclimate conditions within the fruit tray during strawberry storage and handling.