Harvested strawberry fruit is highly perishable because of its soft texture and microbial infestation during postharvest handling. The applications of carbon dioxide (CO2) gas on the quality parameters of strawberry harvested in winter season have shown better effects in several studies. However, very little information is available for the same in summer harvested strawberry. This study was aimed at finding an optimum concentration and duration of CO2 treatment in strawberry fruit var. “Goha” harvested in summer season to increase or maintain postharvest qualities. Fresh strawberries were treated with 15%, 30% and 50% CO2 for 1 or 3 h and then stored at 4?C for up to 13 days along with untreated control. Strawberry samples treated with 50% CO2 for 1 or 3 h and both 15% and 30% for 3 h had higher firmness than samples treated with both 15% and 30% for 1 h and control. In general, total soluble solids (TSS) slightly increased or maintained during storage in all samples except control. The values of pH slightly declined whereas titratable acidity showed opposite trends. However, there was no significant difference found among CO2 treated samples. Lightness (L*) of “Goha” samples with no CO2 treatment decreased gradually while it was almost maintained in CO2 treated strawberries. Strawberry samples treated with 15% CO2 for 3 h maintained better quality with higher scores of overall quality and visual texture until 9 days of storage. Samples treated with 15% CO2 for 3 h also received lower softening scores until 9 days of storage compared to other CO2 treated samples. These results showed that 15% CO2 for 3 h condition could be an effective postharvest treatment for maintaining quality of “Goha” strawberry.
Strawberry (Fragaria × ananassa Duch.) is a non-climacteric fruit with a very short postharvest life. It is highly perishable, being susceptible to mechanical injury, desiccation, water loss, microbial decay and physiological disorders during postharvest handling such as transportation and storage. The main characteristics related to the quality of ripened strawberry fruit are texture, flavour (soluble sugars and organic acids) and color (anthocyanin content). Generally, loss of quality is mostly occurred due to its relatively high metabolic activity and sensitivity to fungal decay. Change in texture is a consequence of the natural process of senescence and also of the atmosphere in which the fruits are stored. Besides, the obvious changes in appearance, mold contamination can also promote undesirable changes in texture and contribute to reduced strawberry shelf-life. Hence, various kinds of physical or chemical methods have been applied to improve the postharvest shelf-life of strawberries.
The storage life of some horticultural produces has shown to be prolonged through the reduction in respiration and other metabolic reactions and a decrease in decay by the alterations in the concentrations of oxygen (O2) and carbon dioxide (CO2) where they are stored. Carbon dioxide is a common, available and non-toxic gas that has been used in many postharvest operations to extend or improve their postharvest life and/or quality. Several studies have shown that CO2-enriched atmospheres could extend the storage life of strawberry by inhibiting fruit softening and decay [
Being a good source of nutrients and vitamins, strawberry is used in different purposes which make it a most versatile fruit. Strawberries can be eaten fresh, cooked or frozen too. The demand of strawberries has been increased and growers and researchers have attempted to produce strawberry all year round in Korea. Production of strawberry varieties developed in Korea has increased with higher potential for export to other countries. The “Goha” strawberry is a new cultivar in Korea, which was developed from a cross between “Elan” and “Flamingo” and now successfully grown in summer with high fruit quality [
Assessment of strawberry quality for the market is focused on visual and internal characteristics, such as size, color, firmness, acidity, sweetness and aroma [
Fresh strawberries (Fragaria × ananassa Duch. cv. Goha) with red color on 70% - 80% of the fruit surface were hand-harvested from a commercial firm in Muju, Republic of Korea. Strawberry fruits were freshly harvested in the early morning and immediately transported to the postharvest laboratory of National Institute of Horticultural and Herbal Science, Suwon by a refrigerated truck maintaining a temperature of 4˚C. Fruits were graded for uniformity of color and size, and damaged fruits were removed. About 300 g fruits were then placed in transparent plastic box (16 × 12 × 8 cm) with several holes on the top and bottom portion of the box. One box of strawberry was considered as one replicate and four replicates were used in each treatment. Strawberry boxes were subjected to different concentrations and time of CO2 treatment using acrylic chamber (60 × 30 × 30 cm) and CO2 cylinder attached to a pressure gauge and a gun-like injector. Strawberries were treated with air (control), 15% CO2 gas for 1 or 3 hours (15% CO2-1 h or 15% CO2-3 h), 30% CO2 gas for 1 or 3 hours (30% CO2-1 h or 30% CO2-3 h), 50% CO2 gas for 1 or 3 hours (50% CO2-1 h or 50%CO2-3 h) and stored at 4˚C for up to 13
days. Strawberry boxes were placed in the chamber, tightened the chamber opening and CO2 was supplied to the chamber using small holes of the chamber where CO2 concentration was monitored with a gas analyzer. The treatments were conducted at room temperature and when CO2 concentration reached at expected level in different treatments, the chamber was completely closed and transferred to 4˚C storage room. After stipulated treatment duration, the chambers were taken out from the storage room, opened and only strawberry boxes were immediately transferred to 4˚C storage room. Evaluations of sensory, physical and biochemical qualities were carried out on 0, 3, 6, 9 and 13 days of storage.
Surface color of randomly selected seven fruit from each replicate was measured using a colorimeter (CR-400 Minolta, Osaka, Japan) which provided CIE L*, a* and b* values. Measurements were taken from opposite sides around the equatorial zone of the fruit. The meter was calibrated using the manufacturer’s standard white plate (Y 93.5, x 0.3155, y 0.3320). L* refers to the lightness and ranges from black = 0 to white = 100. A negative value of a* indicates green, while a higher positive number indicates red color. Positive and negative b* indicate yellow and blue color, respectively. These values were then converted into chroma {
The firmness was measured using a texture analyzer (TA Plus, Lloyd Instruments, Ametek Inc., UK) fitted with a flat probe. Each fruit was placed horizontally on the stationary platform and compressed 8 mm at a rate of 5, 2 and 10 mm∙s−1 as the pre-test, test and post-test speed, respectively. With a running load cell of 20 N, the probe was attached to a creep meter equipped with the software (NEXYGEN™MT v 4.5, Lloyd Instruments, Ametek Inc., UK) for automatic analysis using a computer. The maximum force (N) developed during the test was recorded. Eight strawberry fruit from each replicate were randomly selected and a total of 32 data from four replicates were averaged from each treatment. All measurements were taken at room temperature (20˚C ± 2˚C).
Total soluble solid (TSS), pH and titratable acidity (TA) were measured according to the AOAC [
The sensory analysis of strawberry sample was carried out by an 8-member (aged 24 - 48) expert panel. The members of the panel were trained to recognize and score overall visual quality, appearance, visual texture, of strawberry sample prior to the test. These sensory qualities were evaluated by using 9-point scale (9 = excellent, 7 = good, 5 = fair, 3 = poor and 1 = unusable). A score of 6 was considered as the limit of marketability. Softening score of individual fruit in a box was carried out on a 0 - 4 scale, where 0 = normal (0% surface softened), 1 = trace (up to 10% surface softened), 2 = slight (10 to 25% surface softened), 3 = moderate (25% - 50% surface softened), and 4 = severe (>50% surface softened). Softening index was then calculated from the following formula
The experiment was conducted with four replications per treatment. Statistical analyses of the data were carried out using SAS software (SAS Institute, Cary, NC, USA). The level of significance was calculated from the F value of ANOVA. Mean comparison was achieved by Duncan’s multiple range test. Prior to the final experiment, two preliminary experiments were conducted with limited replications that resulted similar trend.
After treated with CO2 gas, strawberry fruit firmness increased in all longer duration treatments and both of 50% CO2 treatment (
Total soluble solid of control sample declined throughout the storage whereas it slightly increased or maintained in CO2 treated samples (
However, sample treated with 30% and 50% CO2 for 3 h showed significant decline (p < 0.05) in pH compared to control sample on treatment day. Overall, pH of CO2 treated samples did not show significant variation (p > 0.05) either among them or in between storage days which is in consistent with the results of Gil et al. [
Titratable acidity, on the other hand, slightly increased by CO2 treatment and 30% CO2-3 h and both of 50% CO2 treatments showed greater increase (p < 0.05) in TA compared to control or other treatments (
Since color is the most important factor affecting the overall quality and appearance of strawberry, we measured surface color using Hunter color spaces. It revealed that color parameters were less affected by CO2 application (
Using a nine-point scoring method, overall quality, appearance and visual texture were evaluated on each evaluation day. Sensory scores of these three parameters decreased gradually with the increases in storage time in all treatments (
The firmness quality of summer strawberry “Goha” could be increased by CO2 treatment. However, higher doses of CO2 treatment may not ensure other quality parameters other than firmness. We observed that lower concentration but longer duration of CO2 treatment resulted better in maintaining quality than that of higher concentration
Sensory parameter | Treatment | Storage day | ||||
---|---|---|---|---|---|---|
0 | 3 | 6 | 9 | 13 | ||
Overall quality | Control | 9.00 ± 0.00Aa | 7.60 ± 0.22ABb | 6.37 ± 0.34Ac | 5.47 ± 0.17Bd | 4.00 ± 0.44Ae |
15%CO2-1 h | 9.00 ± 0.00Aa | 6.87 ± 0.27Bb | 5.96 ± 0.23Ac | 5.20 ± 0.27Bc | 4.06 ± 0.41Ad | |
15%CO2-3 h | 9.00 ± 0.00Aa | 7.80 ± 0.27ABb | 6.67 ± 0.44Ac | 6.53 ± 0.36Ac | 4.20 ± 0.56Ad | |
30%CO2-1 h | 9.00 ± 0.00Aa | 7.27 ± 0.39ABb | 5.89 ± 0.55Ac | 5.13 ± 0.56Bcd | 4.27 ± 0.42Ad | |
30%CO2-3 h | 9.00 ± 0.00Aa | 7.20 ± 0.29ABb | 7.00 ± 0.32Ab | 5.19 ± 0.30Bc | 4.53 ± 0.17Ac | |
50%CO2-1 h | 9.00 ± 0.00Aa | 6.86 ± 0.43Bb | 6.13 ± 0.39Ab | 4.93 ± 0.29Bc | 4.07 ± 0.47Ac | |
50%CO2-3 h | 9.00 ± 0.00Aa | 8.00 ± 0.28Ab | 6.13 ± 0.37Ac | 5.79 ± 0.30ABc | 4.26 ± 0.16Ad | |
Appearance | Control | 9.00 ± 0.00Aa | 7.47 ± 0.23ABb | 6.73 ± 0.30Ab | 5.34 ± 0.35ABc | 3.32 ± 0.30Ad |
15%CO2-1 h | 9.00 ± 0.00Aa | 6.87 ± 0.27Bb | 6.13 ± 0.13Ac | 5.00 ± 0.18Bd | 3.68 ± 0.29Ae | |
15%CO2-3 h | 9.00 ± 0.00Aa | 8.20 ± 0.34Ab | 6.93 ± 0.34Ab | 6.24 ± 0.48Ab | 3.87 ± 0.61Ac | |
30%CO2-1 h | 9.00 ± 0.00Aa | 7.53 ± 0.40ABb | 6.33 ± 0.38Ac | 5.46 ± 0.43ABc | 4.19 ± 0.33Ad | |
30%CO2-3 h | 9.00 ± 0.00Aa | 7.67 ± 0.35ABb | 7.13 ± 0.40Ab | 5.07 ± 0.47Bc | 4.34 ± 0.20Ac | |
50%CO2-1 h | 9.00 ± 0.00Aa | 7.47 ± 0.40ABb | 6.07 ± 0.25Ac | 4.85 ± 0.26Bd | 3.57 ± 0.11Ae | |
50%CO2-3 h | 9.00 ± 0.00Aa | 7.60 ± 0.41ABb | 6.42 ± 0.47Ac | 5.50 ± 0.31ABc | 3.85 ± 0.24Ad | |
Visual texture | Control | 9.00 ± 0.00Aa | 7.00 ± 0.37Bb | 6.89 ± 0.26Ab | 5.93 ± 0.19ABc | 3.34 ± 0.22Bd |
15%CO2-1 h | 9.00 ± 0.00Aa | 7.20 ± 0.33Bb | 5.87 ± 0.20Ac | 4.80 ± 0.25Cd | 3.36 ± 0.21Be | |
15%CO2-3 h | 9.00 ± 0.00Aa | 8.20 ± 0.08Aa | 6.67 ± 0.37Ab | 6.19 ± 0.31Ab | 3.77 ± 0.44ABc | |
30%CO2-1 h | 9.00 ± 0.00Aa | 7.27 ± 0.29Db | 5.93 ± 0.45Ac | 4.87 ± 0.36Cd | 4.21 ± 0.40ABd | |
30%CO2-3 h | 9.00 ± 0.00Aa | 7.53 ± 0.13ABb | 6.67 ± 0.30Ac | 4.87 ± 0.31Cd | 4.53 ± 0.17Ad | |
50%CO2-1 h | 9.00 ± 0.00Aa | 7.40 ± 0.24Bb | 6.07 ± 0.34Ac | 4.85 ± 0.26Cd | 3.89 ± 0.28Abe | |
50%CO2-3 h | 9.00 ± 0.00Aa | 7.33 ± 0.15Bb | 5.87 ± 0.39Ac | 5.27 ± 0.25BCc | 3.87 ± 0.28ABd | |
Softening index | Control | 0.00 ± 0.00Ad | 0.17 ± 0.04ABCc | 0.20 ± 0.04Bc | 0.34 ± 0.03ABb | 0.68 ± 0.01Aa |
15%CO2-1 h | 0.00 ± 0.00Ac | 0.20 ± 0.03ABb | 0.22 ± 0.05Bb | 0.27 ± 0.03ABb | 0.57 ± 0.03Aa | |
15%CO2-3 h | 0.00 ± 0.00Ac | 0.20 ± 0.02ABb | 0.21 ± 0.04Bb | 0.24 ± 0.03Bb | 0.57 ± 0.06Aa | |
30%CO2-1 h | 0.00 ± 0.00Ac | 0.23 ± 0.03Ab | 0.23 ± 0.02Bb | 0.26 ± 0.03ABb | 0.59 ± 0.06Aa | |
30%CO2-3 h | 0.00 ± 0.00Ae | 0.11 ± 0.01Cd | 0.18 ± 0.03Bc | 0.28 ± 0.04ABb | 0.60 ± 0.02Aa | |
50%CO2-1 h | 0.00 ± 0.00Ae | 0.14 ± 0.02BCd | 0.24 ± 0.03Bc | 0.36 ± 0.05Ab | 0.62 ± 0.04Aa | |
50%CO2-3 h | 0.00 ± 0.00Ad | 0.16 ± 0.01ABCc | 0.39 ± 0.05Ab | 0.41 ± 0.02ABb | 0.56 ± 0.02Aa |
A-DMean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05; a-eMean values with different letters within a row are significantly different by Duncan’s multiple range test at p < 0.05.
of CO2 treatments. Based on our results, we conclude that 15% CO2 for 3 h treatment could provide some beneficial effects during storage of strawberry for certain period.
This work was supported by the ICT R&D Program of Ministry of Science, ICT and Future Planning (I0114- 14-1016, Intelligent Management of Produce Distribution for Export), Republic of Korea and by the Creative Vitamin Project.