The combined effects of phenylurea and gibberellins on quality maintenance and shelf life extension of banana fruit during storage

Scientia Horticulturae 167 (2014) 36–42

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The combined effects of phenylurea and gibberellins on quality maintenance and shelf life extension of banana fruit during storage Hua Huang a,b , Guoxing Jing c , Hui Wang a , Xuewu Duan a , Hongxia Qu a , Yueming Jiang a,∗ a Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, People’s Republic of China b Graduate School of Chinese Academy of Sciences, Beijing 100039, People’s Republic of China c College of Food Science and Biotechnology, Zhejiang Gongshang University, Food Safety Key Laboratory of Zhejiang Province, Hangzhou 310035, People’s Republic of China

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Article history: Received 7 September 2013 Received in revised form 23 December 2013 Accepted 24 December 2013 Keywords: Banana CPPU Fruit GA3 Ripening Quality

a b s t r a c t The combined effects of phenylurea (CPPU) and gibberellins (GA3 ) on quality maintenance and shelf life extension of harvested banana fruit were investigated. Banana fruit were treated with 10 mg L−1 CPPU in combination with GA3 at 25, 50 or 100 mg L−1 and then stored under ambient conditions (23 ± 2 ◦ C and 75–90% relative humidity). The results exhibited that the combined treatments of CPPU and GA3 significantly suppressed fruit softening in association with the delayed peaks of respiration and ethylene production rates and retarded decreases of hue value and the maximal chlorophyll fluorescence (Fv/Fm) of banana fruit during storage. Furthermore, the accumulation of soluble reducing sugars and losses in contents of ascorbic acid and total phenols were delayed. The most beneficial effect of quality maintenance and shelf life extension of postharvest banana fruit was obtained by application of 10 mg L−1 CPPU and 50 mg L−1 GA3 . These results clearly indicated that the combined treatment of CPPU and GA3 could contribute to ripening inhibition, shelf life extension and quality maintenance of banana fruit during storage. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Banana fruit as an important horticultural crop in tropical and sub-tropical areas in the world is rich in carbohydrate compounds (ascorbic acid, ␤-carotene and soluble sugars), phenols, and minerals like potassium and calcium. Particularly, banana fruit can prevent chronic diseases like cardiovascular dysfunction and muscular degeneration because of its antimicrobial and therapeutic properties (Agopian et al., 2008; Kanazawa and Sakakibara, 2000; Prasanna et al., 2007; Sundaram et al., 2011). Banana fruit ripens rapidly in accompany with significant changes of physicochemical and biochemical attributes such as transformation of starch to sucrose, mineral reduction and flavor formation once harvested, which causes green banana fruit into notably perishable (Alkarkhi et al., 2011; Mohapatra et al., 2010). As a typical climacteric fruit, the quality attributes of banana fruit after harvest such as color, texture and flavor, deteriorate easily (Boudhrioua et al., 2003; Jiang et al., 1999), leading to a short shelf life (about 6–8 days under ambient conditions). Currently, the postharvest handling, transportation and marketing of banana fruit need sophisticated techniques and

∗ Corresponding author. Tel.: +86 20 37252525; fax: +86 20 37252831. E-mail addresses: [email protected], [email protected] (Y. Jiang). 0304-4238/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2013.12.028

facilities (Mohapatra et al., 2010). Therefore, great efforts to develop new and simple post-harvest technology will be required to maintain quality and extend shelf life of banana fruit during storage and transportation. Recently, applications of exogenous plant hormones to regulate development and ripening and to maintain quality of horticultural crops have been examined carefully (Huang and Jiang, 2012; Jiang et al., 2000; Marzouk and Kassem, 2011; Zhang and Whiting, 2011). Among plant hormones, gibberellins (GAs) can promote the development of flower bud, initiate the growth of berry, increase cluster length of grape, and delay the disorder of citrus rind (Dayan et al., 2012; Mesejo et al., 2010; Zoffoli et al., 2009). It was also reported that GA was effective in inducing feathering in pears (Palmer et al., 2011) and maintaining the quality of grape (Retamales et al., 1994). Cytokinin (CK) is well-known to play a prominent role in cellular division and expansion in plants (Riou-Khamlichi et al., 1999) while phenylurea (N-(2-chloro-4-pyridil)-N’-phenylurea) (CPPU) as a synthetic cytokinin analogue has been shown the similar effects such as spear bud growth and root elongation (Ku and Woolley, 2006; Subotic´ et al., 2009). Application of CPPU prior to harvest has been reported to increase the berry size and set, maintain the quality and extend the shelf life of grape, kiwifruit or loquat fruit (Kim et al., 2006; Marzouk and Kassem, 2011), and to control black spot caused by fungus in stored persimmon fruit (Kobiler et al., 2011).

H. Huang et al. / Scientia Horticulturae 167 (2014) 36–42

Some research reported that CPPU treatment could increase fruit set or yield by affecting the accumulation of soluble sugars like hexose and sucrose, and maintain the fruit quality (Aloni et al., 2010; Hayata et al., 2000). In addition, the combined treatments of GA and CPPU can effectively reduce water core in pre-mature of pear fruit (Zhang et al., 2008), increase the final fruit size and weight of cherry (Zhang and Whiting, 2011) or affect the post-harvest quality of table grape during cold storage (Zoffoli et al., 2009). Our previous study also showed that postharvest treatment with CPPU or GA3 significantly prevented fungus infection from banana fruit and broccoli during storage (Huang and Jiang, 2012). Unfortunately, little information is available on the influences of the combined two plant hormones on fruit quality and shelf life of harvested banana fruit during storage. In this present study, the combined effects of CPPU and GA3 on postharvest ripening of banana fruit were investigated in association with quality attributes. The firmness, rates of respiration and ethylene production and contents of total soluble sugars and phenolic compounds of banana fruit were measured during storage. Furthermore, the optimal concentration of GA3 in combination with 10 mg L−1 CPPU based on physiological attributes was determined. The study can help to develop further commercial post-harvest handling for quality maintenance and shelf life extension of banana fruit during storage and transportation.

2. Materials and methods 2.1. Fruit materials Fruit of banana (Musa sp., AAA group cultivar ‘Brazil’) were harvested at green mature stage from a local commercial orchard in September 12, 2012. Each banana hand was cut into individual fingers. Fingers were dipped into water to clean fruit surface and then allowed to air-dried until water drops on the fruit surface disappeared completely. Fingers free from visual defects were selected for uniformity of weight, shape, color and size, and then divided randomly into six groups for use in these experiments.

2.2. Treatments In a previous small-scale experiment, the optimum concentration of CPPU to delay post-harvest ripening of banana fruit during storage was assessed. CPPU at 0, 5, 10, 20 and 40 mg L−1 was applied to evaluate the green life of banana fruit under ambient conditions (23 ± 2 ◦ C and 75–90% relative humidity). The green life can be evaluated rapidly based in terms of the changes in fruit firmness and skin color (Jiang et al., 1999). The results showed that immersion into 10 mg L−1 CPPU for 10 min delayed most effectively post-harvest ripening and extending green shelf life of banana fruit during storage. Thus, this concentration of CPPU was used for this study. Fruit were arranged in the following 6 treatments using a 10-min immersion at 25 ◦ C: A, water only (control); B, 10 mg L−1 CPPU; C, 10 mg L−1 CPPU + 25 mg L−1 GA3 ; D, 10 mg L−1 CPPU + 50 mg L−1 GA3 ; and E, 10 mg L−1 CPPU + 100 mg L−1 GA3 . After these treatments, fruit were air-dried, then packed into plastic polyethylene bag (0.03 mm), and finally stored under ambient conditions (23 ± 2 ◦ C and 75–90% relative humidity). Ten fruit fingers selected randomly from each treatment every 4 days were used for measurements of ethylene production and respiration rates, followed by evaluations of fruit firmness, hue angle and photochemical efficiency of photo-system II (PSII and Fv/Fm). Other 10 fruit fingers from each treatment every 4 days were peeled and then the pulp were collected, sliced, frozen in liquid N2 and then stored at −20 ◦ C prior to measurements of contents of soluble

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sugars and ascorbic acid, and high performance liquid chromatography (HPLC) analysis. 2.3. Physical characteristics 2.3.1. Determination of fruit firmness Fruit firmness was determined by a penetrometer (Model GY-3, Zhejiang Scientific Instruments, Zhejiang, China) with a probe of 8 mm in diameter and a penetration thickness of 10 mm by measuring the force required to penetrate into the whole fruit. Ten fruit fingers were withdrawn randomly from each treatment. Each finger was measured at three equidistant points around the middle position of the fruit using a flat probe. The results were expressed as N. 2.3.2. Measurements of respiration and ethylene production rates Fruit fingers withdrawn randomly from each treatment and then three fingers were sealed in a 2.6-L plastic container and held for 2 h at 25 ◦ C. Three replicate groups were used to measure ethylene production rate. One milliliter headspace gas was withdrawn from the container and then injected into a gas chromatograph (GC2010; Shimadzu, Kyoto, Japan) equipped with a 30 m HP-PLOT Q capillary column (Agilent Technologies, USA) and a flame ionization detector (FID). Ethylene production rate was expressed on a fresh weight (FW) basis. Respiration rate was determined with a LI-6262 CO2 /H2 O Analyzer (LI-6262, LI COR, America). Nine fruit fingers were withdrawn randomly from each treatment and then three fingers were sealed into a box that connects the LI-6262 CO2 /H2 O Analyzer before the amount of CO2 was recorded for 4 min. Respiration rate was expressed as the rate of CO2 production on a fresh weight basis. 2.3.3. Measurements of skin color and chlorophyll fluorescence Skin color was estimated by determining a* and b* Hunter using a Minolta Chroma Meter CR-400 (Minolta Camera Co. Ltd., Osaka, Japan), with a few modifications (Clerici et al., 2011). Ten fruit fingers withdrawn randomly from each treatment were used for determination of skin color. Each finger was measured at three equidistant points around the middle position of the fruit surface. Color was recorded using the CIE L*, a* and b* scales. L denotes the lightness or darkness and a* indicates green to red color while b* shows blue to yellow color. Numerical values of L*, a* and b* were converted into the hue angle [h0 = tan−1 (b*/a*)]. Chlorophyll fluorescence was determined using a portable chlorophyll fluorometer (FAM 2100, Walz, Germany) in the Fv/Fm mode (Yang et al., 2011). Each fruit finger was dark-adapted for at least 30 min prior to the measurement. The chlorophyll fluorescence parameters (Fo and Fm) were measured. Fo is the minimal or initial fluorescence when all PSII reaction centers are open while Fm is the maximal fluorescence when all PSII reaction centers are closed and all non-photochemical quenching processes are at minimum. The maximal variable fluorescence (Fv = Fm − Fo) and PSII quantum yield (Fv/Fm) were calculated from the Fo and Fm values. The fluorometer probe was placed on fruit surface and then a pulse of 10 mmol m−1 s−1 was applied for 0.8 s. Measurements of fruit chlorophyll fluorescence were taken each at three different locations from bottom to top from six fruit fingers. 2.4. Assay of phenolic compounds 2.4.1. Extraction and analysis of soluble phenolic compounds of pulp Soluble phenolic compounds were extracted by the method of Bennett et al. (2010), with a little modification. Lyophilized pulp samples (3.0 g) from 10 fingers were extracted with 30 mL methanol. The samples were centrifuged for 20 min at 15,000 × g

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and 4 ◦ C, then the precipitate was collected and dissolved into methanol, and finally the supernatant was collected and concentrated into 5 mL for measurement of total phenolic compounds and reverse-phase HPLC analysis.

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2.4.3. HPLC analysis of soluble phenolics Soluble phenolic compositions were analyzed by the modified method of (Kim et al., 2009). The extract samples (2 mL) were passed through a 0.45 ␮m Millipore membrane and an aliquot of 10 ␮L was injected into HPLC. A gradient HPLC system with a Shim-pack-VP-ODS RP C18 (4.6 × 250 mm, 5 ␮m) column was eluted with solvent A (0.1% trifluoroacetic acid (TFA) in ultrapure water and B (100% methanol). The gradient program was started with Solvent B from 10% to 100% at 10 min, 100% at 15 min, from 100% to 10% at 35 min and 10% B at 45 min, with a flow rate of 1.0 mL min−1 . Monitoring was conducted using a UV detector set at 280 nm. The phenol standards of (−)-gallocatechin (GC), (+)-catechin (C) and (−)-epicatechin (EC) were purchased from Sigma-Aldrich (Shanghai, China). The phenolic compounds were identified by comparing their spectral characteristics with those of the standard compounds at 280 nm.

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2.4.2. Quantification of total soluble phenolic compounds The content of total soluble phenolic compounds was determined by the method of Folin–Ciocalteu (Singleton and Rossi, 1965). The reaction mixture consisted of 0.5 mL of the methanol extract, 5 mL of distilled water and 0.5 mL of the Folin–Ciocalteu reagent. After 8 min of incubation, 1.5 mL of saturated 20% sodium carbonate solution was added. The mixture was thoroughly mixed and allowed to stand for 30 min at 25 ◦ C before the absorbance was measured at 760 nm. Each measurement was repeated three times. Results were expressed as mg of gallic acid equivalents (GAEs) on 100 g fresh weight basis.

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Days after treatment Fig. 1. Changes in hue angle (A) and chlorophyll fluorescence (Fv/Fm) (B) of banana fruit treated with water only (, control), 10 mg L−1 CPPU (䊉), 10 mg L−1 CPPU + 25 mg L−1 GA3 (), 10 mg L−1 CPPU + 50 mg L−1 GA3 () and 10 mg L−1 CPPU + 100 mg L-1 GA3 () during storage at 23 ± 2 ◦ C and75–90% relative humidity. Data were presented as the means ± standard errors.

2.5. Measurement of total soluble sugars The content of total soluble sugars was determined according to 3,5-dinitro salicylic acid (DNS) method (Miller, 1959). Lyophilized pulp tissues (2.5 g) from 10 fruit fingers were extracted with 50 mL of the distilled water for 2 h at 80 ◦ C, and then vacuum-filtrated. This extraction was repeated three times and then the supernatant was combined and collected. After mixing of 1 mL of sample solution with 1 mL DNS reagent, the mixture was boiled for 5 min and then 8 mL of the distilled water was added when the temperature reached the ambient temperature. The mixture was detected by a spectrophotometer (WFZ-UV-2800H, Unico, Shanghai, China) at 540 nm. Standard glucose at a range of 0.2–1.2 mg mL−1 was used to make the calibration curve. The reducing sugar content was calculated and then expressed on a fresh weight basis. 2.6. Determination of ascorbic acid content Ascorbic acid content of pulp tissues was determined by the previous procedure (Odriozolaserrano et al., 2007), with minor modifications. Lyophilized pulp tissues (2.0 g) from 10 fingers were homogenized with 10 mL of 4.5% metaphosphoric solution and then centrifuged for 20 min at 20,000 × g and 4 ◦ C. The supernatant was vacuum-filtered to remove the residues. The vacuum-filtered supernatant (2 mL) was passed through a Millipore 0.45 ␮m membrane for the HPLC measurement. Aliquots of 10 ␮L samples were injected into a Shimadzu C18 (150 × 4.6 mm, 5 ␮m) coupled with Hyper ODS guard column. The mobile phase was 35:65 (v/v) methanol-phosphate buffer (0.01 M KH2 PO4 , pH 2.0), with a flow rate of 0.75 mL min−1 . Monitoring was conducted using a UV

detector set at 254 nm. Ascorbic acid content was quantized using a standard curve and then expressed on a fresh weight basis. 2.7. Statistical analysis The experiments were arranged in completely randomized design. For each parameter measurement, triplicate assays were conducted. Data were expressed as the means and standard errors (SE), and then analyzed by the SigmaPlot 10.0 software. 3. Results 3.1. Changes in firmness, color, chlorophyll fluorescence, and ethylene production and respiration rates As shown in Fig. 1A, the control fruit began to soften rapidly after 10 days of storage and almost unacceptable after 16 days, while the fruit maintained a high firmness (52.55 ± 0.33 N) after the treatment with 10 mg L−1 CPPU and 50 mg L−1 GA3 . Fig. 1 shows that the control fruit exhibited significantly higher peaks in respiration and ethylene production rates after 16 days of storage. The combined CPPU and 50 mg L−1 GA3 treatment delayed the appearance in the peak of the respiration rate but had a steady ethylene production rate. It can be deduced that application of CPPU and GA3 extended the storage life due to the delay of the peak of respiration rate and the inhibition of the peak of ethylene production rate. In accompany with fruit ripening, the skin color obviously changed from green to yellow, which correlated with well the breakdown of chlorophyll. The yellow appearance of the

H. Huang et al. / Scientia Horticulturae 167 (2014) 36–42 80

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Fig. 3. Changes in contents of total reducing sugars in pulp of banana fruit treated with water only (A, control), 10 mg L−1 CPPU (B), 10 mg L−1 CPPU + 25 mg L−1 GA3 (C), 10 mg L−1 CPPU + 50 mg L−1 GA3 (D) and 10 mg L−1 CPPU + 100 mg L−1 GA3 (E) during storage at 23 ± 2 ◦ C and 75–90% relative humidity. Data were presented as the means ± standard errors.

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the first two weeks during storage. The control fruit had a significant accumulation of total reducing sugars (173.69 ± 3.07 ␮g g−1 ) after 16 days of storage along with rapid softening, while the fruit treated by 10 mg L−1 CPPU exhibited a peak (237.31 ± 1.85 ␮g g−1 ) after 18 days of storage. The combined application of 10 mg L−1 CPPU and 50 mg L−1 GA3 delayed accumulation of total reducing sugars and kept a high level of the reducing sugars after 20 days of storage. Thus, the combined treatments delayed obviously the transformation of starch to sucrose of banana fruit during storage. Fig. 4 presents the change of ascorbic acid content in pulp of banana fruit during storage. The ascorbic acid content of the control fruit dramatically increased after 10 days of storage, and then decreased rapidly when the fruit became into edible. The fruit treated with 10 mg L−1 CPPU and 25 or 50 mg L−1 GA3 maintained a higher level of ascorbic acid when they began to soften, as compared to the control fruit. As shown in Fig. 5, the content of total phenolic compounds in pulp increased and then declined slowly. Compared with the control fruit, the content of the total phenolic compounds in the fruit treated with CPPU and GA3 exhibited a higher level.

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control fruit came out after 14 days of storage and the fruit almost became yellow after 18 days of storage, with a low hue value of 94.42 ± 0.30◦ . All the treated fruit in color changed slightly after 16 days of storage (Fig. 2A). Meanwhile, chlorophyll fluorescence (Fv/Fm ratio) exhibited a similar trend. The treated fruit maintained a higher Fv/Fm ratio by the end of storage compared with the control fruit (Fig. 2B).

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3.2. Changes in nutritional quality The major quality parameters of banana fruit were evaluated in terms of contents of total reducing sugars and phenolic compounds, and ascorbic acid during storage. As shown in Fig. 3, the total reducing sugars of pulp did not accumulate almost within

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Content of ascorbic acid (µg g-1 FW)

Fig. 2. Changes in firmness (A), and rates of ethylene production (B) and respiration (C) of banana fruit treated with water only (, control), 10 mg L−1 CPPU (䊉), 10 mg L−1 CPPU + 25 mg L−1 GA3 (), 10 mg L−1 CPPU + 50 mg L−1 GA3 () and 10 mg L−1 CPPU + 100 mg L−1 GA3 () during storage at 23 ± 2 ◦ C and 75–90% relative humidity. Data were presented as the means ± standard errors.

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Days after treatment Fig. 4. Changes in ascorbic acid contents in pulp of banana fruit treated with water only (A, control), 10 mg L−1 CPPU (B), 10 mg L−1 CPPU + 25 mg L−1 GA3 (C), 10 mg L−1 CPPU + 50 mg L−1 GA3 (D), and 10 mg L−1 CPPU + 100 mg L−1 GA3 (E) during storage at 23 ± 2 ◦ C and 75–90% relative humidity Data were presented as the means ± standard errors.

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-1 Content of total phenolics [mg GAE(100g) FW]

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Days after treatment Fig. 5. Changes in total phenolic contents in pulp of banana fruit treated with water only (A, control), 10 mg L−1 CPPU (B), 10 mg L−1 CPPU + 25 mg L−1 GA3 (C), 10 mg L−1 CPPU + 50 mg L−1 GA3 (D), and 10 mg L−1 CPPU + 100 mg L−1 GA3 (E) during storage at 23 ± 2 ◦ C and 75–90% relative humidity. Data were presented as the means ± standard errors.

Meanwhile, the HPLC analysis further indicated a similar trend in various soluble phenolics such as (−)-gallocatechin, (+)-catechin and (−)-epicatechin, but the fruit treated with CPPU and GA3 exhibited a lower level of (−)-epicatechin content as compared with the control fruit (Fig. 6). 4. Discussion Climacteric fruit such as banana and mango during storage are highly perishable, followed by loss of texture and color due to physical, physiological and pathological factors that may occur after harvest (Sivakumar et al., 2011). In commercial fruit markets, the rate of ripening is controlled artificially, thus the transportation and

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Fig. 6. HPLC analysis of phenolic compounds in pulp of banana fruit treated with water only (A, control), and 10 mg L−1 CPPU + 50 mg L−1 GA3 (B) after 18 days of storage at 23 ± 2 ◦ C and 75–90% relative humidity. 1, gallocatechin (GC); 2, catechin (C); and 3, epicatechin (EC).

distribution should be planned carefully. Improved post-harvest technology ensures to control the ripening rate. Plant growth regulators such as GA3 have been reported to have effects on growth of vegetables like asparagus spear or postharvest quality (Ku and Woolley, 2006; Zhang and Whiting, 2011; Zoffoli et al., 2009). Meanwhile, CPPU as a cytokinin analogue has been shown the similar capability as endogenous cytokinin that were efficient for fruit propagation and improved the quality and yield of berry fruit such as grape, kiwi and loquat fruits by pre-harvest application (Adaniya, 2004; Marzouk and Kassem, 2011; Sugiyama and Yamaki, 1995; Taglienti et al., 2011). Furthermore, the combined application of cytokinins and GA improved fruit set or quality (Palmer et al., 2011). In this present study, application of 10 mg L−1 CPPU in combination with GA3 at different concentrations, especially 50 mg L−1 GA3 , markedly delayed the color changes and extend the shelf life. In addition, it demonstrated that the preharvest application of the combined CPPU and GA3 increased pedicel thickness and cuticle content and maintained fruit quality of grape during cold storage (Zoffoli et al., 2009). Thus, it can be concluded that combined treatment of CPPU and GA3 at suitable concentrations would be more efficiency to control postharvest quality of various fruit during storage at low or ambient temperature. Loss of green color is one of the symptoms of ripening, senescence or different environmental stresses (Yang et al., 2011). The ripening extents can be evaluated well by the hue value and the chlorophyll florescence. It has been reported that the cytokinin level would affect the chloroplast activity to regulate leaf senescence (Gan and Amasino, 1995; Riefler et al., 2006) and mitigate chlorotic foliar injury by aphid (Cottrell et al., 2010). Some researchers reported that phenylurea was a competitive and irreversible inhibitor of cytokinin oxidase and dehydrogenase (Kopecny et al., 2010; Kumari and Hoorn, 2011). It was inferred that exogenous application of CPPU could block the activity of these target enzymes by acting as an inhibitor to maintain the endogenous cytokinin level. In addition, chlorophyll degradation may be related to the accumulation of soluble sugars and the inhibition of activities of chlorophyll degradation-related enzymes (Rouphael et al., 2010; Yang et al., 2009). In the present study, the treatment of 10 mg L−1 CPPU in combination with GA3 at different concentrations, especially 50 mg L−1 GA3 , delayed obviously the decreases in the hue value and chlorophyll florescence maximum of Fv/Fm of banana fruit during storage. However, the fine mechanism involving in the degradation of chlorophylls by CPPU and GA3 needs to be further investigated. Green banana fruit contains a significant amount of starch. During fruit ripening the degradation of starch results in the decrease in firmness and the accumulation of soluble sugars to enhance the formation of flesh flavor (Mohapatra et al., 2010; Moscatello et al., 2011). Some investigates reported that CPPU treatment influenced the carbohydrate accumulation and metabolism, and increased the ratio of total soluble solids to titratable acidity and the content of ascorbic acid in kiwi fruit (Kim et al., 2006; Reynolds et al., 1992). Compared to the control fruit, the combined application of CPPU and GA3 obviously delayed the accumulation of reducing sugars of banana fruit, especially at the later stage of storage, which was in agreement with the previous report (Antognozzi et al., 1996; Marzouk and Kassem, 2011). Banana fruit contains various chemical compounds which have strong antioxidant activity, such as vitamin C, vitamin E, ␤carotene, and phenolic compounds (Kanazawa and Sakakibara, 2000). The strong antioxidant capacity of banana fruit may be attributed to the abundant phenolic compounds, especially flavonoids (Someyaa et al., 2002; Vijayakumar et al., 2008). The contents of ascorbic acid and total phenolic compounds of banana pulp maintained at high levels within the first 10 days after storage and then began to decrease along with fruit ripening. However,

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the content of the total phenolic compounds decreased slowly and maintained at a stable level in the banana fruit treated by CPPU and GA3 . Furthermore, it was detected that banana pulp was rich in phenolic compounds such as (−)-gallocatechin, (+)-catechin and (−)-epicatechin (Fig. 6), which was in agreement with the reports of Bennett et al. (2010) and Someyaa et al. (2002). It was thus suggested that the combined application of CPPU and GA3 could maintain relatively a strong antioxidant activity and reduce the decreases in contents of ascorbic acid and phenolic compounds such as (−)-epicatechin. In conclusion, the application of 10 mg L−1 CPPU in combination with GA3 at different concentrations, especially 50 mg L−1 GA3 , delayed color change and transformation of starch to sucrose, and maintained high contents of ascorbic acid and total phenolic compounds of banana fruit during storage at ambient temperature. It suggested that the combined treatment might be a promising postharvest handling to maintain quality and extend shelf life of banana fruit. Further investigation involving the molecular mechanism of these plant regulators to control fruit ripening should be considered in the future. Acknowledgments This work was supported by the National Basic Research Program of China (grant no. 2013CB127102), the National Key Technologies R&D Program (grant no. 2012BAD38B03), Guangdong Natural Science Foundation (grant no. S2011020001156) and Guangdong Province Group Team for Equipment Technology of High Efficiency Drying and Cold Chain Transport of Agricultural Products. References Adaniya, S., 2004. The use of CPPU for efficient propagation of pineapple. Sci. Hortic. 100, 7–14. Agopian, R.G.D., Soares, C.A., Purgatto, E., Cordenunsi, B.R., Lajolo, F.M., 2008. Identification of fructooligosaccharides in different banana cultivars. J. Agric. Food Chem., 3305–3310. Alkarkhi, A.F.M., Ramli, S.b., Yong, Y.S., Easa, A.M., 2011. Comparing physicochemical properties of banana pulp and peel flours prepared from green and ripe fruits. Food Chem. 129, 312–318. Aloni, B., Cohen, R., Karni, L., Aktas, H., Edelstein, M., 2010. Hormonal signaling in rootstock–scion interactions. Sci. Hortic. 127, 119–126. Bennett, R.N., Shiga, T.M., Hassimotto, N.M., Rosa, E.A., Lajolo, F.M., Cordenunsi, B.R., 2010. Phenolics and antioxidant properties of fruit pulp and cell wall fractions of postharvest banana (Musa acuminata Juss.) cultivars. J. Agric. Food Chem. 58, 7991–8003. Boudhrioua, N., Giampaoli, P., Bonazzi, C., 2003. Changes in aromatic components of banana during ripening and air-drying. LWT—Food Sci. Technol. 36, 633–642. Clerici, M.T.P.S., Kallmann, C., Gaspi, F.O.G., Morgano, M.A., Martinez-Bustos, F., Chang, Y.K., 2011. Physical, chemical and technological characteristics of Solanum lycocarpum A. St.—HILL (Solanaceae) fruit flour and starch. Food Res. Int. 44, 2143–2150. Cottrell, T.E., Wood, B.W., Ni, X., 2010. Application of plant growth regulators mitigates chlorotic foliar injury by the black pecan aphid (Hemiptera: Aphididae). Pest Manage. Sci. 66, 1236–1242. Dayan, J., Voronin, N., Gong, F., Sun, T.P., Hedden, P., Fromm, H., Aloni, R., 2012. Leaf-induced gibberellin signaling is essential for internode elongation, cambial activity, and fiber differentiation in tobacco stems. Plant Cell 24, 66–79. Antognozzi, E., Battistelli, A., Famiani, F., Moscatello, S., Stanica, F., Tombesi, A., 1996. Influence of CPPU on carbohydrate accumulation and metabolism in fruits of Actinidia deliciosa (A. Chev.). Sci. Hortic., 37–47. Gan, S., Amasino, R.M., 1995. Inhibition of leaf senescence by autoregulated production of cytokinin. Science 270, 1986–1988. Hayata, Y., Niimi, Y., Inoue, K., Kondo, S., 2000. CPPU and BA, with and without pollination, affect set, growth, and quality of muskmelon fruit. HortScience 35, 868–870. Huang, H., Jiang, Y., 2012. Effect of plant growth regulators on banana fruit and broccoli during storage. Sci. Hortic. 145, 62–67. Jiang, Y.M., Joyce, D.C., Macnish, A.J., 1999. Extension of the shelf life of banana fruit by 1-methylcyclopropene in combination with polyethylene bags. Postharvest Biol. Technol. 16, 187–193. Jiang, Y.M., Joyce, D.C., Macnish, A.J., 2000. Effect of abscisic acid on banana fruit ripening in relation to the role of ethylene. J. Plant Growth Regul. 19, 106–111.

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