Impaginato 159 1. Introduction Banana (Musa spp.) is a climacteric fruit; there- fore, ripening process is induced by ethylene produc- tion via ACC (1-aminocyclopropane 1-carboxylic acid) biosynthesis. The rate of respiration is followed by reaching a threshold level of ethylene within the cells of fruit then rises rapidly to a peak and subsequently falls as ripening progress. During fruit softening, starch is turned to sugars, the peel color changes to yellow and fruit flavor develop by losing its astrin- gency (Pathak et al., 2003). Polyamines as natural compounds suppress ethyl- ene synthesis by inhibition of ethylene biosynthesis enzymes activities (Lee et al., 1997). They are present ubiquitously in plant organs. The main polyamines are putrescine (1, 4-diaminobutane), spermidine (N- 3-aminopropyl-1, 4-diaminobutane), and spermine [bis (N-3-aminopropyl)-1, 4-diaminobutane] which are essential in plant growth, differentiation and stress responses (Valero and Serrano, 2010). They are known to improve the storage life of fruits by inhibiting ethylene production and delaying the ripening process, respectively. Polyamines and ethylene have opposite impacts on fruit ripening and senescence. Thus, a balance between them is crucial to enhance and retard the fruit ripening process. In general, polyamines level declines throughout fruit senescence along with accelerating ethylene synthesis (Valero et al., 2002). Much researches have indicated the positive effects of pre and postharvest polyamines application on retarding fruit softening in mango (Malik et al., 2003) and pear (Franco-Mora et al., 2005), reducing weight loss in apricot (Martinez-Romero et al., 2002), inhibition of ethylene production in peach (Zokaee Khosroshahi and Esna-Ashari, 2008), delaying ripening process in nectarine (Torrigiani et al., 2004) and peach (Bregoli et al., 2002), and maintaining TA at higher levels, diminishing the increase in TSS, and declining color change in plum (Khan et al., 2008). Thus, the present study was carried out to evalu- ate the application of putrescine for extending quali- ty and storage life of Musa acuminata L. Adv. Hort. Sci., 2016 30(3): 159-164 DOI: 10.13128/ahs-20278 Pre-storage putrescine treatment maintains quality and prolongs postharvest life of Musa acuminata L. M.S. Hosseini 1, S.M. Zahedi 2, Z. Fakhar 3 (*) 1 Department of Horticultural Science, Hormozgan University, Bandar Abbas, Iran. 2 Department of Horticultural Science, Faculty of Agriculture, University of Maragheh, 551181-8311 Maragheh, Iran. 3 Department of Horticultural Science, College of Agriculture and Natural Resources, University of Tehran, 31587 Karaj, Iran. Key words: firmness, polyphenol oxidase, postharvest, skin color, weight loss. Abstract: The study was carried out to determine the effect of putrescine on quality and postharvest life of Musa acumi- nata L. during storage. The fruits were dipped at different concentrations of putrescine (0.5, 1 and 2 mM for 30 min) and distilled water as ‘control’. Changes in fruit quality attributes such as weight loss, firmness, skin color (L*, hue angle), total soluble solids (TSS), titratable acidity (TA), pH, ascorbic acid, polyphenol oxidase (PPO) and polygalacturonase (PG) enzymatic activity were calculated at harvest and after 5, 10, 15 and 20 days of storage at 0±1°C, 80-85% relative humidi- ty. Weight loss, fruit softening, skin color changes, TSS, pH, the activity of PPO and PG increased during fruit ripening but the rate of changes was significantly slowed in putrescine treated fruits. Moreover, putrescine application maintained higher levels of TA, ascorbic acid and reduced the loss of sensory acceptability and decay incidence compared to control. In conclusion, the postharvest dip treatment of putrescine could be an effective means for extending the storage life of Musa acuminata L. (*) Corresponding author: za.fakhar@gmail.com Received for publication 21 July 2016 Accepted for publication 20 September 2016 Copyright: © 2016 Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2016 30(3): 159-164 160 2. Materials and Methods Mature green bananas (Musa acuminata L.) were harvested from a commercial orchard in Minab, Iran, and then transported to the laboratory for experi- ments. Fruits uniform in size and color, without any noticeable defects, were selected and dipped in putrescine solution at different concentrations (0.5, 1 and 2 mM for 30 min) and distilled water as ‘control’. Then all of treated and untreated fruits were stored at 13°C and 80-85% relative humidity. Then, some physico-chemical attributes were measured at harvest and after 5, 10, 15 and 20 days of cold stor- age. Quality parameters evaluation Fruit weight was recorded just after harvest and a f t e r t h e d i f f e r e n t s a m p l i n g d a t e s a n d t h e n expressed as percentage of weight loss relative to the initial weight (Soto-Zamora et al., 2005). Fruit firmness was measured using a FG-5020 pen- etrometer (Lutron Electronic Enterprise Co.) of 5 mm in diameter at 2 equatorial points and was expressed as newton (N). Color was determined at opposite sides of each f r u i t f r o m e a c h r e p l i c a t e w i t h a M i n o l t a Chromameter CR400; the following parameters were considered: L* (0= black; 100= white), a* (green to red) and b* (blue to yellow) then expressed as L* and hue angle (h°)= arctan (b* a*-1) (Ozdemir, 2016). Total Soluble solids (TSS) content was assessed by a digital refractometer (Atago N1, Japan) at 20˚C and expressed as a percent. Titratable Acidity (TA) was estimated by titrating 5 ml of diluted juice against 0.1 N NaOH using phenolphthalein as an indicator and was expressed as percent malic acid (%). The pH of fruit juice was measured using a MTT65 (Japan) pH meter calibrated by pH 4 and 7 buffer solutions. Ascorbic acid assessment Ascorbic acid content was estimated using the methods of Marisa and Wall (2006). Polyphenol oxidase (PPO) and Polygalactronase (PG) activities measurement PPO and PG were assessed using the procedure of Marquez Cardozo et al. (2015) and Zhu et al. (2015) respectively. Decay incidence and sensory acceptability determina- tion Fruit deteriorations were measured on individual fruit by visual observations. From each fruit 5 slices were obtained and fruits decay was recorded using the following formula: A/B ×100 in which A is the number of decayed fruit slices and B the initial num- ber of all fruit slices. The fruits were rated by a panel of 10 judges on the basis of color, texture, taste and flavor and over- all acceptability (as 1-2 unusable, 3-4 unsalable, 5-6 salable, 7-8 good, 9-10 very good). Statistical analysis To estimate storability of fruit, a factorial design completely randomized was carried out in three replications. All data were analyzed using SAS soft- ware package 9.4 for windows and mean compar- isons were conducted using Duncan’s multiple range tests. 3. Results and Discussion Weight loss and firmness Weight loss percentage increased in all the treat- ments along the storage. However, all putrescine concentrations demonstrated significantly lower weight loss than control. Fruits treated with 2 mM putrescine exhibited the lowest weight loss amongst the putrescine concentrations during storage while highest weight loss was registered by control (Fig. 1 A). The effect of putrescine on reducing weight loss Fig. 1 - The effect of putrescine at different concentrations (0.5, 1 and 2 mM) on weight loss (A) and firmness (B) of Musa acuminata L. during storage. Hosseini et al. - Prolonging storage life of banana by using putrescine 161 may be ascribed to conjugation of polyamines to the cell membrane phospholipids that result in cell mem- brane integrity (Mirdehghan and Rahimi, 2016). Similar results have been reported in apricot (Enas et al., 2010). As shown in figure 1B irrespective of treatments, fruit firmness decreased significantly over storage but putrescine treated fruits were observed firmer, and especially 2 mM putrescine treatments was more effective than others in keeping the firmness. It is suggested that polyamines maintain fruit firmness by their cross-linkage to the pectin substances car- boxyl groups in the cell wall and lead to rigidification o f c e l l w a l l ; c o n s e q u e n t l y c e l l w a l l d e g r a d i n g enzymes activities of pectin methyl esterase (PME), pectin esterase (PE) and polygalactouronase (PG) are decreased (Valero et al., 2002). The results are in line with peach (Bregoli et al., 2002). Color changes Skin color alteration from green to yellow is a pre- dominant index used for evaluating the stage of ripening in banana (Gomes et al., 2013). As the stor- age time progressed, fruit color changed as a result of chlorophyll degradation along with carotenoid syn- thesis. However, putrescine treated fruits showed higher L* and hue angle than control (Fig. 2 A and B). Delayed color changes can be associated to the effect of putrescine as anti-senescence by reducing ethylene production and subsequently delaying fruit ripening as well as senescence (Drake and Chen, 2000). Similar results have been observed in apricot (Martinez-Romero et al., 2002). Total soluble solids (TSS), titratable acidity (TA) and pH TSS content and TA increased along the storage period while pH demonstrated reverse trend in all treated and untreated fruits (Fig. 3 A, B and C). Lower Fig. 2 - The effect of putrescine at different concentrations (0.5, 1 and 2 mM) on L* (A) and hue angle (B) of Musa acumi- nata L. during storage. Fig. 3 - The effect of putrescine at different concentrations (0.5, 1 and 2 mM) on TSS (A), TA (B) and pH (C) of Musa acuminata L. during storage. Adv. Hort. Sci., 2016 30(3): 159-164 162 values of TSS, TA and higher value of pH content were observed in putrescine treated fruits compared to control (Fig. 3). That is ascribed to the role of putrescine on delaying fruit ripening process by reducing ethylene production and respiration rate in fruit (Valero et al., 2002). The results are in agree- ment with those observed in mango (Malik and Singh, 2006). Ascorbic acid The content of ascorbic acid was significantly influenced by putrescine. The value of ascorbic acid was higher in treated fruits than control throughout the storage (Fig. 4). It is possible that putrescine inhibits ascorbic acid oxidation by decreasing ascor- bate oxidase activity and consequently maintaining ascorbic acid (Ishaq et al., 2009). This result is in line with the finding of Davarynejad et al. (2013). Enzymatic activity of polyphenol oxidase (PPO) Irrespective of treatments, the activity of PPO increased during ripening process and it was signifi- cantly higher in control than treated fruits (Figure 5 A). This trend may be attributed to the role of putrescine on reducing polyphenol oxidase activity (Koushesh saba et al., 2012). Previously, it has been observed in kiwifruit (Jhalegari et al., 2012). Polygalacturonase (PG) activity PG is known as an important enzyme on fruit soft- ening, whereas, a reduction in PG activity results in a delay in fruit softening and consequently an increase in the storage life (Jhalegari et al., 2012). In this study, the activity of PG increased during the storage. As shown in figure 5 B, untreated fruits demonstrat- ed the highest values of PG activity (1.74 mmol kg-1 s-1 on the 20th day of storage). Fruits treated with 2 mM exhibited the lowest PG activity, followed by putrescine at 1 and 0.5 mM respectively. This trend is associated to declining fruit firmness and increasing fruit softening by the loss of membrane integrity (Sitrit and Bennett, 1998). Decay incidence and sensory acceptability The highest rate of fruit decay percent was observed in control while all three concentrations of putrescine reduced the decay development signifi- cantly during storage; in particular, the fruits dipped in 2 mM putrescine showed the lowest decay inci- dence in comparison to others (Fig. 6 A). While time passed, sensor acceptability declined. However, fruit treated by putrescine exhibited higher scores of sen- sor acceptability compared to control at the end stor- age (Fig. 6 B). Fig. 4 - The effect of putrescine at different concentrations (0.5, 1 and 2 mM) on ascorbic acid of Musa acuminata L. dur- ing storage. Fig. 5 - The effect of putrescine at different concentrations (0.5, 1 and 2 mM) PPO (A) and PG (B) activities of Musa acuminata L. during storage. Hosseini et al. - Prolonging storage life of banana by using putrescine 163 4. Conclusions The effect of putrescine treatment at different concentrations (0.5, 1 and 2 mM for 30 min) was investigated to improve and extend storage life of b a n a n a ( M u s a a c u m i n a t a L . ) . A p p l i c a t i o n o f putrescine maintained fruit quality attributes such as firmness, color, TSS, TA, pH and sensory acceptabili- ty. In addition, the reduction of weight loss, PPO, PG, and decay incidence were observed in putrescin t r e a t e d f r u i t s c o m p a r e d t o c o n t r o l . T h u s , t h e postharvest dip treatment of putrescine may be an effective tool for prolonging the storage life of Musa acuminata L. References BREGOLI A.M., SCARAMAGLI S., COSTA G., SABATINI E., ZIOSI V., BIONDI S., TORRIGIANI P., 2002 - Peach (Prunus persica) fruit ripening: aminoethoxyvinylglycine (AVG) and exogenous polyamines affect ethylene emis- sion and flesh firmness. - Physiol. Plant., 114(3): 472- 481. 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