Effects of 1-MCP on External Postharvest Qualities and Shelf Life of ‘Maha Chanok’ Mango Fruit

‘Maha Chanok’ mango is an economic fruit crop widely cultivated commercially throughout Thailand. By nature, mango fruit has a rather limited storage life after harvest. 1-methylcyclopropene (1-MCP) has been accepted as a commercial substance to improve several fruit qualities. The objective of this research was to study the effects of 1-MCP on the external postharvest qualities and storage life on the ‘Maha Chanok’ mango fruit. The experiment was laid out in a Completely Randomized Design with three replicates, ten fruits per replicate. Mango fruit was fumigated with 1-MCP at three concentrations (1000, 1250, or 1500 nl l-1) and three fumigation periods (12, 18, or 24 h), compared with the control fruit. After treating, all treatments were stored under ambient temperature (27 °C, 80%R.H.). The following determinations were made every two days for assessment of fruit weight loss, firmness, chlorophyll content, decay incidence, and storage life. The results showed that fruit treated with 1500 nl l-1 1-MCP for 24 h had the maximal fruit firmness. For chlorophyll content, the results showed that fruit-treated with 1500 nl l-1 1-MCP for 12 h could effectively retain the highest chlorophyll contents. Furthermore, both the lowest fruit decay and the longest storage life of 12 days were achieved from the fruit treated with 1000 nl l-1 1-MCP for 12 h.


Introduction
Mango (Mangifera indica L.) belongs to the Anacardiaceae family which is widely grown in tropical and subtropical regions (Laohaprasit, Kukreja, & Arunrat, 2012). It is also one of the most popular fruits consumed both in fresh and processed form (Vidhu, Chourasia, & Nath, 2005). In Thailand, mango is one of the most preferred and broadly distributed fruits. It can be found throughout the numerous regions in the country, and as such, it is considered an important economic fruit (Wongkhot, Rattanapanone, & Chanasut, 2012). In Thailand, there are many popular cultivars of mangoes grown for export, including, Chok-Anan, Nam Dok Mai, Nang Klangwan, and Maha Chanok (Wongkhot, Rattanapanone, & Chanasut, 2012). The 'Maha Chanok' mango is perhaps the most popular cultivar for consumption at the ripe stage (Thai Mango-Ma-Muang, 2008). Cavan (2012) reported that the Maha Chanok is a hybrid cultivar between Sunset and Nang Klangwan-Thailand's local mangos. When the 'Maha Chanok' mango fruit ripens, its skin turns yellowish-orange with a pink blush color (Cavan, 2012). The reasons why many people like to eat them vary, but primarily it is because their flesh has a buttery taste, is juicy, sweet, and fragrant. In addition, 'Maha Chanok' has a high flesh yield (70.5%) and is a little fibrous (Vásquez-Caicedo et al., 2002;Good Fruit Guide, 2011). For nutritional value the 'Maha Chanok' mango is rich in vitamin C, B 1 , B 2 , beta carotene, carbohydrates, protein, calcium, phosphorus, and antioxidant potential (Vásquez-Caicedo et al., 2002). Thailand is the world's fourth ranked mango producing country (1845.6 thousand tones production), with a 27% share of the world market and an emphasis in Japan and Europe (Wongkaew & Likittrakoolrung, 2009). Unfortunately, mango fruit is a climacteric fruit; it has poor storage life after harvest due to fast ripening caused by the ripening trigger ethylene, which greatly affects a loss in its commercial value (Wongkhot, Rattanapanone, & Chanasut, 2012). The rapid quality loss and short storage life of the mango fruit makes it highly perishable with short shelf-life periods (Pantastico, Chattopadhyay, & Subramanyam, 1975).  is being considered as an emerging tool with satisfactory results in terms of extending shelf life and quality improvement in several fruits (Blankenship & Dole, 2003). It is considered as a non-toxic agent for humans and environment (Yuan, Sun, Yuan, & Wang, 2010). 1-MCP has been reported to have inhibitory effects on ethylene action (Serek, Sisler, & Reid, 1995) for controlling of ripening and senescence of harvested fruits. Thus, 1-MCP is being commercially used in extending storage life in several perishable fruits (Watkins, 2006). Some examples of the beneficial effects of 1-MCP in postharvest fruits have been recently reviewed, including, delay of weight loss (Blankenship and Dole, 2003), maintenance of fruit firmness, a decreased susceptibility to postharvest decay (Hernández, Barrera, Martínez, & Fernández-Trujillo, 2009), and prolonging storage life (Rupinder & Dwivedi, 2008). The aim of this study was to study the effects of 1-MCP treatments at three concentrations (1000, 1250, and 1500 nl l -1 ) with three different fumigation period (12, 18, or 24 h) in an attempt to slow down the external postharvest changes and extending the storage life of 'Maha Chanok' mango fruit stored at ambient temperature.

Method
'Maha Chanok' mango was harvested at commercial maturity based on 98 days after full bloom from a commercial orchard in Kalasin province, in the Northeast region of Thailand. Following the harvest the mangoes were transported to the laboratory within 2 h. Mangoes with uniform fruits size free from visual symptoms of any disease or blemishes were selected for the experiment. The experimental design was Completely Randomized Design, composed of ten treatments, including Control (no treat 1-MCP), treated with 1-MCP at 1000 nl l -1 for 12, 18 or 24 h, treated with 1-MCP at 1250 nl l -1 for 12, 18 or 24 h, treated with 1-MCP at 1500 nl l -1 for 12, 18 or 24 h. Each treatment was carried out in three replicates with 10 mango fruits per replication. The experiment was carried out from September to February 2013 at the Division of Agricultural Technology, Mahasarakham University, in the northeast of Thailand. After selecting, the fruit were placed in a 20 L sealed container and exposed to 1-MCP with three concentrations (1000, 1250, or 1500 nl l -1 for three different duration period (12, 18, or 24 h) at 25 °C. The source of 1-MCP was from Mr. Xisheng Sun, by Agrofresh, Inc., China as a powder (active ingredient 0.43%), that after addition of warm water (40 °C), released the active ingredient to generate 1-MCP gas. The control fruits were also placed in similar closed containers without the addition of 1-MCP treatment. Following 1-MCP treatment, mango from all treatments were placed into corrugated boxes and stored at an ambient temperature of 27 C and 80% R.H. The external postharvest changes, including, fruit weight loss, firmness, chlorophyll content, fruit decay, and storage life, were evaluated in two day intervals. Fruit weight was determined by weighing individual fruit at two day intervals throughout storage and expressed as the percentage of fruit weight loss from the initial weight. Fruit firmness was determined on two opposite sides of each fruit using a hand-held fruit firmness tester (Effegi, Italy) equipped with a cylindrical plunger 0.5 cm in diameter and expressed as kg cm -2 . Chlorophyll content was determined using a procedure as described by Whitham, Blaydes, and Devlin (1986) and expressed as mg m -2 . Disease incidence on mango fruit was assessed by observing the extent of total decayed area on each fruit surface. The visual estimation was then noted as a percentage of fruit decay (Terry & Joyce, 2000). The end of storage life (days) was considered to terminate when 50% of mango fruit senescence. The comparisons among means were done by the Least Significant Difference (LSD) at P ≤ 0.05. The collected data were statistically analyzed using the SPSS Computer Program, Version 6 (SPSS, 1999).

Results
After fumigating with 1-MCP at three different concentrations of 1000, 1250 or 1500 nl l -1 , for three exposure times of 12, 18, or 24 h the fruit were compared with the control and then stored at ambient temperature (27 C, 80%R.H.). The results are presented as follows:

Weight Loss
The data from Table 1 reveal that weight loss of mango fruit in all treatments increased steadily with storage duration. All mango fruits exposed to 1-MCP at three concentrations and three duration periods showed the similar fruit weight loss throughout storage, except on the sixth day after storage (DAS). On the 6 DAS, fruits treated with 1250 nl l -1 1-MCP for 12 h showed the maximal weight loss of 11.24%, while fruit-treated with Note. Data were expressed as mean ± standard deviation (S.D.). Letters within columns indicate least significant differences (LSD) at P* = 0.05, NS = non significant.

Fruit Firmness
Highly significant differences in fruit firmness were found between 1-MCP-treated fruit and controls. Mango fruit firmness began to show significant differences throughout storage. Fruit-treated with 1500 nl l -1 1-MCP for 24 h tended to show the maximal fruit firmness from 4 DAS to 10 DAS. On the contrary, Control fruits firmness was at its lowest level during storage (Table 2). chlorophyll content throughout the storage period. Thus, Control fruit showed dramatically decreased chlorophyll content and turned completely yellow within 6 days under ambient storage. Interestingly, fruit-treated with 1500 nl l -1 1-MCP for 12 h had the maximal chlorophyll contents of 0.298, 0.215, and 0.104 mg/g fresh weight measured on 4, 6 and 8 DAS, respectively (Table 3). These results indicated that fruit-treated with 1500 nl l -1 1-MCP for 12 h still had greener skin than untreated fruit. Note. Data were expressed as mean ± standard deviation (S.D.). Letters within columns indicate least significant differences (LSD) at P* = 0.05.

Decay Incidence
Percentage of decay incidence was obtained by considering the number of fruit that showed signs of decay over the initial number of fruit. The cumulative decay during storage was expressed as a percentage of infected fruit. Anthracnose, caused by Colletotrichum spp. was the main postharvest disease that occurred on stored mango fruit. Degree of disease incidence on fruit skin rapidly increased during storage. The results from Table 4 revealed that a significantly lower rot appearance was found in fruit-treated with 1000 nl l -1 1-MCP for 12 h since 4 DAS. At the end of storage (10 DAS), fruit-treated with 1000 nl l -1 1-MCP for 12 h showed minimal decay incidence by 43.75%.  Note. Data were expressed as mean ± standard deviation (S.D.). Letters within columns indicate least significant differences (LSD) at P* = 0.05.

Storage Life
The results from Table 5 show that fruit-treated with 1000 nl l -1 1-MCP for 12 h showed a marked effect on the maximal storage life of 14 days, while the Control fruit had the minimal postharvest life of only 8 days. Note. Data were expressed as mean ± standard deviation (S.D.). Letters within columns indicate least significant differences (LSD) at P* = 0.05.

Discussion
When considering weight loss, the results revealed that 1-MCP application at three different concentrations with three various exposure periods had no clear effect on the weight loss of 'Maha Chanok' mango fruit. Most of the Control and 1-MCP treated fruits had quite similar weight loss during storage, except on 6 DAS. Thus, the results of this study indicated that weight loss of 'Maha Chanok' mango fruit was ambiguous after treating with 1-MCP. It is possible therefore that 1-MCP treatment were not effective in reducing mango fruit weight loss. There were a few reports that described 1-MCP treatment as being highly effective in reducing weight loss during storage for tomato fruits (Guillén et al., 2006), while some researchers described 1-MCP as not affecting fruit weight loss in papaya (Ashariya, Bayogan, Thumdee, & Paull, 2007).
With respect to pulp firmness, generally, mango ripening is characterized by fruit softening increments (Bassetto, Jacomino, Pinheiro, & Kluge, 2005). Mango is considered to be a climactic fruit, which typically soften very quickly (Xiaolin, Ye, Jiang, Guox, & Li, 2012). Menniti, Gregori, and Donati (2004) reported that mango fruit softens rapidly after harvest, because its softening is regulated by endogenous ethylene biosynthesis. Kashif, Khan, Malik, and Shahid (2013) cited that fruit softening is linked with enzymatic changes and textural modifications leading to breakdown of cell wall polymers, such as, cellulose, hemicelluloses and pectin. In mango, various enzymes documented to be involved in softening are polygalacturonase (PG) (Lazan, Ali, Lee, Voon, & Chaplin, 1986), and β-1,4-glucanases (Ali, Chin, & Lazan, 2004). The activity of endo-PG was significantly increased in the pulp tissues of 'Samar Bashist Chaunsa' mango fruit with the advancement of the ripening period. The results from Table 2 indicate that postharvest firmness of 'Maha Chanok' mango can be maintained by treating with 1500 nl l -1 1-MCP for 24 h during storage. It is possible that 1-MCP treatment was highly effective in reducing ethylene production and delaying fruit softening (Blankenship & Dole, 2003) by blocking ethylene receptors (Sisler & Serek, 1997). These results are in agreement with those obtained by Khan and Singh (2007) who showed that postharvest application of 1-MCP significantly lowered the activities of softening enzymes in plum fruit. They reported that plum fruit treated with 1-MCP showed reduced activities of exo-polygalacturonase (exo-PG), and endo-polygalacturonase (endo-PG) enzymes during fruit ripening, and the reduction was more pronounced at the higher concentrations of 1-MCP. Ahmad and Singh (2009) also cited that the application of higher concentrations of 1-MCP to 'Tegan Blue' plum maintained significantly firmer fruit during storage. The reduction in plum fruit softening with 1-MCP treatment may be attributed to suppressed ethylene production, and consequently, the reduction in fruit softening. Similarly, Ahmad and Singh (2009) reported that 1-MCP could retard fruit softening during fruit ripening in climacteric fruit (Watkins, 2006) through inhibiting the activities of cell wall hydrolytic enzymes (Jeong et al., 2002). Accordingly, Kim, Hewett, and Lallu (2001) also found that 1-MCP reduced softening of intact kiwifruit and the effect tended to be concentration dependent. A similar delayed mango fruit softening was also found in mango treated with 25-100 μl l -1 1-MCP for 14 h at 20 °C (Hofman, Jobin-Décor, Meiburg, Macnish, & Joyce, 2001). However, after treating with 1-MCP, nonpermanent binding of 1-MCP to ethylene receptors could be turned back and led fruit to ripe normally (Blankenship, 2003). Thus, an effective 1-MCP application to delay fruit softening depended upon the concentration and exposure duration (Singh & Pal, 2008). This is consistent with the findings of Ekman, Clayton, Biasi, and Mitcham (2004) who cited that the response of fruit firmness to 1-MCP treatment was highly dependent on the 1-MCP concentration application. While Khan and Singh (2007) reported that the reduction of softening enzymes activities was more pronounced as the higher concentrations of 1-MCP were applied (Ahmad & Singh, 2009). These results are not in agreement with those obtained by Porat et al. (1999) who showed that 1-MCP treatment had no significant effect on firmness retention in citrus fruit and fresh-cut pineapple (Budu & Joyce, 2003). The contradictory results mentioned above concerning the effects of 1-MCP on fruit firmness related to modified softening enzymes still require a full explanation. No information is available on the effects of 1-MCP on 'Maha Chanok' fruit softening or the activities of fruit softening enzymes during storage. Thus, the mechanism of 1-MCP as it relates to delaying mango fruit softening during storage has not been clearly elucidated and warrants further investigations.
For chlorophyll content, the effect of 1-MCP application on chlorophyll content is illustrated in Table 3. Mango fruit-treated with 1500 nl l -1 1-MCP for 12 h showed the highest chlorophyll contents which was significantly different from the other treatments of 4 DAS to 8 DAS. These results also showed the positive effects of 1500 nl l -1 1-MCP for 12 h on delaying the changes of peel color. Peel color of mango fruit-treated with 1500 nl l -1 1-MCP for 12 h turned less yellow than the others (Pongprasert & Srilaong, 2014). Several reports have shown the effects of 1-MCP in retarding ripening (Zhanquan, Tian, Zhu, Xu, & Qin, 2012) by competing with ethylene action, which prevents ethylene from exerting its physiological action (Sisler & Serek, 1997) and leads to better retention of chlorophyll content in 1-MCP-treated fruit. Cefola, Amodio, Rinaldi, Vanadia, and Colelli (2010) also reported that a cause of retention of the green peel color in fruit-treated with 1-MCP can be attributed to 1-MCP itself; it is an effective inhibitor that reduces the activity of chlorophyllase enzymes involved with chlorophyll degradation. These data support the findings of Vera, Saguy, and Pesis (2005) who found that 1-MCP-treated 'Ettinger' and 'Pinkerton' avocado fruit maintained a greener peel color because of their lower levels of chlorophylls activity and less chlorophyll breakdown. Thus, there is documentation available about the effect of 1-MCP in delaying chlorophyll degradation and causing retention of higher chlorophyll content of fruit peel for longer periods of time in several fruits (Cheng et al., 2012), such as avocado (Jeong, Huber, & Sargent, 2002), coriander (Jiang, Sheng, Zhou, Zhang, & Liu, 2002), pear (Liu, Lai, Xu, & Tian, 2013), cucumber (Nilsson, 2005), and peaches . In addition, Bassetto, Jacomino, Pinheiro, and Kluge (2005) cited that 1-MCP efficiency was directly related to concentration and exposure time. They found that the higher the 1-MCP concentration compared with exposure time to the product, the greater the retention of the green skin color in 'Pedro Sato' guava. These results support the findings of Jiang, Joyce, and Macnish (1999) and Jeong, Huber, and Sargent (2002) that a correlation between concentration and exposure time was also observed in treating banana and avocado with 1-MCP, respectively. In contrast, some researchers found that there was no influence of 1-MCP on postharvest color changes in apricots (Dong, Lurie, & Zhou, 2002), and sweet cherries (Gong, Fan, & Mattheis, 2002). While Win, Srilaong, Heyes, Kyu, and Kanlayanarat (2006) found that application with high concentrations of 1-MCP (750 and 1000 nl l -1 ) significantly damaged the fruit of West Indian lime cv. 'Paan' during ambient storage by promoting chlorophyllase activity, which caused the deleterious results. Similar adverse effects on citrus fruit from high concentrations of 1-MCP have been reported by Porat et al. (2001) who found that exposure of 'Oroblanco' pummelo to 1-MCP at 2000 nl l -1 resulted in faster peel yellowing. However, the results from this research found no large differences in 1-MCP efficacy with different exposure durations of 12, 18 or 24 h. However, it is still unclear how 1-MCP affects chlorophyll content of 'Maha Chanok' mango fruit. Further study of the mechanisms of 1-MCP that may delay chlorophyll degradation should be investigated.
For decay incidence, the susceptibility of mango fruit to postharvest diseases increases during storage as a result of the physiological changes and senescence that favor pathogen development (Prusky & Keen, 1993). Table 4 showed the percentage in decay incidence of 'Maha Chanok' mango fruit during postharvest after being treated with 1-MCP. The results indicated that 1-MCP treatments had significant effects on postharvest fruit decay. Treating with 1000 nl l -1 1-MCP for 12 h showed efficacy in slowing the deterioration of 'Maha Chanok' mango fruit during storage at room temperature. These results coincide with previous reports of Pietro, Cocci, Romani, Sacchetti, and Rosa (2009) who found that 1-MCP may be beneficial in controlling microbial growth. Similar results were also reported by several researchers, who reported the positive effects of 1-MCP to enhance the disease resistance in apricots (Dong, Lurie, & Zhou, 2002), jujube (Zhanquan, Tian, Zhu, Xu, & Qin, 2012), plums (Valero, Martínez-Romero, Valverde, Guillén, & Serrano, 2003), loquat (Cai et al., 2006), citrus (Porat et al., 1999). The similar trend in reducing decay appearance after treating with 1-MCP, may be associated with changes in natural antifungal compounds in ripening fruit (Prusky & Keen, 1993). Zhanquan, Tian, Zhu, Xu, and Qin (2012) indicated that the induced resistance in jujube fruit by 1-MCP is related to an increase of enzymes associated with plant phenolic metabolism which produces highly toxic products against pathogen invasion while Bower, Biasi, and Mitcham (2003) cited that 1-MCP had no effect on the decay of strawberry. In contrast, Jiang, Joyce, and Ferry (2001) pointed out the disadvantage of 1-MCP treatment in controlling postharvest pathogens. They found that 1-MCP could accelerate disease development in strawberries. However, these different responses to 1-MCP may be species specific (Blankenship, 2003) and the concentrations of 1-MCP used (Zhanquan, Tian, Zhu, Xu, & Qin, 2012). Furthermore, the effects of 1-MCP treatments on fruit decay varied with concentration-dependent (Chong et al., 2006). Similarly, Guillén et al. (2006) pointed out the induction of decay by 1-MCP in strawberry seemed to be dose-dependent, since disease development was accelerated in fruit treated at high 1-MCP concentrations (500 and 1000 nl l -1 ), mainly due to inhibition of some beneficial metabolic pathway which contributed to the natural defense system. Hofman, Jobin-Décor, Meiburg, Macnish, and Joyce (2001) also found that 'Hass' avocado fruit treated with a very high concentration (25 μl l -1 ) of 1-MCP tended to increase the severity of fruit rotting. It is possible that 1-MCP application at high concentration may be associated with adding stress to the received fruit (Adkins, Hofman, Stubbings, & Macnish, 2005). However, little information is available about the effect of 1-MCP on inducing fruit resistance against postharvest decay and the mechanisms by which 1-MCP shows efficacy in slowing the deterioration of 'Maha Chanok' mango fruit.
With respect to storage life, the best treatment for extending postharvest life proved to be 1000 nl/l 1-MCP for 12 h. Gómez-Lobato, Hasperué, Civello, Chaves, and Martínez (2012) cited that 1-MCP is an effective inhibitor of ethylene action in a range of perishable fruit, which proved to delay ripening or the senescence process, and led to extend the postharvest life of several fruits (Watkins, 2008). 1-MCP is thought to act by binding irreversibly to ethylene receptors in the fruit, thereby preventing the effects of ethylene in plant tissues (Sisler & Serek, 1997). Similar effects of 1-MCP on extending postharvest life have been reported in mango (Jiang & Joyce, 2000), papaya (Jacomino, Kluge, & Brackmann, 2002), loquat (Chong et al., 2006), 'Qiandaowuhe' persimmon (Zisheng, 2007), and avocado (Jeong, Huber, & Sargent, 2002). This is in accordance with findings of Juan, Concellón, Chaves, and Vicente (2011) who cited that 1-MCP treatments delayed senescence and maintained the quality of eggplant fruit. These results are consistent with the findings of Shifeng, Yan, and Zheng (2012).
Results also suggest that 1-MCP at 1.0 μl l -1 applied to green bell pepper was the most effective in delaying senescence, manifested as a delay in chlorophyll degradation and fresh weight loss. In addition, Carrillo,  Hernández, Barrera, Martínez, and Fernández-Trujillo (2011) reported that the successful application of 1-MCP to fruit is strongly dependent on many factors, such as, cultivar, harvest maturity stage, concentration, exposure time, and temperatures (Sozzi & Beaudry, 2007). Blankenship (2003) indicated that 1-MCP treatment duration ranged from 12 to 24 h to achieve a full response. Furthermore, Harima et al. (2003) found that binding of 1-MCP to the ethylene receptor is irreversible; plants could recover their ethylene sensitivity thereafter (Sisler & Serek, 1997). Thus, the length of the protection period by 1-MCP varies with plant species and tissues. Ella, Zion, Nehemia, and Ammon (2003) revealed that the use of low concentrations of 1-MCP may lead to accelerate the senescence, possibly through the relief of the ethylene auto-inhibitory response. The efficacy of 1-MCP protection is also greatly affected by temperature. The effect of 1-MCP on delaying senescence may be attributed to its ability to inhibit ethylene biosynthesis (Sisler & Serek, 1997), leading to delayed senescence and maintenance of external quality, such as, delayed fruit softening or a delay in ripening and other changes which may lead to extending the storage life of the fruit (Blankenship & Dole, 2003). However, the mode of 1-MCP action in delaying senescence and quality deterioration in 'Maha Chanok' mango has not been clearly elucidated. Furthermore, the ability of 1-MCP application in maintaining the internal quality characteristics in stored mango fruit should be studied.
In conclusion, it was found that the shelf life of 'Maha Chanok' mango fruit treated with 1000 nl l -1 1-MCP for 12 h was extended for up to 14 days. The same treatment resulted in the lowest incidence of decay throughout the storage period.