Reducing Postharvest Softening of Papaya (Carica papaya cv. Maradol) by using an aqueous 1-Methylcyclopropene Application
Abstract
The shelf life of ‘Maradol’ papaya fruit (Carica papaya) harvested at one -quarter stage maturity (yellow - orange color in 25% of fruit surface) and treated with aqueous 1 -methylcyclopropene (1 -MCP) was evaluated. The effects of immersion time (30 or 60 seconds) and dose response (50 or 300 ng∙kg-1) on the quality of papaya fruit stored for 12 days at 20 ± 2 °C and 85 ± 5% RH were studied. After 3 days, the control and fruit treated with 50 ng∙kg-1 1-MCP for 30 seconds lost 82% and 72% of the initial firmness, respectively. A 1 -MCP concentration of 300 ng∙kg-1 for 30 or 60 seconds inhibited softening and slowed skin color change for 12 days. The pH, titratable acidity, and soluble solids concentration ranged from 5.3-5.7, 0.06 -0.12 % and 10 -12 %, respectively. The shelf life of papaya was extended up to 3 days in fruit treated with 50 ng∙kg-1 1-MCP for either 30 or 60 seconds of immersion.
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Introduction
Papaya fruit has a high rate of softening “off” the tree, and therefore, a short shelf life because it is highly susceptibility to bruises, mechanical injury and postharvest diseases during postharvest handling. These deterioration problems contribute to substantial losses during handling, storage, transportation, marketing, and at households (Manenoi et al., 2007). ‘Maradol’ papaya produced in Mexico is usually recognized as a Mexican papaya in USA, where most of the production is exported in spite of postharvest limitations as high sensitivity to mechanical damage and diseases. Postharvest handling, storage, transportation and marketing conditions affect quality and, hence, consumer satisfaction. No estimates of wholesale and retail losses of Mexican papaya are reported, however, previous assessment of postharvest losses in Hawaiian papaya due to diseases, physiological disorders, mechanical damage and overripe fruit, have been estimated up to 75% (Paull et al., 1997). Mexican ‘Maradol’ papayas also have been observed to have high losses, but there is not an accurate accountability of wholesale and retail losses.
Papayas are climacteric fruits, thus, ethylene triggers ripening processes that include softening, flavor development, texture and color changes. Conversely, inhibition of ethylene production or action delays ripening changes (Sañudo-Barajas et al., 2009).
The ethylene inhibitor 1-MCP is a widely explored alternative as a strategy to delay papaya ethylene production, climacteric respiration, skin color development and softening without affecting total soluble solids and fruit weight loss (Manenoi et al., 2007; Shiga et al., 2009; Sañudo-Barajas et al., 2009). In Mexico, ‘Maradol’ papayas are harvested at the breaker maturity stage (yellow-reddish color around one-quarter of the fruit surface), while the fruit are still firm, to minimize mechanical during postharvest handling. Previous studies using 50 to 300 nL L-1 1-MCP applied as a gas formulation (SmartFresh™) promoted incomplete softening and undesirable rubbery texture. Furthermore, the lack of ripening was not reversed by later ethylene application (Manenoi et al., 2007; Manenoi and Paull, 2007; Sañudo-Barajas et al., 2009). As SmartFresh™ application required an extra step (12 to 24 hours) in the papaya handling, the short aqueous application (30 to 60 s) of 1MCP application as a spray or immersion could be utilized for current papaya operations when papayas are immersed in water during standard packaging operations (Manganaris et al., 2008).
This short dipping application approach has been tested using aminoethoxyvinylglycine (AVG) (Garner and Crisosto, 2001) and 1-MCP (Blankenship and Dole, 2003) in other commodities. 1-MCP aqueous dipping treatments yielded the same results as the gas formulation in delaying fruit ripening and extending the shelf life of apples (Argenta et al., 2007), tomatoes and avocados (Tay-Choi et al., 2008), and plums (Manganaris et al., 2008). These studies also pointed out that the efficacy of aqueous 1-MCP depends on commodity, maturity stage, active ingredient concentration, and exposure time. To our knowledge, the use of an aqueous 1-MCP formulation to control ripening in papaya has not been studied. The objective of this study was to develop a practical and reliable 1-MCP dipping treatment to reduce the softening rate and extend the shelf life of ‘Maradol’ papaya.
Conclusion
The use of an aqueous 300 ng∙kg-1 1-MCP dose applied for 30 or 60 s delayed the postharvest ripening of ‘Maradol’ papaya by inhibiting fruit softening. Additionally, these same treated fruit showed the highest lightness values in their pulp (internal color), a condition related to less ripen fruit. The dose of 50 ng∙kg-1 1-MCP applied for 60 s also delayed fruit softening, but only during the first 3 d of storage. As a first trial, the application of aqueous 1-MCP at a dose of 50 ng∙kg-1 showed promising results as a good alternative technology to extend the postharvest shelf life of ‘Maradol’ papayas by up to 3 days, according to flesh firmness value above 20 N, which is considered the threshold to fruit manipulation during marketing conditions. Dose of 300 ng∙kg-1 1-MCP inhibited pulp softening. However, future studies should be done to establish a doseresponse curve for 1-MCP, which would require the evaluation of at least five to ten concentrations and a similar number of exposure times.
