Extension of fresh-cut “Blanquilla” pear (Pyrus communis L.) shelf-life by 1-MCP treatment after harvest

Abstract

‘Blanquilla’ pears processed as fresh-cut products are highly sensitive to browning and softening. Common postharvest methods, such as the use of antibrowning compounds and/or modified atmosphere packaging, fail to preserve ‘Blanquilla’ pear slices long enough to be marketable. However, treatment with 1-MCP before cutting and peeling considerably improved their textural properties (9.2 N vs. 1.1 N with and without 1-MCP treatment, respectively) and color (a* values of 1 vs. 5 after 15 d at 4 °C, for slices pear treated with 1-MCP and without treatment, respectively). These positive changes were closely related to a decrease in respiratory activity determined on whole pears after 3 months of storage in air at 0 ± 1 °C and 95% R.H. (0.40 ± 0.05 mmol CO₂ kg⁻¹ h⁻¹ vs. 0.77 ± 0.04 mmol CO₂ kg⁻¹ h⁻¹ with and without 1-MCP treatment, respectively) and ethylene production (1.18 ± 0.36 nmol C₂H₄ kg⁻¹ h⁻¹ vs. 5.751 ± 1.12 nmol C₂H₄ kg⁻¹ h⁻¹ for samples treated with and without 1-MCP, respectively). The use of 1-MCP allows fresh-cut ‘Blanquilla’ pears to be sold up to about 5 d after processing. Treatment with 1-MCP could be a viable alternative to common technologies for extending the shelf-life of ‘Blanquilla’ pears as a fresh-cut product.

Introduction

Fresh-cut fruit and vegetable products for both retail and food service use have increasingly appeared in the market place. These products are fresh fruit or vegetables that have been processed to increase their convenience without greatly changing their fresh-like properties (Ragaert et al., 2004).

Pear is a popular and commercially important fruit served as a fresh-cut item. Like other fruit, fresh-cut pear deteriorates faster than the whole fruit due to the wounding that occurs during processing (Izumi et al., 1996, Watada et al., 1996, Cantwell and Trevor, 2002). Physical damage before, during, and after cutting is a major contributor to tissue browning, juice leakage, and faster deterioration of fresh-cut pear (Kader, 2002). Postharvest quality loss is primarily a function of respiration, onset or progression of ripening (climacteric fruit), water loss (transpiration), enzymatic discoloration of cut surfaces, microbial decay, senescence and mechanical damage suffered during preparation, handling and processing (Watada et al., 1996). Of these, the increase in respiratory rate and the browning reactions catalyzed by polyphenoloxidase (PPO) are the most important (reviewed in Toivonen and Brummell, 2008).

Browning is a particular problem in fruit with white flesh such as pear. Visual acceptance and shelf-life depend on the use of treatments to retard browning beyond that achieved by the use of low temperatures and modified atmospheres (Dong et al., 2000, Gorny et al., 2002a). Chemical dips (such as ascorbic and citric acid, calcium chloride and other compounds) have been shown to be effective in retarding browning and softening of several types of fruit such as apple (Son et al., 2001, Cocci et al., 2006), pineapple (González-Aguilar et al., 2004), and pear (Dong et al., 2000, Arias et al., 2008). On the other hand, packaging fresh-cut fruit products in polymeric films that help in creating a suitable passive modified atmosphere can also be an effective supplement to proper temperature management in maintaining their quality (Martínez-Ferrer et al., 2002, Fonseca et al., 2005). We have recently shown that the use of modified atmospheres combined with an antibrowning treatment (ascorbic acid + 4-hexylresorcinol + CaCl₂) could be successfully applied to ‘Conference’, ‘Williams’ and ‘Abate Fetel’ pears (Arias et al., 2008).

The same approach as in Arias et al. (2008), consisting of modified atmosphere combined with antibrowning treatment, was used with ‘Blanquilla’ pears, one of the most important pear cultivars in Spain (MAPA, 2002). We analyzed the feasibility of using modified atmospheres in order to control respiratory activity as well as applying treatments to prevent superficial darkening and the softening of ‘Blanquilla’ pears. Our previous results (Arias et al., 2008) show that ‘Blanquilla’ pears darken and soften too rapidly to be marketed even if MAP and antibrowning compounds are used, probably due to their particular phenolic composition, polyphenoloxidase activity, high respiratory activity and sensitivity to mechanical bruising and especially high sensitivity to ethylene action (Vilaplana et al., 2007). Therefore alternative treatments have to be sought. To prevent ethylene action seems to be a promising option due to its central role in the ripening process.

In general terms, ethylene has an undesirable effect on the quality of fresh-cut fruit. In some cases, ethylene scrubbing can be a useful supplemental procedure to extend the shelf-life of fresh-cut fruit which are very sensitive to processing operations, such as with banana (Pelayo et al., 2003), watermelon (Zhou et al., 2006), kiwifruit (Antunes et al., 2008), mango and persimmon (Vilas-Boas and Kader, 2006a). 1-Methylcyclopropene (1-MCP) prevents ethylene effects in a broad range of fruit, vegetables and floriculture crops (Blankenship and Dole, 2003). This compound acts at very low concentrations, and its effect consists of delaying ripening and enhancing storage life in some intact and fresh-cut fruit (Blankenship and Dole, 2003, Aguayo et al., 2006, Mao and Fei, 2007).

Accordingly we have also investigated the use of 1-MCP in order to introduce ‘Blanquilla’ into the fresh-cut market. Response of fresh-cut products to 1-MCP treatment depends on the type of crop, maturity or ripening stage and 1-MCP dose, exposure time, temperature and duration. A variety of factors may need to be considered when using 1-MCP including cultivar, developmental stage, and time from harvest to treatment. However, 1-MCP application is rapidly gaining acceptance as a fruit processing option (Jiang et al., 2001, Perera et al., 2003, Calderón-López et al., 2005, Khan and Singh, 2007, Koukounaras and Sfakiotakis, 2007, Nanthachai et al., 2007). The operations used for fresh-cut fruit processing promote many of the ethylene-induced metabolic pathways; therefore, the use of 1-MCP seems a straightforward option for increasing the shelf-life of fresh-cut fruit.

1-MCP can be applied at two stages: either immediately after harvest or just before fresh-cut processing. It is also possible to apply 1-MCP at both steps (Saltveit, 2004, Calderón-López et al., 2005, Vilas-Boas and Kader, 2006a; Mao et al., 2007; Saftner et al., 2007). However, treatment of intact fruit with 1-MCP before fresh-cut processing is much easier and more convenient than after processing. Moreover, the increase in ethylene production promoted by peeling and slicing can be prevented by the previous use of 1-MCP.

The aim of the present work was to investigate if 1-MCP application to intact fruit can improve ‘Blanquilla’ pear suitability for minimal processing. To do this we analyzed several quality characteristics (changes in firmness, color, ethylene production, respiration rate, total phenolic content) of modified atmosphere packaged fresh-cut pear fruit to evaluate shelf-life in 1-MCP-treated and non-treated pears.