Effect of Dips in a 1-Methylcyclopropene-Generating Solution on ‘Harrow Sun’ Plums Stored under Different Temperature Regimes GEORGE A. MANGANARIS, ²,§ ARIEL R. VICENTE, § CARLOS H. CRISOSTO, ² AND JOHN M. LABAVITCH* ,§ Kearney Agricultural Center, University of CaliforniasDavis, 9240 South Riverbend Avenue, Parlier, California 93648, and Department of Plant Sciences, Mail Stop 5, University of CaliforniasDavis, Davis, California 95616 The effect of postharvest dips in a 1-methylcyclopropene-generating solution of the formulation AFxRD- 038 (Rohm & Haas) on plum fruit (Prunus salicina Lindell cv. ‘Harrow Sun’) quality and ripening during storage was determined. Fruit weight loss, tissue firmness, soluble solids content (SSC), titratable acidity (TA), ethylene production, respiration, and the activities of the cell wall modifying enzymes polygalacturonase (PG), 1,4--D-glucanase/glucosidase (EGase), -galactosidase (-gal), and pectin methylesterase (PME) were measured. Fruit reddening, anthocyanin content, and phenylalanine ammonia-lyase (PAL) activity were also analyzed. The 1-MCP-treated fruit showed reduced ethylene production and respiration rate and delayed softening, which was associated with the reduction in the activity of PG, EGase, and -gal. The immersion in 1-MCP-generating solutions also decreased weight and acidity loss without modifying the fruit SSC. The immersion treatment was particularly effective in the fruit stored at 5 °C, keeping higher overall quality, maintaining lower levels of anthocyanins and PAL activity, and preventing flesh reddening. The present data show that beneficial effects in delaying plum fruit ripening and controlling chilling injury can be obtained by dipping the fruits in a solution of this novel 1-MCP-generating formulation. KEYWORDS: 1-MCP; chilling injury; flesh reddening; market life; plum ripening; postharvest storage INTRODUCTION The plum fruit is highly perishable, and postharvest softening and incidence of chilling injury (CI) symptoms are important factors limiting its shelf life, shipping, and storage (1, 2). Plum cultivars with high rates of ethylene production softened and ripened more rapidly than cultivars that are low ethylene producers (3, 4); therefore, strategies to reduce ethylene sensitivity and/or production would be extremely useful to decrease plum softening and deterioration. Besides many other advantages, refrigerated storage is a widely used strategy to reduce ethylene production and sensitiv- ity during postharvest storage of horticultural products (5). However, the use of low-temperature storage has to be carefully managed in plums because of the fruit susceptibility to CI (1). In contrast to other commodities such as peaches, in which the underlying mechanisms of CI have been determined (6, 7), the physiological basis of CI symptoms in plums, including internal browning, gel breakdown, and/or reddening (1, 2, 8), has not been established. Ethylene has been demonstrated to be involved in the development of CI symptoms in several commodities (9- 11), and reduction of low-temperature storage disorders by reducing ethylene sensitivity and production has also been achieved in products such as avocado (11) and pineapple (12). The ethylene action inhibitor 1-methylcyclopropene (1-MCP) has been an excellent tool for studies designed to determine the role of ethylene in biological processes (13). 1-MCP treatments also have been extremely useful for delaying the physical-chemical changes related to the ripening process and reducing decay and weight loss (13, 14). Treatments at doses ranging between 0.25 and 0.75 µLL -1 delayed ripening in several plum cultivars (15-17). In these cases, the applications were achieved by mixing the product with water or a buffer solution to release the 1-MCP gas in enclosed areas. However, the availability of the proper facilities to treat the fruit could be a limitation under certain commercial situations. The identifica- tion of nonvolatile and nontoxic compounds that will counteract ethylene without requiring a closed system for applications would make ethylene action inhibitors a much more versatile tool for postharvest management (18, 19). The objective of the present study was to evaluate the effect of postharvest dips of ‘Harrow Sun’ plums in a solution of the 1-MCP-generating formulation AFxRD-038 (Rohm & Haas) on ripening, quality, and incidence of physiological disorders during storage. * Corresponding author [telephone (530) 752-0920; e-mail jmlabavitch@ ucdavis.edu]. ² Kearney Agricultural Center. § Department of Plant Sciences. J. Agric. Food Chem. 2007, 55, 7015-7020 7015 10.1021/jf071065p CCC: $37.00 © 2007 American Chemical Society Published on Web 07/31/2007