1910 JOURNAL OF FOOD SCIENCE—Vol. 68, Nr. 6, 2003 © 2003 Institute of Food Technologists Further reproduction prohibited without permission Food Chemistry and Toxicology Effect of 1-Methylcyclopropene on the Quality of Fresh-cut Apple Slices C.O. PERERA, L. BALCHIN, E. BALDWIN, R. STANLEY, AND M. TIAN ABSTRACT: The objective of this project was to treat fresh-cut apple slices with the ethylene inhibitor 1- methylcyclopropene (1-MCP) to retard ethylene-induced deterioration and senescence and to prolong the shelf life of such products. Intact Braeburn and Pacific Rose apples were treated at different times with 1-MCP, cut, and stored at 0 ° C. Samples were analyzed initially and then weekly for ethylene, respiration, flesh firmness, tissue color, titratable acidity, and soluble solids content during 5 wk of storage. 1-MCP treatment was effective in reduc- ing ethylene production, respiration, and loss of firmness and color of slices when applied to whole apples directly after harvest. Total sugar and acidity levels were not affected significantly. Keywords: braeburn apple, Pacific Rose apple, ethylene, respiration, firmness, solids, malic acid Introduction I N RECENT YEARS, THERE HAS BEEN A CONSIDERABLE INCREASE IN DE- mand for high quality fruit and vegetables, coupled with conve- nience and safety. Consumers are indicating a strong preference for fresh fruits and vegetables over their processed counterparts (Bolin and Huxsoll 1989). Furthermore, changes in consumer lifestyles have led to an increased desire for ready-to-eat or ready-to-use products, and therefore, interest in “minimally” or “lightly” pro- cessed products. Despite popularity, the production of minimally processed (MP) fruit is limited because of rapid deterioration and senescence. The plant tissues incur damage during processing, leading within minutes to increased rates of respiration and ethyl- ene production (Brecht 1995), and essentially a “wound response” is initiated. Injury stresses caused by minimal processing result in mechanical plant cell rupture and cellular decompartmentation, leading to delocalization and intermixing of enzymes and sub- strates. Because of removal of the protective peel, microbial prolif- eration and desiccation are accelerated. Quality is reduced because of associated degradative processes, and even under ideal storage conditions, the shelf life of these products is limited. Although the shelf life of fresh-cut vegetables and salads is longer, marketing of fresh-cut fruit has been limited to 4 to 7 d (Ahvenainen 1996). The industry, however, would much prefer a 21-d marketing window. One major challenge is to develop techniques that will effec- tively extend the shelf life of these products while ensuring product quality and safety. The gaseous plant hormone ethylene induces syn- thesis of enzymes that lead to fruit ripening, senescence, and degra- dation. Therefore, one strategy to retard deterioration and senescence of MP fruit would be to remove this hormone and/or block its effects. Browning reactions are the main factors that limit acceptance and storage of any type of cut apple (Malus domestica Borkh) product. Apples contain a complex mixture of phenolic com- pounds, catalyzed by phenylalanine ammonia-lyase (PAL), and enzymatic browning involves the oxidation of these phenolics. MP causes these oxidation rates to increase up to 25-fold over the normal physiological rate (Bolin and Huxsoll 1989). Agents used to control enzymatic browning include sulfur dioxide, ascorbic acid, and derivatives, L-cysteine, ethanol, and 4-hexylresorcinol with varying results. Wounding is generally followed by a lag pe- riod preceding a rise in the activities of PAL and PPO. It is known that ethylene plays an important role in this metabolic activation response. The development of flavor and fruit eating quality is determined in large part by the relative amounts of sugars, acids, and astrin- gents. In general, the rate of deterioration (perishability) of harvest- ed commodities is proportional to their rate of respiration. There- fore, regulation of respiration rates has become a common target for the biochemical manipulation of shelf life. Both sugars and acids in apple serve as respiratory substrates (Knee 1993). Malic acid is the major organic acid in apples and can be reduced by 50% dur- ing the life of the fruit (Knee 1993; Tucker 1993). Ethylene production increased in segments excised from apple flesh, reaching a maximum value 24 h after cutting (Rollin 1999). This “wound ethylene” then accelerates deterioration and senes- cence as shown by Brecht (1995) when ethylene produced by the physical action of MP was sufficient to accelerate softening of ba- nana and kiwifruit. Essentially, wounding induces ethylene produc- tion, which in turn, induces ripening. The 1.2- to 7-fold increase in “wound” respiration commonly seen in MP tissue is also thought to be a direct consequence of elevated ethylene levels resulting from the induced production of volatile long-chain aldehydes due to lipid peroxidation (Watada and others 1990). A number of technologies have been used to reduce ethylene synthesis or action, including antisense gene technology (Hamil- ton and others 1990) and application of compounds such as silver in the form of thiosulfate (STS) and diazocyclopentadiene (DACP) (Blankenship and Sisler 1993; Sisler and Serek 1997). However, few of these compounds have been fully successful or their use has been limited to nonfood products. Recently, a new organic molecule, 1- methylcyclopropene (1-MCP), has been discovered that can block the ethylene receptor for extended periods (Blankenship and Dole 2003). This molecule is a cyclic olefin analogous to the photodecom- position product of DACP (Tian and others 1997), is a gas at room temperature, and is relatively stable (compared with the explosive DACP) (Sisler and Serek 1997). Autocatalytic ethylene production requires upregulation, by eth- ylene, of 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase activity (Lelievre and others 1997a, 1997b). They dem- onstrated that treatment with 1-MCP resulted in reduced accumu- lation of ACC synthase/oxidase transcripts and ethylene produc- tion in pears, during chilling. The majority of the climacteric rise in ethylene production was prevented in carnation flowers follow- ing treatment with low concentration (0.5 nL/L) 1-MCP (Sisler and others 1996a). In addition, 1-MCP vapors have also been shown to JFS: Food Chemistry and Toxicology