SHELF LIFE OF PEACHES TREATED WITH 1-METHYLCYCLOPROPENE

Peaches [Prunus persica (L.) Bastch] present reduced post-harvest shelf life, partially, due to their high respiratory rate and fast ripening. These processes are related to ethylene production, as well as its action. Peaches, cv. Aurora-1, were picked at two different ripening stages (mature green and ripe) and treated with 1-methylcyclopropene (1-MCP), the ethylene’s competitive antagonist, at concentrations of 0, 100, 300 and 900 nL L for 12 hours at 25C. After treatment, the fruits were stored at room temperature (25C) for six days. Fruits treated with 1-MCP presented better firmness and less ground color loss than nontreated fruits. The 1-MCP antagonist reduced the development of fruit rot at the mature green stage, but not at the ripe one. The 1-MCP shows commercial application potential in the treatment of peaches in order to delay the ripening process and increase their shelf life.


INTRODUCTION
Peaches have short shelf life under room temperature, partially due to their high respiratory rate and fast ripening process.Loss of pulp firmness and rot development are the main factors that lower the quality of post-harvest fruits.Therefore, these fruits are generally commercialized shortly after being harvested (Kluge et al., 1997).
Peaches are climacteric fruits and the ethylene action regulates their ripening process.At a certain stage of the ripening process, the ethylene links itself to its action site in the cell, promoting a succession of events that result in ripeness and senescence (Burg & Burg, 1967;Lelièvre et al, 1997a).
The 1-methylcyclopropene (1-MCP) has shown to be a powerful blocking agent of the ethylene action and a ripening inhibitor.Acting as an opponent, it links itself to the ethylene's linking site.It has been verified that the 1-MCP increases conservation and shelf life of several climacteric fruits (Lelièvre et al., 1997b;Nakatsuka et al., 1997;Sisler & Serek, 1997;Golding et al., 1998;Fan et al., 1999;Jiang et al., 1999;Abdi et al., 1998;Feng et al., 2000;Fan et al., 2000).This compound has been manufactured in powder form, releasing the 1-MCP when diluted in water or base.
The present work aimed at verifying the effect of 1-MCP on the self life of peaches stored at room temperature.

MATERIAL AND METHODS
This experiment was carried out in Piracicaba, SP, Brazil.Peaches 'Aurora 1' were picked in the Paranapanema region, SP.The harvest was carried out on the 23 rd October, 2000 and the fruits were treated the same day.Faultless peaches presenting 90g average mass (± 10 g) were selected.Two ripening stages were Scientia Agricola, v.59, n.1, p.69-72, jan./mar.2002 employed in this study, based on the ground color of the fruit skin: a) mature green: fruits showing intense green ground coloration and b) ripe: fruits showing green ground color alteration.
Fruits were treated with Ethylbloc TM , powder form, containing 0.14% active ingredient.The following concentrations were employed: 0, 100, 300 and 900 nL L -1 .The application of the product was performed by placing the fruits into small hermetic chambers (1.86 m 3 capacity) and exposing them to the gas for 12 hours at 25 o C. In order to produce the necessary 1-MCP concentrations inside the chambers, Ethylbloc TM was put inside sealed flasks (0.16 g Ethylbloc TM represents 100 nL of 1-MCP in 1 m 3 ).Twenty milliliters of water at 50°C were added to the flasks, that were then stirred until complete dissolution.Next, the flasks were opened inside the chambers, which were immediately closed so as to avoid gas loss.After a 12-hour treatment, chambers were opened and the fruits were stored at room temperature (25°C).
A completely randomized factorial design was used for each ripening stage, with four replicates of 10 fruits per plot.Fruits were evaluated every two days, for 6 days at room temperature.
Firmness was measured at opposite sides of each fruit, which had a small portion of its skin removed.To perform this task, a 6 mm-diameter needle penetrometer was used and the results were given in Newtons (N).The ground color was determined by means of a colorimeter, Minolta CR-300, and the results expressed in hue angle (h°) and chroma (C*).Rot percentage was calculated, considering the number of fruits affected within each replicate.
Data were submitted to analysis of variance and regression for the 1-MCP concentrations using the statistical software SANEST (Zonta & Machado, 1986).

RESULTS AND DISCUSSION
After 4 and 6 days at 25°C, the mature green fruits treated with 1-MCP presented better firmness than the control fruits (Table 1).Firmness was 40 to 60% greater than the one observed in non-treated fruits.At this ripening stage, a 100 nL L -1 concentration showed to be enough to keep fruit firmness, considering the observed results and the quadratic behavior.Ripe fruits treated with 1-MCP showed a similar behavior in relation to the mature green fruits, however, due to the linear regression significance, it may be inferred that concentrations above 900 nL L -1 promote the maintenance of greater firmness.Lelièvre et al. (1997a) consider that fruit softening is one of the processes most affected by ethylene.Firmness is determined by the cohesion force among pectins.As the ripening process progresses, the action of pectic enzymes takes place, turning insoluble pectin into soluble, thus promoting the softening of fruit tissues.
The greater figures of firmness verified for fruits treated with 1-MCP are probably due to a reduction in the action of ethylene.Similar results were obtained with apples (Fan et al., 1999), bananas (Jiang et al., 1999) and apricots (Fan et al., 2000).
Significant interference of 1-MCP in the ground color of fruits after 2 and 4 days at 25 o C (Tables 2 and  3) was verified.There was a quadratic behavior within the periods evaluated, indicating that greater product concentrations do not seem to promote better results in relation to the maintenance of the color.Fruits treated with 1-MCP showed higher hue angle (greener) when compared to control fruits and lower chroma (more intense green).The loss of green color is due to the rupture of chlorophyll molecules, the chlorophyllase enzyme being involved in this process.The increase in the activity of such enzyme seems to be associated to the ethylene action during the ripening process (Tucker, 1993).Once the ethylene action is blocked by 1-MCP, a decrease in the chlorophyllase activity may be possible.
The use of 1-MCP can effectively lengthen the shelf life of peaches stored at room temperature, once it reduces loss of firmness, as well as color alterations, both processes related to fruit ripening.A longer shelf life is important when considering the high perishability of non-refrigerated fruits.Besides, longer shelf life may enable the transportation of such fruits through longer distances.Therefore, it has been confirmed that 1-MCP presents potential use for ripening control and increase of shelf life of peaches.However, the best product concentration is still under study, as it has been verified, through chromatography, that the 1-MCP concentration inside the experimental chamber is not constant.Consequently, it is necessary to check the levels of this ethylene inhibitor in the environment where the application is to be performed, in order to identify the best concentrations for each kind of fruit and cultivar.L, Q, NS, * = Linear behavior, quadratic behavior, non-significant and significant at P ≤ 0.05, respectively.

Table 1 -
Effect of 1-MCP on firmness for peaches picked at two different ripening stages and stored at 25°C.

Table 4 -
Effect of 1-MCP on rot percentage for peaches picked at two different ripening stages and stored at 25°C.

Table 2 -
Effect of 1-MCP on hue angle for peaches picked at two different ripening stages and stored at 25°C.

Table 3 -
Effect of 1-MCP on chroma for peaches picked at two different ripening stages and stored at 25°C.