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Extension of fresh-cut “Blanquilla” pear (Pyrus communis L.) shelf-life by 1-MCP treatment after harvest
Postharvest Biology and Technology 54 (2009) 53–58
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Extension of fresh-cut “Blanquilla” pear (Pyrus communis L.) shelf-life by 1-MCP treatment after harvest Esther Arias, Pascual López-Buesa, Rosa Oria ∗ Tecnología de Alimentos, Facultad de Veterinaria, Universidad de Zaragoza, C/ Miguel Servet, 177, 50013 Zaragoza, Spain
a r t i c l e
i n f o
Article history: Received 24 November 2008 Accepted 25 April 2009 Keywords: Fresh-cut pear Dipping 1-Methylcyclopropene (1-MCP) Browning Softening Modified atmosphere packaging
a b s t r a c t ‘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 C2 H4 kg−1 h−1 vs. 5.751 ± 1.12 nmol C2 H4 kg−1 h−1 for samples treated with and without 1-MCP, respectively). The use of 1-MCP allows freshcut ‘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. © 2009 Published by Elsevier B.V.
1. 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 freshlike 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
∗ Corresponding author. Tel.: +34 976 761584. E-mail address: [email protected] (R. Oria). 0925-5214/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.postharvbio.2009.04.009
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
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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. 2. Material and methods 2.1. Plant materials Pears (Pyrus malus L. cvs. ‘Blanquilla’ and ‘Conference’) were hand-harvested at an experimental orchard in La Almunia (Zaragoza, Spain). The fruit were harvested when they had reached commercial maturity and were carefully selected for uniform size (about 200 g) and color as well as the absence of damage and defects. Fruit were immediately transported to the laboratory and stored at 4 ◦ C for 1 d before processing. 2.2. 1-MCP application and whole fruit storage Fruit (100 kg) were placed in a chamber at 0 ◦ C. A concentration of 300 nL L−1 1-MCP (SmartFreshTM ) was established in the container (effective capacity, 250–300 kg) following instructions for use of the SmartFreshTM tablets provided by AgroFresh Inc.
(Barcelona, Spain). The treatment lasted 24 h. Non-treated and 1MCP-treated pears were stored for 3 months in air at 0 ± 1 ◦ C and 95% R.H. The pears were minimally processed after these 3 months. 2.3. Processing of pears and storage of fresh-cut slices All processing operations were performed at 4 ◦ C. The pears were initially washed with chlorinated water (100 L L−1 of active chlorine for 5 min) to prevent surface contamination. A semiautomatic Pelamatic peeler (model Orange Peel) was used for peeling and removal of the core and slicing were performed manually. Special knives designed for fruit (Granston, mod. Messermeister, England) were used for slicing (10–12 slices/pear). After peeling and slicing, pear samples were immersed in antibrowning aqueous solutions (2% ascorbic acid + 0.01% 4-hexylresorcinol + 1% CaCl2 ) for 15 min at 4 ◦ C (all preservative agents were of food grade). Control slices were dipped in water. Subsequently, all samples were dried for 10 min at 4 ◦ C. For both batches, the ratio of pear:solution was 1:8. The samples were packaged in high permeability microperforated film (PPLUS 30), with 200 g of pear slices placed in 96 cm2 trays (TS500, Linpac, Spain). A semi-automatic packager was used to thermoseal the trays (ORA mod. B160C, Spain). The processing of all fruit was carried out in a cold chamber at 10 ◦ C, previously sanitized with chlorinated water and 70% ethanol. All facilities used to process the fruit were frequently washed and sanitized to ensure reasonably clean conditions. The temperature of the chlorine solution and chemical dips used on fresh-cut pear was 5 ◦ C. The samples were stored in the dark at 4 ± 1 ◦ C for 15 d and examined at three different stages during storage, on the 5th, 10th and 15th days. 2.4. Ethylene production and respiration rate of whole pears A gas chromatograph (Hewlett Packard 4890) with FID detector and stainless steel column (Hewlett Packard 19001 A-QSO) was used to determine the ethylene concentration. Injector and detector temperatures were set at 50 and 200 ◦ C respectively and the carrier gas was nitrogen. The measurement of respiratory activity was determined as described by Ferrer et al. (2005). A sample of two or three intact pears was sealed in a glass jar and the jars were kept at 4 ◦ C. The headspace gas composition was regularly analyzed for O2 , CO2 and N2 by gas chromatography (Hewlett Packard 4890). The initial atmosphere composition was that of air. Concentrations of O2 and CO2 were determined using a thermal conductivity detector. A Chrompack CP-Carboplot P7 column (inside diameter 0.53 mm, length 27.5 m) was used with helium as a carrier gas at a flow rate of 12.6 mL/min. The initial temperature of the oven was set at 40 ◦ C and after 2.5 min this was increased at a rate of 45 ◦ C/min to a final temperature of 115 ◦ C. The temperature of the injector block was 59 ◦ C and the detector temperature was 120 ◦ C. The respiration rate was measured in triplicate for each batch. All measurements were performed at atmospheric pressure and temperature. 2.5. Atmospheric composition Changes in CO2 and O2 concentrations in the headspace of the packaged fresh-cut pears were measured by injection of 50 L samples into a gas chromatograph (Hewlett Packard 4890) equipped with a thermal conductivity detector (TCD) with the same characteristics as described above. Three trays were used to determine atmospheric composition on each monitored day.
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2.6. Ethanol and acetaldehyde analysis Ethanol and acetaldehyde determinations were made following the method used by Gorny et al. (2002b). Five mL of juice was extracted from 100 g of pear tissue and transferred to 10 mL amber-colored tubes. Each tube was hermetically closed with a screw top containing a silicon septum, and was then held in a water bath for 60 min at 60 ◦ C. One mL samples of the headspace were taken through the septa with a Hamilton gas-tight syringe, and were injected into a gas chromatograph (Hewlett Packard 4890) equipped with a flame ionization detector (FID). Three 100 g pear replicates were used in each analysis. 2.7. Fruit firmness determination Fruit firmness was measured with a TA-TX plus texture analyzer (Stable Micro Systems, Godalming, England) compression test, by measuring the force required to ‘bite’ through the product using a Volodkevich probe (HDP/VB) (distance: 19 mm and velocity: 2 mm s−1 ), which simulates a biting action. The sample was a cylinder of pear obtained with a 10-mm diameter punch. Ten replicates were evaluated from each batch. 2.8. Color measurement Colorimetric measurements were carried out with an Instrument System Spectroradiometer IS CAS 140 (Instrument System, Munich, Germany) using a TOP 100 probe. The spectroradiometer was equipped with a Nikon f: 200 mm lens and the instrument was controlled by ISCOLOR software implemented on a PC. Reflectance spectra were measured between 380 and 900 nm every 1 nm. From these spectra CIELAB coordinates L*, a*, b*, C* and h* were calculated with the standard observer CIE64 and the D65 illuminant. Coordinate a* is related with the red-green visual opposition and b* is related with the yellow-blue opposition. Coordinates L* (lightness), C* (chroma) and hab (hue) are related to physiological attributes of visual response. Calibration was performed using a white standard calibration by Labsphere, provided by IS CAS 140 (Instrument System, Munich, Germany). Ten replicates were evaluated from each batch. 2.9. Total phenolic content Total phenolic compounds were measured using the Folin–Ciocalteu reagent. Total phenolics were expressed as mg 100 g−1 of fresh fruit weight. This measurement was done in three replicates from each batch.
Fig. 1. Changes of a* (A) and firmness values (B) of fresh-cut () ‘Blanquilla’ and () ‘Conference’ pears during storage at 4 ◦ C in the dark. (C) Effect of antibrowning treatment (2% ascorbic acid + 0.01% 4-hexylresorcinol + 1% CaCl2 ) on a* values of ‘Conference’ and ‘Blanquilla’ pear slices during storage at 4 ◦ C. Control: () ‘Blanquilla’, () ‘Conference’. Treatment: (䊉) ‘Blanquilla’, () ‘Conference’. Bars represent means ± S.D. of 20 replicates.
2.11. Statistical analysis Analyses were done using the number of replicates specified in each one of the previous sections. Means, standard deviations and graphs were obtained using Microsoft Excel 2000.
2.10. Sensory analysis
3. Results
A trained panel of 10 people evaluated the sensory quality of the samples, initially and subsequently every 5 d throughout the storage period. Each panellist was given several pieces from each batch (two packages of 200 g of fresh-cut pear) and requested to evaluate appearance, flavour (characteristic flavour and off-flavours), taste (characteristic and abnormal taste), firmness and degree of browning. These attributes were scored on a 5-point scale: 1—minimum intensity, 5—maximum intensity. The mid-morning panel sessions were held in a sensory panel room at an ambient temperature of 22 ◦ C (previously, the samples were removed to room temperature). The portions of each piece of pear were shown to the panellists who evaluated visual parameters and odor intensity. The sample order was randomized within sessions and unsalted bread and water were served at room temperature between successive samples.
‘Blanquilla’ pears were processed as fresh-cut products and their color and texture were analyzed over several days. The results for ‘Conference’ pears are presented for comparative purposes (Fig. 1A). ‘Blanquilla’ pears soften (Fig. 1B) and darken (Fig. 1A) considerably during the studied 15-d period, much more than ‘Conference’ pears. The attempt to retard browning reactions using ascorbic acid in combination with 4-hexylresorcinol failed with ‘Blanquilla’ pears. However, the opposite occurred with ‘Conference’ (Fig. 1C). Therefore, we decided to include 1-MCP as a new treatment in our processing protocol. We decided to apply 1-MCP after harvest because of its success in some other fruit. We analyzed first the effect of 1-MCP on respiratory activity and ethylene production of fresh-cut pear slices. These two parameters were determined at two different stages: at
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Table 1 Effect of 1-MCP treatment on ethylene production and respiratory activity of intact ‘Blanquilla’ pears, before and after storage at 0–1 ◦ C during 3 months. Data are the mean ± S.D. of determinations made in three samples. C2 H4 production (nmol C2 H4 kg−1 h−1 )
Respiratory activity (mmol CO2 kg−1 h−1 )
Initial time
0.55 ± 0.04
0.36 ± 0.03
3 months Non-treated Treated 1-MCP
5.75 ± 1.12 1.18 ± 0.36
0.77 ± 0.04 0.40 ± 0.05
the initial time (just after harvest) and after 3 months of storage in air at 0 ◦ C. A clear influence of 1-MCP treatment was observed in both cases: non-treated pears had values five and two times greater for ethylene production and respiratory activity, respectively, than those of pears treated with 1-MCP (Table 1). The difference in the respiration rate of the non-treated pears and the 1-MCP-treated pears resulted in the generation of different atmospheres inside the packages of fresh-cut pears (Fig. 2), where the O2 concentration decreased and the CO2 concentration increased. The modified atmosphere for packaged 1-MCP-treated pear slices was 9% O2 + 13% CO2 , reaching atmospheric equilibrium in 3 d (Fig. 2). The untreated batch, having a much greater respiration rate, produced an atmosphere too high in CO2 (approximately 4–5% O2 + 18% CO2 ), leading to physiological disorders in the tissue. These resulted in a sharp increase in the production of volatile substances, such as ethanol and acetaldehyde (Fig. 3), causing the appearance of off-flavours readily detected by the panel of tasters (Fig. 4). Furthermore, the 1-MCP-treated fresh-cut pears had firmness values much higher than those of untreated samples (7.8 N vs. 1.9 N, approximately) (Fig. 5). Moreover, firmness values of 1-MCPtreated pears were similar to those of pears analyzed immediately after harvest (data not shown). This demonstrates the effectiveness of 1-MCP treatment for maintaining firmness of ‘Blanquilla’ pear tissue, both whole and minimally processed. This feature is very important because the ‘Blanquilla’ variety is very susceptible to softening, in contrast to other pear varieties such as ‘Conference’ (Fig. 1B). A limiting factor in turning the ‘Blanquilla’ cultivar into a minimally processed product is its high susceptibility to browning, in comparison with other varieties (Fig. 1A). Fig. 6 shows the changes in a* values for slices of pears treated with 1-MCP and those of untreated pears. The control samples showed from the beginning, higher a* values (from negative to positive values, approximately 4–5), which indicated a greater degree of surface browning. Fig. 7 shows the total phenolic content of the ‘Blanquilla’ pear tissues. The data presented are for the initial time (after harvest) and after 3 months of cold storage (for both the treated and untreated
Fig. 2. Changes in headspace gas composition during storage at 4 ◦ C for ‘Blanquilla’ pear slices packed in microperforated film (P PLUS 30). () % CO2 without 1-MCP; () % CO2 with 1-MCP; (♦) % O2 without 1-MCP; () % O2 with 1-MCP. Data are means ± S.D. of determinations made from three samples.
Fig. 3. Concentrations of acetaldehyde (A) and ethanol (B) of ‘Blanquilla’ fresh-cut pears treated with 1-MCP (filled bars) or without 1-MCP treatment (open bars) during storage at 4 ◦ C. Data are means ± S.D. of determinations made from three samples.
batches). Initially, the phenolic concentration was approximately 80 mg 100 g−1 fruit. As was expected, due to the maturing process of the fruit during the 3 months at 0 ◦ C, the control samples (without 1-MCP treatment) showed a significant decrease in phenolic concentration (reaching approximately 30 mg 100 g−1 fruit). This reduction was not observed in the pear slices treated with 1-MCP (Fig. 7). 4. Discussion ‘Blanquilla’ is a variety of pear highly sensitive to browning and softening. The high degree of susceptibility to browning of this variety is mostly due to its high concentration of phenolics. This concentration is four or five times higher than the concentration
Fig. 4. Scores of sensory analysis (presence of undesirable flavours) for ‘Blanquilla’ fresh-cut pears, treated (filled bars) or non-treated (open bars) with 1-MCP during storage at 4 ◦ C.
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Fig. 5. Effect of 1-MCP treatment on firmness values of fresh-cut ‘Blanquilla’ pears stored in modified atmosphere, at 4 ◦ C for 15 d: () without 1-MCP treatment; () with 1-MCP treatment. Data are means ± S.D. of determinations made from 20 samples.
Fig. 6. Effect of 1-MCP treatment on a* values of fresh-cut ‘Blanquilla’ pears stored in modified atmosphere, at 4 ◦ C for 15 d: () without 1-MCP treatment; () with 1-MCP treatment. Data are means ± S.D. of determinations made from 20 samples.
of phenolics in other varieties. For example, the values of the ‘Conference’ and ‘Williams’ varieties are around 20 mg total phenolics 100 g−1 fruit. ‘Blanquilla’, however, can reach levels of 80–100 mg total phenolics 100 g−1 fruit (Arias et al., 2008). This limits its suitability for fresh-cut processing. Therefore, alternative processing options need to be evaluated. 1-MCP is an ethylene action inhibitor acting at very low concentrations, which has been shown to delay ripening and enhance storage life in intact and fresh-cut fruit (Antunes et al., 2008). 1-MCP acts at the receptor level delaying ripening in climacteric fruit and blocking ethylene-dependent pro-
Fig. 7. Effect of 1-MCP treatment on total phenolic concentration of ‘Blanquilla’ pears, after storage in air for 3 months at 0–1 ◦ C. Data are means ± S.D. of determinations made from three samples.
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cesses, especially firmness loss and inhibition of aroma production in the treated fruit (Chririboga et al., 2007). At a physiological level, 1-MCP can inhibit the metabolism of 1-aminocyclopropane 1 carboxylic acid (ACC) and also increase the total antioxidant potential of pear tissue mainly through an increase in peroxidase activity. As a consequence, 1-MCP treatment has significant effects on physiological disorder incidence in pears (reviewed in Chririboga et al., 2007). Our experiment has shown that the effects of 1-MCP on several fruit properties last at least during 3 months of storage. Ethylene synthesis in fresh-cut products is probably stimulated by wounding (Mao et al., 2007; Saltveit, 2004; Tomás-Barberán and Espín, 2001; Vilas-Boas and Kader, 2006a,b), and was reduced in the pear tissue almost fivefold by applying 1-MCP (Table 1). Accordingly, the rate of respiratory activity was reduced to about 50% that of control samples. The reduction of ethylene effects is probably the reason for the improvement of several quality attributes in 1-MCP-treated fruit. Results similar to ours have been reported for kiwifruit treated with 1-MCP before slicing (Mao and Fei, 2007) as well as for pineapple slices (Budu and Joyce, 2003). The application of 1-MCP has also been shown to slow down ethylene production in several varieties of minimally processed apples by using uncut fruit treated with 1MCP and cold storage for 1–4 months (Calderón-López et al., 2005). However, Vilas-Boas and Kader (2006b) did not observe any influence of 1-MCP treatment on the ethylene production of fresh-cut banana, although the respiration rate decreased. The best results were achieved in reducing softening (Fig. 5). 1MCP-treated fruit maintained firmness levels similar to fruit that had just been harvested, whereas untreated fruit softened considerably more and continued softening during 15 d. This suggests a decrease in activity of softening enzymes induced by 1-MCP (Lohani et al., 2004). The application of 1-MCP reduced softening of freshcut apples slices taken from whole fruit treated with 1-MCP and subsequently kept at 0 ◦ C (Perera et al., 2003; Calderón-López et al., 2005). Melo and Vilas-Boas (2006) and Kim et al. (2001) obtained similar results with banana and kiwi slices to which 1-MCP was directly applied. Fruit browning was also significantly reduced by 1-MCP. Values of a* in 1-MCP-treated samples were lower than in control samples, especially after 15 d. This occurred in spite of the higher total concentration of phenolics in 1-MCP-treated pears. It is rather surprising, that having a higher phenolic concentration results in lower browning levels of pear slices. This could be related a higher antioxidant potential of 1-MCP-treated pears as found by Larrigaudiere et al. (2004) and/or to the improved tissue integrity of 1-MCP-treated pears (demonstrated in this study by their better texture scores) which would hinder PPO coming into contact with its phenolic substrates, although a simultaneous lower level of PPO activity cannot be discarded. The change in respiratory pattern modified the atmosphere composition of the trays (Fig. 2). The higher respiratory rates of untreated pears led to higher concentrations of CO2 and a lower O2 levels, that results in synthesis of off-flavour metabolites and initiation of fermentation (Fig. 3); as a consequence, the panel rejected the product (Fig. 4). In conclusion, 1-MCP use just after harvest may allow the introduction of ‘Blanquilla’ pears into the fresh-cut market. It improved especially the texture but also color. However, the high phenolic concentrations in this variety promoted browning after 5 d, which makes fresh-cut pears unmarketable after this time. This period is probably not long enough for selling ‘Blanquilla’ fresh-cut pear in supermarkets, but it is long enough for food services and quickservice restaurants (fast food). Therefore, the treatment of intact pears with 1-MCP could be an alternative to the technologies currently in use for extending the shelf-life of the ‘Blanquilla’ pear variety as a fresh-cut product.
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Kim, H.O., Hewett, E.W., Lallu, N., 2001. Softening and ethylene production of kiwifruit reduced with 1-MCP. Acta Hortic. 553, 167–170. Koukounaras, A., Sfakiotakis, E., 2007. Effect of 1-MCP prestorage treatment on ethylene and CO2 production and quality of Hayward kiwifruit during shelf life after short, medium and long term cold storage. Postharvest Biol. Technol. 46, 174–180. Larrigaudiere, Ch., Vilaplana, R., Soria, Y., Recasens, I., 2004. Oxidative behaviour of Blanquilla pears treated with 1-MCP during cold storage. J. Sci. Food Agric. 84, 1871–1877. Lohani, S., Prabodh, K., Pravendra, H., 2004. Changes in activities of cell wall hydrolases during ethylene-induced ripening in banana: effect of 1-MCP, ABA and IAA. Postharvest Biol. Technol. 21, 119–126. Mao, L., Fei, G., 2007. Application of 1-methylciclopropene prior to cutting reduces wound responses and maintains quality in cut kiwifruit. J. Food Eng. 78, 361–365. M.A.P.A. (Ministerio de Agricultura, Pesca y Alimentación), 2002. Encuesta sobre plantaciones de árboles frutales., http://www.mapa.es. ˜ Martínez-Ferrer, M., Harper, C., Pérez-Munoz, F., Chaparro, M., 2002. Modified atmosphere packaging of minimally processed mango and pineapple fruits. J. Food Sci. 67, 3371–3375. Melo, A., Vilas-Boas, E., 2006. Inhibicao do escurecimiento enzimático de banana maca minimamente processada. Ciênc. Tecnol. Aliment. 26, 110–115. Nanthachai, N., Ratanachikorn, B., Kosittrakun, M., Beaudry, R., 2007. Absorption of 1-MCP by fresh produce. Postharvest Biol. Technol. 43, 291–297. Pelayo, C., Vilas-Boas, E.V., de, B., Benichou, M., Kader, A.A., 2003. Variability in responses of partially ripe bananas to 1-MCP. Postharvest Biol. Technol. 28, 75–85. Perera, C.O., Balchin, L., Baldwin, E., Stanley, R., Tian, M., 2003. Effect of 1-MCP on the quality of fresh-cut apple slices. J. Food Sci. 68, 1910–1914. Ragaert, P., Verbeke, W., Devlieghere, F., Debevere, J., 2004. Consumer perception and choice of minimally processed vegetables and packaged fruits. Food Qual. Pref. 15, 259–270. Saftner, R., Luo, Y., McEvoy, J., Abbott, J., Vinyard, B., 2007. Quality characteristics of fresh-cut watermelon slices from non-treated and 1-methylcyclopropene and/or ethylene-treated whole fruit. Postharvest Biol. Technol. 44, 71–79. Saltveit, M., 2004. Effect of 1-MCP on phenylpropanoid metabolism, the accumulation of phenolic compounds, and browning of whole and fresh-cut Iceberg lettuce. Postharvest Biol. Technol. 34, 75–80. Son, S., Moon, K., Lee, C., 2001. Inhibitory effects of various antibrowning agents on apple slices. Food Chem. 73, 23–30. Toivonen, P., Brummell, D., 2008. Biochemical bases of appearance and texture changes in fresh-cut fruit and vegetables. Postharvest Biol. Technol. 48, 1–14. Tomás-Barberán, F., Espín, J.C., 2001. Phenolic compounds and related enzymes as determinants of quality in fruits and vegetables. J. Sci. Food Agric. 81, 853– 867. Vilas-Boas, E., Kader, A., 2006a. Effect of 1-MCP on softening of fresh-cut kiwifruit, mango and persimmon slices. Postharvest Biol. Technol. 43, 238–244. Vilas-Boas, E., Kader, A., 2006b. Effect of atmospheric modification, 1-MCP and chemicals on quality of fresh-cut banana. Postharvest Biol. Technol. 39, 155–162. Vilaplana, R., Soria, Y., Valentines, M., Reig, G., Larrigaudière, C., 2007. Effect of combining 1-MCP treatment and heat treatment on the storage capability of Blanquilla pear. In: Ramina, A. (Ed.), Advances in Plant Ethylene Research: Proceedings of the 7th International Symposium on the Plant Hormone Ethylene. Springer, pp. 437–439. Watada, A., Ko, N., Minott, D., 1996. Factors affecting quality of fresh-cut horticultural products. Postharvest Biol. Technol. 9, 115–125. Zhou, B., McEvoy, J., Luo, Y., Saftner, R., Feng, H., Beltran, T., 2006. 1Methylcyclopropene counteracts ethylene-induced microbial growth on freshcut watermelon. J. Food Sci. 71, M180–M184.
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Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Extension of fresh-cut “Blanquilla” pear (Pyrus communis L.) shelf-life by 1-MCP treatment after harvest Esther Arias, Pascual López-Buesa, Rosa Oria ∗ Tecnología de Alimentos, Facultad de Veterinaria, Universidad de Zaragoza, C/ Miguel Servet, 177, 50013 Zaragoza, Spain
a r t i c l e
i n f o
Article history: Received 24 November 2008 Accepted 25 April 2009 Keywords: Fresh-cut pear Dipping 1-Methylcyclopropene (1-MCP) Browning Softening Modified atmosphere packaging
a b s t r a c t ‘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 C2 H4 kg−1 h−1 vs. 5.751 ± 1.12 nmol C2 H4 kg−1 h−1 for samples treated with and without 1-MCP, respectively). The use of 1-MCP allows freshcut ‘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. © 2009 Published by Elsevier B.V.
1. 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 freshlike 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
∗ Corresponding author. Tel.: +34 976 761584. E-mail address: [email protected] (R. Oria). 0925-5214/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.postharvbio.2009.04.009
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
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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. 2. Material and methods 2.1. Plant materials Pears (Pyrus malus L. cvs. ‘Blanquilla’ and ‘Conference’) were hand-harvested at an experimental orchard in La Almunia (Zaragoza, Spain). The fruit were harvested when they had reached commercial maturity and were carefully selected for uniform size (about 200 g) and color as well as the absence of damage and defects. Fruit were immediately transported to the laboratory and stored at 4 ◦ C for 1 d before processing. 2.2. 1-MCP application and whole fruit storage Fruit (100 kg) were placed in a chamber at 0 ◦ C. A concentration of 300 nL L−1 1-MCP (SmartFreshTM ) was established in the container (effective capacity, 250–300 kg) following instructions for use of the SmartFreshTM tablets provided by AgroFresh Inc.
(Barcelona, Spain). The treatment lasted 24 h. Non-treated and 1MCP-treated pears were stored for 3 months in air at 0 ± 1 ◦ C and 95% R.H. The pears were minimally processed after these 3 months. 2.3. Processing of pears and storage of fresh-cut slices All processing operations were performed at 4 ◦ C. The pears were initially washed with chlorinated water (100 L L−1 of active chlorine for 5 min) to prevent surface contamination. A semiautomatic Pelamatic peeler (model Orange Peel) was used for peeling and removal of the core and slicing were performed manually. Special knives designed for fruit (Granston, mod. Messermeister, England) were used for slicing (10–12 slices/pear). After peeling and slicing, pear samples were immersed in antibrowning aqueous solutions (2% ascorbic acid + 0.01% 4-hexylresorcinol + 1% CaCl2 ) for 15 min at 4 ◦ C (all preservative agents were of food grade). Control slices were dipped in water. Subsequently, all samples were dried for 10 min at 4 ◦ C. For both batches, the ratio of pear:solution was 1:8. The samples were packaged in high permeability microperforated film (PPLUS 30), with 200 g of pear slices placed in 96 cm2 trays (TS500, Linpac, Spain). A semi-automatic packager was used to thermoseal the trays (ORA mod. B160C, Spain). The processing of all fruit was carried out in a cold chamber at 10 ◦ C, previously sanitized with chlorinated water and 70% ethanol. All facilities used to process the fruit were frequently washed and sanitized to ensure reasonably clean conditions. The temperature of the chlorine solution and chemical dips used on fresh-cut pear was 5 ◦ C. The samples were stored in the dark at 4 ± 1 ◦ C for 15 d and examined at three different stages during storage, on the 5th, 10th and 15th days. 2.4. Ethylene production and respiration rate of whole pears A gas chromatograph (Hewlett Packard 4890) with FID detector and stainless steel column (Hewlett Packard 19001 A-QSO) was used to determine the ethylene concentration. Injector and detector temperatures were set at 50 and 200 ◦ C respectively and the carrier gas was nitrogen. The measurement of respiratory activity was determined as described by Ferrer et al. (2005). A sample of two or three intact pears was sealed in a glass jar and the jars were kept at 4 ◦ C. The headspace gas composition was regularly analyzed for O2 , CO2 and N2 by gas chromatography (Hewlett Packard 4890). The initial atmosphere composition was that of air. Concentrations of O2 and CO2 were determined using a thermal conductivity detector. A Chrompack CP-Carboplot P7 column (inside diameter 0.53 mm, length 27.5 m) was used with helium as a carrier gas at a flow rate of 12.6 mL/min. The initial temperature of the oven was set at 40 ◦ C and after 2.5 min this was increased at a rate of 45 ◦ C/min to a final temperature of 115 ◦ C. The temperature of the injector block was 59 ◦ C and the detector temperature was 120 ◦ C. The respiration rate was measured in triplicate for each batch. All measurements were performed at atmospheric pressure and temperature. 2.5. Atmospheric composition Changes in CO2 and O2 concentrations in the headspace of the packaged fresh-cut pears were measured by injection of 50 L samples into a gas chromatograph (Hewlett Packard 4890) equipped with a thermal conductivity detector (TCD) with the same characteristics as described above. Three trays were used to determine atmospheric composition on each monitored day.
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2.6. Ethanol and acetaldehyde analysis Ethanol and acetaldehyde determinations were made following the method used by Gorny et al. (2002b). Five mL of juice was extracted from 100 g of pear tissue and transferred to 10 mL amber-colored tubes. Each tube was hermetically closed with a screw top containing a silicon septum, and was then held in a water bath for 60 min at 60 ◦ C. One mL samples of the headspace were taken through the septa with a Hamilton gas-tight syringe, and were injected into a gas chromatograph (Hewlett Packard 4890) equipped with a flame ionization detector (FID). Three 100 g pear replicates were used in each analysis. 2.7. Fruit firmness determination Fruit firmness was measured with a TA-TX plus texture analyzer (Stable Micro Systems, Godalming, England) compression test, by measuring the force required to ‘bite’ through the product using a Volodkevich probe (HDP/VB) (distance: 19 mm and velocity: 2 mm s−1 ), which simulates a biting action. The sample was a cylinder of pear obtained with a 10-mm diameter punch. Ten replicates were evaluated from each batch. 2.8. Color measurement Colorimetric measurements were carried out with an Instrument System Spectroradiometer IS CAS 140 (Instrument System, Munich, Germany) using a TOP 100 probe. The spectroradiometer was equipped with a Nikon f: 200 mm lens and the instrument was controlled by ISCOLOR software implemented on a PC. Reflectance spectra were measured between 380 and 900 nm every 1 nm. From these spectra CIELAB coordinates L*, a*, b*, C* and h* were calculated with the standard observer CIE64 and the D65 illuminant. Coordinate a* is related with the red-green visual opposition and b* is related with the yellow-blue opposition. Coordinates L* (lightness), C* (chroma) and hab (hue) are related to physiological attributes of visual response. Calibration was performed using a white standard calibration by Labsphere, provided by IS CAS 140 (Instrument System, Munich, Germany). Ten replicates were evaluated from each batch. 2.9. Total phenolic content Total phenolic compounds were measured using the Folin–Ciocalteu reagent. Total phenolics were expressed as mg 100 g−1 of fresh fruit weight. This measurement was done in three replicates from each batch.
Fig. 1. Changes of a* (A) and firmness values (B) of fresh-cut () ‘Blanquilla’ and () ‘Conference’ pears during storage at 4 ◦ C in the dark. (C) Effect of antibrowning treatment (2% ascorbic acid + 0.01% 4-hexylresorcinol + 1% CaCl2 ) on a* values of ‘Conference’ and ‘Blanquilla’ pear slices during storage at 4 ◦ C. Control: () ‘Blanquilla’, () ‘Conference’. Treatment: (䊉) ‘Blanquilla’, () ‘Conference’. Bars represent means ± S.D. of 20 replicates.
2.11. Statistical analysis Analyses were done using the number of replicates specified in each one of the previous sections. Means, standard deviations and graphs were obtained using Microsoft Excel 2000.
2.10. Sensory analysis
3. Results
A trained panel of 10 people evaluated the sensory quality of the samples, initially and subsequently every 5 d throughout the storage period. Each panellist was given several pieces from each batch (two packages of 200 g of fresh-cut pear) and requested to evaluate appearance, flavour (characteristic flavour and off-flavours), taste (characteristic and abnormal taste), firmness and degree of browning. These attributes were scored on a 5-point scale: 1—minimum intensity, 5—maximum intensity. The mid-morning panel sessions were held in a sensory panel room at an ambient temperature of 22 ◦ C (previously, the samples were removed to room temperature). The portions of each piece of pear were shown to the panellists who evaluated visual parameters and odor intensity. The sample order was randomized within sessions and unsalted bread and water were served at room temperature between successive samples.
‘Blanquilla’ pears were processed as fresh-cut products and their color and texture were analyzed over several days. The results for ‘Conference’ pears are presented for comparative purposes (Fig. 1A). ‘Blanquilla’ pears soften (Fig. 1B) and darken (Fig. 1A) considerably during the studied 15-d period, much more than ‘Conference’ pears. The attempt to retard browning reactions using ascorbic acid in combination with 4-hexylresorcinol failed with ‘Blanquilla’ pears. However, the opposite occurred with ‘Conference’ (Fig. 1C). Therefore, we decided to include 1-MCP as a new treatment in our processing protocol. We decided to apply 1-MCP after harvest because of its success in some other fruit. We analyzed first the effect of 1-MCP on respiratory activity and ethylene production of fresh-cut pear slices. These two parameters were determined at two different stages: at
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Table 1 Effect of 1-MCP treatment on ethylene production and respiratory activity of intact ‘Blanquilla’ pears, before and after storage at 0–1 ◦ C during 3 months. Data are the mean ± S.D. of determinations made in three samples. C2 H4 production (nmol C2 H4 kg−1 h−1 )
Respiratory activity (mmol CO2 kg−1 h−1 )
Initial time
0.55 ± 0.04
0.36 ± 0.03
3 months Non-treated Treated 1-MCP
5.75 ± 1.12 1.18 ± 0.36
0.77 ± 0.04 0.40 ± 0.05
the initial time (just after harvest) and after 3 months of storage in air at 0 ◦ C. A clear influence of 1-MCP treatment was observed in both cases: non-treated pears had values five and two times greater for ethylene production and respiratory activity, respectively, than those of pears treated with 1-MCP (Table 1). The difference in the respiration rate of the non-treated pears and the 1-MCP-treated pears resulted in the generation of different atmospheres inside the packages of fresh-cut pears (Fig. 2), where the O2 concentration decreased and the CO2 concentration increased. The modified atmosphere for packaged 1-MCP-treated pear slices was 9% O2 + 13% CO2 , reaching atmospheric equilibrium in 3 d (Fig. 2). The untreated batch, having a much greater respiration rate, produced an atmosphere too high in CO2 (approximately 4–5% O2 + 18% CO2 ), leading to physiological disorders in the tissue. These resulted in a sharp increase in the production of volatile substances, such as ethanol and acetaldehyde (Fig. 3), causing the appearance of off-flavours readily detected by the panel of tasters (Fig. 4). Furthermore, the 1-MCP-treated fresh-cut pears had firmness values much higher than those of untreated samples (7.8 N vs. 1.9 N, approximately) (Fig. 5). Moreover, firmness values of 1-MCPtreated pears were similar to those of pears analyzed immediately after harvest (data not shown). This demonstrates the effectiveness of 1-MCP treatment for maintaining firmness of ‘Blanquilla’ pear tissue, both whole and minimally processed. This feature is very important because the ‘Blanquilla’ variety is very susceptible to softening, in contrast to other pear varieties such as ‘Conference’ (Fig. 1B). A limiting factor in turning the ‘Blanquilla’ cultivar into a minimally processed product is its high susceptibility to browning, in comparison with other varieties (Fig. 1A). Fig. 6 shows the changes in a* values for slices of pears treated with 1-MCP and those of untreated pears. The control samples showed from the beginning, higher a* values (from negative to positive values, approximately 4–5), which indicated a greater degree of surface browning. Fig. 7 shows the total phenolic content of the ‘Blanquilla’ pear tissues. The data presented are for the initial time (after harvest) and after 3 months of cold storage (for both the treated and untreated
Fig. 2. Changes in headspace gas composition during storage at 4 ◦ C for ‘Blanquilla’ pear slices packed in microperforated film (P PLUS 30). () % CO2 without 1-MCP; () % CO2 with 1-MCP; (♦) % O2 without 1-MCP; () % O2 with 1-MCP. Data are means ± S.D. of determinations made from three samples.
Fig. 3. Concentrations of acetaldehyde (A) and ethanol (B) of ‘Blanquilla’ fresh-cut pears treated with 1-MCP (filled bars) or without 1-MCP treatment (open bars) during storage at 4 ◦ C. Data are means ± S.D. of determinations made from three samples.
batches). Initially, the phenolic concentration was approximately 80 mg 100 g−1 fruit. As was expected, due to the maturing process of the fruit during the 3 months at 0 ◦ C, the control samples (without 1-MCP treatment) showed a significant decrease in phenolic concentration (reaching approximately 30 mg 100 g−1 fruit). This reduction was not observed in the pear slices treated with 1-MCP (Fig. 7). 4. Discussion ‘Blanquilla’ is a variety of pear highly sensitive to browning and softening. The high degree of susceptibility to browning of this variety is mostly due to its high concentration of phenolics. This concentration is four or five times higher than the concentration
Fig. 4. Scores of sensory analysis (presence of undesirable flavours) for ‘Blanquilla’ fresh-cut pears, treated (filled bars) or non-treated (open bars) with 1-MCP during storage at 4 ◦ C.
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Fig. 5. Effect of 1-MCP treatment on firmness values of fresh-cut ‘Blanquilla’ pears stored in modified atmosphere, at 4 ◦ C for 15 d: () without 1-MCP treatment; () with 1-MCP treatment. Data are means ± S.D. of determinations made from 20 samples.
Fig. 6. Effect of 1-MCP treatment on a* values of fresh-cut ‘Blanquilla’ pears stored in modified atmosphere, at 4 ◦ C for 15 d: () without 1-MCP treatment; () with 1-MCP treatment. Data are means ± S.D. of determinations made from 20 samples.
of phenolics in other varieties. For example, the values of the ‘Conference’ and ‘Williams’ varieties are around 20 mg total phenolics 100 g−1 fruit. ‘Blanquilla’, however, can reach levels of 80–100 mg total phenolics 100 g−1 fruit (Arias et al., 2008). This limits its suitability for fresh-cut processing. Therefore, alternative processing options need to be evaluated. 1-MCP is an ethylene action inhibitor acting at very low concentrations, which has been shown to delay ripening and enhance storage life in intact and fresh-cut fruit (Antunes et al., 2008). 1-MCP acts at the receptor level delaying ripening in climacteric fruit and blocking ethylene-dependent pro-
Fig. 7. Effect of 1-MCP treatment on total phenolic concentration of ‘Blanquilla’ pears, after storage in air for 3 months at 0–1 ◦ C. Data are means ± S.D. of determinations made from three samples.
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cesses, especially firmness loss and inhibition of aroma production in the treated fruit (Chririboga et al., 2007). At a physiological level, 1-MCP can inhibit the metabolism of 1-aminocyclopropane 1 carboxylic acid (ACC) and also increase the total antioxidant potential of pear tissue mainly through an increase in peroxidase activity. As a consequence, 1-MCP treatment has significant effects on physiological disorder incidence in pears (reviewed in Chririboga et al., 2007). Our experiment has shown that the effects of 1-MCP on several fruit properties last at least during 3 months of storage. Ethylene synthesis in fresh-cut products is probably stimulated by wounding (Mao et al., 2007; Saltveit, 2004; Tomás-Barberán and Espín, 2001; Vilas-Boas and Kader, 2006a,b), and was reduced in the pear tissue almost fivefold by applying 1-MCP (Table 1). Accordingly, the rate of respiratory activity was reduced to about 50% that of control samples. The reduction of ethylene effects is probably the reason for the improvement of several quality attributes in 1-MCP-treated fruit. Results similar to ours have been reported for kiwifruit treated with 1-MCP before slicing (Mao and Fei, 2007) as well as for pineapple slices (Budu and Joyce, 2003). The application of 1-MCP has also been shown to slow down ethylene production in several varieties of minimally processed apples by using uncut fruit treated with 1MCP and cold storage for 1–4 months (Calderón-López et al., 2005). However, Vilas-Boas and Kader (2006b) did not observe any influence of 1-MCP treatment on the ethylene production of fresh-cut banana, although the respiration rate decreased. The best results were achieved in reducing softening (Fig. 5). 1MCP-treated fruit maintained firmness levels similar to fruit that had just been harvested, whereas untreated fruit softened considerably more and continued softening during 15 d. This suggests a decrease in activity of softening enzymes induced by 1-MCP (Lohani et al., 2004). The application of 1-MCP reduced softening of freshcut apples slices taken from whole fruit treated with 1-MCP and subsequently kept at 0 ◦ C (Perera et al., 2003; Calderón-López et al., 2005). Melo and Vilas-Boas (2006) and Kim et al. (2001) obtained similar results with banana and kiwi slices to which 1-MCP was directly applied. Fruit browning was also significantly reduced by 1-MCP. Values of a* in 1-MCP-treated samples were lower than in control samples, especially after 15 d. This occurred in spite of the higher total concentration of phenolics in 1-MCP-treated pears. It is rather surprising, that having a higher phenolic concentration results in lower browning levels of pear slices. This could be related a higher antioxidant potential of 1-MCP-treated pears as found by Larrigaudiere et al. (2004) and/or to the improved tissue integrity of 1-MCP-treated pears (demonstrated in this study by their better texture scores) which would hinder PPO coming into contact with its phenolic substrates, although a simultaneous lower level of PPO activity cannot be discarded. The change in respiratory pattern modified the atmosphere composition of the trays (Fig. 2). The higher respiratory rates of untreated pears led to higher concentrations of CO2 and a lower O2 levels, that results in synthesis of off-flavour metabolites and initiation of fermentation (Fig. 3); as a consequence, the panel rejected the product (Fig. 4). In conclusion, 1-MCP use just after harvest may allow the introduction of ‘Blanquilla’ pears into the fresh-cut market. It improved especially the texture but also color. However, the high phenolic concentrations in this variety promoted browning after 5 d, which makes fresh-cut pears unmarketable after this time. This period is probably not long enough for selling ‘Blanquilla’ fresh-cut pear in supermarkets, but it is long enough for food services and quickservice restaurants (fast food). Therefore, the treatment of intact pears with 1-MCP could be an alternative to the technologies currently in use for extending the shelf-life of the ‘Blanquilla’ pear variety as a fresh-cut product.
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