IJFS#38_PEANO_bozza   Ital. J. Food Sci., vol 28, 2016 - 376 PAPER QUALITY INDICATORS FOR MODIFIED ATMOSPHERE PACKAGING (MAP) STORAGE OF HIGH-QUALITY EUROPEAN PLUM (PRUNUS DOMESTICA L.) CULTIVARS N.R. GIUGGIOLIA, F. SOTTILEB and C. PEANOA* aDepartment of Agricultural, Forest and Food Sciences (DISAFA), Università degli Studi di Torino, Largo Paolo Braccini 2, 10095 Grugliasco, TO, Italy bDepartment of Agricultural and Forest Sciences, Università degli Studi di Palermo, Viale delle Scienze 11, 90128 Palermo, PA, Italy *Corresponding author. Tel.: +39 0116708646; fax: +39 0116708658 E-mail address: cristiana.peano@unito.it ABSTRACT The use of quality indicators is crucial in selling plums in more distant markets and the evaluation of freshness through multiple index is fundamental to evaluate the goodness of the storage technique. In this study we evaluated the quality of two european plums cultivars ('Ramasin' and 'Ariddo di Core' with purple and yellow flesh colour respectively) after modified atmosphere packaging (MAP) storage, through the selection of the most appropriate indicators. The headspace gas composition, the flesh fruit firmness (FFF), the soluble solid content (SSC), the titratable acidity (TA), the colour and the chlorophyll content of plums wrapped with 5 different films (F1, F2, F3, F4 and F5) were evaluated for up 21 days of storage (at 1±1°C and 90-95% relative humidity). For both cultivars, the multilayered films (F1 and F2, 90 and 65 µm respectively) offered better effectiveness over other films. The total chlorophyll concentration, showing a good correlation with the colorimetric parameters of luminance (L*) and chroma (respectively R2=0.92 and R2= 0.96) confirmed, in the case of the Ariddo di Core cultivar, the results obtained by monitoring other parameters thus highlighting the usefulness of integrating multiple indexes in evaluating the performance of the storage methods used. Keywords: Plum, film, quality index, chlorophyll, passive atmosphere   Ital. J. Food Sci., vol 28, 2016 - 377 1. INTRODUCTION Thanks to its adaptive behaviour in different climatic conditions, plums represent one of the most versatile of fruit trees species and its production is considered valuable for the future development of fruit trees sector (BLAZEK, 2007; SOTTILE et al., 2010a). In recent years the recovery and development of high quality local germplasm cultivars, such as the Ramasin in Piedmont and Ariddo di Core in Sicily, have evidenced a high level of diversity along the Italian production of the European plum (Prunus domestica L.). These cultivars have been important for local market since years; more recently they are also being coveted by wider markets for the high nutraceutical characteristics of fruits (SOTTILE et al., 2010b). The wide ripening period for such cultivars, combined with the different areas of cultivation, support an extension to the commercial calendar and represent a good opportunity for expanding the market for these fruits. The availability of numerous varieties, together with quality and price indicate the efficiency of the supply chain and distribution system which is today one of the most important sales channels in the area of horticultural fresh products (DEAN, 2011). The post-harvest management of these fruits appears problematic because plums evidence a cultivar-dependent high perishability, and require specific cares in terms of handling along all the supply chain. If not combined with other storage techniques, low refrigeration temperatures are not sufficient to maintain fruit quality up to the consumer; in fact, prolonged exposure to low temperatures would be responsible for enzymatic browning of the internal tissues and of the formation of skin damages (TAYLOR et al., 1993; ABDI et al., 1997). Among the different storage techniques such the use of absorbers (SHARMA et al., 2012) or antagonists of ethylene (SINGH and SINGH 2012), the modified and the controlled atmospheres (ELZAYAT and MOLINE, 1995; PRANGE and DELONG 2006; GIUGGIOLI et al., 2008; GIRGENTI et al., 2010; DIAZ-MULA et al., 2011 a, DIAZ-MULA et al., 2011 b, SOTTILE et al., 2013) are well known to have positive effect to improve the shelf life of plums. Active MAP on Sanacore and Ariddo di Core plums was performed with wrapped bulk preserving the quality more than 40 days for local consumption (PEANO et al., 2010) and different MAP box liners were used to maintain the shelf life and the quality of 'Friar' plums (CANTÍN et al., 2008). A key issue to success is also represented by high uniformity of the fruits as regards quality parameters (CRISOSTO et al., 2004). For this reason the selection and the monitoring of quality indicators is important not only for defining the time for harvesting but also for the maintainance of the commercial value of the product. There are several studies on the evolution of quality parameters during plum post- harvesting fruit management (USENIK et al., 2008; PÉREZ-MARÍN et al., 2010; SOTTILE et al., 2013;) but the identification of indicators useful to monitor quality along the distribution is still difficult. The pulp firmness and its relative evolution during storage is closely cultivar-dependent and specifically related to the stage of maturity at harvest time (SHARMA et al., 2012); anyway, if not integrated with other quality indicators, this parameter would be impractical for the fresh fruit market due to the absence of reference classes especially for European plums (VALERO et al., 2007; USENIK et al., 2008). In case of deeply pigmented cultivars, due to an usual early change of the skin colour, the pulp firmness is usually adopted as a ripening indicator (CRISOSTO and Kader 2000; SOTTILE et al., 2010 a). Generally, for stone fruits, the skin colour is one of the most important harvesting markers; the quantitative and qualitative development of the pigments in the skin is able to characterise the epidermis (chlorophyll, anthocyanins and carotenoids); the development of these pigments is closely related to the biological and physiological stress during the storage of the fruits (MERZLYAK et al., 1997; ABBOTT 1999). According to previous studies (SHARMA et al., 2012; VALERO et al., 2013) in some case the skin colour of purple-flesh plums is not a parameter useful to assess the effectiveness of differing   Ital. J. Food Sci., vol 28, 2016 - 378 storage treatments. All these aspects are very important in affecting the aesthetic appearance of the product (ABBOTT 1999), while they have several limits and they are not always positively correlated to a correct stage of fruit ripeness (USENIK et al., 2008). It has been reported that a total soluble solids content (SSC) ranging from 14 to 16% (WESTWOOD 1978) or from 10 to 15% (DIAZ-MULA et al., 2009) determines fruit ready for consumption. However, the aromatic profile of plums, as of most stone fruit species, is even more affected by the total titratable acidity (TA) value than to the sugar content (CRISOSTO et al., 2004; CRISOSTO et al., 2007). Many studies (ZIOSI et al., 2008; INFANTE et al., 2011) have revealed a close correlation between chlorophyll content within the pulp tissues of the stone fruit and the ripening degree of the fruit; this evidence demonstrates that visible UV spectroscopy is a non-destructive technique which could be considered useful for monitoring and characterising the different stages of fruit ripening (ZUDE et al., 2003; CECCARELLI et al., 2008). It is therefore evident that the evaluation of the effectiveness of any post-harvest treatment should consider the uniformity of the fruit by including multiple quality indices; this aspect should be more valuable for those cultivars that are often considered minor for the lower diffusion but with a high commercial capacities if new post-harvesting techniques, such as modified atmosphere packaging (MAP), are developed. On the basis of these considerations, the aim of this work was to evaluate the influence of the different packaging films used for MAP storage up to 21 days at 1 ±0.5°C of two European plum cultivars characterized by high tasting excellence and differing pigmentation (yellow and purple) also in order to assess the most important quality indices for fresh consumption. 2. MATERIALS AND METHODS 2.1. Fruit samples Two European plum cultivars (Prunus domestica L.) were used, both belonging to local Italian germplasm and with different pigmentations: the cv. 'Ramasin' with a purple- coloured flesh is from the Piedmont territory and was harvested in mid-July; the cv. 'Ariddo di Core' is a yellow-coloured flesh variety from Sicily and is harvested in August. Both cultivars are characterised by fruits of small size and limited shelf life but with a high tasting quality well recognized by the local consumers. Fruits were picked by hand, and selected based on size uniformity and absence of damage. After a refrigeration (2 hours) they were placed in polyethylene terephthalate (PET) trays and transported within 24 hours to the fruit and vegetable warehouse (Agrifrutta Soc. Coop. S.R.L. - Piedmont, Italy) for storage-testing. 2.2. Packaging and storage conditions The fruit samples were unwashed previously to be packaged. For both cultivars the sampling unit considered was the flowpack. The PET 0.250 kg trays (L14 x w9.5 x h5) were heat sealed with different films using a Taurus 700 model horizontal machine (Delphin, Italy). The materials used for the different packages were: F1: multilayer produced by co-extrusion of PET, EVOH and PE of 90µm, (Corapack, Italy); F2: multilayer produced by co-extrusion of PET, EVOH and PE of 65 µm, (Corapack, Italy); F3: polypropylene (PP) film, 25µm, (Trepack, Italy);   Ital. J. Food Sci., vol 28, 2016 - 379 F4: low density monolayer polyethylene (PE) film, 25 µm, (Trepack, Italy); F5: non commercial biodegradable film, 25 µm, (Novamont, Italy); For each package, the control sample (Control) is represented by fruits preserved using a polypropylene (PP) macroperforated (6 mm diameter holes) film of 25 µm (Trepack, Italy). The O2 and CO2 transmission rate properties of the films were measured at 23°C and 50% of relative humidity in accordance with ASTM F 2622-08 and ASTM F 2476-05 standards (Table 1). With the exception of the biodegradable film (F5) whose water permeability value was supplied directly by the manufacturer (147cm3 m-2 24h), tested films resulted within the high water barrier film classification (VAN TUIL, 2000). All fruits were packed under normal atmospheric conditions (0.2 CO2 kPa /21.2 O2 kPa). This was performed in order to create passive modified atmosphere packaging (MAP) during storage conditions through to the synergistic action of the fruit respiratory metabolism and the selectivity of the film to the gases. Due the macro hole (6-mm-diameter) the PP film (control) has no changed the atmosphere inside the packages along all the storage time. The fruits were stored for all the period under constant refrigeration conditions based on 1±0.5°C with a relative humidity (RH) level of 90-95% and in the dark. Qualitative evaluations were performed at the picking time (0) and after 7, 14 and 21 days of storage. Table 1: Characteristics of film used for MAP storage of plum fruits. Film gas transmission rate at 23°C and 50% UR cm3/(m2 24h bar) Film O2 (ASTM F2622-08) CO2 (ASTM F2476-05) F1 1572 6111 F2 1572 6111 F3 1456 4616 F4 10990 55360 F5 2276 44494 2.3. Headspace Composition and Qualitative Parameters Sampling of the gases (O2 and CO2) within the headspace of the packaging was performed with a Check Point II portable gas analyser (PBI Dansensor, Italy). Three random trays were used for each measurement for a total of 0.750 kg of fruit. In order to avoid any alteration to its internal atmosphere, the air sampled for analysis was fed back into the container using a porous septum (15 mm diameter PBI Dansensor, Italy) positioned on the surface of the film. Instrument calibration was performed after each measurement using a vacuum sample in normal atmosphere (ADAY and CANER, 2011). The value is recorded as kPa and it is the average of three measurements. The weight of each container was measured using an electronic balance (SE622, WVR Science Education, USA) with an accuracy of 0.01 grams, at the harvest and at the end of each storage period. The relative weight loss was expressed as a percentage (%). The fruit flesh firmness (FFF) (kg/cm2) was measured by a manual penetrometer (Facchini, Alfonsine, Italy) using a pipette tip with a 7.9-9 mm diameter in accordance with species standards. The skin of the fruit was not removed. Each value is the average of two measurements taken from opposite sides of each fruit. The data recorded is the average of   Ital. J. Food Sci., vol 28, 2016 - 380 30 measurements (three random trays for a total of 0.750 kg of fruit). Soluble solids content (SSC) were determined in the juice (from three trays randomly chosen for each treatment) with a digital refractometer Atago PR-101 (Atago, Japan) at 20°C. Two readings (30 fruits) were taken on each fruit and averaged; results were expressed as °Brix. The titratable acidity (TA) (meq/L) was measured with an automatic titrator (Titritino plus 484, Metrohm, Switzerland); 5 mL of pulp juice were used for each sample (shaken, centrifuged and filtered), diluted in 15 mL of distilled water which was neutralised with sodium hydroxide (NaOH) 0.1N. The value is the average of 3 measurements (three random plastic containers for a total of 0.750 kg of fruit). 2.4. Colour In this study the colour evolution and total chlorophyll content were monitored only for the yellow-flesh cultivar cv. 'Ariddo di Core'. Colour was measured on the first 15 non- mouldy fruits from each tray (three trays were randomly chosen for each package). The mean of the 30 fruit measurements was used for data analysis. CIELAB or L*a*b* space was used to describe the color. This color space is device-independent and able to create consistent colors regardless of the device used to acquire the image. L* is the luminance or lightness component, which ranges from 0 to 100, while a* (green to red) and b* (blue to yellow) are two chromatic components, with values varying from –120 to +120 (YAM and PAPAKADIS, 2004). These values were used to calculate chroma, which indicates the intensity or color saturation, using the following equation: C* = [a*2 + b*2]1/2 (2) hue angle was calculated as follows: h° = arctangent[b*/ a*] (3) where 0° = red-purple, 90° = yellow, 180° = bluish-green, and 270° = blue (MCGUIRE, 1992). 2.5. Chlorophyll Chlorophyll monitoring was carried out using UV-Vis spectrophotometry, a non- destructive analytical, qualitative and quantitative technique that makes use of a spectrophotometer to allow molecule recognition and quantification as a function of spectrum absorption. The UV-Vis analyses were performed using a Varian Cary 500 double beam spectrophotometer equipped with a Varian DRA-2500 integrating sphere. The background noise was subtracted using the Spectralon® as a reference. The spectra were recorded in a range between 350 and 800 nm at a resolution of 3 nm. Each UV-Vis measurement was made in diffuse reflection (DR) mode positioning the equatorial part of the surface of each fruit (95mm2 area) in line with the reflection sphere. For each sample the chlorophyll concentration was calculated by processing the spectra acquired from each fruit (average of two fruit / 60 fruits / acquisitions) as per the Kubelka Munk (1931) F(R) function. It was first necessary to establish a calibration equation by means of the direct extraction of chlorophyll from plums exhibiting different degrees of maturity as per the official extraction methodology (AOAC, 2006).   Ital. J. Food Sci., vol 28, 2016 - 381 2.6. Statistical analysis All statistics were performed using SPSS for Windows version 20.0. The data obtained were treated with one-way analysis of variance (ANOVA) and the means were separated using the Duncan test (p ≤ 0.05). As the sample sizes were identical, it was possible to perform a parametric test for the percentages. 3. RESULTS AND DISCUSSIONS 3.1. Headspace composition and qualitative parameters Changes of O2 and CO2 (kPa) gases within the package headspaces are shown in Figs. 1 and 2 respectively for cv. 'Ramasin' and cv. 'Ariddo di Core'. For both cultivars each packaging film succeeded in changing the initial atmospheric conditions, equal to 0.2 kPa of CO2 and 21.2 kPa of O2 maintaining different MAP conditions up to the end of the storage period (21 days). Figure 1: O2 and CO2 headspace gas composition of cv. 'Ramasin' plums stored in MAP at 1±0.5°C. Figure 2: O2 and CO2 headspace gas composition of cv. 'Ariddo di Core' plums stored in MAP at 1±0.5°C.   Ital. J. Food Sci., vol 28, 2016 - 382 In general a decreasing trend in O2 content corresponds to an increase in the internal concentration of CO2, product of the respiration of the plums; in this case, the CO2 accumulation, at a constant temperature (1±0.5°C), is determined by the interaction of two factors: the permeability of the film and the storage period (EXAMA et al., 1993; VAROQUAUX et al., 2002). During the first 7 days O2 and CO2 contents did not differ significantly in both varieties. As the storage goes on, the values increases their differences evidencing the active performance of the different packaging films used. According to what reported in previous MAP studies on stone fruits (DIAZ-MULA et al., 2011 a, GIRGENTI et al., 2014) the multilayer films (F1 and F2) are able to maintain higher concentrations of CO2 within the flow pack when compared with other films (F3, F4, F5) due to higher gas barrier properties (Table 1). This condition is maintained by both the cultivars for all the storage time. In particular, after 21 days of storage, CO2 ranged between 9.5 and 13.1 kPa for cv. 'Ramasin' and between 15.0 kPa and 17.4 kPa of CO2 for cv. 'Ariddo di Core'. With the 'Ramasin' cultivar, the highest value is registered with the F1 film, while for the cv. 'Ariddo di Core' with the F2 film. All other films, from the 7th day of storage evidenced CO2 values lower than 5 kPa. For both cultivars the lowest values were obtained with the F4 film (respectively 1.2 kPa for the cv. 'Ramasin' and 2.4 kPa for the cv. 'Ariddo di Core'). Throughout the storage period, the cv. 'Ariddo di Core', under all MAP conditions, presented higher values of CO2 than the cv. 'Ramasin', suggesting a greater respiratory metabolism for the fruit of this cultivar. For the cv. 'Ramasin', the equilibrium point (13.4 kPa O2 and 13.1 kPa CO2) was only reached at the end of the storage period (21 days) with the F1 film, while in the case of the cv. 'Ariddo di Core' it is reached between the 14th and 21st day with both of the multilayer films (F1 and F2) with values ranging between 10 and 15kPa; this condition is however immediately lost. The weight losses observed (data not shown) increase with the storage time, but the rate for both cultivars is a function of the specific film employed. The control showed the greatest weight loss (3 % of the fresh weight after 21 days) confirming what was observed in previous MAP studies for stone fruits (SOTTILE et al., 2013; GIRGENTI et al., 2014). All MAP packages ensure controlled weight loss within a similar range of values (0.5-0.7% for cv. 'Ramasin' and 0.6-0.9 % for 'Ariddo di Core' after 21 days of storage). Based on these results, it is not possible to use the weight loss as quality parameter to identify the MAP film with the best performances. The cv. 'Ramasin' (Table 2) and cv. 'Ariddo di Core' (Table 3) present very different FFF values at harvest (1.1 kg/cm2 and 3.5 kg/cm2 respectively). However both cultivars exhibit a similar evolution for this parameter. In fact, the FFF values decreased with time, reaching their lowest values after 21 days of storage. This result is associated with a decrease of pectin polymerisation within the cell tissues and although this trend is common to all packages, fruit stored under normal atmospheric conditions (control) showed a stronger decreasing trend and evidenced values significantly lower at the end of the storage period respect to MAP storage (0.5 kg/cm2 for cv. 'Ramasin' and 1.1kg/cm2 for 'Ariddo di Core'). As reported in previous studies (SOTTILE et al., 2013) plums stored under MAP conditions with the highest levels of CO2 use to evidence higher pulp firmness; for both cultivars the multilayer films (F1 and F2), ensuring higher values of CO2 (Figs. 1 and 2), are able to better control pulp firmness decay as compared to other films. In particular, for cv. 'Ramasin', the F1 film is significantly different compared to the F2 film, while in the case of the cv. 'Ariddo di Core', these two films do not exhibit significant differences in terms of performance.   Ital. J. Food Sci., vol 28, 2016 - 383 Table 2: Evolution of qualitative characteristics of plums cv. 'Ramasin' stored in MAP at 1±0.5°C. Time (days) Film 7 14 21 Harvest 1.10±0.21 FFF (kg/cm2) F1 0.86±0.2a 0.85±0.1a 0.80±0.2a F2 0.89±0.1 a 0.84±0.1a 0.80±0.1b F3 0.77±0.1a 0.70±0.1a 0.78±0.2b F4 0.78±0.1b 0.70±0.1a 0.71±0.1b F5 0.76±0.1b 0.72±0.1a 0.73±0.1b Control 0.62±0.1c 0.53±0.1b 0.49±0.2c Harvest 16.0±0.7 SSC (°Brix) F1 17.0±0.3n.s 17.5±0.3d 17.9±0.5d F2 17.0±0.4 n.s 17.7±0.3d 17.9±0.7d F3 16.9±0.6 n.s 18.2±0.8bc 18.6±0.5bc F4 17.1±0.8 n.s 18.0±0.5c 18.5±0.6c F5 17.1±0.3 n.s 18.3±0.6b 18.8±0.3b Control 17.0±0.6 n.s 18.8±0.3a 20.1±0.5a Harvest 5.1±0.0 TA (meq/L) F1 4.9±0.0n.s 4.8±0.2a 4.5±0.0a F2 4.9±0.2 n.s 4.8±0.1a 4.5±0.1a F3 5.1±0.1 n.s 4.6±0.3a 4.5±0.0ab F4 5.0±0.1 n.s 4.6±0.1a 4.4±0.0ab F5 5.0±0.1 n.s 4.5±0.1a 4.4±0.0b Control 5.0±0.1 n.s 4.2±0.2b 3.7±0.1c Results were expressed as means ± standard deviation. Values in the column followed by different letters are significantly (P<0.05) different according to Duncan’s test. At harvest, the two cultivars present different SSC (16.0° Brix and 18.5° Brix respectively for cv. 'Ramasin' and cv. 'Ariddo di Core'). After the first 7 days of storage, in spite of the low refrigeration temperatures (1 ±0.5°C), all packages presented an increase in the soluble solids content values in accordance with the observations of GUERRA and CASQUERO (2008), with the Green Gage variety and SOTTILE et al., (2013) yellow-fleshcultivars; this trend is evident with continued storage. The increase is related to the concentration of sugars resulting from weight loss of the fruit (loss of water) and also due to the increasing extractability (sucrose inversion) during the increasing of the ripening degree. For both cultivars, over the whole storage period, the control presented a higher soluble solid content compared to the MAP packaged ones thus confirming the CO2 effect during storage and its ability to delay the ripening processes in accordance with DÍAZ-MULA et al. (2009). The F1 and F2 films showed statistically significant differences compared to the other MAP films (F3, F4 and F5) after 14 days of storage in the case of the cv. 'Ramasin' (Table 2) and after only 7 days of storage for the cv. 'Ariddo di Core' (Table 3) evidencing a better control of the soluble solids content dinamics and maintaining these values close to those measured at harvest.   Ital. J. Food Sci., vol 28, 2016 - 384 Table 3: Evolution of qualitative characteristics of plums cv. 'Ariddo di Core' stored in MAP at 1±0.5°C. Time (days) Film 7 14 21 Harvest 3.55±0.11 FFF (kg/cm2) F1 3.25±0.1 a 3.25±0.3 a 2.39±0.1 a F2 3.25±0.1 a 3.04±0.1 a 2.49±0.2 a F3 2.85±0.2 b 2.50±0.1 b 1.32±0.2 c F4 2.79±0.1 b 2.47±0.1 b 1.35±0.2 c F5 2.87±0.1 b 2.50±0.1 b 1.53±0.2 b Control 2.53±0.1 c 2.24±0.4 c 1.04±0.1 d Harvest 18.5±0.1 SSC (°Brix) F1 18.6±0.1 bc 18.7±0.1 c 19.1±0.2 c F2 18.6±0.1 bc 18.7±0.1 c 19.0±0.1 c F3 18.7±0.1 b 19.1±0.0 b 19.5±0.1 b F4 18.7±0.1 b 19.0±0.1 b 19.5±0.1 b F5 18.7±0.1 b 19.0±0.1 b 19.5±0.1 b Control 18.9±0.1 a 19.6±0.1 a 20.0±0.1 a Harvest 8.6±0.7 TA (meq/L) F1 5.0±0.1 n.s 4.3±0.0 n.s 4.1±0.1 a F2 5.0±0.1 n.s 4.4±0.1 n.s 4.1±0.0 a F3 4.5±0.0 n.s 4.3±0.0 n.s 3.6±0.0 b F4 4.5±0.1 n.s 4.3±0.0 n.s 3.5±0.0 b F5 4.5±0.0 n.s 4.3±0.1 n.s 3.5±0.0 b Control 4.5±0.0 n.s 4.1±0.1 n.s 3.9±0.0 c Results were expressed as means ± standard deviation. Values in the column followed by different letters are significantly (P<0.05) different according to Duncan’s test. Over the entire storage period, compared to the values measured at harvest (5.1 meq/L for cv. 'Ramasin' and 10.2 meq/L for cv. 'Ariddo di Core'), the TA diminished for all packages for both cultivars; both for Ramasin and Ariddo di Core cvs., MAP determined higher TA values compared to the control. The maturity index obtained from the SSC/TA ratio (data not shown) indicates a progressively increase during the whole storage period for both cultivars; for all MAP packages this value is lower respect to the control, thus confirming the observations reported from previous studies (DÍAZ-MULA et al., 2009). The colour variables a* and b* are not independent and their difficult perception to the human eye force to their correlation in order to calculate Chroma (C) and Hue angle parameters (ALCOBENDAS et al., 2012). Table 4 reports the colour components L*, Chroma and Hue angle as measured for the yellow flesh fruit cv. 'Ariddo di Core'. Just after 7 days of storage each film packaging influenced a change in skin colour thus indicating the presence of a maturation process even at low storage temperatures (1±0.5°C). 3.2. Colour and chlorophyll monitoring The luminance values (L*) decrease compared to those measured at harvest (46.9) thus indicating a darkening of the tissues as a result of the ripening (Table 4). Each of the MAP   Ital. J. Food Sci., vol 28, 2016 - 385 packages presented no statistically significant differences compared to control as the fruit maintained higher L* values. The multilayer films (F1 and F2), to which correspond higher concentrations of CO2 within the flow pack headspace (Fig. 2), are more differentiated than the other films presenting significantly higher values of L* over the entire storage period and reaching after 21 days values equal to 42.4. The chroma values follow in a similar way the decreasing trend of L* values. For each film the Hue angle values decreased at increasing storage time in accordance with findings reported by DÍAZ-MULA et al. (2011 a), but statistically significant lower values (redder fruit) were observed throughout the storage period in respect to control packed fruit. Table 4: Colorimetric parameters of plums cv. 'Ariddo di Core' stored in MAP at 1±0.5°C. Time (days) Film L* Chroma h angle Harvest 46.9±0.5a 21.1±0.4a -1.31±0.01d 7 F1 43.7±0.2b 17.0±0.6bc -1.39±0.02c F2 43.7±0.3b 17.1±0.9bc 1.39±0.02c F3 43.6±0.2b 16.9±0.6c -1.42±0.01b F4 43.3±0.3c 16.9±0.8b -1.40±0.01b F5 43.4±0.3c 16.9±0.9c -1.42±0.01b Control 42.5±0.3d 15.8±0.9d -1.48±0.03a Harvest 46.9±0.5a 21.1±0.4a -1,31±0.01c 14 F1 43.5±0.2b 16.3±0.5b -1.36±0.54bc F2 43.6±0.3b 16.3±0.6b -1.45±0.04ab F3 42.4±0.2d 15.6±0.7c -1.47±0.02a F4 42.5±0.2cd 15.7±0.4c -1.48±0.03a F5 42.5±0.3c 15.6±0.3c -1.48±0.01a Control 41.6±0.4e 13.2±0.7d 1.53±0.00a Harvest 46.9±0.5a 21.1±0.4a -1.31±0.01c 21 F1 42.4±0.3b 15.6±0.8b -1.47±0.04b F1 42.4±0.5b 15,3±0.8b -1.47±0.02b F1 41.6±0.2c 14.3±0.8c -1.47±0.02b F1 41.7±0.2c 14,6±0.7c -1.48±0.02b F1 41.6±0.4c 14.6±0.6c -1.48±0.02b Control 39.5±0.3d 12.6±0.8d -1.55±0.03a Results were expressed as means ± standard deviation. Values in the column followed by different letters are significantly (P<0.05) different according to Duncan’s test. The skin changes from green to yellow color are closely correlated to the chlorophyll degradation process during ripening (ABDI et al., 1997; CRISOSTO et al., 2004) as shown in Fig. 3. The total pigment content, measured using UV-Vis spectrophotometry, decreases progressively throughout the storage period thus confirming evolution of the ripening processes even at low temperatures (ZUDE-SASSE et al., 2002; SOLOVCHENKO et al., 2005). For each quality control all MAP film tested evidenced to be able to manage the loss of total chlorophyll content maintaining higher values than the control. The high barrier capacity films (F1 and F2) were differentiated already within 7 days of storage thanks to the fruits have maintained the main quality values near to the time of harvest.   Ital. J. Food Sci., vol 28, 2016 - 386 Figure 3: Chlorophyll total content (mM) in cv. 'Ariddo di Core' plums stored in MAP at 1±0.5°C. The high CO2 levels, corresponding to F1 and F2 films, (Fig. 2) would be responsible for the proper maintenance of the integrity and fluidity of cell membranes which are indispensable conditions for the stabilisation of the photosynthetic pigment content (PONGPRASERT et al., 2011). The total chlorophyll content showed a good correlation to the colour components L* (Fig. 4) and Chroma (Fig. 5) according to a linear regression index equal to R2= 0.92 and R2= 0.96, respectively. In particular, decreasing values in chlorophyll correspond to a loss of brightness and chromaticity (Table 4) associated with the concentration of carotenoids that are responsible for the change in colour from green to yellow (increasing value of a*) of the fruit skin. Figure 4: Linear regression of total chlorophyll content and the L* colour parameter in cv. 'Ariddo di Core' plums stored in MAP at 1±0.5°C.   Ital. J. Food Sci., vol 28, 2016 - 387 Figure 5: Linear regression of total chlorophyll content and the Chroma colour parameter in cv. 'Ariddo di Core' plums stored in MAP at 1±0.5°C. 4. CONCLUSIONS Differents and multiples indexes of quality have been considered to evaluate the goodness of the MAP technique for the storage of 'Ramasin' and 'Ariddo di Core' plum cultivars. The headspace composition showed how high CO2 increments associated with higher barrier capacity films (multilayer) are usually related to a higher fruit quality at the end of the storage period. Among the qualitative index considered, for both cultivars, the flesh fruit firmness allowed a better evaluation of the effectiveness of different packaging since the beginning of the storage test. The colour parameter (lightness and chromaticity), linked to the chlorophyll content of the plums, is well known to be particularly appreciated by the consumers and for this it can be suggested to further evaluation of the performance of the tested films for the management of a MAP storage protocol. Results of this research confirm the correlation that exists between colour and the pigments content in organic matrices and more generally within food systems (RAMAKRISHNAN and FRANCIS, 1973; FRANCIS, 1985; WATADA and ABBOTT, 1975; TAKAHATA et al., 1993; AMENY and WILSON, 1997; CHEN and TANG, 1998; ARIAS et al., 2000; BRON et al., 2005; CECCARELLI et al., 2008). According to McGuire (1992) the monitoring of the total total chlorophyll content is highly correlated with the colour parameters, then it is important to consider also that it derives from a non-destructive technique such as UV-Vis whose numerous advantages are even more interesting when they can be applied to cultivars of excellence and high perishability such as those considered within this study. ACKNOWLEDGEMENTS This work has been carried out as a part of the PRIN research program - Quality and Safety Monitoring of the Fruit Supply Chain: New Technologies For Post-Harvest Management, and it was entirely supported by the Italian Ministry of Education, University and Research (MIUR). The authors wish to thank Agrifrutta Soc.Coop.Agr. (Peveragno, CN) for their technical support and for the storage facilities. REFERENCES AOAC. 2006. Official Methods of Analysis, 17th Ed., Association of Official Analytical Chemists, Gaithersburg, Maryland, USA. Abbott J.A. 1999. Quality measurement of fruit and vegetables. Postharvest Biol. Technol. 15:207.   Ital. J. Food Sci., vol 28, 2016 - 388 Abdi N., Holford P. and McGlasson W.B. 1997. Effects of harvest maturity on the storage life of Japanese type plums. Aust. J. Exp.Agric. 37:391. Aday M.S. and Caner C. 2011. The applications of ‘active packaging and chlorine dioxide’ for extended shelf life of fresh strawberries. Pack. Technol. Sci. 24:123. Alcobendas R., Mirás-Avalos J.M., Alarcón J.J., Pedrero F. and Nicolás E. 2012. Combined effects of irrigation, crop load and fruit position on size, color and firmness of fruits in an extra-early cultivar of peach. Scientia Hortic. 142:128. Ameny M. and Wilson P. 1997. Relationship between Hunter colorvalues and ß-carotene contents in white fleshed African sweet potatoes (Ipomoea batatas Lam). J. Sci. Food Agric. 73:301. Arias R., Lee T.C., Logendra L. and Janes H. 2000. Correlation of Lycopene Measured by HPLC with the L*, a*, b* Color Readings of a Hydroponic Tomato and the Relationship of Maturity with Color and Lycopene Content. J.Agric. Food Chem. 48:1697. Blazek J. 2007. A survey of the genetic resources used in plum breeding. Acta Hortic. 734:31. Bron I.U. 2005. Chlorophyll fluorescence emission and its relation to skin color and firmness during ripening of guava fruit. Fruits 60:25. Cantín C.M., Crisosto C.H., Day K.R. 2008. Evaluation of the effect of different modified atmosphere packaging box liners on the quality and shelf life of 'Friar' plums. HortTechnology 18:261. Castillo S., Serrano M. and Valero D. 2009. Changes in hydrophilic and lipophilic antioxidant activity and related bio- active compounds during postharvest storage of yellow and purple plum cultivars. Postharvest Biol. Technol. 51:354. Ceccarelli R., Venturello A., Giuggioli N., Peano C. and Geobaldo F. 2008. Diffuse reflectance UV-VIS Spettroscopy in food monitoring. Ital. J. Food Sci. 175. Chen B.H. and Tang Y.C. 1998. Processing and stability of carotenoid powder from carrot pulp waste. J. Agric. Food Chem. 46:2312. Crisosto G.M., Crisosto C.H., Echeverria G. and Puy J. 2007. Segregation of plum and pluot cultivars according to their organoleptic characteristics. Postharvest Biol. Technol. 44: 271. Crisosto C.H. and Kader A.A. (Eds.) 2000. Plum and fresh prune postharvest quality maintenance guidelines. Department of Plant Sciences, University of California, Davis, CA 95616. Crisosto C.H., Garner D., Crisosto G.M. and Bowerman E. 2004. Increasing ‘Blackamber’ plum (Prunus salicina Lindell) consumer acceptance. Postharvest Biol. Technol. 34:237. Dean W.R. and Sharkey J.R. 2011. Rural and urban differences in the associations between characteristics of the community food environment and fruit and vegetable intake. J. Nut. Educ. Beh. 43:426. aDíaz-Mula H.M, Martínez-Romero D., Castillo S., Serrano M. and Valero D. 2011. Modified atmosphere packaging of yellow and purple plum cultivars. 1. Effect on organoleptic quality. Postharvest Biol. Technol. 6:1103. bDíaz-Mula H.M., Zapata P.J., Guillén F., Valverde J.M., Valero D. and Serrano M. 2011. Modified atmosphere packaging of yellow and purple plum cultivars. 2. Effect on bioactive compounds and antioxidant activity. Postharvest Biol.Technol. 61:110. Elzayat H. E. E. and Moline H. E. 1995. Effect of some gas mixture on storage quality of plums. J. Food Qual. 18:511. Exama A., Arul J., Lencki R.W., Lee L.Z. and Toupin C. 1993. Suitability of plastic films for modified atmosphere packaging of fruits and vegetables. J. Food Sci. 58:1365. Francis F. 1985. Blueberries as a colorant ingredient in food products. J. Food Sci. 50:754. Giuggioli N., Ceccarelli R., Geobaldo F., Girgenti V. and Peano C. 2008. Improved shelf life of plum belonging to Sicilian Germoplasm. Ital. J. Food Sci. 254. Girgenti V., Impallari F.M., Monte M., Giuggioli N. and Reita G. 2010. Effect of post harvest fruit conditioning of two different plum cultivars: first results on qualitative traits evolution. Acta Hortic. 874:131. Girgenti V., Peano C. and Giuggioli N. 2014. Experiences of innovative packaging materials on apricot fruits (cv Tom Cot®). Fruits 69:1.   Ital. J. Food Sci., vol 28, 2016 - 389 Guerra M. and Casquero P.A. 2008. Effect of harvest date on cold storage and postharvest quality of plum cv. Green Gage. Postharvest Biol. Technol. 47:325. Infante R., Rubio P., Contador L., Noferini M. and Costa G. 2011. Harvest maturity determination of D’Agen plums through the chlorophyll absorbance index. Ciencia e investigación agrarian 38:199. Kubelka P. and Munk F. 1931. Ein beitrag zur optik der farbanstriche. Z. Tech. Phys. 12:593. McGuire R.G. 1992. Reporting of objective color measurements. Hort Sci. 27:1254. Merzlyak M.N., Gitelson A.A., Pogosyan S.I., Chivkunova O.B., Lekhimena L., Garson M., Buzulukova N.P., Shevyryova V.V. and Rumyantseva V.B. 1997. Reflectance spectra of plant leaves and fruits during their development, senescence and under stress. Russ. J. Plant Physiol. 44:614. Peano C., GirgentiV., Sottile F. and Giuggioli. 2010. Improvment of plum storage with modified atmosphere packaging. Acta Hortic. 876:183. Pérez-Marín D., Paz P., Guerrero J.E., Garrido-Varo A. and Sánchez M.T. 2010. Miniature handheld NIR sensor for the on-site non-destructive assessment of post-harvest quality and refrigerated storage behavior in plums. J. Food Eng. 99:294. Pongprasert N., Sekozawa Y., Sugaya S. and Gemma H. 2011. A novel postharvest UV-C treatment to reduce chilling injury (membrane damage, browning and chlorophyll degradation) in banana peel. Sci.Hortic. 130:73. Prange R.K. and DeLong J.M. 2006. Controlled-atmosphere related disorders of fruits and vegetables. Stewart Postharvest Review 5:1. Ramakrishnan T. and Francis F. 1973. Color and carotenoid changes in heated paprika. J. Food Sci. 39:25. Sharma S., Sharma R. R., Pal R. K., Jhalegar Md. J., Singh J., Singh S. P. and Singh Z. 2012. Postharvest oxidative behaviour of 1-methylcyclopropene treated Japanese plums (Prunus salicina Lindell) during storage under controlled and modified atmospheres. Postharvest Biol. Technol. 74:26. Solovchenko A.E., Chivkunova O.B., Merzlyak M.N. and Gudkovsky V.A. 2005. Relationships between chlorophyll and carotenoid pigments during on-and off-tree ripening of apple fruit as revealed non-destructively with reflectance spectroscopy. Postharvest Biol.Technol 38:9. aSottile F., Bellini E., Nencetti V., Peano C., Palara U., Pirazzini P., Mezzetti B., Capocasa F., Mennone C. and Catalano L. 2010. Plum production in Italy: state of the art and perspectives. Acta Hortic. 874:25. bSottile F., Impallari M., Peano C. and Giuggioli N. 2010. Antioxidant compounds and qualitatitive traits in European (Prunus domestica L.) and Japanese (P. triflora) plum fruits as affected by cold storage. Acta Hortic. 877:1145. Sottile F., Peano C., Giuggioli N. R. and Girgenti V. 2013. The effect of modified atmosphere packaging on the physical and chemical quality of fresh yellow plum cultivars. J. Food Agric. Env. 11:363. Srivastav M. and Dhiman M.R. 2012. Ethylene absorbents influence fruit firmness and activity of enzymes involved in fruit softening of Japanese plum (Prunus salicina Lindell) cv. Santa Rosa. Fruits 67:257. Takahata Y., Noda T. and Nagata T. 1993. HPLC determination of ß -carotene content of sweet potato cultivars and its relationship with color values. Jap. J. Breed. 43:421. Taylor M.A. and Jacobs G. 1993. Physiological factors associated with over- ripeness, internal breakdown and gel breakdown in plums stored at low temperature. J. Hortic. Sci. Biotech. 68:825. Usenik V., Kastelec D., Veberic R. and Štampar F. 2008. Quality changes during ripening of plums (Prunus domestica L.). Food Chem. 111:830. Valero C., Crisosto C. H. and Slaughter D. 2007. Relationship between non-destructive firmness measurements and commercially important ripening fruit stages for peaches, nectarines and plums. Postharvest Biol. Technol. 44:248. Valero D., Díaz-Mula H. M., Zapata P. J., Guillén F., Martínez-Romero D., Castillo S. and Serrano M. 2013. Effects of alginate edible coating on preserving fruit quality in four plum cultivars during postharvest storage. Postharvest Biol.Technol. 77:1. Van Tuil R., Fowler P., Lawther M. and Weber C.J. 2000. Properties of biobased packaging materials, in Biobased Packaging Materials for the Food Industry Status and Perspectives (C.J. Weber, Eds.) pp. 8-33.   Ital. J. Food Sci., vol 28, 2016 - 390 Varoquaux P., Gouble B., Ducamp M.N. and Self G. 2002. Procedure to optimize modified atmosphere packaging for fruit. Fruits 57:313. Watada A. and Abbott J. 1975. Objective method of estimating anthocyanin content for determining color grade of grapes. J. Food Sci. 40:1278. Westwood M.N. 1978. Temperate-Zone-Pomology (Postharvest, Storage and Nutritional Value). Vol. 428, New York: W. N. Freeman and Company, pp. 280-281. Ziosi V., Noferini M., Fiori G., Tadiello A., Trainotti L., Casadoro G. and Costa G. 2008. A new index based on vis spectroscopy to characterize the progression of ripening in peach fruit. Postharvest Biol. Technol. 49: 319. Zude-Sasse M., Truppel I. and Herold B. 2002. An approach to non-destructive apple fruit chlorophyll determination. Postharvest Biol. Technol. 25:123. Zude-Sasse M. 2003. Non-destructive prediction of banana fruit quality using VIS/NIR spectroscopy. Fruits 58:135. Yam K.L. and Papakadis S.E. 2004. A simple digital imaging method for measuring and analysing color of food surfaces. J. Food Eng. 61:137. Paper Received January 20, 2015 Accepted July 22, 2015