Effects of new packaging solutions on physico-chemical, nutritional and aromatic characteristics of red raspberries (Rubus idaeus L.) in postharvest storage

Postharvest Biology and Technology 98 (2014) 72–81

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Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio

Effects of new packaging solutions on physico-chemical, nutritional and aromatic characteristics of red raspberries (Rubus idaeus L.) in postharvest storage Gabriella Giovanelli ∗ , Sara Limbo, Susanna Buratti Department of Food, Environmental and Nutritional Sciences, University of Milan, via Celoria 2, 20133 Milan, Italy

a r t i c l e

i n f o

Article history: Received 21 March 2014 Accepted 5 July 2014 Keywords: Raspberries (Rubus idaeus L.) Packaging Plastic materials Shelf-life Firmness Electronic nose

a b s t r a c t Postharvest life of raspberries (Rubus idaeus L.) is limited due to their high respiration rate, loss of firmness and freshness and susceptibility to fruit rot. The aim of this research was to evaluate the effects of various packaging solutions on physico-chemical, nutritional and aromatic properties of raspberries during storage at +4 ◦ C up to 7 days. Plastic materials with low (LDPE) and high (LDPE/EVOH/LDPE) gas barrier, a biopolymeric film (PLA) with medium gas barrier and micro perforated stretch film (PVC) were used. The packaging material modified the composition of the atmosphere in the package, which depended on the combined action of the respiration activity of the fruit and the permeability of the material. Results showed that the most sensitive parameters for the assessment of raspberry decay were percentage of damaged berries, weight loss, fruit softening and the aromatic profile development, evaluated by an electronic nose; these parameters showed significant changes during storage and were influenced by the packing material. All samples showed a clear loss of firmness after 4 days of storage, which was maximally reduced in the case of LDPE/EVOH/LDPE and PLA packages. Raspberries stored in PVC packaging material had an aromatic development similar to the control, whereas berries stored in the medium and high barrier materials showed important changes in the aromatic profile, reflecting anaerobic metabolism of fruit. Soluble solids, pH, total phenolics and ascorbic acid did not change significantly; changes in colour and total anthocyanins were observed, with differences depending on the kind of packaging. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Red raspberry fruit (Rubus idaeus L.) are grown in all continents and mainly cultivated in Eastern Europe and in the USA, with a world production which is continuously increasing. These fruit, as well as other small red fruit, are increasingly appreciated by the consumers for their high sensory quality and their nutritional value, being rich in nutrients with health-promoting effects, in particular vitamin C and polyphenolic compounds such as ellagic acid and anthocyanins (Beekwilder et al., 2005; Sariburun et al., 2010). The high concentrations of these components contributes to their high antioxidant activity (Borges et al., 2010; Sariburun et al., 2010) and is related to the beneficial role in the prevention of chronic disease and some forms of cancer (Beattie et al., 2005; Ross et al., 2007; Seeram, 2008). The postharvest life of red raspberries is limited to a few days (generally 2–3 days from picking), mainly because of loss

∗ Corresponding author. Tel.: +39 0250319182; fax: +39 0250319190. E-mail address: [email protected] (G. Giovanelli). http://dx.doi.org/10.1016/j.postharvbio.2014.07.002 0925-5214/© 2014 Elsevier B.V. All rights reserved.

of firmness and susceptibility to fruit rot (Khanizadeh et al., 2009). This is due to their high respiration rate compared to other kind of fruit (Haffner et al., 2002) and to their structural fragility. Therefore, in Europe, fresh fruit are mainly consumed locally and are available only in the ripening season, generally from June to September. Some studies have investigated the effects of ripening degree and storage temperature and conditions, including controlled atmosphere, on the storage quality of red raspberries (Wang and Lin, 2000; Haffner et al., 2002; Siro et al., 2006; Kruger et al., 2011; Piljac-Zegarac and Samec, 2011). These studies demonstrated the effectiveness of storage under low O2 (from 3 to 10%) and high CO2 (from 5 to 30%) controlled atmosphere for the extension of raspberry shelf-life, but external systems for the modification of the storage gas composition were required. Modification of the local atmosphere might be obtained by the use of plastic packaging materials with specific gas permeability, achieving similar results in a simpler and more economical way. The aim of our research was to evaluate the effects of some packaging solutions for the shelf-life extension of raspberries. The objective of packaging operations is to slow the respiration and

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Table 1 Packaging materials used in the research and their main characteristics. Sample

Code

Package material

Characteristics

Control

Control

Master-bag in coextruded LDPE/EVOH/LDPE (high barrier) Master-bag in LDPE (low barrier)

HB-Mb

Lid: 14.3 × 3 × 9.5 cm Tray: 13.5 × 3 × 9 cm OTR* = 7 cm3 m−2 24 h−1

LB-Mb

Master-bag in PLA (medium barrier)

PLA-Mb

PVC wrapping film micro perforated

PVC

Oxygen absorber (Freshpax CR8® )

O2 abs

Rigid tray with lid in PET with macro-holes Master-bag (50 × 30 cm), containing 3 trays of berries Master-bag (50 × 30 cm), containing 3 trays of berries Master-bag (30 × 20 cm), containing 2 trays of berries Single tray of berries wrapped with the PVC stretch film Iron based, self-activated scavenger. Single bag in laminated material

* **

OTR* = 4500 cm3 m−2 24 h−1 OTR** = 400 cm3 m−2 24 h−1 Laser micro perforated Density: 1 pore/2.86 cm2 Pore diameter: 152.4 ␮m Scavenger capacity: 800 cm3

OTR: oxygen transmission rate at 23 ◦ C, 0% RH, 1 bar O2 . OTR: oxygen transmission rate at 23 ◦ C, 80% RH, 1 bar O2 .

transpiration of the fruit, thus altering the natural process of ripening and senescence. To reduce respiration rates and retard softening and physiological changes in the product, passive and active atmospheres were used in this study. The term “passive” stands for the modification of atmospheric composition around the product due to the combination of respiration rate and gas permeability of the packaging film. The term “active” means that the modification in gaseous composition is due to a combined effect of the film and of gas scavenging or emitting systems, able to accelerate gas changes. For this purpose, fruit belonging to the ‘Erika’ cultivar, typically grown in Northern Italy, were picked at the commercial ripening stage and packed using low, medium and high permeability materials, using a master-bag solution, and with a micro-perforated PVC film. The combined use of an oxygen absorber (active packaging) was also tested with low and high permeability materials. Fruit were stored at +4 ◦ C for 7 days and main quality parameters (physico-chemical and instrumental sensory characteristics) were monitored during the storage period. 2. Materials and methods 2.1. Fruit Red raspberries (R. idaeus L.) cv. Erika (ripening period September–October) were provided by Sant’Orsola (Pergine Valsugana, TN, Italy), an organization of producers in the cultivation and distribution of small red fruit. Berries were picked at the commercial ripening stage, packed in lidded PET macro-perforated trays (capacity 125 g), and transferred to the laboratory in the early morning of the subsequent day. At the laboratory, fruit were immediately sorted to eliminate damaged or rotten berries and packed using the various treatments tested in the research. 2.2. Packaging and storage For each trial, sound berries were put in new PET trays (capacity 125 g), weighted and coded, and packed using a master-bag treatment, made of plastic materials with different permeabilities to oxygen and carbon dioxide (high, medium and low barrier), as reported in Table 1. In some cases, an iron-based oxygen scavenger sachet (Freshpax CR8® ) was added to the headspace of the masterbag. A micro-perforated PVC film wrapped around individual trays without the lid was also considered as a packaging treatment. The control sample consisted of the PET lidded tray; due to the presence of a number of macro-holes, this package does not provide any gas barrier effect.

To compare the effect of a number of packaging materials, two trials were carried out on two lots of fresh raspberries; the details of the trials are given in Table 2. In trial 1, master-bags with high and low oxygen permeability were tested (HB-Mb and LB-Mb, respectively), with and without oxygen absorbers in the bag. Each HB-Mb and LB-Mb contained three trays of berries. In trial 2, a masterbag made of polylactic acid film with an intermediate OTR value was considered (PLA-Mb) together with a micro-perforated PVC film (PVC). Each PLA-Mb contained two trays of berries, whereas the PVC film was wrapped around a single tray. In both trials, the lidded PET macro-perforated rigid trays were used as controls. All samples were stored in a dark cold room at +4 ◦ C (±0.5 ◦ C), with no atmosphere and relative humidity control. For all trials, sampling and analyses were performed at 0, 2, 4 and 7 days of storage. In this way, a range of materials were evaluated in their ability to modulate or reduce the oxygen and carbon dioxide transmission through the bag during storage. The gas changes inside the packages during storage were monitored by means of a gas checking system (Mocon, Pac Check Model 333, Minneapolis, MN, USA).

2.3. Respiration rate Apparent respiration rate of the raspberries was measured at 5 ◦ C using the closed system method as reported by Kang and Lee (1997). The measurements were carried out in triplicate on fresh raspberries used in trial 1. Raspberries and the jars were equilibrated for 1 h at 5 ◦ C. Samples of about 100 g were then placed in air in 0.5 L glass jars and tightly covered with metal caps equipped with silicone sampling ports. Headspace gas was sampled at 1 h intervals for 12 h by means of a gas-tight syringe. Oxygen and carbon dioxide were detected and quantified by a gas chromatograph (Hewlett-Packard HP 5890 series II) equipped with a thermoconductivity detector and a steel column (2 m × 6 mm, CTR I Alltech, Milano), until the CO2 level inside the jars reached 5% (10–12 h). Respiration rate was calculated from the linear regression of O2 and CO2 concentrations measured during the first 5 h of the experiment, which corresponded to a linear evolution; data were expressed as mg kg−1 h−1 .

Table 2 List of packages used in the two storage trials. Trial no.

Raspberry cv.

Packaging material

1

Erika

2

Erika

Control; HB-Mb + O2 abs; HB-Mb; LB-Mb + O2 abs; LB-Mb Control; PLA-Mb; PVC

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2.4. Chemical and physical analyses Two master-bags (HB-Mb, LB-Mb and PLA-Mb, corresponding to 4–6 trays) and four individual trays (control and PVC) for each sample were taken from the cold room and used for analytical determinations. The gas composition was first measured in every master-bag or individual tray, then each tray was weighed using a technical balance. Weight loss was determined gravimetrically, as the difference in weight at time zero and at each sampling time. Data were expressed percentage of weight loss as mean value of 4–6 trays. Damaged berries (both physically damaged and mouldy berries) were visually estimated at each sampling time and results were expressed as percentage of sound berries (no. sound berries/no. total berries %), obtained as the mean value of 4–6 trays. The damaged berries were discarded. Colour of berries was measured on 20 fruit randomly chosen from all trays by Tristimulus colorimeter (Minolta, Tokyo, Japan). L*, a* and b* colour coordinates and a*/b* colour index were obtained and results were expressed as mean values of the twenty measurements. For each sample, 15 berries for aroma evaluation and 10 berries for firmness determination were set aside. The remaining berries were homogenized by a food blender (Black & Decker, Hunt Valley, MD, USA). The following analytical determinations were carried out on the homogenate: total solids were determined in triplicate by drying to constant weight at 70 ◦ C under vacuum according to AOAC 37.1.12 (1995); soluble solids were determined by digital refractometer (ATAGO DBX-55, Tokyo, Japan) in triplicate; pH was determined by pHmeter (pH M62, Standard Radiometer, Copenhangen, DK), in duplicate. Ascorbic acid was determined by HPLC analysis and electrochemical detection: 4 g of homogenate were extracted with 16 mL of diluted metaphosphoric acid (0.001%), which was prepared daily. The mixture was stirred for 20 min and centrifuged at 11,000 × g for 10 min at 10 ◦ C. The clear supernatant was injected in the HPLC apparatus and the analysis was performed as reported by Mannino and Pagliarini (1988). This analysis was carried out in triplicate. Total phenolics, total anthocyanins and the antioxidant activity were determined on the methanolic extract obtained as reported by Kalt et al. (2001): briefly, 5 g of homogenate were weighted in a centrifuge tube and added with 15 mL of acidic methanol (methanol: HCl 99:1 v/v). The mixture was stirred for 1 h in the dark and centrifuged at 11,000 × g for 10 min at 10 ◦ C. The solids were extracted two more times using 15 and 10 mL of the extraction solvent for 15 min with shaking in the dark, and centrifuged in the above-described conditions. Finally, the extracts were made up to 50 mL with acidic methanol. Total phenolics were determined on the extract by the Folin–Ciocalteau method (Singleton and Rossi, 1965) and expressed as mg gallic acid equivalents (GAE)/100 g, by comparison with a calibration curve built with the pure standard compound. Total monomeric anthocyanins were determined by the differential pH method (Giusti and Wrolstad, 2000) and data were expressed as mg cyanidin-3-glucoside equivalents (CYE)/100 g, using a molar absorbance coefficient ε = 26,900. The antioxidant activity was evaluated by ferric reducing capacity assay (FRAP), as described by Aaby et al. (2004), and was expressed as mmol trolox equivalents (TE)/g. Each extract was produced in duplicate and determinations of total phenolics, total monomeric anthocyanins and antioxidant activity were performed in duplicate on every extract, so that the mean values for these parameters are derived from four data points. Firmness of raspberries was determined with a Texture Analyser (TXT, Stable Micro System, Godalming, UK) by single compression test on single berries. Ten berries were evaluated each time. Each berry was positioned under the probe plate (45 mm diameter) and compressed to 80% deformation using a load cell of 1 kg

Table 3 Analytical characteristics (mean value ± standard deviation)a of fresh raspberries used in the two trials.

Soluble solids (g/100 g) Total solids (g/100 g) pH Colour L* a* b* Ascorbic acid (mg/100 g) Total phenolics (GAE mg/100 g) Total anthocyanins (CYE mg/100 g) Antioxidant activity (TE mmol/100 g) a

Trial 1

Trial 2

9.2 ± 0.1 13.5 ± 0.3 3.03 ± 0.01

10.2 ± 0.2 14.1 ± 0.1 3.03 ± 0.01

32.5 24.9 11.6 20.1 270 22.7 2.4

± ± ± ± ± ± ±

1.5 2.4 2.5 0.4 41 2.9 0.1

33.9 25.4 11.9 17.0 219 23.4 2.1

± ± ± ± ± ± ±

2.1 2.4 2.3 0.4 6 1.3 0.1

Number of replicates is given in Section 2.

(10 N), at 2 mm s−1 test speed. Firmness of samples was evaluated as energy at 40% deformation (N mm), which corresponds to the force needed to compress the berries at 40% of initial height. Results are expressed as mean values of the 10 determinations. 2.5. Electronic nose analysis Aromatic profile was evaluated by a Portable Electronic Nose (PEN2) from Win Muster Airsense (WMA) Analytics Inc. (Schwerin, Germany). It consists of a sampling apparatus, a detector unit containing the sensor array, and a pattern recognition software (Win Muster v. 3.0) for data recording and elaboration. The sensor array is composed of 10 Metal Oxide Semiconductor (MOS) type chemical sensors: W1C (aromatic compounds), W5S (broadrange compounds, polar compounds, nitrogen oxides and ozone), W3C (ammonia, aromatic compounds, aldehydes, ketones),W6S (broad-range compounds), W5C (alkanes, aromatic compounds, less polar compounds), W1S (methane, broad-range compounds), W1W (terpenes and sulphur organic compounds), W2S (alcohols, partially aromatic compounds, ketones), W2W (aromatic compounds, sulphur organic compounds) and W3S (broad-range compounds methane). The sensor response is expressed as resistivity (). Five berries (corresponding to 25 ± 1 g) were placed in a 100 mL Pyrex® vial provided with a pierceable Silicon/Teflon disk in the cap. After 30 min of equilibration at 30 ◦ C ± 1, the measurement started and the sample headspace was pumped over the sensor surfaces for 60 s (injection time) at a flow rate of 300 mL min−1 , during this time the sensor signals were recorded. After sample analysis, the system was purged for 180 s with filtered air prior to the next sample injection to allow reestablishment of the base line. All samples were analysed in triplicate and the average of the sensor responses was used for subsequent statistical analysis. 2.6. Statistical analysis Data were statistically evaluated by one-way ANOVA and multiple range test (LSD method) to put in evidence significant differences among treatments, using Statgraphics Plus v. 5.1 package. E-nose responses and pooled analytical data were treated by Principal Component Analysis (PCA) using Minitab16 software package. 3. Results and discussion The analytical parameters of the two lots of raspberries cv. Erika at harvest are reported in Table 3. Since they were obtained by the same producer at analogue maturity stage, the two lots showed similar physico-chemical characteristics. Values for total solids (13.5–14.1 g/100 g), soluble solids (9.2–10.2 g/100 g), pH (3.3) and ascorbic acid (17–20 mg/100 g) are in agreement with data reported

2.43 b 2.33 bB 2.48 bBC 2.05 aA 2.43 b 1.93 aA 2.75 cC 2.37 bB 2.43 a 2.39 aB 2.41 aB 2.46 aBC 2.43 a 2.42 aB 2.42 aB 2.44 aBC 2.43 b 2.43 bB 2.11 aA 2.63 bC All data are expressed as mean values of replicated measurements, as detailed in Section 2. Different lowercase letters in the same column indicate significant difference as obtained by multiple range test, at P ≤ 0.05%. Different capital letters in the same row for each parameter indicate significant difference as obtained by multiple range test, at P ≤ 0.05%.

20.1 d 15.3 aB 18.9 cB 18.1 bB 20.1 c 14.2 aA 17.8 bA 17.6 bAB 20.1 c 21.7 dD 19.3 bB 16.2 aA 20.1 c 16.3 aC 18.9 bB 18.2 bB 20.1 c 15.6 aBC 18.9 bB 21.3 dC 22.7 a 28.3 bB 31.4 cAB 26.1 bA 22.7 a 24.4 aA 30.5 bA 32.0 bB 22.7 a 27.6 bB 31.0 cAB 35.6 dC

HB-Mb HB-Mb + O2 abs LB-Mb LB-Mb + O2 abs

22.7 a 32.0 bC 33.0 bB 34.6 cBC 22.7 a 32.6 bC 32.0 bAB 39.8 cD 0 2 4 7

HB-Mb LB-Mb LB-Mb + O2 abs C HB-Mb HB-Mb + O2 abs LB-Mb C

LB-Mb + O2 abs

Ascorbic acid (mg/100 g)

C

Total anthocyanins (mg/100 g) Time (days)

0 2 4 7

Time(days)

Antioxidant activity (TE mmol/100 g)

HB-Mb + O2 abs

2.21 a 2.33 abA 2.45 bA 2.32 abA 2.21 a 2.35 aA 2.66 aA 2.37 aA 2.21 a 2.42 abA 2.53 bA 2.50 abA 2.21 a 2.37 abA 2.59 bA 2.58 bA 2.21 a 2.48 abA 2.64 b 2.45 ab 32.5 b 32.30abBC 31.7 abBC 31.4 aA 32.5 ab 33.1 bC 32.3 abC 31.4 aA 32.5 b 30.9 aA 31.4 aABC 31.5 aA

HB-Mb HB-Mb + O2 abs LB-Mb LB-Mb + O2 abs

32.5 b 30.8 aA 30.9 aAB 31.0 aA

LB-Mb LB-Mb + O2 abs a*/b*

C

L*

C

32.5 b 31.4 aB 30.8 aA 31.1 aA

HB-Mb + O2 abs

HB-Mb

14.1 b 10.4 aA 9.5 aAB 9.4 aB 14.1 b 10.4 aA 11.3 aB 9.7 aB

HB-Mb + O2 abs LB-Mb

14.1 c 12.2 bcA 10.2 abB 9.4 aB 14.1 b 10.2 aA 10.4 aB 9.5 aB

LB-Mb + O2 abs C

14.1 c 11.3 bA 8.4 aA 6.7 aA – 0.01 aA 0.25 bA 0.50 cA

HB-Mb HB-Mb + O2 abs

– 0.28 bB 0.26 bA 0.50 cA – 0.20 bB 0.31 bAB 0.57 cA

LB-Mb LB-Mb + O2 abs

– 0.28 bB 0.33 bB 0.81 cB – 1.48 bC 3.49 bcC 4.90 cC

C

100 b 97 bA 98 bB 84 aA

HB-Mb HB-Mb + O2 abs

100 b 96 bA 95 bB 78 aA 100 b 99 bA 82 aAB 80 aA

LB-Mb LB-Mb + O2 abs

100 b 97 bA 92 aB 79 aA

C

75

100 b 94 bA 65 aA 66 aA 0 2 4 7

Firmness (N mm) Weight loss (%) Sound berries (%) Time (days)

Table 4 Changes in raspberry characteristics during storage in the various packaging conditions in trial 1.

for other raspberry cultivars (Haffner et al., 2002; Pantelidis et al., 2007; Khanizadeh et al., 2009). With regard to total phenolics and total anthocyanins, the concentrations detected in the two lots are similar to those detected in raspberries from Eastern Europe (PiljacZegarac and Samec, 2011; Pantelidis et al., 2007) and generally lower than those reported in the literature for other red raspberry cultivars (Haffner et al., 2002; Khanizadeh et al., 2009; Sariburun et al., 2010; Chen et al., 2013). The antioxidant activity was higher in raspberries used in trial 1, in agreement with their higher total phenolic and ascorbic acid concentrations. The respiration rate was determined on the fresh fruit at 5 ◦ C and values obtained were RRO2 = 26.3 mg O2 kg−1 h−1 and RRCO2 = 43.9 mg CO2 kg−1 h−1 . In general, high respiration rates are associated with poor quality after harvest: the respiration rate determined on raspberries was relatively high, the carbon dioxide production being higher than 40 mg kg−1 h−1 , with a high respiratory quotient (RRCO2 /RRO2 = 1.67). Fig. 1 shows the changes in O2 and CO2 in the packages during storage of raspberries in trials 1 and 2. Points represent the average value obtained from two master-bags (HB-Mb, LB-Mb), three master-bags (PLA-Mb) and four wrapped trays (PVC); the relative standard deviation was always lower than 5%. Differences in the barrier effect of the various packages are clearly demonstrated, as well as the effect of the oxygen absorber. A decrease in oxygen concentration, due to fruit respiration, was recorded in all packages, except for the micro-perforated PVC film which exerted no barrier effect. Without an oxygen absorber, a similar decrease in O2 concentration was observed in all packages (HB-Mb, and PLA-Mb) at 2 days of storage, when residual oxygen was about 9%; at 4 days of storage, HB-Mb and PLA-Mb showed a residual O2 concentration close to 1%, whereas 4.5% oxygen was detected in LB-Mb. The presence of an oxygen absorber produced a faster decrease in oxygen concentration at the 2nd day (nearly 5% residual O2 in both HB and LB materials). At the end of the storage period, oxygen concentration was negligible in HB-Mb (with and without O2 abs), in LB-Mb + O2 abs and PLA-Mb, whereas 8.5% O2 was still detected in LB-Mb. Concurrently, the amount of CO2 increased during time, because of the intense respiration activity of raspberries. Again, the PVC package did not provide any barrier effect and CO2 concentration remained always very low. Increase in CO2 was almost linear in HB material with and without O2 abs and in PLA package, reaching final concentrations of about 30%. LB-Mb allowed some exchange with the external atmosphere and in this case, differences due to the presence of the oxygen absorber could be seen at all storage times. CO2 concentration was higher in the absence of an O2 absorber, because more oxygen was available for respiration of the fruit. An equilibrium of CO2 concentration was obtained after 4 days in LB-Mb with and without oxygen absorber (8% and 11%, respectively). It is known from the literature that low O2 and increased CO2 concentrations can retard mould growth and extend the shelf-life of raspberries (Haffner et al., 2002), even if these conditions can promote fermentation (Joles et al., 1994; Agar and Streif, 1996). The most representative analytical data of raspberries during storage are reported in Table 4 (trial 1) and in Table 5 (trial 2). After 4 days, percentage of sound berries was significantly higher in HB-Mb and LB-Mb packages with and without oxygen absorber (Table 4) and in PLA-Mb (Table 5) with respect to control samples; after 7 days, percentage sound berries was still higher in packaged samples, though differences with respect to the control were not statistically significant (95% confidence level). Wrapping in PVC film did not improve this parameter (Table 5). Research studies evaluated quality of red raspberries stored at 7 ◦ C for 7 days or more in normal and controlled atmosphere with high CO2 (15 and 31%) and low O2 (10%) concentrations (Haffner et al., 2002), and equilibrium modified atmosphere (approximately 10% O2 and 15%

HB-Mb

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G. Giovanelli et al. / Postharvest Biology and Technology 98 (2014) 72–81

A

25

B

35 30

20

HB-Mb + O2 abs

15

% CO2

% O2

25

10

LB-Mb + O2 abs

15

LB-Mb PLA-Mb

10

5 0

HB-Mb

20

PVC

5 2

0

4

6

0

8

0

2

4

Time (days)

6

8

Time (days)

Fig. 1. Changes in O2 and CO2 concentrations in the packages during storage of raspberries.

Table 5 Changes in raspberry characteristics during storage in the various packaging conditions in trial 2. Sound berries (%)

Time (days) 0 2 4 7

Weight loss (%)

Firmness (N mm)

L*

a*/b*

C

PVC

PLA-Mb

C

PVC

PLA-Mb

C

PVC

PLA-Mb

C

PVC

PLA-Mb

C

PVC

PLA-Mb

100 b 71 aA 74 aA 69 aA

100 c 83 bAB 68 aA 69 aA

100 c 90 bB 84 abB 78 aA

– 1.31 bB 2.97 cB 4.64 dB

– 0.56 bA 1.41 cA 2.23 dA

– 0.54 bA 1.24 bA 2.13 cBA

13.5 c 10.2 bA 8.5 abA 6.9 aA

13.5 b 8.9 aA 9.2 aA 7.3 aA

13.5 b 10.7 aA 10.8 aB 9.5 aB

33.9 b 32.8 abA 31.8 aA 32.9 bB

33.9 b 32.5 aA 32.4 aAB 31.7 aA

33.9 a 33.0 aA 33.0 aB 33.1 aB

2.19 a 2.55 bA 2.69 bB 2.68 bB

2.19 a 2.52 bA 2.63 bcB 2.75 cB

2.19 a 2.41 bA 2.47 bA 2.34 abA

Total anthocyanins (mg/100 g)

Time (days) 0 2 4 7

Ascorbic acid (mg/100 g)

Antioxidant activity (TE mmol/100 g)

C

PVC

PLA-Mb

C

PVC

PLA-Mb

C

PVC

PLA-Mb

23.4 a 32.9 bA 38.9 cB 40.9 dB

23.4 a 35.2 bC 41.1 dC 39.0 cB

23.4 a 27.4 bA 30.7 cA 22.3 aA

17.0 ab 17.9 bA 19.0 bB 15.2 aA

17.0 a 20.4 bA 15.8 aA 15.8 aA

17.0 a 19.3 bA 18.0 abAB 16.6 aA

2.1 a 2.4 bA 2.7 cB 2.7 cA

2.1 a 2.6 bA 2.6 bB 3.0 cA

2.1 a 2.9 bB 2.2 aA 2.8 bA

All data are expressed as mean values of replicated measurements, as detailed in Section 2. Different lowercase letters in the same column indicate significant difference as obtained by multiple range test, at P ≤ 0.05%. Different capital letters in the same row for each parameter indicate significant difference as obtained by multiple range test, at P ≤ 0.05%.

CO2 ) (Siro et al., 2006), reporting that storage in controlled atmosphere suppressed rotting significantly. Weight loss progressively occurred in all samples and data clearly evidence the positive effect of the packaging, especially in the case of HB and LB materials. The presence of the oxygen adsorber did not affect or only marginally affected this parameter (Table 4). Considering trial 2 (Table 5), it can be observed that PLA and PVC packaging reduced weight loss to a lesser extent and in a similar way. Firmness of raspberries declined during storage in all conditions, and softening was the highest in the control sample, in both trials 1 and 2. The values of firmness

were greatly influenced by the variability in individual berries, and this did not allow to evidence statistically significant differences between treatments. In any case, it appears that raspberries stored in HB-Mb and LB-Mb were firmer than the control after 4 and 7 days, and that the presence of the O2 adsorber did not influence fruit softening (Table 4). The PVC film had no effect on the evolution of fruit texture, whereas raspberries packed in the PLA maintained a higher consistency throughout the storage time (Table 5). Fig. 2 represents the effects of all the packaging conditions on weight loss (A) and firmness decrease (B) of raspberries. For both

A

6

B 100 HB-Mb + O2 abs HB-Mb

4

Firmness (%)

% Weight loss

5

3 2

LB-Mb +O2 abs

80

LB-Mb PLA-Mb PVC

60

Control

1 0

0

2

4

Time (days)

6

8

40

0

2

4

6

Time (days)

Fig. 2. Weight loss (A) and firmness decrease (B) of raspberries during storage in the various packages.

8

G. Giovanelli et al. / Postharvest Biology and Technology 98 (2014) 72–81

A

77

3

Second Principal Component (20.5%)

HB-Mb +O2abs t3

2

HB-Mb t3 t0 HB-Mb t2

1

LB-Mb t1 LB-Mb +O2abs t1 C t1

0

LB-Mb t3 LB-Mb +O2abs t3 LB-Mb +O2abs t2

-1 HB-Mb t1

C t2

C t3 LB-Mb t2

HB-Mb +O2abs t1

-2 -5

B

HB-Mb +O2abs t2

-4

-3 -2 -1 0 1 First Principal Component (65.6%)

2

3

4

0,50

Second Principal Component (20.5%)

W5S

W2S

0,25

0,00

W1S

W1C W3C W5C W1W

-0,25 W6S W3S

-0,50

W2W

-0,4

-0,3

-0,2 -0,1 0,0 0,1 0,2 First Principal Component (65.6%)

0,3

0,4

Fig. 3. PCA-score plot (A) and loading plot (B) of electronic nose data of raspberries during storage in the various packages (trial 1).

parameters, results of the two control trials were averaged, since they had similar behaviour; to allow comparison of all the packaging solutions tested in trials 1 and 2, variations in firmness were expressed as percentage decrease. Weight loss is essentially due to respiration and water transpiration rates. Data demonstrate the high barrier effect of both HB and LB materials against water vapour: in fact weight loss after 7 days was limited to 0.5%. In the control samples weight loss was almost linear during storage and reached final 5%. An intermediate and similar barrier effect to water evaporation was observed in the PLA and PVC packages, with final weight loss of about 2% (Fig. 2A). It can be concluded that packaging materials with high barriers towards water vapour and gases establish a local environment with high relative humidity, low O2 and high CO2 concentrations, and all these factors slow down respiration and transpiration rates, thus limiting weight loss. Data in the literature report variable results for weight losses of raspberries during storage, from nearly 1% for 7 days at 1.7 ◦ C at 95% relative humidity in normal and controlled atmospheres (Haffner et al., 2002) to 7–9% after 3 days at 2–4 ◦ C at 85–90% relative humidity followed by 1 day at 20 ◦ C (Kruger et al.,

2011). Siro et al. (2006) detected 7% weight loss after 10 days of storage at 7 ◦ C in air, which was reduced to 0.5% in samples packaged in modified atmosphere using low barrier plastic films. This high variability may be due to the cultivar and the ripening degree of raspberries, even if storage conditions such as temperature and relative humidity seem to play a major role in weight loss. The decrease in the texture index was significantly slowed by packaging into the master-bag solutions (Fig. 2B); in particular, after 4 days the highest firmness was detected in PLA and HBMb with O2 absorber (80% of initial value) and after 7 days berries stored in PLA-Mb, HB-Mb and LB-Mb showed about 67% of initial firmness, whereas berries packed with PVC micro-perforated film and the control samples showed the highest loss in firmness (about 50% of initial value). The presence of the O2 absorber did not significantly affect the texture variation after 7 days, both in LB and HB materials. These results are particularly interesting, since softening of berries is one of the primary indexes of fruit decay (Haffner et al., 2002). Considering the antioxidant compounds, anthocyanins increased in all samples (Tables 4 and 5) during storage: the

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A 3 Second Principal Component (27.9%)

PLA-Mb t2

2 1

PVC t1

C t1

t0

PLA -Mb t1

0

PLA -Mb t3

PVC t2

C t2

-1 -2

PVC t3

C t3

-3 -3

-2

-1 0 1 2 First Principal Component (57.2%)

3

4

B W6S

Second Principal Component (27.9%)

0,50

W3S

W2S

0,25

W1S

W5S W1C W3C

0,00 W5C

-0,25 W1W W2W

-0,50 -0,5

-0,4

-0,3

-0,2 -0,1 0,0 0,1 0,2 First Principal Component (57.2%)

0,3

0,4

Fig. 4. PCA-score plot (A) and loading plot (B) of electronic nose data of raspberries during storage in the various packages (trial 2).

highest final concentrations were observed in the control samples (39.8 and 40.9 mg/100 g in trials 1 and 2, respectively) and the lowest in HB-Mb (26.1 mg/100 g) and PLA-Mb (22.3 mg/100 g). Ascorbic acid concentration decreased slightly but significantly in all samples, except for the control, in trial 1 (Table 4), with similar final values in HB and LB materials. Considering trial 2, no significant variations were detected during storage and between packages (Table 5). The antioxidant activity did not significantly change in trial 1 (Table 4); in trial 2 (Table 5), the antioxidant activity slightly increased, with no clear differences between the various packaging conditions. This result can be correlated with the significant increase in anthocyanin concentrations. Total phenolics did not show statistically significant variations during storage in both trials (data not shown). It is known that the antioxidant activity of raspberries depends on its ascorbic acid and polyphenolic content, and among the various polyphenolic components ellagitannins exhibit the highest antioxidant activity (Beekwilder et al., 2005). Our results on the changes in antioxidant constituents and antioxidant activity of raspberries during storage substantially confirm previous findings: literature studies show an increase in

anthocyanin concentration during storage of raspberries under various temperature and atmosphere conditions (Kruger et al., 2011; Piljac-Zegarac and Samec, 2011), whereas no significant changes (Kruger et al., 2011) or a slight increase (Piljac-Zegarac and Samec, 2011) were observed in total phenolic concentrations. With regard to ascorbic acid, a minor decrease (Agar et al., 1997) or substantial stability (Haffner et al., 2002; Kruger et al., 2011) was detected during postharvest life of raspberries. According to our results and to previous studies, the antioxidant compounds and the antioxidant activity of raspberries are substantially stable and little affected by the storage conditions; it appears rather that reactions taking place in the earliest postharvest period may facilitate the formation of compounds with antioxidant activity in raspberries, as well as in other fruit (Kevers et al., 2007). For all samples, colour changes were found: fruit became darker, with a deepening of the colour and a shift from light red to blue–red hue, as shown by a decrease in L* value and an increase in a*/b* colour index. Colour variation was less evident and in some cases non-significant in Hb-Mb packages, especially in the presence of

G. Giovanelli et al. / Postharvest Biology and Technology 98 (2014) 72–81

A

79

C

Second Principal Component (24.5%)

3

t0 t2 trial 1 t2 trial 2

C

PVC

2

1 LB-Mb

0

LB-Mb (+O2abs) t0 (trial 1)

-1

PLA-Mb

HB-Mb

t0 (trial 2)

-2 HB-Mb (+O2abs)

-3 -5.0

-2.5 0.0 2.5 First Principal Component (53.3%)

5.0

B weight loss

0.4 Second Principal Component (24.5%)

total anthocy anins

0.3

W5C

a/b

0.2 W3C

0.1

W2W

W1C

W1W

ascorbic acid antioxidant activ ity

0.0

W3S

-0.1

W6S

-0.2

L W1S

-0.3

W5S

firmness %

-0.4

W2S

sound berr ies %

-0.5 -0.4

-0.3

-0.2 -0.1 0.0 0.1 First Principal Component (53.3%)

0.2

0.3

Fig. 5. PCA-score plot (A) and loading plot (B) of electronic nose, chemical and physical data of raspberries stored for 4 days in the various packages (trials 1 and 2).

O2 absorber (Table 4), and in PLA-Mb (Table 5). Colour changes were in agreement with the evolution of anthocyanin concentrations, which showed lower variations in the case of Hb-Mb and PLA packages, and the variations observed are in accordance with results reported by other authors (Haffner et al., 2002; Kruger et al., 2011). Data about total and soluble solids are not shown, since only minor changes were observed: in trial 1, the weight loss in the control sample produced an increase in solid concentration (from 13.5 to 13.9 and from 9.2 to 10.3 for total and soluble solids, respectively), whereas statistically non-significant differences were detected in the other packaging solutions; in trial 2 non-significant differences were observed in these parameters. pH increased in all samples in trial 1, from starting value 3.02 to final values 3.11–3.20, whereas no differences were observed in trial 2 (data not shown). Other research on storage of fresh raspberries has reported similar results about the changes in total and soluble

solids and pH values (Haffner et al., 2002; Siro et al., 2006; Kruger et al., 2011). The aromatic profile analyses carried out on trial 1 and 2 are shown in Fig. 3 and in Fig. 4. In particular, Fig. 3 shows the score plot (A) and the loading plot (B) of the e-nose data collected on trial 1, in the plane defined by the first two Principal Component (explained variance: 86.1%). As it can be observed, the development of the aromatic profile was on the first Principal Component (PC1) from left to right (Fig. 3A); t0 sample, control sample (C) and LB-Mb samples (with and without oxygen absorber) stored for 2 days (t1) were located at the left of the plot and were characterized by WC sensors (Fig. 3B). Raspberries stored for 4 (t2) and 7 days (t3) were located at the right of the plot and were discriminated on the second Principal Component (PC2) on the basis of the packaging material (Fig. 3A). Control samples, LB-Mb samples (with and without oxygen absorber) stored for 4 and 7 days, and HB-Mb samples stored for 2 days were located in the negative part of PC2; their aromatic

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profile was characterized by WW sensors and by W3S and W6S sensors of broad range sensitivity (Fig. 3B). HB-Mb samples (with and without oxygen absorber) stored for 4 and 7 days were positioned in the positive part of PC2 and were discriminated by WS sensors (W1S, W2S and W5S) sensitive to volatile compounds typically produced by fermentative paths (Buratti et al., 2006, 2011) A similar trend can be observed from the score plot and the loading plot of trial 2 (Fig. 4) (explained variance: 85.1%). In this case, PLAMb samples moved rapidly from left to right along PC1 according to the storage time. After 4 (t2) and 7 days (t3) of storage, PLA-Mb samples were located in the positive part of PC2 (Fig. 4A), characterized by WS sensors (Fig. 4B), clearly separated from the Control and the PVC samples located in the negative part of PC2 and characterized by W1W and W2W sensors. The development of the aromatic profile of berries stored in the various packages is in accordance with other published work, reporting that the aroma of fresh vegetable products was perceived by WC sensors while WW and WS sensors were relevant in monitoring changes in the volatiles during shelf-life (Gomez et al., 2006, 2007; Benedetti et al., 2010). In order to compare the effects of the different packaging materials on the raspberry shelf-life, data obtained by e-nose and by the more significant chemical and physical parameters were jointly analysed by PCA; t0 and t2 (4 days of storage) samples were considered. Fig. 5 reports the score plot (A) and the loading plot (B) in the plane defined by the first two Principal Components (explained variance 77.8%). In the score plot (Fig. 5A), a clear separation between samples can be observed; moving from right to left along PC1, t0 samples, located in the negative part of PC1, were differentiated from t2 samples at the right of the plot; considering the loading plot (Fig. 5B) the electronic nose variables were dominant on the PC1 and were relevant in the discrimination between t0 and t2 samples. On the PC2 of score plot (Fig. 5A) samples were discriminated on the basis of the packaging materials. In particular, control (C) and PVC samples were located close to each other in the positive part of PC2, whereas samples packaged in the low, medium and high permeability materials were in the negative part of PC2. From the loading plot (Fig. 5B) it can be observed that raspberries stored for 4 days in the PET lidded tray (C) and in PET tray wrapped with micro perforated PVC film showed similar characteristics, with increased weight loss, higher total anthocyanin content and darker (a/b) colour, whereas they were negatively correlated to percentage of sound berries, firmness and lightness (L). Compared to control and PVC, the master-bag treatments (with and without oxygen absorber) ensured higher percentage of sound berries, less evident colour variation, higher firmness and lower weight loss. In particular, after 4 days of storage berries packaged in PLA-Mb and HB-Mb materials were similar to t0 samples in terms of colour, firmness, percentage of sound berries and weight loss, showing that a significant shelf-life extension was obtained, though the electronic nose pointed out a clear change in the aromatic profile towards volatile compounds typically produced by fermentative paths, especially in the case of Hb-Mb with oxygen absorber.

4. Conclusions Results obtained in this research showed that most sensitive parameters of raspberry quality decay, i.e. percentage of damaged berries, weight loss, softening and odour changes, were significantly influenced by the use of different packaging materials during shelf-life at 4 ◦ C. In particular, the use of high and medium barrier materials (HB-Mb and PLA) allowed retardation of over-ripening and perishability, thus extending postharvest life of raspberries. This can be primarily related to the low O2 and high CO2 concentrations which are produced in the package during storage. However, berries stored in these conditions showed changes in the

aromatic profile towards compounds typically produced in fermentative processes, especially in the presence of an oxygen absorber. Storage up to 7 days in the various conditions did not negatively affect the nutritional and antioxidant characteristics of raspberries, maintaining or even increasing their antioxidant activity. In particular, in the case of PLA, the good performance of the material is associated with its complete biodegradability, which makes it particularly interesting for food packaging applications.

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