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Effect of active-modified atmosphere packaging on the respiration rate and quality of pomegranate arils (cv. Wonderful)
Postharvest Biology and Technology 109 (2015) 97–105
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Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Effect of active-modified atmosphere packaging on the respiration rate and quality of pomegranate arils (cv. Wonderful) Kalenga Bandaa , Oluwafemi J. Caleba,b , Karin Jacobsc , Umezuruike Linus Oparaa,b,* a Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Horticultural Science, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa b Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Food Science, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa c Department of Microbiology, Faculty of Science, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa
A R T I C L E I N F O
A B S T R A C T
Article history: Received 2 February 2015 Received in revised form 3 June 2015 Accepted 6 June 2015 Available online xxx
Two experiments were conducted to investigate the effects of active- and passive-modified atmosphere packaging (MAP) on respiration rate (RR) and quality attributes of minimally processed pomegranate arils (cv. Wonderful) stored at 5 C for 12 d. In experiment 1, pomegranate arils were packaged in low barrier bi-axially oriented polyester (BOP) film under active-MA (5 kPa O2 + 10 kPa CO2, 30 kPa O2 + 40 kPa CO2), passive-MA and in clamshell trays. In experiment 2, a high barrier Polylid1 film was used with arils packaged under three active-MAs (5 kPa O2 + 10 kPa CO2 + 85 kPa N2; 30 kPa O2 + 10 kPa O2 + 60 kPa N2; 100 kPa N2) and passive-MA. Arils packed in clamshell trays had lowest RR (RCO2) compared to the other MA treatments in experiment 1, ranging from 41.1 nmol kg1 s1 on day 3 to 238.8 nmol kg1 s1 on day 12. Respiration rate of arils packaged in the high barrier polylid film was significantly affected by MA treatments. At the end of 12 d storage, total anthocyanin content (TAC) in arils was highest for clamshell packages (0.31 0.01 g L1) and lowest in passive-MAP (0.27 0.02 g L1). Packaging arils in high O2 atmosphere and 100 kPa N2 significantly lower aerobic mesophilic bacteria counts throughout the storage duration. Based on sensory scores obtained and microbial load, the shelf life for arils packaged in clamshell trays, passive-MA, and high O2 level MA was 6, 9 and 12 d, respectively. ã2015 Elsevier B.V. All rights reserved.
Keywords: Shelf life Respiration rate Anthocyanin Aerobic mesophilic bacteria Packaging
1. Introduction Modified atmosphere packaging (MAP) combined with low temperature storage has been successfully used to prolong the shelf life of fresh fruit and vegetables (Mahajan et al., 2014). Modified atmospheres are achieved by hermetically sealing fresh respiring produce in polymeric film and allowing the atmosphere within the package to be modified passively by the interplay of produce respiration rate (RR) and the film permeability properties, or actively by flushing the desired gas mixtures inside a package before sealing (Kader and Watkins, 2000; Rico et al., 2007; Mangaraj et al., 2009). Modified atmosphere packaging slows down physiological and biochemical processes and retards senescence (Caleb et al., 2012a). Thereby maintaining packaged produce freshness, quality attributes and microbial safety. Failure
* Corresponding author at: Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Horticultural Science, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa. Fax: +27 21 808 3743. E-mail address: [email protected] (U.L. Opara). http://dx.doi.org/10.1016/j.postharvbio.2015.06.002 0925-5214/ ã 2015 Elsevier B.V. All rights reserved.
to create this suitable atmosphere may result in a shortened shelf life (Mangaraj et al., 2009). Suitable equilibrium atmospheres are achieved by proper matching of fresh produce RR and film permeability characteristics (Jacxsens et al., 2002; Kader, 2002; Caleb et al., 2012a). Desired atmospheric equilibrium/compositions inside packaged fresh produce are low oxygen (O2) (2–5 kPa) and/or moderate carbon dioxide (CO2) (10 kPa) (Rico et al., 2007; Sandhya, 2010). Previous studies have reported on the RR of minimally processing pomegranate arils under different conditions (Ersan et al., 2010; Caleb et al., 2012b). Ayhan and Estürk (2009) reported an increase in antioxidant activity and lower mesophilic bacteria counts in minimally processed pomegranate arils (cv. Hicaznar) stored under super atmospheric O2 (70 kPa) atmospheres compared to those stored under low O2 (5 kPa) and in normal air at 5 C. Super atmospheric O2 atmospheres (>21 kPa) have also been used in MAP of minimally processed products because of their ability to prevent anaerobic fermentation, inhibit enzymatic discolouration and microbial growth (Jacxsens et al., 2001). O2 concentrations >25 kPa are nonetheless considered highly explosive and, as they pose a hazard should be used with caution (Jacxsens et al., 2001).
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Nitrogen (N2) is a non-reactive gas that is used to exclude more reactive gases from packages and acts as a filler gas to prevent package collapse (Brandenburg and Zagory, 2009). Several studies with minimally processed products have explored the use of 100 kPa N2 atmospheres in MAP (Ayhan and Estürk, 2009; Ahmed et al., 2011) because of their ability to maintain fresh produce quality. Firmness, colour and chemical properties were maintained and shelf life extended in persimmon fruit packaged in 100 kPa N2, stored at 0 C and 85–95% relative humidity (RH) for 90 d (Ahmed et al., 2011). Similarly, fresh-cut cabbage and lettuce in packages initially flushed with 100 kPa N2 atmospheres at 1 and 5 C maintained their quality and appearance by the end of the 5 d storage period (Koseki and Itoh, 2002). Active-MAP achieved by flushing desired gas mixtures into packages allows earlier establishment of equilibrium atmospheres than passive-MAP and has, therefore, been recommended for minimally processed products (Bai et al., 2003; Rodov et al., 2007). Equilibrium atmospheres in active-MAP of litchi (cvs. Mauritius and McLeans Red) were established almost from the first day of storage, whereas those in passive-MAP were established 6–10 d after packaging (Sivakumar et al., 2008). Thus, the selection of packaging films with suitable barrier properties is of crucial importance in developing a suitable gas composition to maintain quality and assure a long shelf life for packaged fresh produce (Martínez-Romero et al., 2013). Despite the successful application of active-MAP in a wide range of minimally processed products, few studies have investigated the effects of active-MAP and the use of different barrier polymeric film on the physiological response and overall quality of minimally processed pomegranate arils. The objective of this study was, therefore, to determine the effects of different packaging atmospheres on respiration rate (RR), quality attributes and shelf life of minimally processed pomegranate arils (cv. Wonderful) packaged in low barrier bi-axially oriented polyester (BOP) and polylid film and stored at 5 C and 90 2% RH. 2. Materials and methods 2.1. Sample preparation and packaging Pomegranate fruit (cv. Wonderful) was harvested at commercially ripened stage with characteristic deep-red skin and deep-red arils with mature kernels (Mphahlele et al., 2015), from Houdconstant Farm, Porterville, Western Cape (33 0100000 S, 18 590 0000 E), South Africa. Fruits were sorted, cleaned and minimally processed at the farm pack house. Fruit free from visible physical defects were washed in sterilised water and arils extracted using a commercial extraction machine (Arilsystem, Juran Metal Works, Israel). Extracted arils were bulk packaged in sterilized polyethylene bags and transported in sterile ice boxes to the postharvest research laboratory at Stellenbosch University. Arils (300 g) were packaged in polyethylene terephthalate (PET) trays (ZIBO Containers, Pty, Ltd., Kuilsrivier, South Africa) and flushed with food grade gas mixtures (Air Products Pty, Kempton Park, South Africa) using a tray sealer (Model T200 Multivac, Wolfertschwenden, Germany). Two experiments were conducted consecutively. In the first experiment, a low barrier BOP polymeric film (with 26 mm thickness, permeance rate 3.5 1013 mol m2 s1 Pa1 O2, 7.0– 9.4 1014 mol m2 s1 Pa1 CO2 and 9.4 105 mol m2 s1 Pa1 water vapour at 23 C and 85% RH) supplied by Knilam Packaging (Pty) Ltd. (Cape Town, South Africa) was used to heat-seal the PET trays. The following gas mixtures were used: MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2); MAP-B (30 kPa O2 + 40 kPa CO2 + 30 kPa N2); MAP-C (normal atmospheric composition; passive-MAP). Additionally, arils were packaged in PET clamshell
containers (420 mm thickness, 11.5 11.5 3.5 cm3) as control. In the second experiment, a high barrier polymeric film Polylid1 107HB55 (with 55 mm thickness, permeance rate of 9.8– 10.8 1014 mol m2 s1 Pa1 O2, 7.0–9.4 1014 mol m2 s1 Pa1 CO2 and 2.4–3.3 105 mol m2 s1 Pa1 water vapour at 23 C and 85% RH) supplied by Barkai Polyon Industries Ltd. (Tel Aviv, Isreal) was used. The following gas mixtures were applied in the second study: MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2); MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2); MAP-F (100 kPa N2) and MAP-G (passive-MAP). All the samples were stored at 5 C and 90 2% RH for 12 d and analyses were conducted in triplicate on days 0, 3, 6, 9, and 12. 2.2. Headspace gas composition Headspace O2 and CO2 composition of packaged pomegranate arils was determined using an O2/CO2 gas analyser (Checkmate 3, PBI Dansensor, Ringstead, Denmark). Gas analysis was done by inserting a needle attached to the gas analyser through a rubber septum on the packaging film. Gas sampling was done before opening the package to remove the arils. Three additional replications per treatment were used to monitor in-package head space gas composition during the entire storage period. 2.3. Respiration rate Post-storage RR of pomegranate arils was determined using the closed system method at 5 C. On each sampling day, 150 g pomegranate arils from each of the MAP treatments were separately weighed into 1.1 L glass jars using a balance (Bosch SAE200, Denver Instrument GmbH, Germany). The glass jars were hermetically sealed by incorporating Vaseline petroleum jelly in the gap between the lid and the jar. Gas samples were drawn at hourly intervals over a period of 4 h through a rubber septum fitted on the jar and the gas composition was monitored by gas analyser (Checkmate 3, PBI Dansensor, Ringstead, Denmark). Measurements were repeated on each of the sampling days using fresh samples each time in order to determine the effect of modified MAP and storage duration on pomegranate arils RR (Fonseca et al., 2002; Bhatia et al., 2013). The RR was calculated by fitting experimentally obtained data in the following Eqs (1) and (2): yO2 ¼ yiO2
RO2 W ðt ti Þ Vf
yCO2 ¼ yiCO2 þ
RCO2 W ðt ti Þ Vf
(1)
(2)
where RO2 and RCO2 are the O2 consumption and CO2 production rate (RR); yiO2 and yO2 are O2 concentration (kPa) at the initial time t1 (s) (time zero) and at time t (s), respectively and yiCO2 and yCO2 are the CO2 concentration (kPa) at the initial time t1 (s) (time zero) and at time t (s), respectively. W is the total weight of product (kg) and Vf is the free volume inside jar (L); determined by subtracting volume of product from the total volume of the glass jar (Caleb et al., 2012b). RR values were expressed as nmol kg1 s1 (Banks et al., 1995). 2.4. Total soluble solids, titratable acidity and pH Arils were juiced separately for each of the treatments on each sampling day using a LiquaFresh juice extractor (Mellerware, Cape Town, South Africa). Pomegranate juice was used to determine pH using a pH metre (Crison, Barcelona, Spain), total soluble solids
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(TSS) expressed as percentage (%) using a digital refractometer (Atago, Tokyo, Japan). Titratable acidity (TA) measured by titration with 0.1 mol L1 NaOH to an end-point of pH 8.2 using a Metrohmn 862 compact titrosampler (Herisau, Switzerland). TA was expressed as gram of per litre of pomegranate juice (g L1) of citric acid. TSS:TA was calculated based on % ratio. All values are presented as mean standard deviation (SD). 2.5. Total anthocyanin concentration Total anthocyanin concentration (TAC) was quantified using the pH differential method with two buffer systems comprising of potassium chloride (pH 1, 0.025 mol L1) and sodium acetate (pH 4.5, 0.4 mol L1). The juice sample (1 mL) was mixed with 9 mL of pH 1 and pH 4.5 buffers, separately. The absorbance of the mixtures was measured at 520 and 700 nm using a UV–vis spectrophotometer (Thermo Fisher Scientific, Madison, MI, USA), after 10 min incubation of the mixture in a dark cabinet. TAC was expressed as cyanidin-3-glucoside (Cyd-3-glucoside) using the following equations: A = (A510–A700)pH 1.0 (A510–A700)pH 4.0 Total monomeric anthocyanin ¼
A MW DF eL
(3)
(4)
where A = absorbance (nm), e = 26,900 molar extinction coefficient, MW = molecular weight of Cyd-3-glucoside (449.2 g mol1), DF = dilution factor and L = cell path length (1 cm). Results were expressed gram Cyd-3-glucoside equivalent per litre of pomegranate juice (g L1) (Fawole et al., 2011). All analyses were carried out in triplicates (n = 3) and values are presented as mean SD.
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2.6. Microbial analysis Microbial quality of arils was screened on days 0, 6 and 12 of storage. Approximately 10 g of arils was weighed and put into 100 mL of physiological solution and shaken for 5 min. Furthermore, 3-fold dilutions were prepared using 1 mL of diluents into 9 mL of physiological solution. In order to enumerate microbial load, 1 mL of each dilution was pour-plated in triplicate onto appropriate media. Total aerobic mesophilic bacterial count was determined using plate count agar incubated at 30 C for 48 h, while yeast and mould counts were determined using potato dextrose agar and incubated at 26 C for 5 d. After incubation, the colonies grown on plates were counted (counts between 30 and 300 colonies), and the result was presented as log of colony forming units per gram (log CFU mL1). 2.7. Sensory evaluation Sensory evaluation of arils was done by a panel of 6 untrained judges who are regular consumers of pomegranate and are familiar with its quality attributes. Aril quality attributes, taste, off-odour, flavour, aroma and overall acceptability were scored on scale of 0–5. The score 0 corresponded to poor/none and 5 to excellent/ prominent. Scores below 3 were considered the cut-off point for quality attributes, taste, flavour, aroma and overall acceptability, while scores above 3 were used as indicators of the end of acceptable quality for off-odour. 2.8. Statistical analysis A factorial analysis of variance (ANOVA) was performed on experimental data at 95% confidence interval using Statistica software (Statistica 10.0, Statsoft Inc., USA). All values are
Fig. 1. Changes in headspace gas composition in minimally processed pomegranate arils packaged in PET trays and heat-sealed with different polymeric films stored at 5 C for 12 d: (A) changes in O2 and (B) CO2 (kPa) levels for low barrier BOP film and clamshell packages; (C) changes in O2 and (D) CO2 (kPa) levels in high barrier Polylid1 film. Error bars represent standard deviation (SD) of mean values (n = 3).
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presented as mean SD. All parameters were measured in triplicate (n = 3) for each treatment. 3. Results and discussion 3.1. Headspace gas composition In the first experiment with the lower barrier film, equilibrium O2 and CO2 levels were attained by day 3 in packaged arils across all MAP treatments (Fig. 1A and B). However, the steady state gas composition of O2 observed in this study (16–18 kPa) was above the recommended level of 2–5 kPa O2 (López-Rubira et al., 2005). This could be attributed to the high O2 transmission rate of the BOP film used in the study. CO2 levels attained were also slightly lower (7 kPa) than those recommended (10–20 kPa) for pomegranate arils (Hess-Pierce and Kader, 1997; Irtwange, 2006). In the second experiment, O2 decreased and CO2 increased continuously, across all the treatments regardless of MAP treatment (Fig. 1). O2 levels in packages flushed with low O2 (2 kPa O2 + 10 kPa CO2 + 85 kPa N2) went below the critical limit of 2 kPa by day 12 (Fig. 1C), a condition that is known to be ideal for occurrence of anaerobic respiration (Gorny, 2003; Artés et al., 2006). Carbon dioxide levels also accumulated (27–43 kPa) beyond levels recommended for MAP of pomegranate arils across all MAP treatments (Fig. 1D). CO2 is soluble at high concentrations and low temperatures forming carbonic acid which has bacteriostatic effects on tissues of fresh-cut produce. On the other hand, accumulation of carbon acid causes changes in organoleptic properties of some minimally processed products (Sandhya, 2010). The barrier films used in both experiments did not create suitable equilibrium O2 and CO2 levels for pomegranate arils. 3.2. Respiration rate Modified atmospheres, storage duration and their interaction had significant effects (P < 0.05) on RR of pomegranate arils packaged in the low barrier BOP film and clamshell trays in experiment 1 (Fig. 2A). Furthermore, RR (RCO2) of arils reduced initially with increase in storage duration from 89.9 nmol kg1 s1 on day 0 to a range of 41.1–95.0 nmol kg1 s1 on day 3 across the treatments, and then increased significantly (P < 0.05) from day 3 until the end of the storage period. Arils packed in clamshell trays maintained the lowest RR throughout the storage duration, ranging from 41.1 nmol kg1 s1 on day 3 to 238.8 nmol kg1 s1 on day 12. In experiment 1, arils packaged under passive-MAP (MAP-C) had the highest RR value (RCO2) of 338.9 27.8 nmol kg1 s1. The RR (RCO2) of arils packed in the high barrier film Polylid1 was generally higher (from 138.6 nmol kg1 s1 on day 3 to 984.8 nmol kg1 s1 on day 12) than those of low barrier film experiment (Fig. 2B). This may be attributed to differences in headspace gas composition created inside the barrier films. Aril RR response was similar to those reported by Bhatia et al. (2013), for minimally processed ‘Mridula’ pomegranate arils under MAP at 5 C for 15 d. The authors reported a progressive increase in RR (RCO2) of arils during the storage duration, ranging from 311.4 nmol kg1 s1 to 979.1 nmol kg1 s1 at the end of storage period. Similarly, in experiment 2 the RR of arils in our study increased throughout the storage duration across all the treatments. By day 3, RR (RCO2) of arils in MAP-F (100 kPa N2) and MAP-G (passive) was 138.6 13.3 nmol kg1 s1 and 148.8 4.3 nmol kg1 s1, respectively, and this was significantly lower than in the other MA treatments. Arils packed in 100 kPa N2 maintained significantly lowest RRs than the other MAP treatments from day 6 (214.8 6.9 nmol kg1 s1) to day 12
Fig. 2. Respiration rate (RCO2) of minimally processed pomegranate arils packaged under passive- and active-modified atmospheres and stored at 5 C for 12 d in: (A) low barrier BOP film and clamshell packages and (B) high barrier Polylid1 film. Error bars represent standard deviation (SD) of mean values (n = 3).
(588.8 12.5 nmol kg1 s1). The low RRs could be attributed to the low levels of O2 maintained in the 100 kPa N2 packages compared to the other MAP treatments (Fig. 1C). Other studies have shown that MAPs with low O2 (2–5 kPa) and high CO2 (10–20 kPa) levels reduced RR of minimally processed fresh produce (Gorny, 2003; Rattanapanone et al., 2001). Ersan et al. (2010) investigated the effects of varying combinations of O2 (2, 10 and 21 kPa) and CO2 (0, 10 and 20 kPa) concentrations on RR of minimally processed pomegranate arils (cv. Hicaznar) stored at 4 C. The studies revealed that combinations of low O2 2 kPa and high CO2 10 kPa significantly reduced RRs (6.1 nmol kg1 s1) of arils. The experimental setup used by Ersan et al. (2010) was different from the one reported in this study, the authors did not measure RR of packaged arils on sampling day. The use of high O2 atmospheres (>21 kPa) has been suggested as an alternative to low O2 in order to prevent anaerobic respiration (Jacxsens et al., 2001). However, respiratory response to high O2 atmospheres varies in different products (Kader and Ben-Yehoshua, 2000). High O2 atmospheres (100 kPa O2; 95 kPa O2 + 5 kPa CO2; 80 kPa O2 + 20 kPa CO2; 75 kPa O2 + 25 kPa CO2) significantly reduced RR of fresh-cut onions stored at room temperature for 9 d (Chunyang et al., 2010). In contrast, Maghoumi et al. (2013) reported an increase in RR within the range of 17.7–23.0 nmol kg1 s1 for minimally processed pomegranate arils (cv. Molar de Elche) packaged under high oxygen atmospheres (90 kPa O2) compared to those under passive MAP at 5 C. The authors suggested that high O2 levels enhanced the production of reactive O2 species and caused respiratory stress leading to increased aril RR. This consistent with the arils RR observed in this study, although RR obtained are higher than those reported by Maghoumi et al. (2013).
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3.3. Total soluble solids (TSS), titratable acidity (TA) and pH MAP had no significant effects (P > 0.05) on chemical attributes of minimally processed arils in both experiments 1 and 2, except for TSS in arils packaged in low barrier BOP film. Initial TSS (17.1 0.32%) and TA (16.1 1.60 g L1 citric acid) for minimally processed arils packaged in low barrier BOP film (experiment 1) was indicative of good maturity indices as recommended for ‘Wonderful’ pomegranate arils (Kader, 2002). The TSS values of arils in low barrier BOP film (experiment 1) reduced significantly (P < 0.05) with storage and ranged from 17.1% to 15.3% across all the treatments by the end of the storage period (Table 1). Arils packaged in passively modified atmospheres (MAP-C) and clamshell containers maintained significantly higher (P < 0.05) TSS than MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) and MAP-B (30 kPa O2 + 40 kPa CO2 + 30 kPa N2), throughout the storage duration (Table 1). Arils packaged under passive MAP (MAP-C) had the highest TA (17.8 2.17 g L1) by the end of storage duration. Interaction of MAP and storage duration had a significant effect (P < 0.05) on pH of arils in experiment 1. The pH levels were highest on day 9 across all the treatments and then they reduced significantly to an average of 2.9 by day 12 across all the treatments. This decrease in pH could have been caused by formation of carbonic acid in the aril tissues resulting from increased solubility of CO2 on the surface of arils at low storage temperature and accumulation of CO2 in the MA packages (Ayhan and Estürk, 2009; Caleb et al., 2013). Pomegranate arils packaged in the high barrier Polylid1 film (experiment 2) had a slightly higher initial TSS:TA than those packaged in the low barrier BOP film, but it was well within the range recommended for ‘Wonderful’ pomegranate (Table 2). Chemical attributes TA, TSS and pH were not significantly (P > 0.05) affected by MAP treatments. The TSS fluctuated with storage duration across all the treatments, values ranged from 16.1% to 17.8% by the end of the storage period, but did not differ significantly (P > 0.05) from the initial. Titratable acidity (citric acid) reduced initially across all the treatments until day 6 after which it increased significantly until day 12. Furthermore, the
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range of TSS, TA and pH values found in our studies are similar to those reported by Sepúlveda et al. (2000) for ‘Wonderful’ pomegranate arils pre-treated with antioxidant solutions and packaged in semi-permeable films (PE, BB4 and BE). The authors reported initial values of pH, TSS and TA as 3.1, 15.8% and 11 g L1, respectively, however, TSS values increased to 17% in PE bag, while it remained unchanged in the other packages. Artés et al. (2000) reported a large increase in pH for MAP-stored sweet ‘Mollar de Elche’ pomegranate arils compare to the pH values at harvest and at end of shelf life. In addition, all the MAP treatments investigated by the authors maintained or had an increase in pH values. In contrast pH values decreased only slightly to a range of 2.9–3 by the end of storage across all the treatments. Other studies have also reported minimal changes in chemical attributes such as TA, TSS and pH of pomegranate arils under MAP storage (Ayhan and Estürk, 2009; Maghoumi et al., 2013). Maghoumi et al. (2013) reported minimal changes in chemical attributes of minimally processed ‘Mollar of Elche’ pomegranate arils packaged in high O2 atmospheres (90 kPa O2) at 5 C, despite their RR being higher than that of arils in passive-MAP. The differences and similarities in pH, TSS and TA reported from the various studies could be attributed to several factors such as postharvest treatment applied, cultivar specific attributes, and impact of CO2 accumulation due to its relative solubility in water molecules surrounding the arils (Ayhan and Estürk, 2009; Caleb et al., 2013). 3.4. Total anthocyanin concentration Anthocyanins are water soluble polyphenolic compounds responsible for the red colouration in pomegranate fruit peel and arils (Alighourchi et al., 2008; Arendse et al., 2014). Total anthocyanin concentration fluctuated with storage in MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2), MAP-B (30 kPa O2 + 40 kPa CO2 + 85 kPa N2) and clamshell packages, throughout the storage (Table 1). On the other hand, arils in passive-MAP generally maintained the levels of total anthocyanins with only a slight increase during storage. However, by the end of storage TAC of arils across all MAP treatments was significantly (P < 0.05) higher than
Table 1 Experiment 1: Effect of active- and passive-MAP and storage duration on chemical attributes (pH, TA, TSS, TSS:TA and total anthocyanin) of minimally processed pomegranate arils packaged in BOP low barrier film and stored at 5 C for 12 d. Parameter
Application
pH
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
3.1 0.03d 3.1 0.03d 3.1 0.03d 3.1 0.03d
TA (citric acid) (g L1)
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
TSS (%)
Day 0
Day 3
Day 6
Day 9
Day 12
2.9 0.04f 2.9 0.02f 3.0 0.03e 3.0 0.02ef
3.1 0.02d 3.1 0.02d 3.1 0.02d 3.1 0.02d
3.3 0.02a 3.2 0.03cb 3.2 0.01c 3.3 0.01ab
2.9 0.02f 2.9 0.06f 2.9 0.02ef 2.8 0.04g
16.1 1.6ab 16.1 1.6ab 16.1 1.6ab 16.1 1.6ab
14.6 0.41b 14.6 1.84abc 16.6 3.14abc 14.3 0.41bc
14.1 0.41bc 14.0 0.17c 13.8 0.42c 14.3 0.31cb
18.8 3.57a 14.8 2.03cb 14.5 0.37cb 14.3 0.50cb
16.3 1.88ac 13.6 0.29c 17.8 2.17ab 16.3 3.21abc
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
17.1 0.32a 17.1 0.32a 17.1 0.32a 17.1 0.32a
16.1 0.66fb 16.0 0.38fb 16.7 0.12ab 17.0 0.46a
16.4 0.25abcd 16.1 0.40fb 16.3 0.44abcde 16.6 0.53abc
15.6 1.11fd 15.7 0.81fc 16.7 0.35ab 16.1 0.31fb
15.5 0.58fe 15.6 0.40fd 16.0 0.46fb 15.3 0.55f
TSS:TA
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
10.7 0.88abcd 10.7 0.88abcd 10.7 0.88abcd 10.7 0.88abcd
11.0 0.40abcd 11.1 1.10abcd 10.4 1.76ae 11.9 0.14a
11.6 0.4abc 11.5 0.15abc 11.8 0.12ab 11.6 0.10abc
8.6 1.88e 10.8 1.1abcd 11.5 0.21abc 11.2 0.24abc
9.6 1.20ec 11.5 0.11abc 9.2 1.22ed 9.8 1.94eb
Total anthocyanin content (g L1)
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
0.22 0.01e 0.22 0.01e 0.22 0.01e 0.22 0.01e
0.27 0.01ad 0.24 0.02cde 0.25 0.02cde 0.27 0.01ad
0.30 0.4ab 0.26 0.01db 0.25 0.05cde 0.30 0.002ab
0.23 0.03de 0.21 0.02e 0.25 0.03bde 0.26 0.06ade
0.27 0.01ad 0.29 0.01abc 0.27 0.02ad 0.31 0.01a
Means with the same letters across each coloumn and row are significantly different (P < 0.05).
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Table 2 Experiment 2: Effect of active and passive MAP and storage duration on chemical attributes (pH, TA, TSS, TSS:TA and total anthocyanin content) of minimally processed pomegranate arils packaged in high barrier Polylid1 film and stored at 5 C for 12 d. Parameter
Application
pH
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 10 kPa CO2) MAP-F (100 kPa N2) MAP-G (passive)
3.1 0.2ef 3.1 0.2ef 3.1 0.2ef 3.1 0.2ef
2.1 0.04g 2.1 0.04g 2.1 0.04g 2.1 0.04g
3.7 0.01a 3.7 0.02a 3.7 0.01a 3.6 0.01a
3.3 0.10bcd 3.4 0.19b 3.1 0.04ef 3.2 0.01ed
3.2 0.06ec 3.1 0.01ef 3.3 0.13bc 3.0 0.02f
TA (citric acid) (g L1)
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 10 kPa CO2) MAP-F (100 kPa N2) MAP-G (passive)
13.4 1.02b 13.4 1.02b 13.4 1.02b 13.4 1.02b
11.9 0.34c 12.0 0.48bc 12.7 0.73bc 13.4 1.09bc
11.7 0.25cd 11.3 0.16d 11.3 0.17d 11.9 1.15bcd
16.6 2.57ab 13.7 4.08abcd 15.4 3.58ab 14.3 2.75ab
13.3 0.92b 16.8 1.97a 16.0 2.66ab 14.1 0.61ab
TSS (%)
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 10 kPa CO2) MAP-F (100 kPa N2) MAP-G (passive)
16.6 0.1abc 16.6 0.1abc 16.6 0.1abc 16.6 0.1abc
15.8 0.23cb 15.8 0.36cb 15.8 0.61cb 16.1 0.53ac
16.2 0.72ac 15.4 0.29cb 15.6 0.15cb 16.0 0.40cb
17.1 0.55ab 14.5 2.15c 17.0 0.32ab 15.6 0.40cb
17.8 2.67a 16.2 0.62ac 15.7 1.73c 16.1 0.49ac
TSS:TA
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (5 kPa O2 + 10 kPa CO2) MAP-F (100 kPa N2) MAP-G (passive)
12.5 1.05ac 12..5 1.05ac 12.5 1.05ac 12.5 1.05ac
13.2 0.35ac 13.2 0.57ac 12.5 0.88ac 12.1 1.20ac
13.8 0.28a 13.7 0.35a 13.8 0.23a 13.5 1.75ab
10.6 2.17ac 11.7 5.09ac 11.6 2.91ac 11.2 2.11ac
13.5 3.20ab 9.8 1.88ab 10.1 2.70cb 11.4 0.36ac
Total anthocyanin content (g L1)
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 10 kPa CO2) MAP-F (100 kPa N2) MAP-G (passive)
0.19 0.01b 0.19 0.01b 0.19 0.01b 0.19 0.01b
0.19 0.01b 0.18 0.01bc 0.21 0.03ab 0.27 0.03a
0.22 0.04ab 0.20 0.01b 0.20 0.001b 0.20 0.02b
0.19 0.02bc 0.19 0.01b 0.21 0.04abc 0.17 0.003c
0.21 0.02b 0.17 0.01bc 0.21 0.02b 0.20 0.04abc
Day 0
Day 3
Day 6
Day 9
Day 12
Means with the same letters across each coloumn and row are significantly different (P < 0.05).
at day 0. The lowest TAC (C3gE) values were observed in arils in passive MAP (0.27 0.02 g L1) and the highest in clamshell packages (0.31 0.01 g L1). In experiment 2 (Table 2), the TAC fluctuated with storage across all the MAP treatments and by the end of storage, 100 kPa N2 atmospheres had the highest TAC (0.21 0.02 g L1) and MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) had the lowest (0.17 0.01 g L1) (Table 2). This finding is consistent with the report by Ayhan and Estürk (2009), who reported that packaging and storage duration had significant impacts on TAC (0.31–0.26 g L1) of pomegranate arils ‘Hicazna’. The range of TAC values found in our study is similar to those reported by Caleb et al. (2013) for minimally processed pomegranate arils ‘Acco’ (0.21–0.13 g L1) and ‘Herskawitz’ (0.20–0.12 g L1) packaged under passive-MAP at 5 C, 10 C and 15 C for 14 d. In addition, higher TAC was observed in arils packaged under passive-MAP compared to clamshell containers across all the temperatures, which could suggest that MAP is effective in retarding anthocyanin degradation. Total anthocyanin content of ‘Primosole’ pomegranate arils (0.29 g L1) packaged under passive-MAP at 5 C was also maintained after 10 d of storage (Palma et al., 2009). However, the TAC of arils in experiment 2 of our study was not significantly altered by MAP
and storage duration, while TAC of arils in experiment 1 increased significantly (P < 0.05) with storage across all the MAP treatments. This might have been as a result of the low barrier characteristics of the packaging film used in experiment 1, which provided a higher water vapour permeability and moisture loss. In addition, the highest increase in TAC was observed in arils in clamshell containers which might have suffered more moisture loss compared to those packaged in polymeric film. Gil et al. (1996) also reported an increase in TAC with storage in unpackaged ‘Molar’ pomegranate arils at 1, 4 and 8 C and attributed it to enhanced moisture loss. Anthocyanins are unstable and susceptible to degradation, during processing and storage. Various factors such as processing temperature, storage conditions, application postharvest treatments, the chemical nature of anthocyanins, pH, sugars, exposure to light and metals can affect the stability of anthocyanins (Maghoumi et al., 2013). 3.5. Microbial analysis Modified atmospheres packaging (MAP), storage duration and interaction of MAP and storage duration had significant effects (P < 0.05) on total aerobic mesophilic bacteria counts in arils in low barrier BOP film (Table 3). High O2 atmospheres
Table 3 Experiment 1: Effect of active and passive MAP and storage duration on total aerobic mesophilic bacteria, and mould and yeast counts of minimally processed pomegranate arils packaged in low barrier BOP film and clamshell packages and stored at 5 C for 12 d. Mean values (n = 9) SD, presented are approximated to significant digit. Parameters
Treatments
Storage duration (d) 0
6
12
Total aerobic mesophilic bacteria counts (log CFU mL1)
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
<1.0g <1.0g <1.0g <1.0g
5.4 0.05e 4.1 0.04f 6.0 0.05c 5.5 0.02d
6.1 0.02b 6.2 0.05a 6.2 0.02ab 6.0 0.03c
Yeast and mould counts (log CFU mL1)
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
<0.5d <0.5d <0.5d <0.5d
3.6 0.05c 3.6 0.24c 3.6 0.13c 3.5 0.12c
4.2 0.28b 4.5 0.25a 4.2 0.35ab 4.3 0.10ab
Means with the same letters across each column and row are not significantly different (P < 0.05).
K. Banda et al. / Postharvest Biology and Technology 109 (2015) 97–105
(MAP-B) extended the lag phase of total aerobic mesophilic bacteria until day 6. Total aerobic mesophilic counts in this treatment (MAP-B) increased threefold from the initial count (<1.2 log CFU mL1) on day 0 compared to a five-fold increase in passive-MAP conditions (MAP-C). However, by the end of the storage, aerobic mesophilic counts in high O2 atmospheres (MAP-B) had increased to the same levels as the other MAP treatments. In contrast, yeast and mould counts did not differ significantly (P > 0.05) across the MAP treatments in the low barrier BOP film. The counts were below considered limit (<5 colonies) on day 0 and increased significantly with storage to a range of 4.2–4.5 log CFU mL1 by day 12 across all the treatments. Aerobic mesophilic bacteria counts in arils packaged in the high barrier Polylid1 film increased significantly with storage from an initial <1.0 log CFU mL1 on day 0 to a range of about 5.8 log CFU mL1 across all the treatments by the end of the storage duration. Pomegranate arils packaged in 100 kPa N2 (MAP-F) and high oxygen O2 atmospheres (MAP-E) maintained significantly lower aerobic mesophilic bacteria counts throughout the storage duration compared to those packaged in MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) and passive-MAP (Table 4). Total aerobic bacteria and yeast and mould counts were below the maximum limits of 7 log CFU mL1 and 5 log CFU mL1 respectively, for fresh cuts in the South African legislation (FCD, Act 57 1979) in both experiments 1 and 2 by the end of the storage period. The inhibitory effect of high O2 atmospheres to microbial growth on minimally processed produce has also been reported in other studies on fresh-cut pineapple and berries (Zheng et al., 2008; Zhang et al., 2013). High O2 atmospheres have been suggested to lead to intracellular generation of reactive oxygen species such as superoxide (O2), hydroxyl (OH), hydrogen peroxide (H2O2), and singlet oxygen (1O2), which damage vital cellular components and reduce cell viability when oxidative stresses overwhelm cellular protection systems (Kader and Ben-Yehoshua, 2000). The range of values of aerobic mesophilic bacteria, and yeast and mould counts in the present study is similar to those reported by López-Rubira et al. (2005) for minimally processed pomegranate arils (cv. Mollar of Elche) stored at 5 C. The ability of high O2 atmospheres to suppress aerobic mesophilic growth in arils packaged in low barrier polylid film corroborates findings by Ayhan and Estürk (2009). The authors reported the lowest aerobic mesophilic counts in high O2 atmospheres (70 kPa O2 + 10 kPa CO2) packages. Furthermore, in our studies 100 kPa N2 atmospheres (MAP-F) were also found to be effective in suppressing aerobic mespohilic growth in arils packaged in low barrier polylid film. Nitrogen displaces O2 and therefore helps to retard growth of aerobic spoilage microorganisms (Sandhya, 2010).
103
3.6. Sensory evaluation Table 5 shows the sensory scores of arils packaged in low barrier BOP and Polylid1 films. In experiment 1, package type and low O2 atmospheres had a significant impact (P < 0.05) on the sensory evaluation scores for taste and aroma of arils. The shelf life based on overall acceptability scores was limited to 6 d for arils packaged in clamshell containers. Arils packed in low O2 atmospheres (MAP-A) fell below the consumer acceptance limit of 3 out of a score of 5 by day 9. The arils also had the highest scores for off-odour by the end of the storage duration. In contrast, arils in passive-MAP remained acceptable until day 9, while those in MAP-B (30 kPa O2 + 40 kPa CO2 + 30 kPa N2) scored above the acceptance limit by day 9. Arils in low O2 atmospheres (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) and 100 kPa N2 (MAP-F) in the high barrier Polylid1 film fell below the acceptance limit by day 9 with overall acceptability scores of 2.8 and 2.5, respectively (Table 6). However, arils in passive-MAP (MAP-G) remained acceptable until day 9 and those in O2 atmospheres (MAP-E) scored above the acceptable limit for overall consumer acceptability by day 9. The highest scores for off-odour observed in low O2 atmospheres (MAP-A), low oxygen (MAP-D) and 100 kPa N2 (MAP-F) packages could be attributed to possible increase in fermentative metabolites in the arils, due to the accumulation of CO2 (Watkins, 2000). Ayhan and Estürk (2009) also reported a lower shelf life for minimally processed pomegranate arils packaged in low oxygen atmospheres (5 kPa O2 + 10 kPa CO2) compared to those packaged in air, nitrogen and enriched oxygen. Additionally, the sensory analysis indicated that the development of off-odour of arils packaged under low O2 atmospheres played a critical role in the overall acceptance score. This is consistent with other studies that the development of offodours can serve as an indicator of postharvest shelf-life (Caleb et al., 2013; Zhang et al., 2013). 4. Conclusions This study showed that although equilibrium gas composition of 16–18 kPa O2 and 7 kPa CO2 levels was established in the low barrier BOP film, they were not within the recommended levels (2– 5 kPa O2 and 10–20 kPa CO2) for minimally processed pomegranate arils. In contrast, O2 decreased and CO2 increased continuously in the high barrier Polylid1 film during storage, with O2 levels in packages initially flushed with low O2 further reduced below critical limit (2 kPa). This suggests the need for further optimisation of the initial gas composition flushed into packages with low barrier film via the application of integrated mathematical models. Additionally, perforation-medicated MAP (micro-perforation) technique can be applied towards improving gas permeability of the high barrier film. Shelf life of arils based on overall acceptability sensory scores was limited to 6 and 9 d in clamshell containers and
Table 4 Experiment 2: Effect of active and passive MAP and storage duration on total aerobic mesophilic bacteria, and mould and yeast counts of minimally processed pomegranate arils packaged in high barrier Polylid1 film and stored at 5 C for 12 d. Mean values (n = 9) SD, presented are approximated to significant digit. Parameters
Treatments
Storage duration (d) 0
6
12
Total aerobic mesophilic bacteria counts (log CFU mL1)
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 10 kPa CO2) MAP-F(100 kPa N2) MAP-G (passive)
<1.0e <1.0e <1.0e <1.0e
5.8 0.14ab 5.5 0.15cd 5.4 0.06d 5.7 0.06ab
5.8 0.12a 5.5 0.08cb 5.6 0.07cb 5.8 0.15a
Yeast and mould counts (log CFU mL1)
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 40 kPa CO2) MAP-F(100 kPa N2) MAP-G (passive)
<0.5d <0.5d <0.5d <0.5d
3.1 0.12c 3.8 0.17b 3.1 0.17c 3.4 0.09c
4.7 0.15a 4.5 0.20a 4.5 0.13a 4.7 0.27a
Means with the same letters across each column and row are not significantly different (P < 0.05).
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Table 5 Experiment 1: Scores for sensory quality attributes of minimally processed pomegranate arils stored under active and passive MAP in low barrier BOP film at 5 C for 9 d. Mean values (n = 6) SD, presented are approximated to significant decimal place. Quality parameters
Treatments
0
3
6
9
Taste
MAP-C (passive) MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-B (30 kPa O2 + 40 kPa CO2 + 60 kPa N2) Clamshell
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
4.3 0.51b 3.5 1.38c 4.0 0.63b 3.8 1.17b
3.5 0.84c 3.8 1.69b 3.3 0.52bc 2.5 0.55c
3.3 0.75bc 3.7 1.11bc 3.2 0.37bc 2.3 0.47c
Off-odour
MAP-C (passive) MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-B (30 kPa O2 + 40 kPa CO2 + 85 kPa N2) Clamshell
0 0 0 0
0 0.2 0.41a 0.8 2.04a 0.3 0.82a
0.5 0.84a 0.8 0.98a 0.5 0.55a 1.2 1.47a
0.7 0.25a 1.0 0.82a 0.7 0.47a 1.3 1.25a
Flavour
MAP-C (passive) MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-B (30 kPa O2 + 40 kPa CO2 + 85 kPa N2) Clamshell
4.8 0.37a 4.8 0.37a 4.8 0.37a 4.8 0.37a
4.2 0.75a 4.0 1.26a 3.8 0.98ab 4.0 1.26a
3.5 0.84ab 3.7 0.88ab 3.5 0.55ab 2.8 0.41c
3.3 0.75ab 3.6 0.84ab 3.3 0.47ab 2.7 0.47c
Aroma
MAP-C (passive) MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-B (30 kPa O2 + 40 kPa CO2 + 85 kPa N2) Clamshell
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
3.7 0.82b 3.5 1.22b 3.7 1.21b 3.3 1.63b
3.3 0.52b 3.8 1.17ab 3.7 0.52b 2.8 0.41b
3.2 0.37b 3.7 0.94b 3.5 0.5b 2.7 0.47b
Overall acceptability
MAP-C (passive) MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-B (30 kPa O2 + 40 kPa CO2 + 85 kPa N2) Clamshell
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
4.3 0.52b 4.2 0.98b 4.2 0.75b 3.8 1.17bc
3.7 0.42bc 3.9 1.02bc 3.7 0.52bc 3.0 0.63c
3.1 0.19c 2.9 0.19c 3.5 0.5bc 2.3 0.47c
Storage duration (d)
Means with the same letters across each column and row are not significantly different (P < 0.05).
Table 6 Experiment 2: Scores for sensory quality attributes of minimally processed pomegranate arils stored under active and passive MAP in high barrier Polylid1 film at 5 C for 9 d. Mean values (n = 6) SD, presented are approximated to significant decimal place. Quality parameters
Treatments
Storage duration (d) 0
3
6
9
Taste
MAP-G (passive) MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) MAP-F (100 kPa N2)
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
3.7 0.18b 3.5 1.22b 3.7 1.03b 3.7 1.03b
3.2 0.75b 3.3 1.03b 3.7 0.82b 3.3 1.21b
3.0 0.58b 3.2 0.90b 3.7 0.75b 3.0 0.82b
Off-odour
MAP-G (passive) MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) MAP-F (100 kPa N2)
0 0 0 0
0.5 0.55b 0 0 1.0 0.17b
2.5 1.05a 2.7 1.51a 2.3 1.37a 2.5 1.05a
2.7 0.47a 2.7 0.94a 2.2 0.68a 2.3 0.74a
Flavour
MAP-G (passive) MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) MAP-F (100 kPa N2)
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
3.7 0.52ab 4.0 0.63ab 3.8 0.75ab 3.8 0.75ab
3.7 0.52ab 3.8 0.41ab 3.5 0.55ab 3.5 0.84ab
3.7 0.47ab 3.7 0.47ab 3.5 0.5ab 3.2 0.69b
Aroma
MAP-G (passive) MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) MAP-F (100 kPa N2)
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
4.5 0.55a 4.2 0.41ab 4.5 0.55a 4.5 0.55a
3.7 0.52b 3.8 0.75ab 4.2 0.75ab 3.8 0.98ab
3.7 0.47b 3.7 0.47b 3.8 0.69ab 3.7 0.74b
Overall acceptability
MAP-G (passive) MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) MAP-F (100 kPa N2)
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
3.7 0.82b 4.0 0.63b 4.0 0.63b 4.0 0.89b
3.5 0.55b 3.5 0.55b 3.8 0.75b 3.3 0.82b
3.0 0.00b 2.8 0.37bc 3.3 0.47b 2.5 0.5c
Means with the same letters across each column and row are not significantly different (P < 0.05).
passive-MAP, respectively. On the other hand, packages flushed with high level of O2 atmospheres for both the low and high barrier polymeric films maintained sensory quality beyond 9 d in comparison with packages initially flushed with low O2 atmosphere under the high barrier polymeric film. Thus, in order to avoid anoxic condition and the development of off-odour due to excessive accumulation of CO2 and depletion of O2 inside activeMA packaged arils, the combination of gas flushing with initially low O2 atmosphere level and heat-sealing trays with high barrier polymeric film is not recommended.
Acknowledgements This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology and the National Research Foundation. Dr O.J. Caleb received the NRF Free-Standing Postdoctoral Fellowship 2013/2014 (Grant No. 85243). The authors are grateful to Mr. Fan Olivier of Houdconstant Pack-House, Porterville, South Africa for assistance with fruit procurement and processing.
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Jacxsens, L., Devlieghere, F., Debevere, J., 2002. Temperature dependence of shelflife as affected by microbial proliferation and sensory quality of equilibrium modified atmosphere packaged fresh produce. Postharvest Biol. Technol. 26, 59–73. Jacxsens, L., Devlieghere, F., Van, D.S., Debevere, J., 2001. Effect of high oxygen modified atmosphere packaging on microbial growth and sensorial qualities of fresh-cut produce. Int. J. Food Microbiol. 71, 197–210. Kader, A.A., 2002. Postharvest Technology of Horticultural Crops. University of California, Agriculture and Natural Resources, Oakland, California. Kader, A.A., Ben-Yehoshua, S., 2000. Effects of superatmospheric oxygen levels on postharvest physiology and quality of fresh fruits and vegetables. Postharvest Biol. Technol. 20, 1–13. Kader, A.A., Watkins, C.B., 2000. Modified atmosphere packaging 2000 and beyond. HortTechnology 10, 483–486. Koseki, S., Itoh, K., 2002. Effect of nitrogen gas packaging on the quality and microbial growth of fresh-cut vegetables under low temperatures. J. Food Prot. 920, 326–332. López-Rubira, V., Conesa, A., Allende, A., Artés, F., 2005. Shelf life and overall quality of minimally processed pomegranate arils modified atmosphere packaged and treated with UV-C. Postharvest Biol. Technol. 37, 174–185. Maghoumi, M., Gómez, P.A., Artés-Hernández, F., Mostofi, Y., Zamani, Z., Artés, F., 2013. Hot water, UV-C and superatmospheric oxygen packaging as hurdle techniques for maintaining overall quality of fresh-cut pomegranate arils. J. Sci. Food Agric. 93, 1162–1168. Mahajan, P.V., Caleb, O.J., Singh, Z., Watkins, C.B., Geyer, M., 2014. Postharvest treatments of fresh produce. Philos. Trans. R. Soc. A 372, 1471–2962. Mangaraj, S., Goswami, T.K., Mahajan, P.V., 2009. Applications of plastic films for modified atmosphere packaging of fruits and vegetables: a review. Food Eng. Rev. 1, 133–158. Martínez-Romero, D., Castillo, S., Guillén, F., Díaz-Mula, H.M., Zapata, P.J., Valero, D., Serrano, M., 2013. Aloe vera gel coating maintains quality and safety of readyto-eat pomegranate arils. Postharvest Biol. Technol. 86, 107–112. Mphahlele, R.R., Caleb, O.J., Fawole, O.A., Opara, U.L., 2015. Effects of different maturity stages and growing locations on changes in chemical, biochemical and aroma volatile composition of ‘Wonderful’ pomegranate juice. J. Sci. Food Agric. doi:http://dx.doi.org/10.1002/jsfa.7186. Palma, A., Schirra, M., Aquino, D., La Malfa, S., Continella, G., 2009. Chemical properties changes in pomegranate seeds packaged in polyethylene trays, in: Ozguven, A.I., (Ed.) Proceedings of the 1st IS on pomegranate. Acta Hortic. 818, 1–4. Rattanapanone, N., Lee, Y., Wu, T., Watada, A.E., 2001. Quality and microbial changes in fresh-cut mango cubes held in controlled atmosphere. HortScience 36, 1091– 1095. Rico, D., Martín-Diana, A.B., Barat, J.M., Barry-Ryan, C., 2007. Extending and measuring the quality of fresh-cut fruit and vegetables: a review. Trends Food Sci. Technol. 18, 373–386. Rodov, V., Horev, B., Goldman, G., Vinokur, Y., Fishman, S., 2007. Model-driven development of microperforated active modified-atmosphere packaging for fresh-cut produce. Acta Hortic. 746, 83–88. Sandhya, 2010. Modified atmosphere packaging of fresh produce: current status and future needs. LWT Food Sci. Technol. 43, 381–392. Sepúlveda, E., Galletti, L., Sáenz, C., Tapia, M., 2000. Minimal processing of pomegranate var. Wonderful. CIHEAM-Opitions Mediterr. 42, 237–242. Sivakumar, D., Arrebola, E., Korsten, L., 2008. Postharvest decay control and quality retention in litchi (cv. McLean’s Red) by combined application of modified atmosphere packaging and antimicrobial agents. Crop Prot. 27, 1208–1214. Watkins, C.B., 2000. Response of horticultural commodities to high carbon dioxide as related to modified atmosphere packaging. HortTechnology 10, 501–506. Zhang, B.-Y., Samapundo, S., Pothakos, V., de Baenst, I., Surengil, G., Noseda, B., Devlieghere, F., 2013. Effect of atmospheres combining high oxygen and carbon dioxide levels on microbial spoilage and sensory quality of fresh-cut pineapple. Postharvest Biol. Technol. 86, 73–84. Zheng, Y., Yang, Z., Chen, X., 2008. Effect of high oxygen atmosphere on fruit decay and quality in Chinese bayberries, strawberries and blueberries. Food Control 19, 470–474.
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Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Effect of active-modified atmosphere packaging on the respiration rate and quality of pomegranate arils (cv. Wonderful) Kalenga Bandaa , Oluwafemi J. Caleba,b , Karin Jacobsc , Umezuruike Linus Oparaa,b,* a Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Horticultural Science, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa b Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Food Science, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa c Department of Microbiology, Faculty of Science, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa
A R T I C L E I N F O
A B S T R A C T
Article history: Received 2 February 2015 Received in revised form 3 June 2015 Accepted 6 June 2015 Available online xxx
Two experiments were conducted to investigate the effects of active- and passive-modified atmosphere packaging (MAP) on respiration rate (RR) and quality attributes of minimally processed pomegranate arils (cv. Wonderful) stored at 5 C for 12 d. In experiment 1, pomegranate arils were packaged in low barrier bi-axially oriented polyester (BOP) film under active-MA (5 kPa O2 + 10 kPa CO2, 30 kPa O2 + 40 kPa CO2), passive-MA and in clamshell trays. In experiment 2, a high barrier Polylid1 film was used with arils packaged under three active-MAs (5 kPa O2 + 10 kPa CO2 + 85 kPa N2; 30 kPa O2 + 10 kPa O2 + 60 kPa N2; 100 kPa N2) and passive-MA. Arils packed in clamshell trays had lowest RR (RCO2) compared to the other MA treatments in experiment 1, ranging from 41.1 nmol kg1 s1 on day 3 to 238.8 nmol kg1 s1 on day 12. Respiration rate of arils packaged in the high barrier polylid film was significantly affected by MA treatments. At the end of 12 d storage, total anthocyanin content (TAC) in arils was highest for clamshell packages (0.31 0.01 g L1) and lowest in passive-MAP (0.27 0.02 g L1). Packaging arils in high O2 atmosphere and 100 kPa N2 significantly lower aerobic mesophilic bacteria counts throughout the storage duration. Based on sensory scores obtained and microbial load, the shelf life for arils packaged in clamshell trays, passive-MA, and high O2 level MA was 6, 9 and 12 d, respectively. ã2015 Elsevier B.V. All rights reserved.
Keywords: Shelf life Respiration rate Anthocyanin Aerobic mesophilic bacteria Packaging
1. Introduction Modified atmosphere packaging (MAP) combined with low temperature storage has been successfully used to prolong the shelf life of fresh fruit and vegetables (Mahajan et al., 2014). Modified atmospheres are achieved by hermetically sealing fresh respiring produce in polymeric film and allowing the atmosphere within the package to be modified passively by the interplay of produce respiration rate (RR) and the film permeability properties, or actively by flushing the desired gas mixtures inside a package before sealing (Kader and Watkins, 2000; Rico et al., 2007; Mangaraj et al., 2009). Modified atmosphere packaging slows down physiological and biochemical processes and retards senescence (Caleb et al., 2012a). Thereby maintaining packaged produce freshness, quality attributes and microbial safety. Failure
* Corresponding author at: Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Horticultural Science, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa. Fax: +27 21 808 3743. E-mail address: [email protected] (U.L. Opara). http://dx.doi.org/10.1016/j.postharvbio.2015.06.002 0925-5214/ ã 2015 Elsevier B.V. All rights reserved.
to create this suitable atmosphere may result in a shortened shelf life (Mangaraj et al., 2009). Suitable equilibrium atmospheres are achieved by proper matching of fresh produce RR and film permeability characteristics (Jacxsens et al., 2002; Kader, 2002; Caleb et al., 2012a). Desired atmospheric equilibrium/compositions inside packaged fresh produce are low oxygen (O2) (2–5 kPa) and/or moderate carbon dioxide (CO2) (10 kPa) (Rico et al., 2007; Sandhya, 2010). Previous studies have reported on the RR of minimally processing pomegranate arils under different conditions (Ersan et al., 2010; Caleb et al., 2012b). Ayhan and Estürk (2009) reported an increase in antioxidant activity and lower mesophilic bacteria counts in minimally processed pomegranate arils (cv. Hicaznar) stored under super atmospheric O2 (70 kPa) atmospheres compared to those stored under low O2 (5 kPa) and in normal air at 5 C. Super atmospheric O2 atmospheres (>21 kPa) have also been used in MAP of minimally processed products because of their ability to prevent anaerobic fermentation, inhibit enzymatic discolouration and microbial growth (Jacxsens et al., 2001). O2 concentrations >25 kPa are nonetheless considered highly explosive and, as they pose a hazard should be used with caution (Jacxsens et al., 2001).
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Nitrogen (N2) is a non-reactive gas that is used to exclude more reactive gases from packages and acts as a filler gas to prevent package collapse (Brandenburg and Zagory, 2009). Several studies with minimally processed products have explored the use of 100 kPa N2 atmospheres in MAP (Ayhan and Estürk, 2009; Ahmed et al., 2011) because of their ability to maintain fresh produce quality. Firmness, colour and chemical properties were maintained and shelf life extended in persimmon fruit packaged in 100 kPa N2, stored at 0 C and 85–95% relative humidity (RH) for 90 d (Ahmed et al., 2011). Similarly, fresh-cut cabbage and lettuce in packages initially flushed with 100 kPa N2 atmospheres at 1 and 5 C maintained their quality and appearance by the end of the 5 d storage period (Koseki and Itoh, 2002). Active-MAP achieved by flushing desired gas mixtures into packages allows earlier establishment of equilibrium atmospheres than passive-MAP and has, therefore, been recommended for minimally processed products (Bai et al., 2003; Rodov et al., 2007). Equilibrium atmospheres in active-MAP of litchi (cvs. Mauritius and McLeans Red) were established almost from the first day of storage, whereas those in passive-MAP were established 6–10 d after packaging (Sivakumar et al., 2008). Thus, the selection of packaging films with suitable barrier properties is of crucial importance in developing a suitable gas composition to maintain quality and assure a long shelf life for packaged fresh produce (Martínez-Romero et al., 2013). Despite the successful application of active-MAP in a wide range of minimally processed products, few studies have investigated the effects of active-MAP and the use of different barrier polymeric film on the physiological response and overall quality of minimally processed pomegranate arils. The objective of this study was, therefore, to determine the effects of different packaging atmospheres on respiration rate (RR), quality attributes and shelf life of minimally processed pomegranate arils (cv. Wonderful) packaged in low barrier bi-axially oriented polyester (BOP) and polylid film and stored at 5 C and 90 2% RH. 2. Materials and methods 2.1. Sample preparation and packaging Pomegranate fruit (cv. Wonderful) was harvested at commercially ripened stage with characteristic deep-red skin and deep-red arils with mature kernels (Mphahlele et al., 2015), from Houdconstant Farm, Porterville, Western Cape (33 0100000 S, 18 590 0000 E), South Africa. Fruits were sorted, cleaned and minimally processed at the farm pack house. Fruit free from visible physical defects were washed in sterilised water and arils extracted using a commercial extraction machine (Arilsystem, Juran Metal Works, Israel). Extracted arils were bulk packaged in sterilized polyethylene bags and transported in sterile ice boxes to the postharvest research laboratory at Stellenbosch University. Arils (300 g) were packaged in polyethylene terephthalate (PET) trays (ZIBO Containers, Pty, Ltd., Kuilsrivier, South Africa) and flushed with food grade gas mixtures (Air Products Pty, Kempton Park, South Africa) using a tray sealer (Model T200 Multivac, Wolfertschwenden, Germany). Two experiments were conducted consecutively. In the first experiment, a low barrier BOP polymeric film (with 26 mm thickness, permeance rate 3.5 1013 mol m2 s1 Pa1 O2, 7.0– 9.4 1014 mol m2 s1 Pa1 CO2 and 9.4 105 mol m2 s1 Pa1 water vapour at 23 C and 85% RH) supplied by Knilam Packaging (Pty) Ltd. (Cape Town, South Africa) was used to heat-seal the PET trays. The following gas mixtures were used: MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2); MAP-B (30 kPa O2 + 40 kPa CO2 + 30 kPa N2); MAP-C (normal atmospheric composition; passive-MAP). Additionally, arils were packaged in PET clamshell
containers (420 mm thickness, 11.5 11.5 3.5 cm3) as control. In the second experiment, a high barrier polymeric film Polylid1 107HB55 (with 55 mm thickness, permeance rate of 9.8– 10.8 1014 mol m2 s1 Pa1 O2, 7.0–9.4 1014 mol m2 s1 Pa1 CO2 and 2.4–3.3 105 mol m2 s1 Pa1 water vapour at 23 C and 85% RH) supplied by Barkai Polyon Industries Ltd. (Tel Aviv, Isreal) was used. The following gas mixtures were applied in the second study: MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2); MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2); MAP-F (100 kPa N2) and MAP-G (passive-MAP). All the samples were stored at 5 C and 90 2% RH for 12 d and analyses were conducted in triplicate on days 0, 3, 6, 9, and 12. 2.2. Headspace gas composition Headspace O2 and CO2 composition of packaged pomegranate arils was determined using an O2/CO2 gas analyser (Checkmate 3, PBI Dansensor, Ringstead, Denmark). Gas analysis was done by inserting a needle attached to the gas analyser through a rubber septum on the packaging film. Gas sampling was done before opening the package to remove the arils. Three additional replications per treatment were used to monitor in-package head space gas composition during the entire storage period. 2.3. Respiration rate Post-storage RR of pomegranate arils was determined using the closed system method at 5 C. On each sampling day, 150 g pomegranate arils from each of the MAP treatments were separately weighed into 1.1 L glass jars using a balance (Bosch SAE200, Denver Instrument GmbH, Germany). The glass jars were hermetically sealed by incorporating Vaseline petroleum jelly in the gap between the lid and the jar. Gas samples were drawn at hourly intervals over a period of 4 h through a rubber septum fitted on the jar and the gas composition was monitored by gas analyser (Checkmate 3, PBI Dansensor, Ringstead, Denmark). Measurements were repeated on each of the sampling days using fresh samples each time in order to determine the effect of modified MAP and storage duration on pomegranate arils RR (Fonseca et al., 2002; Bhatia et al., 2013). The RR was calculated by fitting experimentally obtained data in the following Eqs (1) and (2): yO2 ¼ yiO2
RO2 W ðt ti Þ Vf
yCO2 ¼ yiCO2 þ
RCO2 W ðt ti Þ Vf
(1)
(2)
where RO2 and RCO2 are the O2 consumption and CO2 production rate (RR); yiO2 and yO2 are O2 concentration (kPa) at the initial time t1 (s) (time zero) and at time t (s), respectively and yiCO2 and yCO2 are the CO2 concentration (kPa) at the initial time t1 (s) (time zero) and at time t (s), respectively. W is the total weight of product (kg) and Vf is the free volume inside jar (L); determined by subtracting volume of product from the total volume of the glass jar (Caleb et al., 2012b). RR values were expressed as nmol kg1 s1 (Banks et al., 1995). 2.4. Total soluble solids, titratable acidity and pH Arils were juiced separately for each of the treatments on each sampling day using a LiquaFresh juice extractor (Mellerware, Cape Town, South Africa). Pomegranate juice was used to determine pH using a pH metre (Crison, Barcelona, Spain), total soluble solids
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(TSS) expressed as percentage (%) using a digital refractometer (Atago, Tokyo, Japan). Titratable acidity (TA) measured by titration with 0.1 mol L1 NaOH to an end-point of pH 8.2 using a Metrohmn 862 compact titrosampler (Herisau, Switzerland). TA was expressed as gram of per litre of pomegranate juice (g L1) of citric acid. TSS:TA was calculated based on % ratio. All values are presented as mean standard deviation (SD). 2.5. Total anthocyanin concentration Total anthocyanin concentration (TAC) was quantified using the pH differential method with two buffer systems comprising of potassium chloride (pH 1, 0.025 mol L1) and sodium acetate (pH 4.5, 0.4 mol L1). The juice sample (1 mL) was mixed with 9 mL of pH 1 and pH 4.5 buffers, separately. The absorbance of the mixtures was measured at 520 and 700 nm using a UV–vis spectrophotometer (Thermo Fisher Scientific, Madison, MI, USA), after 10 min incubation of the mixture in a dark cabinet. TAC was expressed as cyanidin-3-glucoside (Cyd-3-glucoside) using the following equations: A = (A510–A700)pH 1.0 (A510–A700)pH 4.0 Total monomeric anthocyanin ¼
A MW DF eL
(3)
(4)
where A = absorbance (nm), e = 26,900 molar extinction coefficient, MW = molecular weight of Cyd-3-glucoside (449.2 g mol1), DF = dilution factor and L = cell path length (1 cm). Results were expressed gram Cyd-3-glucoside equivalent per litre of pomegranate juice (g L1) (Fawole et al., 2011). All analyses were carried out in triplicates (n = 3) and values are presented as mean SD.
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2.6. Microbial analysis Microbial quality of arils was screened on days 0, 6 and 12 of storage. Approximately 10 g of arils was weighed and put into 100 mL of physiological solution and shaken for 5 min. Furthermore, 3-fold dilutions were prepared using 1 mL of diluents into 9 mL of physiological solution. In order to enumerate microbial load, 1 mL of each dilution was pour-plated in triplicate onto appropriate media. Total aerobic mesophilic bacterial count was determined using plate count agar incubated at 30 C for 48 h, while yeast and mould counts were determined using potato dextrose agar and incubated at 26 C for 5 d. After incubation, the colonies grown on plates were counted (counts between 30 and 300 colonies), and the result was presented as log of colony forming units per gram (log CFU mL1). 2.7. Sensory evaluation Sensory evaluation of arils was done by a panel of 6 untrained judges who are regular consumers of pomegranate and are familiar with its quality attributes. Aril quality attributes, taste, off-odour, flavour, aroma and overall acceptability were scored on scale of 0–5. The score 0 corresponded to poor/none and 5 to excellent/ prominent. Scores below 3 were considered the cut-off point for quality attributes, taste, flavour, aroma and overall acceptability, while scores above 3 were used as indicators of the end of acceptable quality for off-odour. 2.8. Statistical analysis A factorial analysis of variance (ANOVA) was performed on experimental data at 95% confidence interval using Statistica software (Statistica 10.0, Statsoft Inc., USA). All values are
Fig. 1. Changes in headspace gas composition in minimally processed pomegranate arils packaged in PET trays and heat-sealed with different polymeric films stored at 5 C for 12 d: (A) changes in O2 and (B) CO2 (kPa) levels for low barrier BOP film and clamshell packages; (C) changes in O2 and (D) CO2 (kPa) levels in high barrier Polylid1 film. Error bars represent standard deviation (SD) of mean values (n = 3).
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presented as mean SD. All parameters were measured in triplicate (n = 3) for each treatment. 3. Results and discussion 3.1. Headspace gas composition In the first experiment with the lower barrier film, equilibrium O2 and CO2 levels were attained by day 3 in packaged arils across all MAP treatments (Fig. 1A and B). However, the steady state gas composition of O2 observed in this study (16–18 kPa) was above the recommended level of 2–5 kPa O2 (López-Rubira et al., 2005). This could be attributed to the high O2 transmission rate of the BOP film used in the study. CO2 levels attained were also slightly lower (7 kPa) than those recommended (10–20 kPa) for pomegranate arils (Hess-Pierce and Kader, 1997; Irtwange, 2006). In the second experiment, O2 decreased and CO2 increased continuously, across all the treatments regardless of MAP treatment (Fig. 1). O2 levels in packages flushed with low O2 (2 kPa O2 + 10 kPa CO2 + 85 kPa N2) went below the critical limit of 2 kPa by day 12 (Fig. 1C), a condition that is known to be ideal for occurrence of anaerobic respiration (Gorny, 2003; Artés et al., 2006). Carbon dioxide levels also accumulated (27–43 kPa) beyond levels recommended for MAP of pomegranate arils across all MAP treatments (Fig. 1D). CO2 is soluble at high concentrations and low temperatures forming carbonic acid which has bacteriostatic effects on tissues of fresh-cut produce. On the other hand, accumulation of carbon acid causes changes in organoleptic properties of some minimally processed products (Sandhya, 2010). The barrier films used in both experiments did not create suitable equilibrium O2 and CO2 levels for pomegranate arils. 3.2. Respiration rate Modified atmospheres, storage duration and their interaction had significant effects (P < 0.05) on RR of pomegranate arils packaged in the low barrier BOP film and clamshell trays in experiment 1 (Fig. 2A). Furthermore, RR (RCO2) of arils reduced initially with increase in storage duration from 89.9 nmol kg1 s1 on day 0 to a range of 41.1–95.0 nmol kg1 s1 on day 3 across the treatments, and then increased significantly (P < 0.05) from day 3 until the end of the storage period. Arils packed in clamshell trays maintained the lowest RR throughout the storage duration, ranging from 41.1 nmol kg1 s1 on day 3 to 238.8 nmol kg1 s1 on day 12. In experiment 1, arils packaged under passive-MAP (MAP-C) had the highest RR value (RCO2) of 338.9 27.8 nmol kg1 s1. The RR (RCO2) of arils packed in the high barrier film Polylid1 was generally higher (from 138.6 nmol kg1 s1 on day 3 to 984.8 nmol kg1 s1 on day 12) than those of low barrier film experiment (Fig. 2B). This may be attributed to differences in headspace gas composition created inside the barrier films. Aril RR response was similar to those reported by Bhatia et al. (2013), for minimally processed ‘Mridula’ pomegranate arils under MAP at 5 C for 15 d. The authors reported a progressive increase in RR (RCO2) of arils during the storage duration, ranging from 311.4 nmol kg1 s1 to 979.1 nmol kg1 s1 at the end of storage period. Similarly, in experiment 2 the RR of arils in our study increased throughout the storage duration across all the treatments. By day 3, RR (RCO2) of arils in MAP-F (100 kPa N2) and MAP-G (passive) was 138.6 13.3 nmol kg1 s1 and 148.8 4.3 nmol kg1 s1, respectively, and this was significantly lower than in the other MA treatments. Arils packed in 100 kPa N2 maintained significantly lowest RRs than the other MAP treatments from day 6 (214.8 6.9 nmol kg1 s1) to day 12
Fig. 2. Respiration rate (RCO2) of minimally processed pomegranate arils packaged under passive- and active-modified atmospheres and stored at 5 C for 12 d in: (A) low barrier BOP film and clamshell packages and (B) high barrier Polylid1 film. Error bars represent standard deviation (SD) of mean values (n = 3).
(588.8 12.5 nmol kg1 s1). The low RRs could be attributed to the low levels of O2 maintained in the 100 kPa N2 packages compared to the other MAP treatments (Fig. 1C). Other studies have shown that MAPs with low O2 (2–5 kPa) and high CO2 (10–20 kPa) levels reduced RR of minimally processed fresh produce (Gorny, 2003; Rattanapanone et al., 2001). Ersan et al. (2010) investigated the effects of varying combinations of O2 (2, 10 and 21 kPa) and CO2 (0, 10 and 20 kPa) concentrations on RR of minimally processed pomegranate arils (cv. Hicaznar) stored at 4 C. The studies revealed that combinations of low O2 2 kPa and high CO2 10 kPa significantly reduced RRs (6.1 nmol kg1 s1) of arils. The experimental setup used by Ersan et al. (2010) was different from the one reported in this study, the authors did not measure RR of packaged arils on sampling day. The use of high O2 atmospheres (>21 kPa) has been suggested as an alternative to low O2 in order to prevent anaerobic respiration (Jacxsens et al., 2001). However, respiratory response to high O2 atmospheres varies in different products (Kader and Ben-Yehoshua, 2000). High O2 atmospheres (100 kPa O2; 95 kPa O2 + 5 kPa CO2; 80 kPa O2 + 20 kPa CO2; 75 kPa O2 + 25 kPa CO2) significantly reduced RR of fresh-cut onions stored at room temperature for 9 d (Chunyang et al., 2010). In contrast, Maghoumi et al. (2013) reported an increase in RR within the range of 17.7–23.0 nmol kg1 s1 for minimally processed pomegranate arils (cv. Molar de Elche) packaged under high oxygen atmospheres (90 kPa O2) compared to those under passive MAP at 5 C. The authors suggested that high O2 levels enhanced the production of reactive O2 species and caused respiratory stress leading to increased aril RR. This consistent with the arils RR observed in this study, although RR obtained are higher than those reported by Maghoumi et al. (2013).
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3.3. Total soluble solids (TSS), titratable acidity (TA) and pH MAP had no significant effects (P > 0.05) on chemical attributes of minimally processed arils in both experiments 1 and 2, except for TSS in arils packaged in low barrier BOP film. Initial TSS (17.1 0.32%) and TA (16.1 1.60 g L1 citric acid) for minimally processed arils packaged in low barrier BOP film (experiment 1) was indicative of good maturity indices as recommended for ‘Wonderful’ pomegranate arils (Kader, 2002). The TSS values of arils in low barrier BOP film (experiment 1) reduced significantly (P < 0.05) with storage and ranged from 17.1% to 15.3% across all the treatments by the end of the storage period (Table 1). Arils packaged in passively modified atmospheres (MAP-C) and clamshell containers maintained significantly higher (P < 0.05) TSS than MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) and MAP-B (30 kPa O2 + 40 kPa CO2 + 30 kPa N2), throughout the storage duration (Table 1). Arils packaged under passive MAP (MAP-C) had the highest TA (17.8 2.17 g L1) by the end of storage duration. Interaction of MAP and storage duration had a significant effect (P < 0.05) on pH of arils in experiment 1. The pH levels were highest on day 9 across all the treatments and then they reduced significantly to an average of 2.9 by day 12 across all the treatments. This decrease in pH could have been caused by formation of carbonic acid in the aril tissues resulting from increased solubility of CO2 on the surface of arils at low storage temperature and accumulation of CO2 in the MA packages (Ayhan and Estürk, 2009; Caleb et al., 2013). Pomegranate arils packaged in the high barrier Polylid1 film (experiment 2) had a slightly higher initial TSS:TA than those packaged in the low barrier BOP film, but it was well within the range recommended for ‘Wonderful’ pomegranate (Table 2). Chemical attributes TA, TSS and pH were not significantly (P > 0.05) affected by MAP treatments. The TSS fluctuated with storage duration across all the treatments, values ranged from 16.1% to 17.8% by the end of the storage period, but did not differ significantly (P > 0.05) from the initial. Titratable acidity (citric acid) reduced initially across all the treatments until day 6 after which it increased significantly until day 12. Furthermore, the
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range of TSS, TA and pH values found in our studies are similar to those reported by Sepúlveda et al. (2000) for ‘Wonderful’ pomegranate arils pre-treated with antioxidant solutions and packaged in semi-permeable films (PE, BB4 and BE). The authors reported initial values of pH, TSS and TA as 3.1, 15.8% and 11 g L1, respectively, however, TSS values increased to 17% in PE bag, while it remained unchanged in the other packages. Artés et al. (2000) reported a large increase in pH for MAP-stored sweet ‘Mollar de Elche’ pomegranate arils compare to the pH values at harvest and at end of shelf life. In addition, all the MAP treatments investigated by the authors maintained or had an increase in pH values. In contrast pH values decreased only slightly to a range of 2.9–3 by the end of storage across all the treatments. Other studies have also reported minimal changes in chemical attributes such as TA, TSS and pH of pomegranate arils under MAP storage (Ayhan and Estürk, 2009; Maghoumi et al., 2013). Maghoumi et al. (2013) reported minimal changes in chemical attributes of minimally processed ‘Mollar of Elche’ pomegranate arils packaged in high O2 atmospheres (90 kPa O2) at 5 C, despite their RR being higher than that of arils in passive-MAP. The differences and similarities in pH, TSS and TA reported from the various studies could be attributed to several factors such as postharvest treatment applied, cultivar specific attributes, and impact of CO2 accumulation due to its relative solubility in water molecules surrounding the arils (Ayhan and Estürk, 2009; Caleb et al., 2013). 3.4. Total anthocyanin concentration Anthocyanins are water soluble polyphenolic compounds responsible for the red colouration in pomegranate fruit peel and arils (Alighourchi et al., 2008; Arendse et al., 2014). Total anthocyanin concentration fluctuated with storage in MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2), MAP-B (30 kPa O2 + 40 kPa CO2 + 85 kPa N2) and clamshell packages, throughout the storage (Table 1). On the other hand, arils in passive-MAP generally maintained the levels of total anthocyanins with only a slight increase during storage. However, by the end of storage TAC of arils across all MAP treatments was significantly (P < 0.05) higher than
Table 1 Experiment 1: Effect of active- and passive-MAP and storage duration on chemical attributes (pH, TA, TSS, TSS:TA and total anthocyanin) of minimally processed pomegranate arils packaged in BOP low barrier film and stored at 5 C for 12 d. Parameter
Application
pH
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
3.1 0.03d 3.1 0.03d 3.1 0.03d 3.1 0.03d
TA (citric acid) (g L1)
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
TSS (%)
Day 0
Day 3
Day 6
Day 9
Day 12
2.9 0.04f 2.9 0.02f 3.0 0.03e 3.0 0.02ef
3.1 0.02d 3.1 0.02d 3.1 0.02d 3.1 0.02d
3.3 0.02a 3.2 0.03cb 3.2 0.01c 3.3 0.01ab
2.9 0.02f 2.9 0.06f 2.9 0.02ef 2.8 0.04g
16.1 1.6ab 16.1 1.6ab 16.1 1.6ab 16.1 1.6ab
14.6 0.41b 14.6 1.84abc 16.6 3.14abc 14.3 0.41bc
14.1 0.41bc 14.0 0.17c 13.8 0.42c 14.3 0.31cb
18.8 3.57a 14.8 2.03cb 14.5 0.37cb 14.3 0.50cb
16.3 1.88ac 13.6 0.29c 17.8 2.17ab 16.3 3.21abc
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
17.1 0.32a 17.1 0.32a 17.1 0.32a 17.1 0.32a
16.1 0.66fb 16.0 0.38fb 16.7 0.12ab 17.0 0.46a
16.4 0.25abcd 16.1 0.40fb 16.3 0.44abcde 16.6 0.53abc
15.6 1.11fd 15.7 0.81fc 16.7 0.35ab 16.1 0.31fb
15.5 0.58fe 15.6 0.40fd 16.0 0.46fb 15.3 0.55f
TSS:TA
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
10.7 0.88abcd 10.7 0.88abcd 10.7 0.88abcd 10.7 0.88abcd
11.0 0.40abcd 11.1 1.10abcd 10.4 1.76ae 11.9 0.14a
11.6 0.4abc 11.5 0.15abc 11.8 0.12ab 11.6 0.10abc
8.6 1.88e 10.8 1.1abcd 11.5 0.21abc 11.2 0.24abc
9.6 1.20ec 11.5 0.11abc 9.2 1.22ed 9.8 1.94eb
Total anthocyanin content (g L1)
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
0.22 0.01e 0.22 0.01e 0.22 0.01e 0.22 0.01e
0.27 0.01ad 0.24 0.02cde 0.25 0.02cde 0.27 0.01ad
0.30 0.4ab 0.26 0.01db 0.25 0.05cde 0.30 0.002ab
0.23 0.03de 0.21 0.02e 0.25 0.03bde 0.26 0.06ade
0.27 0.01ad 0.29 0.01abc 0.27 0.02ad 0.31 0.01a
Means with the same letters across each coloumn and row are significantly different (P < 0.05).
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Table 2 Experiment 2: Effect of active and passive MAP and storage duration on chemical attributes (pH, TA, TSS, TSS:TA and total anthocyanin content) of minimally processed pomegranate arils packaged in high barrier Polylid1 film and stored at 5 C for 12 d. Parameter
Application
pH
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 10 kPa CO2) MAP-F (100 kPa N2) MAP-G (passive)
3.1 0.2ef 3.1 0.2ef 3.1 0.2ef 3.1 0.2ef
2.1 0.04g 2.1 0.04g 2.1 0.04g 2.1 0.04g
3.7 0.01a 3.7 0.02a 3.7 0.01a 3.6 0.01a
3.3 0.10bcd 3.4 0.19b 3.1 0.04ef 3.2 0.01ed
3.2 0.06ec 3.1 0.01ef 3.3 0.13bc 3.0 0.02f
TA (citric acid) (g L1)
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 10 kPa CO2) MAP-F (100 kPa N2) MAP-G (passive)
13.4 1.02b 13.4 1.02b 13.4 1.02b 13.4 1.02b
11.9 0.34c 12.0 0.48bc 12.7 0.73bc 13.4 1.09bc
11.7 0.25cd 11.3 0.16d 11.3 0.17d 11.9 1.15bcd
16.6 2.57ab 13.7 4.08abcd 15.4 3.58ab 14.3 2.75ab
13.3 0.92b 16.8 1.97a 16.0 2.66ab 14.1 0.61ab
TSS (%)
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 10 kPa CO2) MAP-F (100 kPa N2) MAP-G (passive)
16.6 0.1abc 16.6 0.1abc 16.6 0.1abc 16.6 0.1abc
15.8 0.23cb 15.8 0.36cb 15.8 0.61cb 16.1 0.53ac
16.2 0.72ac 15.4 0.29cb 15.6 0.15cb 16.0 0.40cb
17.1 0.55ab 14.5 2.15c 17.0 0.32ab 15.6 0.40cb
17.8 2.67a 16.2 0.62ac 15.7 1.73c 16.1 0.49ac
TSS:TA
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (5 kPa O2 + 10 kPa CO2) MAP-F (100 kPa N2) MAP-G (passive)
12.5 1.05ac 12..5 1.05ac 12.5 1.05ac 12.5 1.05ac
13.2 0.35ac 13.2 0.57ac 12.5 0.88ac 12.1 1.20ac
13.8 0.28a 13.7 0.35a 13.8 0.23a 13.5 1.75ab
10.6 2.17ac 11.7 5.09ac 11.6 2.91ac 11.2 2.11ac
13.5 3.20ab 9.8 1.88ab 10.1 2.70cb 11.4 0.36ac
Total anthocyanin content (g L1)
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 10 kPa CO2) MAP-F (100 kPa N2) MAP-G (passive)
0.19 0.01b 0.19 0.01b 0.19 0.01b 0.19 0.01b
0.19 0.01b 0.18 0.01bc 0.21 0.03ab 0.27 0.03a
0.22 0.04ab 0.20 0.01b 0.20 0.001b 0.20 0.02b
0.19 0.02bc 0.19 0.01b 0.21 0.04abc 0.17 0.003c
0.21 0.02b 0.17 0.01bc 0.21 0.02b 0.20 0.04abc
Day 0
Day 3
Day 6
Day 9
Day 12
Means with the same letters across each coloumn and row are significantly different (P < 0.05).
at day 0. The lowest TAC (C3gE) values were observed in arils in passive MAP (0.27 0.02 g L1) and the highest in clamshell packages (0.31 0.01 g L1). In experiment 2 (Table 2), the TAC fluctuated with storage across all the MAP treatments and by the end of storage, 100 kPa N2 atmospheres had the highest TAC (0.21 0.02 g L1) and MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) had the lowest (0.17 0.01 g L1) (Table 2). This finding is consistent with the report by Ayhan and Estürk (2009), who reported that packaging and storage duration had significant impacts on TAC (0.31–0.26 g L1) of pomegranate arils ‘Hicazna’. The range of TAC values found in our study is similar to those reported by Caleb et al. (2013) for minimally processed pomegranate arils ‘Acco’ (0.21–0.13 g L1) and ‘Herskawitz’ (0.20–0.12 g L1) packaged under passive-MAP at 5 C, 10 C and 15 C for 14 d. In addition, higher TAC was observed in arils packaged under passive-MAP compared to clamshell containers across all the temperatures, which could suggest that MAP is effective in retarding anthocyanin degradation. Total anthocyanin content of ‘Primosole’ pomegranate arils (0.29 g L1) packaged under passive-MAP at 5 C was also maintained after 10 d of storage (Palma et al., 2009). However, the TAC of arils in experiment 2 of our study was not significantly altered by MAP
and storage duration, while TAC of arils in experiment 1 increased significantly (P < 0.05) with storage across all the MAP treatments. This might have been as a result of the low barrier characteristics of the packaging film used in experiment 1, which provided a higher water vapour permeability and moisture loss. In addition, the highest increase in TAC was observed in arils in clamshell containers which might have suffered more moisture loss compared to those packaged in polymeric film. Gil et al. (1996) also reported an increase in TAC with storage in unpackaged ‘Molar’ pomegranate arils at 1, 4 and 8 C and attributed it to enhanced moisture loss. Anthocyanins are unstable and susceptible to degradation, during processing and storage. Various factors such as processing temperature, storage conditions, application postharvest treatments, the chemical nature of anthocyanins, pH, sugars, exposure to light and metals can affect the stability of anthocyanins (Maghoumi et al., 2013). 3.5. Microbial analysis Modified atmospheres packaging (MAP), storage duration and interaction of MAP and storage duration had significant effects (P < 0.05) on total aerobic mesophilic bacteria counts in arils in low barrier BOP film (Table 3). High O2 atmospheres
Table 3 Experiment 1: Effect of active and passive MAP and storage duration on total aerobic mesophilic bacteria, and mould and yeast counts of minimally processed pomegranate arils packaged in low barrier BOP film and clamshell packages and stored at 5 C for 12 d. Mean values (n = 9) SD, presented are approximated to significant digit. Parameters
Treatments
Storage duration (d) 0
6
12
Total aerobic mesophilic bacteria counts (log CFU mL1)
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
<1.0g <1.0g <1.0g <1.0g
5.4 0.05e 4.1 0.04f 6.0 0.05c 5.5 0.02d
6.1 0.02b 6.2 0.05a 6.2 0.02ab 6.0 0.03c
Yeast and mould counts (log CFU mL1)
MAP-A (5 kPa O2 + 10 kPa CO2) MAP-B (30 kPa O2 + 40 kPa CO2) MAP-C (passive) Clamshell
<0.5d <0.5d <0.5d <0.5d
3.6 0.05c 3.6 0.24c 3.6 0.13c 3.5 0.12c
4.2 0.28b 4.5 0.25a 4.2 0.35ab 4.3 0.10ab
Means with the same letters across each column and row are not significantly different (P < 0.05).
K. Banda et al. / Postharvest Biology and Technology 109 (2015) 97–105
(MAP-B) extended the lag phase of total aerobic mesophilic bacteria until day 6. Total aerobic mesophilic counts in this treatment (MAP-B) increased threefold from the initial count (<1.2 log CFU mL1) on day 0 compared to a five-fold increase in passive-MAP conditions (MAP-C). However, by the end of the storage, aerobic mesophilic counts in high O2 atmospheres (MAP-B) had increased to the same levels as the other MAP treatments. In contrast, yeast and mould counts did not differ significantly (P > 0.05) across the MAP treatments in the low barrier BOP film. The counts were below considered limit (<5 colonies) on day 0 and increased significantly with storage to a range of 4.2–4.5 log CFU mL1 by day 12 across all the treatments. Aerobic mesophilic bacteria counts in arils packaged in the high barrier Polylid1 film increased significantly with storage from an initial <1.0 log CFU mL1 on day 0 to a range of about 5.8 log CFU mL1 across all the treatments by the end of the storage duration. Pomegranate arils packaged in 100 kPa N2 (MAP-F) and high oxygen O2 atmospheres (MAP-E) maintained significantly lower aerobic mesophilic bacteria counts throughout the storage duration compared to those packaged in MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) and passive-MAP (Table 4). Total aerobic bacteria and yeast and mould counts were below the maximum limits of 7 log CFU mL1 and 5 log CFU mL1 respectively, for fresh cuts in the South African legislation (FCD, Act 57 1979) in both experiments 1 and 2 by the end of the storage period. The inhibitory effect of high O2 atmospheres to microbial growth on minimally processed produce has also been reported in other studies on fresh-cut pineapple and berries (Zheng et al., 2008; Zhang et al., 2013). High O2 atmospheres have been suggested to lead to intracellular generation of reactive oxygen species such as superoxide (O2), hydroxyl (OH), hydrogen peroxide (H2O2), and singlet oxygen (1O2), which damage vital cellular components and reduce cell viability when oxidative stresses overwhelm cellular protection systems (Kader and Ben-Yehoshua, 2000). The range of values of aerobic mesophilic bacteria, and yeast and mould counts in the present study is similar to those reported by López-Rubira et al. (2005) for minimally processed pomegranate arils (cv. Mollar of Elche) stored at 5 C. The ability of high O2 atmospheres to suppress aerobic mesophilic growth in arils packaged in low barrier polylid film corroborates findings by Ayhan and Estürk (2009). The authors reported the lowest aerobic mesophilic counts in high O2 atmospheres (70 kPa O2 + 10 kPa CO2) packages. Furthermore, in our studies 100 kPa N2 atmospheres (MAP-F) were also found to be effective in suppressing aerobic mespohilic growth in arils packaged in low barrier polylid film. Nitrogen displaces O2 and therefore helps to retard growth of aerobic spoilage microorganisms (Sandhya, 2010).
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3.6. Sensory evaluation Table 5 shows the sensory scores of arils packaged in low barrier BOP and Polylid1 films. In experiment 1, package type and low O2 atmospheres had a significant impact (P < 0.05) on the sensory evaluation scores for taste and aroma of arils. The shelf life based on overall acceptability scores was limited to 6 d for arils packaged in clamshell containers. Arils packed in low O2 atmospheres (MAP-A) fell below the consumer acceptance limit of 3 out of a score of 5 by day 9. The arils also had the highest scores for off-odour by the end of the storage duration. In contrast, arils in passive-MAP remained acceptable until day 9, while those in MAP-B (30 kPa O2 + 40 kPa CO2 + 30 kPa N2) scored above the acceptance limit by day 9. Arils in low O2 atmospheres (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) and 100 kPa N2 (MAP-F) in the high barrier Polylid1 film fell below the acceptance limit by day 9 with overall acceptability scores of 2.8 and 2.5, respectively (Table 6). However, arils in passive-MAP (MAP-G) remained acceptable until day 9 and those in O2 atmospheres (MAP-E) scored above the acceptable limit for overall consumer acceptability by day 9. The highest scores for off-odour observed in low O2 atmospheres (MAP-A), low oxygen (MAP-D) and 100 kPa N2 (MAP-F) packages could be attributed to possible increase in fermentative metabolites in the arils, due to the accumulation of CO2 (Watkins, 2000). Ayhan and Estürk (2009) also reported a lower shelf life for minimally processed pomegranate arils packaged in low oxygen atmospheres (5 kPa O2 + 10 kPa CO2) compared to those packaged in air, nitrogen and enriched oxygen. Additionally, the sensory analysis indicated that the development of off-odour of arils packaged under low O2 atmospheres played a critical role in the overall acceptance score. This is consistent with other studies that the development of offodours can serve as an indicator of postharvest shelf-life (Caleb et al., 2013; Zhang et al., 2013). 4. Conclusions This study showed that although equilibrium gas composition of 16–18 kPa O2 and 7 kPa CO2 levels was established in the low barrier BOP film, they were not within the recommended levels (2– 5 kPa O2 and 10–20 kPa CO2) for minimally processed pomegranate arils. In contrast, O2 decreased and CO2 increased continuously in the high barrier Polylid1 film during storage, with O2 levels in packages initially flushed with low O2 further reduced below critical limit (2 kPa). This suggests the need for further optimisation of the initial gas composition flushed into packages with low barrier film via the application of integrated mathematical models. Additionally, perforation-medicated MAP (micro-perforation) technique can be applied towards improving gas permeability of the high barrier film. Shelf life of arils based on overall acceptability sensory scores was limited to 6 and 9 d in clamshell containers and
Table 4 Experiment 2: Effect of active and passive MAP and storage duration on total aerobic mesophilic bacteria, and mould and yeast counts of minimally processed pomegranate arils packaged in high barrier Polylid1 film and stored at 5 C for 12 d. Mean values (n = 9) SD, presented are approximated to significant digit. Parameters
Treatments
Storage duration (d) 0
6
12
Total aerobic mesophilic bacteria counts (log CFU mL1)
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 10 kPa CO2) MAP-F(100 kPa N2) MAP-G (passive)
<1.0e <1.0e <1.0e <1.0e
5.8 0.14ab 5.5 0.15cd 5.4 0.06d 5.7 0.06ab
5.8 0.12a 5.5 0.08cb 5.6 0.07cb 5.8 0.15a
Yeast and mould counts (log CFU mL1)
MAP-D (5 kPa O2 + 10 kPa CO2) MAP-E (30 kPa O2 + 40 kPa CO2) MAP-F(100 kPa N2) MAP-G (passive)
<0.5d <0.5d <0.5d <0.5d
3.1 0.12c 3.8 0.17b 3.1 0.17c 3.4 0.09c
4.7 0.15a 4.5 0.20a 4.5 0.13a 4.7 0.27a
Means with the same letters across each column and row are not significantly different (P < 0.05).
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Table 5 Experiment 1: Scores for sensory quality attributes of minimally processed pomegranate arils stored under active and passive MAP in low barrier BOP film at 5 C for 9 d. Mean values (n = 6) SD, presented are approximated to significant decimal place. Quality parameters
Treatments
0
3
6
9
Taste
MAP-C (passive) MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-B (30 kPa O2 + 40 kPa CO2 + 60 kPa N2) Clamshell
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
4.3 0.51b 3.5 1.38c 4.0 0.63b 3.8 1.17b
3.5 0.84c 3.8 1.69b 3.3 0.52bc 2.5 0.55c
3.3 0.75bc 3.7 1.11bc 3.2 0.37bc 2.3 0.47c
Off-odour
MAP-C (passive) MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-B (30 kPa O2 + 40 kPa CO2 + 85 kPa N2) Clamshell
0 0 0 0
0 0.2 0.41a 0.8 2.04a 0.3 0.82a
0.5 0.84a 0.8 0.98a 0.5 0.55a 1.2 1.47a
0.7 0.25a 1.0 0.82a 0.7 0.47a 1.3 1.25a
Flavour
MAP-C (passive) MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-B (30 kPa O2 + 40 kPa CO2 + 85 kPa N2) Clamshell
4.8 0.37a 4.8 0.37a 4.8 0.37a 4.8 0.37a
4.2 0.75a 4.0 1.26a 3.8 0.98ab 4.0 1.26a
3.5 0.84ab 3.7 0.88ab 3.5 0.55ab 2.8 0.41c
3.3 0.75ab 3.6 0.84ab 3.3 0.47ab 2.7 0.47c
Aroma
MAP-C (passive) MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-B (30 kPa O2 + 40 kPa CO2 + 85 kPa N2) Clamshell
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
3.7 0.82b 3.5 1.22b 3.7 1.21b 3.3 1.63b
3.3 0.52b 3.8 1.17ab 3.7 0.52b 2.8 0.41b
3.2 0.37b 3.7 0.94b 3.5 0.5b 2.7 0.47b
Overall acceptability
MAP-C (passive) MAP-A (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-B (30 kPa O2 + 40 kPa CO2 + 85 kPa N2) Clamshell
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
4.3 0.52b 4.2 0.98b 4.2 0.75b 3.8 1.17bc
3.7 0.42bc 3.9 1.02bc 3.7 0.52bc 3.0 0.63c
3.1 0.19c 2.9 0.19c 3.5 0.5bc 2.3 0.47c
Storage duration (d)
Means with the same letters across each column and row are not significantly different (P < 0.05).
Table 6 Experiment 2: Scores for sensory quality attributes of minimally processed pomegranate arils stored under active and passive MAP in high barrier Polylid1 film at 5 C for 9 d. Mean values (n = 6) SD, presented are approximated to significant decimal place. Quality parameters
Treatments
Storage duration (d) 0
3
6
9
Taste
MAP-G (passive) MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) MAP-F (100 kPa N2)
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
3.7 0.18b 3.5 1.22b 3.7 1.03b 3.7 1.03b
3.2 0.75b 3.3 1.03b 3.7 0.82b 3.3 1.21b
3.0 0.58b 3.2 0.90b 3.7 0.75b 3.0 0.82b
Off-odour
MAP-G (passive) MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) MAP-F (100 kPa N2)
0 0 0 0
0.5 0.55b 0 0 1.0 0.17b
2.5 1.05a 2.7 1.51a 2.3 1.37a 2.5 1.05a
2.7 0.47a 2.7 0.94a 2.2 0.68a 2.3 0.74a
Flavour
MAP-G (passive) MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) MAP-F (100 kPa N2)
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
3.7 0.52ab 4.0 0.63ab 3.8 0.75ab 3.8 0.75ab
3.7 0.52ab 3.8 0.41ab 3.5 0.55ab 3.5 0.84ab
3.7 0.47ab 3.7 0.47ab 3.5 0.5ab 3.2 0.69b
Aroma
MAP-G (passive) MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) MAP-F (100 kPa N2)
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
4.5 0.55a 4.2 0.41ab 4.5 0.55a 4.5 0.55a
3.7 0.52b 3.8 0.75ab 4.2 0.75ab 3.8 0.98ab
3.7 0.47b 3.7 0.47b 3.8 0.69ab 3.7 0.74b
Overall acceptability
MAP-G (passive) MAP-D (5 kPa O2 + 10 kPa CO2 + 85 kPa N2) MAP-E (30 kPa O2 + 10 kPa CO2 + 60 kPa N2) MAP-F (100 kPa N2)
5.0 0.0a 5.0 0.0a 5.0 0.0a 5.0 0.0a
3.7 0.82b 4.0 0.63b 4.0 0.63b 4.0 0.89b
3.5 0.55b 3.5 0.55b 3.8 0.75b 3.3 0.82b
3.0 0.00b 2.8 0.37bc 3.3 0.47b 2.5 0.5c
Means with the same letters across each column and row are not significantly different (P < 0.05).
passive-MAP, respectively. On the other hand, packages flushed with high level of O2 atmospheres for both the low and high barrier polymeric films maintained sensory quality beyond 9 d in comparison with packages initially flushed with low O2 atmosphere under the high barrier polymeric film. Thus, in order to avoid anoxic condition and the development of off-odour due to excessive accumulation of CO2 and depletion of O2 inside activeMA packaged arils, the combination of gas flushing with initially low O2 atmosphere level and heat-sealing trays with high barrier polymeric film is not recommended.
Acknowledgements This work was supported by the South African Research Chairs Initiative of the Department of Science and Technology and the National Research Foundation. Dr O.J. Caleb received the NRF Free-Standing Postdoctoral Fellowship 2013/2014 (Grant No. 85243). The authors are grateful to Mr. Fan Olivier of Houdconstant Pack-House, Porterville, South Africa for assistance with fruit procurement and processing.
K. Banda et al. / Postharvest Biology and Technology 109 (2015) 97–105
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