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Effects of modified atmosphere package (MAP) with a silicon gum film window on the quality of stored green asparagus (Asparagus officinalis L) spears
LWT - Food Science and Technology 60 (2015) 1046e1053
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Effects of modified atmosphere package (MAP) with a silicon gum film window on the quality of stored green asparagus (Asparagus officinalis L) spears Tiehua Li a, *, Min Zhang b a b
College of Forestry, Central South University of Forestry and Technology, 410004, Changsha, Hunan, China School of Food Science and Technology, Jiangnan University, 214036, Wuxi, Jiangsu, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 August 2012 Received in revised form 28 October 2014 Accepted 31 October 2014 Available online 7 November 2014
Packages of green asparagus (Asparagus officinalis L.) spears with or without silicon gum film windows were flushed in two different modified systems (50 mL L1 O2 with 100 mL L1 CO2 and 100 mL L1 O2 with 100 mL L1 CO2, with N2 as a balance gas) and stored at 2 ± 1 C for 30 days. The changes in gas headspace, sensory, respiration rate, ascorbic acid content, soluble solid content and chlorophyll content were investigated. The results showed that green asparagus spears stored in MAP with silicon gum film windows, the gas exchange between packages and surrounding atmosphere through the silicon gum film windows induced an in-package optimum atmosphere for green asparagus spears stored at O2 above 21 mL L1, CO2 below 157 mL L1 and ethylene below 15.84 mL L1. These packages prevented anaerobic respiration to get good odour score, and were able to keep a relatively low respiration rate and reduce loss of ascorbic acid. A low concentration of ethylene atmosphere was effective for inhibiting chlorophyll degradation, which resulted in a high appearance score. The initial atmosphere in packs also affect the quality attributes, where 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere was preferred. © 2014 Elsevier Ltd. All rights reserved.
Keywords: MAP Green asparagus Storage Modified atmosphere Ethylene Chemical compounds studied in this article: Ethylene (PubChem CID: 6325) Ethanol (PubChem CID: 702) Ascorbic acid (PubChem CID: 54670067) Chlorophyll (PubChem CID: 6477652)
1. Introduction As one of the important fresh vegetables, green asparagus (Asparagus officinalis L.) is becoming more and more popular in recent years in China due to its special flavour, taste and abundance of various nutrients such as vitamins, amino acids and trace elements (Li, Zhang, & Yu, 2006; Saltveit & Kasmire, 1985). However, it is also a highly perishable vegetable, which deteriorates rapidly after harvest, and only has a shelf life of 3e5 days under normal post-harvest handling at ambient temperatures (Baxter & Waters, 1991; Lipton, 1990). A lot of research has been done on the postharvest physiological changes, post-harvest senescence control, storage life extension and post-harvest loss reduction of green asparagus (An, Zhang, Wang, & Tang, 2008; Li et al., 2006). Physiological and compositional changes during storage that reduce the spear quality include bract opening (feathering), toughening and
* Corresponding author. Fax: þ86 (0)731 85623460. E-mail address: [email protected] (T. Li). http://dx.doi.org/10.1016/j.lwt.2014.10.065 0023-6438/© 2014 Elsevier Ltd. All rights reserved.
loss of water, chlorophyll degradation and changes in ascorbic acid, carbohydrates, protein and amino acids (Chang, 1987; Siomos, Sfakiotakis, & Dogras, 2000). These undesirable changes can be reduced by certain methods, including refrigeration storage and controlled atmospheric storage or modified atmosphere storage (Gariepy, Raghavan, Castaigne, Arul, & Willemot, 1991; Lipton, 1990; Siomos et al., 2000). However, ideal storage effects can hardly be attained because the harmful gases released by asparagus are not expelled in time. In order to improve the MAP conditions, packaging films with improved permeability has been studied and developed successfully for some fruits and vegetables storage (Fonseca, Fernanda, Oliveira, & Chau, 1999; Van der Steen, Jacxsens, Devlieghere, & Debevere, 2002). Because respiration rates differ greatly with different vegetable products, packaging films with a wide range of permeability for O2, CO2 and other gases are needed to meet various preservation requirements (Jacxsens, Devlieghere, Falcato, & Debevere, 1999). Another effective method to improve the permeability of packages has also been studied and developed using a silicone membrane system (Vigneault, Orsat, Panneton, & Raghavan, 1992). Gariepy, Raghavan, and Theriault (1986) used a
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silicone membrane system for long term storage of celery under controlled atmosphere conditions. Reeleder, Raghavan, Monette, and Gariepy (1989) fitted silicone membranes of varying surface areas on containers to maintain the atmosphere for controlling storage rot of carrot. Stewart, Raghavan, Golden, & Gariepy, 2005 found that silicone membrane systems with modified atmospheres were effective for storing bananas, maintaining the fruit with a harvest-fresh appearance, good colour and excellent marketability after 42 days of storage. Li, Zhang, and Wang (2007) reported that MAP with silicon gum film as window was effective for maintaining the post-harvest quality of mushroom Agrocybe chaxingu for up to 21 days. So far, there have been few reports on MAP with permeable films as a window for gas exchange to store green asparagus. In this study, a silicon gum film with high permeability for O2, CO2 and other gases was used as a window material on packages to store green asparagus in two different initial modified atmosphere systems (50 mL L1 O2 with 100 mL L1 CO2 and 100 mL L1 O2 with 100 mL L1 CO2, with N2 as a balance gas) at a temperature of 2 ± 1 C. The storage effects were investigated by evaluating the physical, chemical, physiological and sensory characteristics of the asparagus spears. 2. Materials and methods 2.1. Plant material The fresh green asparagus (A. officinalis L. cv. ‘UC800’) spears used in this study were obtained from Natong Hualin Agricultural Products Co., Ltd. in Suzhou city, Jiangsu province, China. The asparagus spears were cut at ground level from 8:00 to 9:30 AM and transported to the laboratory within 3 h. They were then used in the experiment within 2 h. The green asparagus spears used were about 180 mm in length and 8e15 mm in diameter. 2.2. Equipment The gas supply system for MAP consisted of bottled N2, O2 and CO2, a 10 L mixing cylinder and a vacuum pump to remove the air in the gas supply system. The gas composition established in the packages was checked using a gas analyzer (CYES-II, Xuelian Analytical Instrument Co. Ltd., Shanghai, China) with a system accuracy of ±0.5%. The MAP equipment (ADFM-V3000, air controlled atmosphere packing machine, Hengzhong Packing Co., Lianyungang City, Jiangsu Province, China) was connected to the mixing cylinder of the gas supply system. 2.3. Modified atmosphere packaging Polystyrene (PS) packaging trays (18 cm length 12 cm width 4 cm depth) (Fig. 1), with a wall thickness of 0.3 mm and a total surface area of 456 cm2, which achieves an O2 permeability of
Fig. 1. The sketch of packaging tray with silicon gum film window and PP membrane.
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14.62 1016 mol s1m2 Pa1 and CO2 permeability of 53.51 1016 mol s1m2 Pa1 at 20 C and 90% RH were used. A total of 108 PS packaging trays were divided into 2 groups, one group had a window (0.8 cm 1.0 cm, the preliminary test showed this size of window was optimum) cut into it at the central part on the side of each tray, and the other group was kept unchanged as the control. The window was covered with high permeability film (FC-8 silicon gum film, Lanzhou Physical & Chemical Research Institute of the Academy of Sciences of China, Lanzhou, China), which was made by spreading 50 ± 5 g silicon gum on a 1 m2 cloth to achieve an O2 permeability of 4.08 109 mol s1m2 Pa1 and CO2 permeability of 12.24 109 mol s1m2 Pa1 at 20 C and 90% RH. There were two combinations of modified atmosphere systems in this study: 50 mL L1 O2 with 100 mL L1 CO2, and 100 mL L1 O2 with 100 mL L1 CO2, with N2 as a balance gas. For each modified atmosphere system, 54 trays were packaged, where 27 trays (three replicates with 9 time measurements for each treatment) of them had FC-8 silicon gum film windows. In each tray, approximately 160 g of green asparagus was packaged and sealed with 35 mm thick polypropylene (PP) membrane, which has a total surface area of 216 cm2 with an O2 permeability of 7.04 1016 mol s1m2 Pa1 and CO2 permeability of 27.69 1016 mol s1m2 Pa1 at 20 C and 90% RH. The total storage period was 30 days, at a temperature of 2 ± 1 C with a relative humidity of 95e100% inside the packages and of about 85% in the storage room. Gas analysis, sensory quality, and physical and chemical analysis (respiration rate, ascorbic acid, chlorophyll content, and soluble solid content) were conducted on the 12 h, the first day, then at 5-day interval up to day 30. 2.4. Gas analysis The headspace gas concentrations of O2, CO2, ethylene and ethanol in the sealed trays during storage were measured in each package before opened. The gases were pumped out with syringes and then injected into analysis equipments for measuring respectively. The headspace gas concentrations of O2 and CO2 was analysed using a gas analyzer (CYES-II, Xuelian Analytical Instrument Co. Ltd., Shanghai, China) at 12 and 24 h on the first day and then every 5 days. The headspace gas concentration of ethylene was analysed on the first day and then every 5 days, using a gas chromatograph (Shimadzu GC-2010, Japan) equipped with a flame ionization detector (FID) and a DB-1 column. Nitrogen was used as a carrier gas at a flow rate of 10 mL min1. The headspace gas concentration of ethanol was analysed on the third day and then every 5 days, using a gas chromatograph (Agilent GC-6890A, USA) equipped with a FID and a PP-20000 column. Nitrogen was used as a carrier gas at a flow rate of 2 mL min1. 2.5. Sensory quality Van der Steen et al., 2002 and An, Zhang, Lu, & Zhang, 2006 methods with some modifications were used to evaluate the sensory quality. A panel of ten judges consisted of 5 men and 5 women with age from 21 to 42 years old, who had been trained for evaluating fruits and vegetables sensory quality before. They were invited to evaluate the sensory quality characteristics of all the green asparagus from each tray. The typical characteristics of the green asparagus and the possibilities of deterioration were explained before the experiment started. All sensory tests (general appearance, firmness and odour) were performed in a special taste room with separated boxes. The general appearance was judged under normal light and the sensory characteristics such as firmness and odour were evaluated under IR light to exclude the influence of
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the visual characteristics. General appearance was evaluated on a scale of 9e1, where 9 represents excellent (dark green, no feathering, no rotten areas or water-soaked areas), 7 represents good (dark green, 5% feathering, 1e2 of 0.5 mm2 rotten or water-soaked areas), 5 represents fair and limited marketability (light green, 6e10% feathering, 3e5 of 0.5 mm2 rotten or water-soaked areas), 3 represents poor and limited usability (yellowish green, 10e15% feathering, 6e8 of 0.5 mm2 rotten or water soaked areas), and 1 represents very poor and inedible (yellowish green, more than 15% feathering and more than 8 0.5 mm2 rotten or water-soaked areas). Firmness was evaluated by pressing the green asparagus between the thumb and index finger, on a scale of 9e1, where 9 represents tender, 7 represents slightly tender, 5 represents firm, 3 represents hard, and 1 represents very hard. Off-odours, mainly because of fermentation, were evaluated on a scale of 9e1, where 9 represents none, 7 represents slight, 5 represents moderate, 3 represents moderately severe, and 1 represents severe. The cut-off score was set at 5. Above this score, the sample was considered acceptable. 2.6. Physical and chemical analysis 2.6.1. Respiration rate A static method was used to assess the respiration rate. Before assessment, the green asparagus (160 g ± 5 g) was taken out from the packages and exposed to ambient conditions in a storage room (3000 L) for 1 h to allow the CO2 accumulated in the tissue to diffuse into the air. The sample was then put into an air-tight jar of 260 mm diameter, with 10 mL of 0.4 mol L1 NaOH in a Petri dish, and the jars were placed in a chamber set at 2 C. The Petri dish was taken out after 30 min and the NaOH titrated with 0.1 mol L1 oxalic acid (C2H2O4) immediately. The change in the concentration of CO2 was used to estimate the respiration rates (Li et al., 2006). 2.6.2. Ascorbic acid Ascorbic acid was determined by the indophenol titration method (Favell, 1998). 15 asparagus spears were taken out randomly from 3 trays (5 asparagus spears for each tray), and chopped them with a knife, then mixed them thoroughly as experiment materials, and randomly took 3 samples (approximately 10 g for each sample). One sample was ground in a mortar with the same quantity of 2 g 100 g1 oxalic acid. 1 g 100 g1 oxalic acid solution was used to wash the paste into a 100 mL volumetric flask and made to volume. Five mL filtered solution was titrated with 2,6-dichlorophenol indophenols solution until the distinct light rose pink colour persisted for more than 5 s. 2.6.3. Chlorophyll content 15 asparagus spears were taken out randomly from 3 trays (5 asparagus spears for each tray), and chopped them with a knife, then mixed them thoroughly as experiment materials, and randomly took 3 samples (approximately 1.0 g for each sample). One sample was ground manually in a glass mortar for chlorophyll content determination. Chlorophyll was extracted from the sample by homogenizing it in 20 mL of 80 g 100 g1 acetone with a tissue homogenizer (DS-1, Shanghai, China) at a moderate speed for 30 s, and 80 g 100 g1 acetone solution was used to wash the paste into a 50 mL volumetric flask and made to volume. The homogenate was filtered through two layers of filter papers, centrifuged at 15,000 g for 15 min, and the absorbance read at 647 and 664.5 nm with an UVeVis recording spectrophotometer (UV-754; Shanghai Precision & Scientific Instrument Co., Ltd., Shanghai, China). The total chlorophyll content was calculated by chlorophyll (mg 100 g1 FW) ¼ 5* [17.95*Abs647 þ 8.08*Abs664.5] (Inskeep & Bloom, 1985).
2.6.4. Soluble solid content 9 asparagus spears were taken out randomly from 3 trays (5 asparagus spears for each tray), and cut them into pieces, then mixed them thoroughly and randomly took 3 samples (approximately 5.0 g for each sample). The juice was squeezed out from the samples respectively, and then its content of soluble solid was measured with an ABBE Bausch and Lomb refractometer (2WAJ, Shanghai optical instruments factory, Shanghai, China). 2.7. Statistical analysis All experiments were conducted in triplicate and the average values with standard deviation were used in the analysis. All data were evaluated by multi-factorial analysis of variance (ANOVA) using SPSS (Windows XP) with silicon gum film window and gas composition as the main effects. To determine the differences between treatments, Duncan tests were applied and the significant differences were established at P < 0.05. 3. Results and discussion 3.1. Gas change in headspace of packs Fig. 2a shows the O2 concentration to decrease rapidly in the first day for all treatments, and then remained relatively stable during the following storage days. The O2 concentrations in the headspace of packs with silicon gum film windows exceeded 21 mL L1 during the 30-day storage, while the O2 concentration in the headspace of control packs were less than 10 mL L1 (generally harmful for vegetable and fruit storing) from the first storage day. The CO2 concentrations in the headspace of packs with silicon gum film windows increased slowly and reached a peak of 132 mL L1 and 157 mL L1 on the 5th storage day with 50 mL L1 O2 and 100 mL L1 O2 initial atmosphere respectively, then dropped slowly until the 10th and 15th storage day, and remained relatively stable over the later storage time, and only 1.21 times and 1.35 times of the initial value respectively at the end of the storage period. However, the CO2 concentrations in the headspace of controls increased with increasing storage time and reached 2.98 times and 3.16 times of the initial value respectively at the end of the storage period (Fig. 2b). The ethanol concentration changes in the headspace of green asparagus packs are shown in Table 1. There were significant differences (P < 0.05) in the ethanol concentration among these treatments after 5 days of storage. No ethanol was detected in the packs with silicon gum film windows over the entire storage period, whereas the controls registered the presence of ethanol from Day 5. The concentration of ethanol was found to increase throughout the subsequent storage period. Without silicon gum film windows, the ethanol concentrations increased from 0.184 mL L1 to 1.115 mL L1 during Day 5 to Day 30 in packs with 100 mL L1 O2 initial atmosphere, and the ethanol concentrations increased from 0.107 mL L1 to 0.724 mL L1 during Day 5 to Day 30 in packs with 50 mL L1 O2 initial atmosphere, the former was higher than the latter. The injury effects caused by high CO2 concentration and low O2 concentration have been demonstrated for some fruits and vegetables (Beaudry, 1999; Lopez-Briones et al., 1992; Villaescusa & Gil, 2003). Extremely low O2 levels or excessively high CO2 levels induce fermentation and will result in the generation of off-flavours (Dostal-Lange & Beaudry, 1991; Richardson & Kosittrakun, 1995) or visible tissue damage (Lidster, Blanpied, & Prange, 1990). Some studies show that there is an interaction between O2 and CO2, where elevated CO2 levels make plant material more sensitive to low levels of O2, and the fermentation threshold may occur at
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all treatments. There were significant differences (P < 0.05) in the ethylene concentration between the packs with and without silicon gum film windows. The ethylene concentration in packs with silicon gum film windows increased slowly, from the initial 0.09 mL L1 to 15.84 mL L1 at the end of 30-day storage, while the ethylene concentration in controls increased quickly, which from the initial 0.20 mL L1 to the highest value of 185.64 mL L1, much higher than the former. 3.2. Sensory evaluation
Fig. 2. Changes of O2 (a) and CO2 (b) concentrations (mean ± S.D. for three replicates) in packages for green asparagus stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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higher O2 partial pressures with an increase in CO2 partial pressure (Beaudry, Cameron, Shirazi, & Dostal-Lange, 1992). Kupferman (1997) and Saltveit (1997) reported that some apple cultivars and vegetables required an O2 concentration of above 1% for storage. The packs with silicon gum film windows provided a favourable storage atmosphere for green asparagus because these windows have high permeability for O2, CO2 and other gases, whereas the controls experienced fermentation caused by low O2 and excessively high CO2 from the respiration of green asparagus (Fig. 2a, b and Table 1). The change in ethylene concentration is shown in Table 2. The ethylene concentration increased with increasing storage time for
Fig. 3 shows the score pattern for appearance, firmness, and odour of green asparagus stored in MAP with and without silicon gum film windows in different modified atmospheres. The scores for appearance, firmness and odour decreased with increasing storage time, irrespective of treatment methods. As shown in Fig. 3a, silicon gum film window and modified atmosphere had significant effects (P < 0.05) on the appearance of green asparagus after 10 days of storage. These differences were primarily attributed to the presence of silicon gum film window, with modified atmosphere as a secondary factor. With silicon gum film window, the appearance scores of green asparagus stored in packs with initial atmosphere of 100 mL L1 O2 and 100 mL L1 CO2 decreased slowly before Day 15 (from 9 to 7.5), and then rapidly until Day 30 (from 7.5 to 4.6). Meanwhile, the appearance scores of green asparagus stored in packs with initial atmosphere of 50 mL L1 O2 and 100 mL L1 CO2 decreased slowly before Day 20, and then quickly until the end of storage period. Without silicon gum film window, the appearance scores of green asparagus decreased quickly from Day 5 and Day 10 until the end of storage for the packs with initial atmosphere of 100 mL L1 O2, 100 mL L1 CO2 and 50 mL L1 O2, 100 mL L1 CO2, which dropped from 8.4 to 3.2 and 7.9 to 3.6 respectively. The appearance scores of green asparagus stored in MAP with silicon gum film window in initial atmosphere of 50 mL L1 O2 and 100 mL L1 CO2 had the slowest decrease (from 9.0 to 5.2) during the storage time. Based on the acceptable score of 5.0, only green asparagus in MAP with silicon gum film window in initial atmosphere of 50 mL L1 O2 and 100 mL L1 CO2 could be stored for 30 days. Fig. 3b shows a similar trend for firmness as general appearance. The firmness scores of green asparagus stored in MAP with silicon gum film window in initial atmosphere of 50 mL L1 O2 and 100 mL L1 CO2 had the slowest decrease (from 9.0 to 5.0) during the storage time, and was the only treatment that scored above 5.0 at the end of the 30-day storage. There were significant differences (P < 0.05) in the scores for odour between the green asparagus stored in MAP with and without silicon gum film window (Fig. 3c). The odour scores for green asparagus stored in MAP with silicon gum film windows remained above the acceptable value of 5.0 until the end of 30-day storage, irrespective of the initial modified atmosphere. Without silicon gum film windows, the scores of green asparagus stored in
Table 1 Changes in headspace ethanol concentration in green asparagus packs with silicon gum film as windows and different atmosphere during 30 days storage. Treatments
Ethanol concentration (mL L1) 3 day
5 days
10 days
15 days
20 days
25 days
30 days
50 mL/LO2 þ 100 mL/L CO2 þ W 50 mL/LO2 þ 100 mL/L CO2 þ NW 100 mL/LO2 þ 100 mL/LCO2 þ W 100 mL/LO2 þ 100 mL/LCO22 þ NW
0 0 0 0
0a 0.107 ± 0.018 b 0a 0.184 ± 0.014 c
0a 0.226 ± 0.026 b 0a 0.375 ± 0.021 c
0a 0.338 ± 0.031 b 0a 0.572 ± 0.036 c
0a 0.505 ± 0.048 b 0a 0.811 ± 0.053 c
0a 0.619 ± 0.053 b 0a 0.947 ± 0.065 c
0a 0.724 ± 0.056 b 0a 1.115 ± 0.073 c
Values were mean ± SD for 3 replicates. Different letters in the same column indicate that means are significantly different (P < 0.05). W: window; NW: no window.
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Table 2 Changes in headspace ethylene concentration in green asparagus packs with silicon gum film as windows and different atmosphere during 30 days storage. Treatments
50 mL/L O2 þ 100 mL/L CO2 þ W 50 mL/L O2 þ 100 mL/L CO2 þ NW 100 mL/L O2 þ 100 mL/L CO2 þ W 100 mL/L O2 þ 100 mL/L CO22 þ NW
Ethylene concentration (mL L1) 0 day
1 day
0 0 0 0
0.09 0.20 0.10 0.24
± ± ± ±
5 days 0.01a 0.04b 0.01a 0.02b
0.81 5.87 1.26 7.23
± ± ± ±
10 days 0.03a 0.31b 0.04a 0.35b
2.65 53.58 3.43 68.21
± ± ± ±
15 days 0.13a 3.23b 0.11a 3.24b
5.32 102.45 7.22 113.15
± ± ± ±
20 days 0.22a 5.44b 0.34a 5.11b
8.14 126.37 11.05 148.26
± ± ± ±
25 days 0.41a 4.67b 0.47a 4.28b
10.67 142.44 13.58 163.89
± ± ± ±
30 days 0.46a 6.21b 0.44a 7.22b
11.83 171.56 15.84 185.64
± ± ± ±
0.44a 8.35b 0.63a 6.45b
Values were mean ± SD for 3 replicates. Different letters in the same column indicate that means are significantly different (P < 0.05). W: window; NW: no window.
packs with initial atmosphere of 50 mL L1 O2, 100 mL L1 CO2 and 100 mL L1 O2, 100 mL L1 were below 5.0 after Day 20 and Day 15, respectively. 3.3. Respiration rate Fig. 4 shows the changes in respiration rates during storage for all treatments. The initial respiration rates were very high before storage, reaching 153.2 ± 6.5 mg CO2 kg1 h1, and similar observations were reported by An et al. (2006) and Li et al. (2006). For all the treatments in our study, the respiration rate dropped by 46e59% for the first 5 days. After this decline, the respiration rate of the green asparagus in the controls increased thereafter, but remained relatively stable from Day 5 to 20, and increased quickly after Day 20 in the packages with silicon gum film windows and the respiration rate increased 43.2e72.0% from Day 20 to Day 30. Li et al. (2006) reported the similar results for storing the green asparagus in room temperature and in refrigeration (3 C), and the
respiration rate increased from Day 3 and Day 10 respectively. In this study, the poor atmosphere in packages, i.e. low concentration O2, high concentration CO2 and the presence and accumulation of ethylene (Fig. 2 and Tables 1 and 2) will cause physiological injuries, which may induce the respiration rate of the green asparagus increase from Day 10 in the controls and Day 20 in the packages with silicon gum film windows. Some researchers reported that carbon dioxide stimulated respiration in lettuce (Kubo, Inaba, & Nakamura, 1990; Siriphanich & Kader, 1986) and spinach (Kubo et al., 1990). These increases in respiration by exposure to elevated carbon dioxide may be related to physiological injury (Kader, 1986). Saltveit, (1999) thought that ethylene stimulated the increase of respiration. There were significant differences (P < 0.05) for the respiration rates of green asparagus among treatments during Day 10e30. The presence of silicon gum film windows and a lower initial O2 concentration of 50 mL L1 had resulted in a lower respiration rate in the green asparagus. As shown in Fig. 4, the respiration rate of the green asparagus in the package with silicon gum film windows
Fig. 3. Changes in scores (mean ± SD for 3 replicates) of appearance (a), firmness (b) and odour (c) for green asparagus packaged and stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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Fig. 4. Respiration rate (mean ± S.D. for three replicates) changes for green asparagus packaged and stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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with 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere was the lowest since Day 1. Low respiration rate is beneficial in maintaining the quality of fruits and vegetables during storage (Concellon, Anon, & Chaves, 2007). It is important to control the respiration rate as lowering the respiration rate could extend the shelf life and preserve the quality of products (Day, 2001; McLaughlin & O'Berne, 1999). 3.4. Ascorbic acid contents Fig. 5 shows the changes in ascorbic acid contents as a function of storage time. The ascorbic acid content in the fresh condition was 27.2 mg 100 g FW1, which decreased gradually during storage for all treatments, and loss of the value varied from 10.9 mg 100 g1 FW to 19.3 mg 100 g1 FW during the storage period by different storage conditions. Significant differences (P < 0.05) in ascorbic acid contents were observed among treatments after 15 days of storage, and these differences were primarily caused by the
Fig. 5. Ascorbic acid content (mean ± S.D. for three replicates) changes for green asparagus packaged and stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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presence of silicon gum film window, with the initial atmosphere as a secondary factor. The green asparagus in packs with the silicon gum film windows had a relatively favourable atmosphere during the storage period with a slow loss in ascorbic acid. On the other hand, the atmosphere with low O2 and high CO2 concentrations, coupled with anaerobic respiration (Table 1) and high ethylene levels (Table 2) for the green asparagus in controls had likely caused cell injury and senescence, which induced a more rapid decline in the ascorbic acid contents. At the end of Day 30, the green asparagus in the packs with silicon gum film windows and 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere had lost 40% of its ascorbic acid contents, with a final reading of 16.3 mg 100 g1 FW, whereas the controls with 100 mL L1 O2 and 100 mL L1 CO2 initial atmosphere lost 71% of its ascorbic acid contents with only 7.9 mg 100 g1 FW remaining, which was much lower than the former. Ascorbic acid is one of the most sensitive materials to be destructed when a fresh produce is subject to adverse handling and storage conditions. Ascorbic acid losses are enhanced by many factors, including extended storage, higher storage temperatures, chilling injury and bad atmosphere (Lee & Kader, 2000; Li et al., 2007; Paull, 1999). In this study, the green asparagus stored in MAP with silicon gum film window had a more favourable atmosphere during storage period, which reduced the losses of ascorbic acid. As observed in the previous study (Li et al., 2007), the silicon gum film window on the MAP helped to retain high ascorbic acid content in mushrooms during storage.
3.5. Total chlorophyll contents The total chlorophyll contents of the green asparagus decreased with extended storage time for all treatments, and the rate of decrease differed with treatments, dropping 23.0%e65.9% during the storage period (Fig. 6). There were significant differences (P < 0.05) in the total chlorophyll contents of the green asparagus among different treatments since Day 10, primarily caused by the silicon gum film windows, with the initial modified atmosphere as a secondary factor. Over the 30-day storage, the green asparagus stored in packs with silicon gum film windows and 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere had a remaining total chlorophyll content of 10.4 mg 100 g1 FW (a loss of 23%), while the controls with 100 mL L1 O2 and 100 mL L1 CO2 initial atmosphere
Fig. 6. Total chlorophyll contents (mean ± S.D. for three replicates) changes for green asparagus packaged and stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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had only 4.6 mg 100 g1 FW of total chlorophyll content left (66% loss). Ethylene is a naturally produced, simple two carbon gaseous plant growth regulator that has numerous effects on the growth, development and storage life of many fruits, vegetables and ornamental crops (Saltveit, 1999). Ethylene inducing senescence has been well documented in many studies (Able, Wong, Prasad, & O'Hare, 2003; Li & Zhang, 2010; Sala & Lafuente, 2004). Ethylene accelerates senescence in the leaves of some species (Leopold & Nooden, 1984; Mattoo & Aharoni, 1988), and promotes processes characteristic of leaf senescence, such as decline in chlorophyll and photosynthesis, reduction in the levels of proteins and starch, and increase in the activities of many hydrolytic enzymes (Ella, Zion, Nehemia, & Amnon, 2003). Lers, Jiang, Lomaniec, and Aharoni (1998) reported external ethylene to have an evident effect in enhancing the degradation rate of chlorophyll and protein, and accumulation of amino acids for stored parsley leaves. In this study, the green asparagus stored in packs with silicon gum film windows lost chlorophyll slowly due to the low concentration of ethylene atmosphere (Table 2). The chlorophyll content of the controls decreased quickly, which dropped from 10.9 mg 100 g1 FW to 5.1 mg 100 g1 FW in 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere and from 10.1 mg 100 g1 FW to 4.6 mg 100 g1 FW in 100 mL L1 O2 and 100 mL L1 CO2 initial atmosphere since the 10th day because of accumulated ethylene (Table 2 and Fig. 6), resulting in a fading green, thus a fall in the appearance scores (Fig. 3a). 3.6. Soluble solid contents Fig. 7 shows the change of soluble solid contents during the 30day storage for green asparagus. The soluble solid contents increased for all treatments at the beginning, which increased from 4.9 g 100 g1 juice to the peaks (6.5 g 100 g1 juice and 6.8 g 100 g1 juice respectively) on the 15th storage day in the packages with silicon gum film windows and increased from 4.9 g 100 g1 juice to the peaks (7.0 g 100 g1 juice and 7.2 g 100 g1 juice respectively) on the 10th storage day in the packages without silicon gum film windows, and then declined. The soluble solid contents of the green asparagus changed gradually in packs with silicon gum film windows, but rapid increased with a higher peak, followed by a faster decline in the controls. It was also found that the soluble solid
Fig. 7. Soluble solid contents (mean ± S.D. for three replicates) changes for green asparagus packaged and stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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contents of green asparagus and “Fuyu” persimmon increased in the early stage of storage (Cia et al., 2006; Li et al., 2006). In this study, at the beginning of storage, the respiration rate dropping quickly from Day 0 to Day 5 (Fig. 4) may cause the temporary accumulation of soluble solid in plant which mainly resulted in the rise of soluble solid contents. The water loss of green asparagus also made some contribution to the increasing soluble solid contents. It was reported that respiration was a major factor contributing to post-harvest losses, which converted stored soluble solid (sugar mainly) into energy in the presence of an oxygen substrate (Nourian, Ramaswamya, & Kushalappa, 2003). In this study, from Day 15, a correlation existed between the level of soluble solid contents and respiration rate, where a treatment with a high respiration rate was found to have a quickly dropping in the soluble solid content and thus showed a relatively low value (Figs. 4 and 7). The green asparagus stored in packs with silicon gum film windows and 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere had the lowest respiration rate during the storage period, with the highest soluble solid content (4.3 g 100 g1 juice) at the end of storage.
4. Conclusion The gas exchange between packages and surrounding atmosphere through the silicon gum film windows induced an optimum in-package atmosphere for storing green asparagus with O2 above 21 mL L1, CO2 below 157 mL L1 and ethylene below 15.84 mL L1, which prevented anaerobic respiration and achieved a high odour score, with relatively low respiration rate and reduced rate of ascorbic acid loss. An atmosphere with low ethylene concentration is effective for inhibiting chlorophyll degradation, hence a high appearance score. The initial atmosphere in packs also had some effects on the quality attributes. Compared to the 100 mL L1 O2 and 100 mL L1 CO2 initial atmosphere, 50 mL L1 O2 and 100 mL L1 CO2 was preferred for maintaining the quality of stored green asparagus.
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Lopez-Briones, G., Varoquaux, P., Chambroy, Y., Bouquant, J., Bureau, G., & Pascat, B. (1992). Storage of common mushroom under controlled atmospheres. International Journal of Food Technology, 27, 493e505. Mattoo, K. M., & Aharoni, N. (1988). Ethylene and plant senescence. In L. D. Nooden, & A. C. Leopold (Eds.), Senescence and aging in plants (pp. 241e279). San Diego: Academic Press. McLaughlin, C. P., & O'Berne, D. (1999). Respiration rate of a dry coleslaw mix as affected by storage temperature and respiratory gas concentrations. Journal of Food Science, 64, 116e119. Nourian, F., Ramaswamya, H. S., & Kushalappa, A. C. (2003). Kinetics of quality change associated with potatoes stored at different temperatures. LWT-Food Science and Technology, 36, 49e65. Paull, R. E. (1999). Effect of temperature and relative humidity on fresh commodity quality. Postharvest Biology and Technology, 15, 263e277. Reeleder, R. D., Raghavan, G. S. V., Monette, S., & Gariepy, Y. (1989). Use of modified atmospheres to control storage rot of carrot caused by Sclerotinia sclerotiorum. International Journal of Refrigeration, 12, 159e163. Richardson, D. G., & Kosittrakun, M. (1995). Off-flavor development of apples, pears, berries and plums under anaerobiosis and partial reversal in air. In R. L. Rouseff, & M. L. Leahy (Eds.), Fruit flavors, biogenesis, characterization and authentication (pp. 211e275). Washington, DC: American Chemical Society. Sala, J. M., & Lafuente, M. T. (2004). Antioxidant enzymes activities and rindstaining in “Navelina” oranges as affected by storage relative humidity and ethylene conditioning. Postharvest Biology and Technology, 31, 277e285. Saltveit, M. E. (1997). A summary of CA and MA requirements and recommendations for harvested vegetables. In , Postharvest horticulture ser. 18: Vol. 4. Seventh International controlled atmosphere research conference. Vegetables and Ornamentals (pp. 98e117). Davis: University of California. Saltveit, M. E. (1999). Effect of ethylene on quality of fresh fruits and vegetables. Postharvest Biology and Technology, 15, 279e292. Saltveit, M. E., & Kasmire, R. F. (1985). Changes in respiration and composition of different length asparagus spears during storage. Hortscience, 20, 479e494. Siomos, A. S., Sfakiotakis, E. M., & Dogras, C. C. (2000). Modified atmosphere packaging of white asparagus spears: composition, color and textural quality response to temperature and light. Scientia Horticulturae, 84, 1e13. Siriphanich, J., & Kader, A. A. (1986). Changes in cytoplasmic and vacuolar pH in harvested lettuce tissue as influenced by CO2. Journal of the American Society for Horticultural Science, 111, 73e77. Stewart, O. J., Raghavan, G. S. V., Golden, K. D., & Gariepy, Y. (2005). MA storage of Cavendish bananas using silicone membrane and diffusion channel systems. Postharvest Biology and Technology, 35, 309e317. Van der Steen, C., Jacxsens, L., Devlieghere, F., & Debevere, J. (2002). Combining high oxygen modified atmosphere packaging to improving the keeping quality of strawberries and raspberries. Postharvest Biology and Technology, 26, 49e58. Vigneault, C., Orsat, V., Panneton, B., & Raghavan, G. S. V. (1992). Oxygen permeability and airtightness measuring method for breathing bags. Canadian Agricultural Engineering, 34, 183e187. Villaescusa, R., & Gil, M. I. (2003). Quality improvement of Pleurotus mushrooms by modified atmosphere packaging and moisture absorbers. Postharvest Biology and Technology, 28, 169e179.
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LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Effects of modified atmosphere package (MAP) with a silicon gum film window on the quality of stored green asparagus (Asparagus officinalis L) spears Tiehua Li a, *, Min Zhang b a b
College of Forestry, Central South University of Forestry and Technology, 410004, Changsha, Hunan, China School of Food Science and Technology, Jiangnan University, 214036, Wuxi, Jiangsu, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 August 2012 Received in revised form 28 October 2014 Accepted 31 October 2014 Available online 7 November 2014
Packages of green asparagus (Asparagus officinalis L.) spears with or without silicon gum film windows were flushed in two different modified systems (50 mL L1 O2 with 100 mL L1 CO2 and 100 mL L1 O2 with 100 mL L1 CO2, with N2 as a balance gas) and stored at 2 ± 1 C for 30 days. The changes in gas headspace, sensory, respiration rate, ascorbic acid content, soluble solid content and chlorophyll content were investigated. The results showed that green asparagus spears stored in MAP with silicon gum film windows, the gas exchange between packages and surrounding atmosphere through the silicon gum film windows induced an in-package optimum atmosphere for green asparagus spears stored at O2 above 21 mL L1, CO2 below 157 mL L1 and ethylene below 15.84 mL L1. These packages prevented anaerobic respiration to get good odour score, and were able to keep a relatively low respiration rate and reduce loss of ascorbic acid. A low concentration of ethylene atmosphere was effective for inhibiting chlorophyll degradation, which resulted in a high appearance score. The initial atmosphere in packs also affect the quality attributes, where 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere was preferred. © 2014 Elsevier Ltd. All rights reserved.
Keywords: MAP Green asparagus Storage Modified atmosphere Ethylene Chemical compounds studied in this article: Ethylene (PubChem CID: 6325) Ethanol (PubChem CID: 702) Ascorbic acid (PubChem CID: 54670067) Chlorophyll (PubChem CID: 6477652)
1. Introduction As one of the important fresh vegetables, green asparagus (Asparagus officinalis L.) is becoming more and more popular in recent years in China due to its special flavour, taste and abundance of various nutrients such as vitamins, amino acids and trace elements (Li, Zhang, & Yu, 2006; Saltveit & Kasmire, 1985). However, it is also a highly perishable vegetable, which deteriorates rapidly after harvest, and only has a shelf life of 3e5 days under normal post-harvest handling at ambient temperatures (Baxter & Waters, 1991; Lipton, 1990). A lot of research has been done on the postharvest physiological changes, post-harvest senescence control, storage life extension and post-harvest loss reduction of green asparagus (An, Zhang, Wang, & Tang, 2008; Li et al., 2006). Physiological and compositional changes during storage that reduce the spear quality include bract opening (feathering), toughening and
* Corresponding author. Fax: þ86 (0)731 85623460. E-mail address: [email protected] (T. Li). http://dx.doi.org/10.1016/j.lwt.2014.10.065 0023-6438/© 2014 Elsevier Ltd. All rights reserved.
loss of water, chlorophyll degradation and changes in ascorbic acid, carbohydrates, protein and amino acids (Chang, 1987; Siomos, Sfakiotakis, & Dogras, 2000). These undesirable changes can be reduced by certain methods, including refrigeration storage and controlled atmospheric storage or modified atmosphere storage (Gariepy, Raghavan, Castaigne, Arul, & Willemot, 1991; Lipton, 1990; Siomos et al., 2000). However, ideal storage effects can hardly be attained because the harmful gases released by asparagus are not expelled in time. In order to improve the MAP conditions, packaging films with improved permeability has been studied and developed successfully for some fruits and vegetables storage (Fonseca, Fernanda, Oliveira, & Chau, 1999; Van der Steen, Jacxsens, Devlieghere, & Debevere, 2002). Because respiration rates differ greatly with different vegetable products, packaging films with a wide range of permeability for O2, CO2 and other gases are needed to meet various preservation requirements (Jacxsens, Devlieghere, Falcato, & Debevere, 1999). Another effective method to improve the permeability of packages has also been studied and developed using a silicone membrane system (Vigneault, Orsat, Panneton, & Raghavan, 1992). Gariepy, Raghavan, and Theriault (1986) used a
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silicone membrane system for long term storage of celery under controlled atmosphere conditions. Reeleder, Raghavan, Monette, and Gariepy (1989) fitted silicone membranes of varying surface areas on containers to maintain the atmosphere for controlling storage rot of carrot. Stewart, Raghavan, Golden, & Gariepy, 2005 found that silicone membrane systems with modified atmospheres were effective for storing bananas, maintaining the fruit with a harvest-fresh appearance, good colour and excellent marketability after 42 days of storage. Li, Zhang, and Wang (2007) reported that MAP with silicon gum film as window was effective for maintaining the post-harvest quality of mushroom Agrocybe chaxingu for up to 21 days. So far, there have been few reports on MAP with permeable films as a window for gas exchange to store green asparagus. In this study, a silicon gum film with high permeability for O2, CO2 and other gases was used as a window material on packages to store green asparagus in two different initial modified atmosphere systems (50 mL L1 O2 with 100 mL L1 CO2 and 100 mL L1 O2 with 100 mL L1 CO2, with N2 as a balance gas) at a temperature of 2 ± 1 C. The storage effects were investigated by evaluating the physical, chemical, physiological and sensory characteristics of the asparagus spears. 2. Materials and methods 2.1. Plant material The fresh green asparagus (A. officinalis L. cv. ‘UC800’) spears used in this study were obtained from Natong Hualin Agricultural Products Co., Ltd. in Suzhou city, Jiangsu province, China. The asparagus spears were cut at ground level from 8:00 to 9:30 AM and transported to the laboratory within 3 h. They were then used in the experiment within 2 h. The green asparagus spears used were about 180 mm in length and 8e15 mm in diameter. 2.2. Equipment The gas supply system for MAP consisted of bottled N2, O2 and CO2, a 10 L mixing cylinder and a vacuum pump to remove the air in the gas supply system. The gas composition established in the packages was checked using a gas analyzer (CYES-II, Xuelian Analytical Instrument Co. Ltd., Shanghai, China) with a system accuracy of ±0.5%. The MAP equipment (ADFM-V3000, air controlled atmosphere packing machine, Hengzhong Packing Co., Lianyungang City, Jiangsu Province, China) was connected to the mixing cylinder of the gas supply system. 2.3. Modified atmosphere packaging Polystyrene (PS) packaging trays (18 cm length 12 cm width 4 cm depth) (Fig. 1), with a wall thickness of 0.3 mm and a total surface area of 456 cm2, which achieves an O2 permeability of
Fig. 1. The sketch of packaging tray with silicon gum film window and PP membrane.
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14.62 1016 mol s1m2 Pa1 and CO2 permeability of 53.51 1016 mol s1m2 Pa1 at 20 C and 90% RH were used. A total of 108 PS packaging trays were divided into 2 groups, one group had a window (0.8 cm 1.0 cm, the preliminary test showed this size of window was optimum) cut into it at the central part on the side of each tray, and the other group was kept unchanged as the control. The window was covered with high permeability film (FC-8 silicon gum film, Lanzhou Physical & Chemical Research Institute of the Academy of Sciences of China, Lanzhou, China), which was made by spreading 50 ± 5 g silicon gum on a 1 m2 cloth to achieve an O2 permeability of 4.08 109 mol s1m2 Pa1 and CO2 permeability of 12.24 109 mol s1m2 Pa1 at 20 C and 90% RH. There were two combinations of modified atmosphere systems in this study: 50 mL L1 O2 with 100 mL L1 CO2, and 100 mL L1 O2 with 100 mL L1 CO2, with N2 as a balance gas. For each modified atmosphere system, 54 trays were packaged, where 27 trays (three replicates with 9 time measurements for each treatment) of them had FC-8 silicon gum film windows. In each tray, approximately 160 g of green asparagus was packaged and sealed with 35 mm thick polypropylene (PP) membrane, which has a total surface area of 216 cm2 with an O2 permeability of 7.04 1016 mol s1m2 Pa1 and CO2 permeability of 27.69 1016 mol s1m2 Pa1 at 20 C and 90% RH. The total storage period was 30 days, at a temperature of 2 ± 1 C with a relative humidity of 95e100% inside the packages and of about 85% in the storage room. Gas analysis, sensory quality, and physical and chemical analysis (respiration rate, ascorbic acid, chlorophyll content, and soluble solid content) were conducted on the 12 h, the first day, then at 5-day interval up to day 30. 2.4. Gas analysis The headspace gas concentrations of O2, CO2, ethylene and ethanol in the sealed trays during storage were measured in each package before opened. The gases were pumped out with syringes and then injected into analysis equipments for measuring respectively. The headspace gas concentrations of O2 and CO2 was analysed using a gas analyzer (CYES-II, Xuelian Analytical Instrument Co. Ltd., Shanghai, China) at 12 and 24 h on the first day and then every 5 days. The headspace gas concentration of ethylene was analysed on the first day and then every 5 days, using a gas chromatograph (Shimadzu GC-2010, Japan) equipped with a flame ionization detector (FID) and a DB-1 column. Nitrogen was used as a carrier gas at a flow rate of 10 mL min1. The headspace gas concentration of ethanol was analysed on the third day and then every 5 days, using a gas chromatograph (Agilent GC-6890A, USA) equipped with a FID and a PP-20000 column. Nitrogen was used as a carrier gas at a flow rate of 2 mL min1. 2.5. Sensory quality Van der Steen et al., 2002 and An, Zhang, Lu, & Zhang, 2006 methods with some modifications were used to evaluate the sensory quality. A panel of ten judges consisted of 5 men and 5 women with age from 21 to 42 years old, who had been trained for evaluating fruits and vegetables sensory quality before. They were invited to evaluate the sensory quality characteristics of all the green asparagus from each tray. The typical characteristics of the green asparagus and the possibilities of deterioration were explained before the experiment started. All sensory tests (general appearance, firmness and odour) were performed in a special taste room with separated boxes. The general appearance was judged under normal light and the sensory characteristics such as firmness and odour were evaluated under IR light to exclude the influence of
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the visual characteristics. General appearance was evaluated on a scale of 9e1, where 9 represents excellent (dark green, no feathering, no rotten areas or water-soaked areas), 7 represents good (dark green, 5% feathering, 1e2 of 0.5 mm2 rotten or water-soaked areas), 5 represents fair and limited marketability (light green, 6e10% feathering, 3e5 of 0.5 mm2 rotten or water-soaked areas), 3 represents poor and limited usability (yellowish green, 10e15% feathering, 6e8 of 0.5 mm2 rotten or water soaked areas), and 1 represents very poor and inedible (yellowish green, more than 15% feathering and more than 8 0.5 mm2 rotten or water-soaked areas). Firmness was evaluated by pressing the green asparagus between the thumb and index finger, on a scale of 9e1, where 9 represents tender, 7 represents slightly tender, 5 represents firm, 3 represents hard, and 1 represents very hard. Off-odours, mainly because of fermentation, were evaluated on a scale of 9e1, where 9 represents none, 7 represents slight, 5 represents moderate, 3 represents moderately severe, and 1 represents severe. The cut-off score was set at 5. Above this score, the sample was considered acceptable. 2.6. Physical and chemical analysis 2.6.1. Respiration rate A static method was used to assess the respiration rate. Before assessment, the green asparagus (160 g ± 5 g) was taken out from the packages and exposed to ambient conditions in a storage room (3000 L) for 1 h to allow the CO2 accumulated in the tissue to diffuse into the air. The sample was then put into an air-tight jar of 260 mm diameter, with 10 mL of 0.4 mol L1 NaOH in a Petri dish, and the jars were placed in a chamber set at 2 C. The Petri dish was taken out after 30 min and the NaOH titrated with 0.1 mol L1 oxalic acid (C2H2O4) immediately. The change in the concentration of CO2 was used to estimate the respiration rates (Li et al., 2006). 2.6.2. Ascorbic acid Ascorbic acid was determined by the indophenol titration method (Favell, 1998). 15 asparagus spears were taken out randomly from 3 trays (5 asparagus spears for each tray), and chopped them with a knife, then mixed them thoroughly as experiment materials, and randomly took 3 samples (approximately 10 g for each sample). One sample was ground in a mortar with the same quantity of 2 g 100 g1 oxalic acid. 1 g 100 g1 oxalic acid solution was used to wash the paste into a 100 mL volumetric flask and made to volume. Five mL filtered solution was titrated with 2,6-dichlorophenol indophenols solution until the distinct light rose pink colour persisted for more than 5 s. 2.6.3. Chlorophyll content 15 asparagus spears were taken out randomly from 3 trays (5 asparagus spears for each tray), and chopped them with a knife, then mixed them thoroughly as experiment materials, and randomly took 3 samples (approximately 1.0 g for each sample). One sample was ground manually in a glass mortar for chlorophyll content determination. Chlorophyll was extracted from the sample by homogenizing it in 20 mL of 80 g 100 g1 acetone with a tissue homogenizer (DS-1, Shanghai, China) at a moderate speed for 30 s, and 80 g 100 g1 acetone solution was used to wash the paste into a 50 mL volumetric flask and made to volume. The homogenate was filtered through two layers of filter papers, centrifuged at 15,000 g for 15 min, and the absorbance read at 647 and 664.5 nm with an UVeVis recording spectrophotometer (UV-754; Shanghai Precision & Scientific Instrument Co., Ltd., Shanghai, China). The total chlorophyll content was calculated by chlorophyll (mg 100 g1 FW) ¼ 5* [17.95*Abs647 þ 8.08*Abs664.5] (Inskeep & Bloom, 1985).
2.6.4. Soluble solid content 9 asparagus spears were taken out randomly from 3 trays (5 asparagus spears for each tray), and cut them into pieces, then mixed them thoroughly and randomly took 3 samples (approximately 5.0 g for each sample). The juice was squeezed out from the samples respectively, and then its content of soluble solid was measured with an ABBE Bausch and Lomb refractometer (2WAJ, Shanghai optical instruments factory, Shanghai, China). 2.7. Statistical analysis All experiments were conducted in triplicate and the average values with standard deviation were used in the analysis. All data were evaluated by multi-factorial analysis of variance (ANOVA) using SPSS (Windows XP) with silicon gum film window and gas composition as the main effects. To determine the differences between treatments, Duncan tests were applied and the significant differences were established at P < 0.05. 3. Results and discussion 3.1. Gas change in headspace of packs Fig. 2a shows the O2 concentration to decrease rapidly in the first day for all treatments, and then remained relatively stable during the following storage days. The O2 concentrations in the headspace of packs with silicon gum film windows exceeded 21 mL L1 during the 30-day storage, while the O2 concentration in the headspace of control packs were less than 10 mL L1 (generally harmful for vegetable and fruit storing) from the first storage day. The CO2 concentrations in the headspace of packs with silicon gum film windows increased slowly and reached a peak of 132 mL L1 and 157 mL L1 on the 5th storage day with 50 mL L1 O2 and 100 mL L1 O2 initial atmosphere respectively, then dropped slowly until the 10th and 15th storage day, and remained relatively stable over the later storage time, and only 1.21 times and 1.35 times of the initial value respectively at the end of the storage period. However, the CO2 concentrations in the headspace of controls increased with increasing storage time and reached 2.98 times and 3.16 times of the initial value respectively at the end of the storage period (Fig. 2b). The ethanol concentration changes in the headspace of green asparagus packs are shown in Table 1. There were significant differences (P < 0.05) in the ethanol concentration among these treatments after 5 days of storage. No ethanol was detected in the packs with silicon gum film windows over the entire storage period, whereas the controls registered the presence of ethanol from Day 5. The concentration of ethanol was found to increase throughout the subsequent storage period. Without silicon gum film windows, the ethanol concentrations increased from 0.184 mL L1 to 1.115 mL L1 during Day 5 to Day 30 in packs with 100 mL L1 O2 initial atmosphere, and the ethanol concentrations increased from 0.107 mL L1 to 0.724 mL L1 during Day 5 to Day 30 in packs with 50 mL L1 O2 initial atmosphere, the former was higher than the latter. The injury effects caused by high CO2 concentration and low O2 concentration have been demonstrated for some fruits and vegetables (Beaudry, 1999; Lopez-Briones et al., 1992; Villaescusa & Gil, 2003). Extremely low O2 levels or excessively high CO2 levels induce fermentation and will result in the generation of off-flavours (Dostal-Lange & Beaudry, 1991; Richardson & Kosittrakun, 1995) or visible tissue damage (Lidster, Blanpied, & Prange, 1990). Some studies show that there is an interaction between O2 and CO2, where elevated CO2 levels make plant material more sensitive to low levels of O2, and the fermentation threshold may occur at
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all treatments. There were significant differences (P < 0.05) in the ethylene concentration between the packs with and without silicon gum film windows. The ethylene concentration in packs with silicon gum film windows increased slowly, from the initial 0.09 mL L1 to 15.84 mL L1 at the end of 30-day storage, while the ethylene concentration in controls increased quickly, which from the initial 0.20 mL L1 to the highest value of 185.64 mL L1, much higher than the former. 3.2. Sensory evaluation
Fig. 2. Changes of O2 (a) and CO2 (b) concentrations (mean ± S.D. for three replicates) in packages for green asparagus stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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higher O2 partial pressures with an increase in CO2 partial pressure (Beaudry, Cameron, Shirazi, & Dostal-Lange, 1992). Kupferman (1997) and Saltveit (1997) reported that some apple cultivars and vegetables required an O2 concentration of above 1% for storage. The packs with silicon gum film windows provided a favourable storage atmosphere for green asparagus because these windows have high permeability for O2, CO2 and other gases, whereas the controls experienced fermentation caused by low O2 and excessively high CO2 from the respiration of green asparagus (Fig. 2a, b and Table 1). The change in ethylene concentration is shown in Table 2. The ethylene concentration increased with increasing storage time for
Fig. 3 shows the score pattern for appearance, firmness, and odour of green asparagus stored in MAP with and without silicon gum film windows in different modified atmospheres. The scores for appearance, firmness and odour decreased with increasing storage time, irrespective of treatment methods. As shown in Fig. 3a, silicon gum film window and modified atmosphere had significant effects (P < 0.05) on the appearance of green asparagus after 10 days of storage. These differences were primarily attributed to the presence of silicon gum film window, with modified atmosphere as a secondary factor. With silicon gum film window, the appearance scores of green asparagus stored in packs with initial atmosphere of 100 mL L1 O2 and 100 mL L1 CO2 decreased slowly before Day 15 (from 9 to 7.5), and then rapidly until Day 30 (from 7.5 to 4.6). Meanwhile, the appearance scores of green asparagus stored in packs with initial atmosphere of 50 mL L1 O2 and 100 mL L1 CO2 decreased slowly before Day 20, and then quickly until the end of storage period. Without silicon gum film window, the appearance scores of green asparagus decreased quickly from Day 5 and Day 10 until the end of storage for the packs with initial atmosphere of 100 mL L1 O2, 100 mL L1 CO2 and 50 mL L1 O2, 100 mL L1 CO2, which dropped from 8.4 to 3.2 and 7.9 to 3.6 respectively. The appearance scores of green asparagus stored in MAP with silicon gum film window in initial atmosphere of 50 mL L1 O2 and 100 mL L1 CO2 had the slowest decrease (from 9.0 to 5.2) during the storage time. Based on the acceptable score of 5.0, only green asparagus in MAP with silicon gum film window in initial atmosphere of 50 mL L1 O2 and 100 mL L1 CO2 could be stored for 30 days. Fig. 3b shows a similar trend for firmness as general appearance. The firmness scores of green asparagus stored in MAP with silicon gum film window in initial atmosphere of 50 mL L1 O2 and 100 mL L1 CO2 had the slowest decrease (from 9.0 to 5.0) during the storage time, and was the only treatment that scored above 5.0 at the end of the 30-day storage. There were significant differences (P < 0.05) in the scores for odour between the green asparagus stored in MAP with and without silicon gum film window (Fig. 3c). The odour scores for green asparagus stored in MAP with silicon gum film windows remained above the acceptable value of 5.0 until the end of 30-day storage, irrespective of the initial modified atmosphere. Without silicon gum film windows, the scores of green asparagus stored in
Table 1 Changes in headspace ethanol concentration in green asparagus packs with silicon gum film as windows and different atmosphere during 30 days storage. Treatments
Ethanol concentration (mL L1) 3 day
5 days
10 days
15 days
20 days
25 days
30 days
50 mL/LO2 þ 100 mL/L CO2 þ W 50 mL/LO2 þ 100 mL/L CO2 þ NW 100 mL/LO2 þ 100 mL/LCO2 þ W 100 mL/LO2 þ 100 mL/LCO22 þ NW
0 0 0 0
0a 0.107 ± 0.018 b 0a 0.184 ± 0.014 c
0a 0.226 ± 0.026 b 0a 0.375 ± 0.021 c
0a 0.338 ± 0.031 b 0a 0.572 ± 0.036 c
0a 0.505 ± 0.048 b 0a 0.811 ± 0.053 c
0a 0.619 ± 0.053 b 0a 0.947 ± 0.065 c
0a 0.724 ± 0.056 b 0a 1.115 ± 0.073 c
Values were mean ± SD for 3 replicates. Different letters in the same column indicate that means are significantly different (P < 0.05). W: window; NW: no window.
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Table 2 Changes in headspace ethylene concentration in green asparagus packs with silicon gum film as windows and different atmosphere during 30 days storage. Treatments
50 mL/L O2 þ 100 mL/L CO2 þ W 50 mL/L O2 þ 100 mL/L CO2 þ NW 100 mL/L O2 þ 100 mL/L CO2 þ W 100 mL/L O2 þ 100 mL/L CO22 þ NW
Ethylene concentration (mL L1) 0 day
1 day
0 0 0 0
0.09 0.20 0.10 0.24
± ± ± ±
5 days 0.01a 0.04b 0.01a 0.02b
0.81 5.87 1.26 7.23
± ± ± ±
10 days 0.03a 0.31b 0.04a 0.35b
2.65 53.58 3.43 68.21
± ± ± ±
15 days 0.13a 3.23b 0.11a 3.24b
5.32 102.45 7.22 113.15
± ± ± ±
20 days 0.22a 5.44b 0.34a 5.11b
8.14 126.37 11.05 148.26
± ± ± ±
25 days 0.41a 4.67b 0.47a 4.28b
10.67 142.44 13.58 163.89
± ± ± ±
30 days 0.46a 6.21b 0.44a 7.22b
11.83 171.56 15.84 185.64
± ± ± ±
0.44a 8.35b 0.63a 6.45b
Values were mean ± SD for 3 replicates. Different letters in the same column indicate that means are significantly different (P < 0.05). W: window; NW: no window.
packs with initial atmosphere of 50 mL L1 O2, 100 mL L1 CO2 and 100 mL L1 O2, 100 mL L1 were below 5.0 after Day 20 and Day 15, respectively. 3.3. Respiration rate Fig. 4 shows the changes in respiration rates during storage for all treatments. The initial respiration rates were very high before storage, reaching 153.2 ± 6.5 mg CO2 kg1 h1, and similar observations were reported by An et al. (2006) and Li et al. (2006). For all the treatments in our study, the respiration rate dropped by 46e59% for the first 5 days. After this decline, the respiration rate of the green asparagus in the controls increased thereafter, but remained relatively stable from Day 5 to 20, and increased quickly after Day 20 in the packages with silicon gum film windows and the respiration rate increased 43.2e72.0% from Day 20 to Day 30. Li et al. (2006) reported the similar results for storing the green asparagus in room temperature and in refrigeration (3 C), and the
respiration rate increased from Day 3 and Day 10 respectively. In this study, the poor atmosphere in packages, i.e. low concentration O2, high concentration CO2 and the presence and accumulation of ethylene (Fig. 2 and Tables 1 and 2) will cause physiological injuries, which may induce the respiration rate of the green asparagus increase from Day 10 in the controls and Day 20 in the packages with silicon gum film windows. Some researchers reported that carbon dioxide stimulated respiration in lettuce (Kubo, Inaba, & Nakamura, 1990; Siriphanich & Kader, 1986) and spinach (Kubo et al., 1990). These increases in respiration by exposure to elevated carbon dioxide may be related to physiological injury (Kader, 1986). Saltveit, (1999) thought that ethylene stimulated the increase of respiration. There were significant differences (P < 0.05) for the respiration rates of green asparagus among treatments during Day 10e30. The presence of silicon gum film windows and a lower initial O2 concentration of 50 mL L1 had resulted in a lower respiration rate in the green asparagus. As shown in Fig. 4, the respiration rate of the green asparagus in the package with silicon gum film windows
Fig. 3. Changes in scores (mean ± SD for 3 replicates) of appearance (a), firmness (b) and odour (c) for green asparagus packaged and stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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Fig. 4. Respiration rate (mean ± S.D. for three replicates) changes for green asparagus packaged and stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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with 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere was the lowest since Day 1. Low respiration rate is beneficial in maintaining the quality of fruits and vegetables during storage (Concellon, Anon, & Chaves, 2007). It is important to control the respiration rate as lowering the respiration rate could extend the shelf life and preserve the quality of products (Day, 2001; McLaughlin & O'Berne, 1999). 3.4. Ascorbic acid contents Fig. 5 shows the changes in ascorbic acid contents as a function of storage time. The ascorbic acid content in the fresh condition was 27.2 mg 100 g FW1, which decreased gradually during storage for all treatments, and loss of the value varied from 10.9 mg 100 g1 FW to 19.3 mg 100 g1 FW during the storage period by different storage conditions. Significant differences (P < 0.05) in ascorbic acid contents were observed among treatments after 15 days of storage, and these differences were primarily caused by the
Fig. 5. Ascorbic acid content (mean ± S.D. for three replicates) changes for green asparagus packaged and stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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presence of silicon gum film window, with the initial atmosphere as a secondary factor. The green asparagus in packs with the silicon gum film windows had a relatively favourable atmosphere during the storage period with a slow loss in ascorbic acid. On the other hand, the atmosphere with low O2 and high CO2 concentrations, coupled with anaerobic respiration (Table 1) and high ethylene levels (Table 2) for the green asparagus in controls had likely caused cell injury and senescence, which induced a more rapid decline in the ascorbic acid contents. At the end of Day 30, the green asparagus in the packs with silicon gum film windows and 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere had lost 40% of its ascorbic acid contents, with a final reading of 16.3 mg 100 g1 FW, whereas the controls with 100 mL L1 O2 and 100 mL L1 CO2 initial atmosphere lost 71% of its ascorbic acid contents with only 7.9 mg 100 g1 FW remaining, which was much lower than the former. Ascorbic acid is one of the most sensitive materials to be destructed when a fresh produce is subject to adverse handling and storage conditions. Ascorbic acid losses are enhanced by many factors, including extended storage, higher storage temperatures, chilling injury and bad atmosphere (Lee & Kader, 2000; Li et al., 2007; Paull, 1999). In this study, the green asparagus stored in MAP with silicon gum film window had a more favourable atmosphere during storage period, which reduced the losses of ascorbic acid. As observed in the previous study (Li et al., 2007), the silicon gum film window on the MAP helped to retain high ascorbic acid content in mushrooms during storage.
3.5. Total chlorophyll contents The total chlorophyll contents of the green asparagus decreased with extended storage time for all treatments, and the rate of decrease differed with treatments, dropping 23.0%e65.9% during the storage period (Fig. 6). There were significant differences (P < 0.05) in the total chlorophyll contents of the green asparagus among different treatments since Day 10, primarily caused by the silicon gum film windows, with the initial modified atmosphere as a secondary factor. Over the 30-day storage, the green asparagus stored in packs with silicon gum film windows and 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere had a remaining total chlorophyll content of 10.4 mg 100 g1 FW (a loss of 23%), while the controls with 100 mL L1 O2 and 100 mL L1 CO2 initial atmosphere
Fig. 6. Total chlorophyll contents (mean ± S.D. for three replicates) changes for green asparagus packaged and stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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had only 4.6 mg 100 g1 FW of total chlorophyll content left (66% loss). Ethylene is a naturally produced, simple two carbon gaseous plant growth regulator that has numerous effects on the growth, development and storage life of many fruits, vegetables and ornamental crops (Saltveit, 1999). Ethylene inducing senescence has been well documented in many studies (Able, Wong, Prasad, & O'Hare, 2003; Li & Zhang, 2010; Sala & Lafuente, 2004). Ethylene accelerates senescence in the leaves of some species (Leopold & Nooden, 1984; Mattoo & Aharoni, 1988), and promotes processes characteristic of leaf senescence, such as decline in chlorophyll and photosynthesis, reduction in the levels of proteins and starch, and increase in the activities of many hydrolytic enzymes (Ella, Zion, Nehemia, & Amnon, 2003). Lers, Jiang, Lomaniec, and Aharoni (1998) reported external ethylene to have an evident effect in enhancing the degradation rate of chlorophyll and protein, and accumulation of amino acids for stored parsley leaves. In this study, the green asparagus stored in packs with silicon gum film windows lost chlorophyll slowly due to the low concentration of ethylene atmosphere (Table 2). The chlorophyll content of the controls decreased quickly, which dropped from 10.9 mg 100 g1 FW to 5.1 mg 100 g1 FW in 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere and from 10.1 mg 100 g1 FW to 4.6 mg 100 g1 FW in 100 mL L1 O2 and 100 mL L1 CO2 initial atmosphere since the 10th day because of accumulated ethylene (Table 2 and Fig. 6), resulting in a fading green, thus a fall in the appearance scores (Fig. 3a). 3.6. Soluble solid contents Fig. 7 shows the change of soluble solid contents during the 30day storage for green asparagus. The soluble solid contents increased for all treatments at the beginning, which increased from 4.9 g 100 g1 juice to the peaks (6.5 g 100 g1 juice and 6.8 g 100 g1 juice respectively) on the 15th storage day in the packages with silicon gum film windows and increased from 4.9 g 100 g1 juice to the peaks (7.0 g 100 g1 juice and 7.2 g 100 g1 juice respectively) on the 10th storage day in the packages without silicon gum film windows, and then declined. The soluble solid contents of the green asparagus changed gradually in packs with silicon gum film windows, but rapid increased with a higher peak, followed by a faster decline in the controls. It was also found that the soluble solid
Fig. 7. Soluble solid contents (mean ± S.D. for three replicates) changes for green asparagus packaged and stored at 2 C for 30 days. (A) 50 mL L1 O2, 100 mL L1 CO2, W; (◊) 50 mL L1 O2, 100 mL L1 CO2, NW; (-) 100 mL L1 O2, 100 mL L1 CO2, W; ( ) 100 mL L1 O2, 100 mL L1 CO2, NW. W, packaged with silicon gum window, NW, packaged without silicon gum window.
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contents of green asparagus and “Fuyu” persimmon increased in the early stage of storage (Cia et al., 2006; Li et al., 2006). In this study, at the beginning of storage, the respiration rate dropping quickly from Day 0 to Day 5 (Fig. 4) may cause the temporary accumulation of soluble solid in plant which mainly resulted in the rise of soluble solid contents. The water loss of green asparagus also made some contribution to the increasing soluble solid contents. It was reported that respiration was a major factor contributing to post-harvest losses, which converted stored soluble solid (sugar mainly) into energy in the presence of an oxygen substrate (Nourian, Ramaswamya, & Kushalappa, 2003). In this study, from Day 15, a correlation existed between the level of soluble solid contents and respiration rate, where a treatment with a high respiration rate was found to have a quickly dropping in the soluble solid content and thus showed a relatively low value (Figs. 4 and 7). The green asparagus stored in packs with silicon gum film windows and 50 mL L1 O2 and 100 mL L1 CO2 initial atmosphere had the lowest respiration rate during the storage period, with the highest soluble solid content (4.3 g 100 g1 juice) at the end of storage.
4. Conclusion The gas exchange between packages and surrounding atmosphere through the silicon gum film windows induced an optimum in-package atmosphere for storing green asparagus with O2 above 21 mL L1, CO2 below 157 mL L1 and ethylene below 15.84 mL L1, which prevented anaerobic respiration and achieved a high odour score, with relatively low respiration rate and reduced rate of ascorbic acid loss. An atmosphere with low ethylene concentration is effective for inhibiting chlorophyll degradation, hence a high appearance score. The initial atmosphere in packs also had some effects on the quality attributes. Compared to the 100 mL L1 O2 and 100 mL L1 CO2 initial atmosphere, 50 mL L1 O2 and 100 mL L1 CO2 was preferred for maintaining the quality of stored green asparagus.
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