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Effect of prestorage short-term Anoxia treatment and modified atmosphere packaging on the physical and chemical changes of green asparagus
Postharvest Biology and Technology 117 (2016) 64–70
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Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Effect of prestorage short-term Anoxia treatment and modified atmosphere packaging on the physical and chemical changes of green asparagus Chairat Techavuthiporna,* , Panida Boonyaritthongchaib,c a b c
Division of Biological Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn 10540, Thailand Division of Postharvest Technology, School of Bioresources and Technology, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand Postharvest Innovation Center-KMUTT, Bangkhuntien, Bangkok 10150, Thailand
A R T I C L E I N F O
A B S T R A C T
Article history: Received 11 October 2015 Received in revised form 28 January 2016 Accepted 29 January 2016 Available online xxx
The effects of prestorage short-term Anoxia treatment combined with modified atmosphere packaging (MAP) on quality changes during the storage of green asparagus (Asparagus officinalis L.) spears were investigated. Two sets of asparagus were used in this study. The first set underwent short-term Anoxia treatment via the administration of gaseous N2 for 8 h at room temperature, while the second set was kept in ambient air at the same temperature. Consequently, treated and untreated spears were stored either freely or packaged in plastic bags with low density polyethylene, in which a passive modification of the atmosphere was allowed to develop. All samples were stored at 4 C for 8 days, followed by 8 days at 10 C. Samples treated with neither Anoxia nor MAP were used as a control. Our results show that treating the asparagus samples with Anoxia and MAP (Anoxia + PE) caused lower respiration, slowing the decrease in headspace O2. In the Anoxia + PE treated samples, spears lost <12% fresh weight after 8 days at 10 C. All treatments showed less increase in shear force while exposed at 4 C for 8 days, as compared with the significant increase found when transferred to 10 C. This increase in shear force was accompanied by the accumulation of fiber and lignin content. There was a positive relationship between toughening and fiber (R2 = 0.958) and toughening and lignin (R2 = 0.915). Moreover, the degradation of chlorophyll, sugar and ascorbic acid content under the Anoxia and MAP treatments were significantly reduced. The results of the present work indicate that Anoxia treatment, a non-chemical and simple postharvest technology, feasible for use in developing countries where food storage technologies are lacking. ã 2016 Elsevier B.V. All rights reserved.
Keywords: Asparagus Anoxia Modified atmosphere packaging Pretreatment Quality
1. Introduction In recent years, asparagus (Asparagus officinalis L.) has been increasingly consumed due to its nutritional value and flavor. However, it is a perishable commodity with a short shelf-life after harvest due to its high respiration rate that rapidly leads to senescence (Hennion and Hartmann, 1990; Lill et al., 1990; Irving and Hurst, 1993). Issues arising from the loss of quality in asparagus after harvest include the shriveling of spears, toughening as a result of lignification of pericyclic fibers (Bhowmik et al., 2001), chlorophyll degradation (Albanese et al., 2007), and changes in organic acid and sugar content (Baxter and Waters, 1991; Bhowmik et al., 2000). The perishable nature of asparagus poses a challenge to the development of effective methods to
* Corresponding author. E-mail address: [email protected] (C. Techavuthiporn). http://dx.doi.org/10.1016/j.postharvbio.2016.01.016 0925-5214/ ã 2016 Elsevier B.V. All rights reserved.
extend its postharvest consumption. The above undesirable effects can be reduced by quick cooling upon harvesting, refrigeration (below 5 C for long term storage), and storage in a modified atmosphere (Lipton, 1990). The storage of asparagus by controlled or modified the atmosphere may prevent or lessen postharvest changes such as texture, flavor, color and chemical composition (McKenzie et al., 2004; Villanueva et al., 2005; An et al., 2006, 2007; Sothornvit and Kiatchanapaibul, 2009). This method involves removing O2 and increasing the concentration of CO2. Because vegetables are living organisms, they require optimal concentrations of O2 and CO2 for respiratory activity. Below a threshold of O2 or above a threshold of CO2, cells undergo anaerobic respiration and produce lactic acid, acetaldehyde and ethanol (Peppelenbos and Oosterhaven, 1998). The extent of anaerobic activity depends on the amount of time cells are exposed to air. Treating fresh produce with an anaerobic atmosphere or anoxic conditions using pure N2 prior to storage slows the ripening of tomatoes (Kelly and Saltveit, 1988) and
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avocados (Pesis et al., 1993), delays skin browning in litchi (Jiang et al., 2004), and reduces the decrease in the firmness of kiwifruit (Song et al., 2009). Torres-Penaranda and Saltveit (1994) reported that short-term Anoxia treatment of asparagus for up to 6 h benefited its quality retention. Lill et al. (1990) reported that the rapid deterioration of stored asparagus was a major problem in retail display in supermarkets because stored spears had a shorter shelf-life after a simulated transit period. Bhowmik et al. (2000) indicated that the length of storage affected textural and compositional changes of asparagus after transfer in a simulation of retail sale. Although much research has focused on improving asparagus storage, few reports document the changes that usually occur during simulations of storage, transportation, and display in the supermarket. Additionally, modified atmosphere packaging (MAP) techniques have been extensively described. MAP improves quality and extends the shelf-life of many types of fresh produce, including asparagus. However, very little information exists regarding the application of MAP in combination with pre-storage treatment of asparagus spears. The objective of the present work was to evaluate the effect of Anoxia treatment and/or MAP application on the quality of green asparagus. This work also focused on physical and chemical changes in different portions of spears (upper and lower portions) during storage at 4 C and during an ensuing simulation of retail sale at 10 C. 2. Materials and methods 2.1. Plant material and handling Fresh green asparagus (A. officinalis L.) spears were obtained from commercial farms in the Nakhon Pathom province (Thailand) and transported to the laboratory. No damaged samples with closed bracts and 0.8–1.2 cm in diameter were selected. Spears were cut at 18 cm from the tip using a stainless steel knife. The asparagus was submerged in a 150 mg L 1 sodium hypochlorite solution for 2 min at 4 C and briefly air dried with ambient air at 25 C to remove surface liquid. 2.2. Sample treatments Two different sets (12 kg per set) of asparagus were prepared. The first set was subjected to short-term Anoxia treatment with gaseous N2. The asparagus was placed in a 10 L plastic chamber, then flushed with pure N2. The O2 concentration in the chamber was less than 0.05 kPa, as determined using a handheld Gas Analyzer (model: Oxybaby M + X, Germany). The samples were maintained in humidified N2 for 8 h at room temperature (approximately 25 C). The second set was kept in ambient air at the same temperature and 90–95% (Relative Humidity; RH) for 8 h. Consequently, both short-term Anoxia and ambient air treatments were established. N2-treated or untreated spears were placed in polystyrene trays measuring 13 20 cm, then either left unpackaged or packaged in plastic bags with 40 mm low density polyethylene (LDPE, 15 22 cm dimension), in which a passive modification of the atmosphere was developed. The O2 transmission rate was 187 mL m 2 h 1 at 23 C and standard pressure (Well Plas Co., Ltd., Thailand). Each tray contained samples, with an average weight of 120 5 g. One tray was performed for one replicate. All samples were refrigerated at 4 C and 90–95% RH for 8 days and then moved to simulate display at 10 C for 8 days. All analyses were performed at 0, 4 and 8 days of storage at 4 C and at 4 and 8 days of storage at 10 C, respectively. Each treatment was applied to four replicates in randomly of four trays.
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2.3. Gas headspace analyses The headspace gas concentrations in the sealed trays were measured in the same tray of each treatment at 0, 4 and 8 days of storage at 4 C and at 4 and 8 days of storage at 10 C. One milliliter of gas sample was withdrawn with a gastight syringe and then injected into gas chromatograph (Model GC-8A, Shimadzu, Japan) for measuring CO2 and O2. The injected gas sample was separated by a WG-100 column and analyzed with a thermal conductivity detector (TCD). Both gas concentrations were expressed in terms of partial pressure (kPa). 2.4. Weight loss Weight loss was measured periodically by weighing samples on a digital balance (model PA2102, OHAUS Corporation, USA). Weights were recorded on day 0, 4 and 8 at 4 C and day 4 and 8 at 10 C. The results are reported as a percentage loss based on the initial weight of the same package. 2.5. Physical and chemical analysis The asparagus spears, 0.8–1.2 cm in diameter and 18 cm in length and marked from the tip, were sectioned and separated into two cylindrical portions including the tip and the base at 9 cm intervals. The following determinations (physical and chemical changes) were made for each portion of the sample: texture, fiber, lignin, total chlorophyll, total sugar and total ascorbic acid. 2.5.1. Texture Texture or toughening was determined by taking nine spears from each tray. The texture of each sample was measured at the middle point of each spear section by performing a cutting test with a texture analyzer (TA-XT plus, Stable Microsystems) a method which was modified from Rodríguez et al. (2004). Values are expressed as maximum shear force (N) using a single blade (7 12 cm) that cut each sample at a cross-head speed of 2.0 mm s 1 over 12 mm. 2.5.2. Fiber content Fiber content was determined according to the AOAC (2000). Five grams of each fresh sample (tip and base) was individually heated in 25 mL of hot water and 6.25 mL of 50% (w/v) NaOH (Merck KGaA, Germany) for 5 min. The fiber was washed in running tap water through a size 30 mesh sieve containing the sample, then weighed to determine initial extracted weight. The extracts were dried at 100 C for 2 h and weighed again to calculate the percentage of fiber content. 2.5.3. Lignin content Lignin content was determined using the thioacidoglycolysis method, modified from Bruce and West (1989). Twenty-five grams of each fresh tissue (tip and base) was homogenized individually using 95% ethanol for 5 min then filtered using Whatman No. 4 filter paper under vacuum. The residue was washed with 17 mL of ethanol and dried at 50 C for 24 h. Approximately 0.25 g of the dried residue was mixed with 7.5 mL of 2 N HCl (Merck KGaA, Germany) and 0.5 mL of thioglycolic acid (Carlo Erba Reagenti SpA., Italy), then boiled in a water bath for 4 h. The mixture was centrifuged at 7500 g at 4 C for 15 min. The residue (lignin thioglycolate) was washed with 10 mL of water, resuspended in 10 mL of 0.5 N NaOH for 18 h at room temperature and centrifuged. 2 mL of concentrated HCl was added to the supernatant. The lignin thioglycolic acid complex was precipitated at 4 C for 4 h and centrifuged. The residue was then dissolved in 10 mL of 0.5 N NaOH. After performing appropriate dilutions, the absorbance was
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read at 280 nm using a spectrophotometer (UV-1600; Shimadzu Co., Japan). The lignin content was expressed as mg kg 1 on a fresh weight basis. 2.5.4. Chlorophyll content Chlorophyll content was separately analyzed in each portion of the spear. A fresh sample of outer tissue (0.25 g) was extracted in 10 mL of N,N-dimethylformamide (Riedel-de Haen, Germany) at 4 C for 24 h (Moran, 1982). The absorbance of each sample was measured at 645 and 663 nm to calculate total chlorophyll (g kg 1) using an estimation of the contribution of chlorophyll a and chlorophyll b content described by Inskeep and Bloom (1985). 2.5.5. Total sugar content Total sugar content was measured according to a modification from the method of Dubois et al. (1956). One gram of each spear portion was homogenized with 10 mL of 80% ethanol. The slurry was heated in a water bath at 60 C for 1 h, then filtered with filter paper (Whatman No. 4). One milliliter of the extract was mixed with 5% phenol (1 mL) and concentrated sulfuric acid (5 mL) to catalyze the reaction. After the mixture was cooled to room temperature, the absorbance at 490 nm was measured with a spectrophotometer. The concentration of sugar was determined using a standard curve with glucose and expressed as mg kg 1 of sugar on a fresh weight basis. 2.5.6. Ascorbic acid content Ascorbic acid content was analyzed according to the Roe et al. (1948) 2,4-dinitrophenol hydrazine method, in which 2 g samples are extracted with 5% metaphosphoric acid solution (Merck KGaA, Germany). The absorbance of the sample solution at 540 nm was measured with a spectrophotometer. A calibration curve was generated using standard ascorbic acid solutions (Carlo Erba Reagenti SpA., Italy). Values for ascorbic acid content were expressed as mg kg 1 on a fresh weight basis. 2.6. Statistical analysis The experimental data were the average of four replications from four independent trays. All experiments were performed using a completely randomized design. All results herein are presented as the mean S.D. Statistical significance was assessed using a 2-way ANOVA at the 99% confidence level. The sources of variations were treatments and storage period. Statistical analyses were performed by SAS Institute (1999).
Fig. 1. Changes in CO2 (upper) and O2 (lower) in packed green asparagus during 8 day at 4 C followed by 8 day at 10 C (PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
Saltveit (1994) found that the peak of relative respiration of spears after exposed to Anoxia condition. The possibility exists that accumulated products of anaerobic respiration may be responsible for the stimulation in respiration by spears exposed to Anoxia condition. Although the O2 level of Anoxia-treated sample was lower than to untreated sample, slightly higher level of CO2 between packaged spears was found. It probably due to a CO2:O2 permeability ratio of the bag being more than 1 (Silva et al., 1999). The CO2 accumulation in package of Anoxia-treated and untreated samples did not show a significant difference.
3. Results and discussion 3.1. Gas composition in package The evolution of CO2 and O2 of the headspace gas in the LDPE bags is shown in Fig. 1. An increase in CO2 concentration and a decrease in O2 content were found after packing. No significant differences in CO2 evolution were observed in packages during storage at 4 C in both Anoxia-treated and untreated samples. After transfer to the simulated retail temperature, the CO2 in samples subjected to Anoxia treatment was slightly higher than that of samples without Anoxia treatment. At equilibrium, the CO2 concentration of Anoxia-treated and untreated samples reached approximately 6.08 kPa and 5.07 kPa, respectively. In contrast, significant changes in O2 levels were found on day 8 at 4 C and when transferred to storage at 10 C (P < 0.01). The O2 concentrations at equilibrium were approximately 5.07 kPa and 11.15 kPa for Anoxia-treated and untreated samples, respectively. Although, low O2 conditions are well known to reduce the respiration of asparagus after harvest (Lipton, 1990), Torres-Penaranda and
Fig. 2. Weight loss percentage evolution of green asparagus during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
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3.2. Weight losses The percent of weight loss in green asparagus during storage at simulated temperatures (4 C and 10 C) is presented in Fig. 2. During storage at 4 C, the weight loss of the Anoxia + PE samples was significantly lower than that of other samples. This phenomenon was especially pronounced after the transfer of all samples to 10 C; the control sample had a maximum weight loss of 18%. In our experiment, the weight losses and also other analyses of control and Anoxia were measured and limited on another 4 days (8 + 4) after transferring to 10 C before deterioration such as a wilting and spoilage. In the Anoxia + PE samples, spears lost less than 12% after 8 days (8 + 8) at 10 C and wilting did not occur in this treatment. However, the difference in weight loss of packaged spears (PE and Anoxia + PE) was insignificant. Among all the treatments, storage period and interaction of treatments and storage period, the increase in weight loss was statistically significant with P-value < 0.01. It has been shown that storage temperature, postharvest treatment and storage duration have significant effects on the rate of weight loss (Javanmardi and Kubota, 2006). It is possible that the higher rate of transpiration and metabolism of nonpackaged spears in comparison to packaged spears could be the main cause for the acceleration of mass loss. In asparagus, weight loss is mainly attributed due to differences in the water vapor pressure of water between the spear surface area and atmosphere (Tzoumaki et al., 2009). Maintaining higher humidity in packages may minimize this change. In addition, the large difference loss of mass between control and Anoxia spears in this experiment is probably considered to be due to a loss of moisture via stomata. In tomato plant, the stomata begin to close after the condition of oxygen deprivation with a parallel decrease in
Fig. 4. Changes in fiber content of green asparagus (Tip; upper and Base; lower) during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
transpiration (Else et al., 1995). With short-term Anoxia treatment, therefore, closing of stomata may help treated spears to decrease transpiration. 3.3. Texture, fiber and lignin content
Fig. 3. Changes in texture of green asparagus (Tip; upper and Base; lower) during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
In determining the marketability of asparagus, the most important factor is spear toughness. Changes in texture, fiber and lignin content after harvest are of primary interest. Fig. 3 represents the textures of each asparagus portion using the different treatments (measured as maximum cutting force). Force increased in both the tip and base throughout the experimental period. Although the development followed the same patterns, the shear force was greater in the base than in the top portion. The rates of increase in shear force were slightly higher at 4 C and increased further when transferred to 10 C. However, this increase was not as great in samples treated with Anoxia prior to packaging in LDPE bags (Anoxia + PE). Anoxia pretreatment was found to have a significant impact on fiber content. Additionally, asparagus stored in LDPE bags exhibited significant fluctuations in fiber content. As shown in Fig. 4, the fiber content of each asparagus spear portion changed with storage conditions. The fiber content in the top portions was approximately half that in the bottom portions. All treatments were significantly effective in maintaining fiber content during storage at 4 C. Individual treatment of asparagus with Anoxia was much less effective but still significant compared to storage in air. Moreover, combining Anoxia and packaging significantly maintained the content of fiber in the basal section of spears and slightly increased fiber content in the tip portion compared to other samples, especially the control spears. The biosynthesis of lignin in green asparagus is controlled by multiple enzymes, including phenylalanine ammonialyase (PAL)
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Fig. 7. Correlation between shear force and lignin content of green asparagus (tip and base) during 8 day at 4 C followed by 8 day at 10 C.
Fig. 5. Changes in lignin content of green asparagus (Tip; upper and Base; lower) during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
which is a key enzyme in the synthesis of flavonoids such as anthocyanins and lignin (Flores et al., 2005; Tzoumaki et al., 2009). The lignin content of both the top and bottom portions of green asparagus are shown in Fig. 5. The initial lignin content was approximately 10.95 and 45.94 mg kg 1 in the tip and basal portions, respectively. An increase in lignin content was observed in untreated asparagus during the change in storage from 4 C to 10 C. Both Anoxia and MA treatments significantly maintained the lignin content of green asparagus at 4 C and delayed lignin formation after transfer to 10 C. Moreover, slight changes in lignin were detected in combination treatments, indicating that pretreatment with Anoxia and MA treatments prevented the accumulation of lignin during postharvest refrigeration and retail simulation temperature. Li and Zhang (2006) have also found that under hypobaric conditions, the increase in lignin and cell structure can be retarded, effectively helping to inhibit the
Fig. 6. Correlation between shear force and fiber content of green asparagus (tip and base) during 8 day at 4 C followed by 8 day at 10 C.
senescence of asparagus. Among all the treatments, storage period and interaction of treatments and storage period, the change in fiber and lignin contents were statistically significant with P-value < 0.01. We found a positive correlation between toughening and the production of fiber and lignin content in green asparagus, as shown in Figs. 6 and 7 (R2 = 0.958 and 0.915, respectively). Texture is one of the most critical parameters that consumers use to assess asparagus quality (Barrett et al., 2010; Siomos et al., 2000). During refrigeration in this experiment, fiber and lignin content increased gradually over time and increased sharply after the temperature was increased to 10 C, especially in the control. Fibrousness and the process of hardening are correlated, occurring after harvesting and accompanied by lignification of the sclerenchyma. In addition, these results are consistent with the mass loss of green asparagus. Changes in texture may also reflect losses of tissue water (Rodríguez et al., 2004; Tzoumaki et al., 2009). Modified atmosphere packaging with green asparagus has generally been reported to improve the rigidity of spears (Villanueva et al., 2005). Herein, slower changes in texture were observed upon combining Anoxia pre-treatment with MAP, which is likely linked to the accumulation of fermented compounds such as ethanol and acetaldehyde in anaerobic conditions (Polenta et al., 2005), as well as the inhibition of ethylene synthesis (Saltveit and Mencarelli, 1988). The exact mechanisms of the delay in textural changes using Anoxia treatment are still unclear. Pre-storage anoxic treatment might slow the metabolism of green asparagus and also inhibit textural changes. 3.4. Chlorophyll, total sugar and ascorbic acid content Chlorophyll is the pigment that causes the green color in asparagus. At the beginning of storage, the top spear portions contained slightly higher total chlorophyll than the bottom portion (2.39 and 2.14 g kg 1, respectively) (Fig. 8). Visually, the green color gradually faded during storage. A significant loss of chlorophyll was observed during the storage period at 4 C and after moving to 10 C in control samples compared with Anoxia and MAP treated samples. On the fourth day at 10 C, the total chlorophyll content at the top spear portions in the controls, Anoxia, PE, and Anoxia + PEtreated green asparagus were 1.29, 1.60, 1.72 and 1.88 g kg 1, respectively. In contrast, the total chlorophyll content at the bottom portions of the spears of control, Anoxia, PE, and Anoxia + PE-treated green asparagus were 1.01, 1.41, 1.58 and 1.63 g kg 1, respectively. Based on the above results, the combination treatment exhibited a significant beneficial effect on reducing chlorophyll changes in asparagus, which suppressed respiration during storage in LDPE bags. Additionally, there is a relationship
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Fig. 8. Changes in chlorophyll content of green asparagus (tip; upper and base; lower) during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
Fig. 9. Changes in sugar content of green asparagus (tip; upper and base; lower) during 8 day at 4 C followed by 8 d at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
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Fig. 10. Changes in ascorbic acid of green asparagus (tip; upper and base; lower) during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
between respiratory rate and chlorophyll degradation, according to Cantwell and Reid (1993). Fig. 9 shows the change in total sugar content at 4 C for 8 days and at 10 C for 8 days. The sugar content decreased in all samples toward the beginning of storage, decreasing from 112.63 mg kg 1 (tip portion) and 103.87 mg kg 1 (bottom portion). It has been reported that respiration is a major factor that contributes to postharvest losses (Brash et al., 1995; Uchino et al., 2004). Respiratory processes convert stored soluble solids, mainly sugar, into energy in the presence of oxygen (Nei et al., 2006). Our results clearly reflect a significant decrease in total sugar content over time in untreated samples and smaller decreases in spears treated with Anoxia, whether they be stored under MAP or non–MAP conditions. Significant changes were found in unpackaged samples after transfer to 10 C (P < 0.01). The percentage of sugar retention after 4 days of simulating resale temperature at 10 C for untreated and Anoxia samples were 41.49% and 49.64%, respectively. At the same temperature, the percentages detected for the MAP and combination samples were 68.51% and 71.70%, respectively. This demonstrates that total sugar content is mainly preserved in the latter two treatments when compared with unpackaged samples. At the end of storage (after 8 days at 10 C), the retention levels detected for MAP and combination samples were 47.85% and 65.17%, respectively. Initially, the ascorbic acid levels of the top spear portions were approximately 20% higher than in the bottom portion (Fig. 10). These results show that ascorbic acid content decreased significantly during storage in all samples analyzed. After transfer to 10 C, ascorbic acid retention percentages at the fourth day of refrigeration for untreated and Anoxia samples were 26.35% and 43.43%, respectively. At the same time, the percentages detected for the MAP and combination samples were 54.19% and 78.87%,
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respectively. The retention levels at the end of storage detected in MAP and combination samples were 42.02% and 66.54%, respectively. Among all the treatments, storage period and interaction of treatments and storage period, the change in sugar and ascorbic acid contents were statistically significant with P-value < 0.01, indicating that the deterioration rate varied depending upon the treatments applied. The highest rate was in non-treated spears, followed by samples treated individually with either Anoxia or MAP. Jiang et al. (2004) also found that exposure of litchi fruit to Anoxia environments preserved higher levels of ascorbic acid. 4. Conclusion The results of the present work show that treatment with Anoxia prior to packaging in slightly modified packages reduced postharvest losses of green asparagus. A combination of prepackaging Anoxia with packaging inhibited shear force increase, and fiber, and lignin formation. This combination treatment also better retained chlorophyll, total sugar, and ascorbic acid during storage and shelf life. Asparagus treated with Anoxia and packaging showed a minimal deterioration of the physical and chemical attributes compared to other treatments. As a nonchemical and facile postharvest technology, Anoxia treatment would benefit from further development, especially in developing countries where storage technology is currently inadequate. Acknowledgement This research work was financially supported by Postharvest Technology Innovation Center, Commission of Higher Education of Thailand. References Albanese, D., Russo, L., Cinquanta, L., Brasiello, A., Di Matteo, M., 2007. Physical and chemical changes in minimally processed green asparagus during cold-storage. Food Chem. 101, 274–280. An, J., Zhang, M., Lu, Q., Zhang, Z., 2006. Effect of a prestorage treatment with 6benzylaminopurine and modified atmosphere packaging storage on the respiration and quality of green asparagus spears. J. Food Eng. 77, 951–957. An, J., Zhang, M., Lu, Q., 2007. Changes in some quality indexes in fresh-cut green asparagus pretreated with aqueous ozone and subsequent modified atmosphere packaging. J. Food Eng. 78, 340–344. Association of Official Analytical Chemists (AOAC), 2000. Official methods of analysis of AOAC international, 17th ed. AOAC, Washington, DC, USA. Barrett, D.M., Beaulieu, J.C., Shewfelt, R., 2010. Color, flavor, texture, and nutritional quality of fresh-cut fruits and vegetables: desirable levels, instrumental and sensory measurement, and the effects of processing. Crit. Rev. Food Sci. Nutr. 50, 369–389. Baxter, L., Waters Jr., L., 1991. Quality changes in asparagus spears stored in flowthrough CA system or in consumer packages. HortScience 26, 399–402. Bhowmik, P.K., Matsui, T., Kawada, K., 2000. Textural and compositional changes of asparagus spears during storage at 1 C and subsequent senescence at 25 C. Pak. J. Biol. Sci. 3, 787–790. Bhowmik, P.K., Matsui, T., Kawada, K., Suzuki, H., 2001. Seasonal changes of asparagus spears in relation to enzyme activities and carbohydrate content. Sci. Hort. 88, 1–9. Brash, D.W., Charles, C.M., Wright, S., Bycroft, B.L., 1995. Shelf-life of stored asparagus is strongly related to postharvest respiratory activity. Postharvest Biol. Technol. 5, 77–81. Bruce, R.J., West, C.A., 1989. Elicitation of lignin biosynthesis and isoperoxidase activity by pectic fragments in suspension cultures of castor bean. Plant Physiol. 91, 889–897. Cantwell, M., Reid, M.S., 1993. Postharvest physiology and handling of fresh culinary herbs. J. Herbs Spices Med. Plants 1, 93–127. Dubois, M., Gilles, K.A., Hamilton, J.K., Rebers, P.A., Smith, F., 1956. Colorimetric method for determination of sugars and related substances. Anal. Chem. 28, 350–356.
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Variation of lycopene, antioxidant activity, total soluble solids and weight loss of tomato during postharvest storage. Postharvest Biol. Technol. 41, 151–155. Jiang, Y., Su, X., Duan, X., Lin, W., Li, Y., 2004. Anoxia treatment for delaying skin browning, inhibiting disease development and maintaining the quality of litchi fruit. Food Technol. Biotechnol. 42, 131–134. Kelly, M.O., Saltveit Jr., M.E., 1988. Effect of endogenously synthesized and exogenously applied thanol on tomato fruit ripening. Plant Physiol. 88, 143–147. Li, W., Zhang, M., 2006. Effect of three-stage hypobaric storage on cell wall components, texture and cell structure of green asparagus. J. Food Eng. 77, 112– 118. Lill, R.E., King, G.A., O’Donoghue, E.M., 1990. Physiological changes in asparagus spears immediately after harvest. Sci. Hort. 44, 191–199. Lipton, W.J., 1990. Postharvest biology of fresh asparagus. Hortic. Rev. 12, 69–155. McKenzie, M.J., Greer, L.A., Heyes, J.A., Hurst, P.L., 2004. Sugar metabolism and compartmentation in asparagus and broccoli during controlled atmosphere storage. Postharvest Biol. Technol. 32, 45–56. Moran, R., 1982. Formulae for determination of chlorophylous pigments extracted with N,N-dimethylformamide. Plant Physiol. 69, 1376–1381. Nei, D., Uchino, T., Sakai, N., Tanaka, S., 2006. Prediction of sugar consumption in shredded cabbage using respiratory model. Postharvest Biol. Technol. 41, 56–61. Peppelenbos, H., Oosterhaven, J., 1998. A theoretical approach on the role of fermentation in harvested plant products. Acta Hort. 464, 381–386. Pesis, E., Marinansky, R., Zauberman, G., Fuchs, Y., 1993. Reduction of chilling injury symptoms of stored avocado fruit by prestorage treatment with high nitrogen atmosphere. Acta Hort. 343, 251–255. Polenta, G., Budde, C., Murray, R., 2005. Effects of different pre-storage anoxic treatments on ethanol and acetaldehyde content in peaches. Postharvest Biol. Technol. 38, 247–253. Rodríguez, R., Jaramillo, S., Heredia, A., Guillén, R., Jiménez, A., Fernández-Bolanos, J., 2004. Mechanical properties of white and green asparagus: changes related to modifications of cell wall components. J. Sci. Food Agric. 84, 1478–1486. Roe, J.H., Mills, M.B., Oesterling, M.J., Damron, C.M., 1948. The determination of diketo-1-gulonic acid, dehydro-1-ascorbic acid, and 1-ascorbic acid in the same tissue extract by the 2,4-dinitrophenyl-hydrazine method. J. Biol. Chem. 174, 201–208. SAS Institute Inc., 1999. SAS/STAT User Guide. SAS Institute, Cary NC, Version 8. Saltveit Jr., M., Mencarelli, F., 1988. Inhibition of ethylene synthesis and action in ripening tomato fruit by ethanol vapors. J. Am. Soc. Hortic. Sci. 113, 572–576. Silva, F.M., Chau, K.V., Brecht, J.K., Sargent, S.A., 1999. Modified atmosphere packaging for mixed loads of horticultural commodities exposed to two postharvest temperatures. Postharvest Biol. Technol. 17, 1–9. Siomos, A.S., Sfakiotakis, E.M., Dogras, C.C., 2000. Modified atmosphere packaging of white asparagus spears composition, colour and textural quality responses to temperature and light. Sci. Hort. 84, 1–13. Song, L., Gao, H., Chen, H., Mao, J., Zhou, Y., Chen, W., Jiang, Y., 2009. Effects of shortterm anoxic treatment on antioxidant ability and membrane integrity of postharvest kiwifruit during storage. Food Chem. 114, 1216–1221. Sothornvit, R., Kiatchanapaibul, P., 2009. Quality and shelf-life of washed fresh-cut asparagus in modified atmosphere packaging. LWT-Food Sci. Technol. 42, 1484– 1490. Torres-Penaranda, A.V., Saltveit, M.E., 1994. Effects of brief anaerobic exposures on carbon dioxide production and quality of harvested asparagus. J. Amer. Soc. Hortic. Sci. 119, 551–555. Tzoumaki, M.V., Biliaderis, C.G., Vasilakakis, M., 2009. Impact of edible coatings and packaging on quality of white asparagus (Asparagus officinalis L.) during cold storage. Food Chem. 117, 55–63. 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Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Effect of prestorage short-term Anoxia treatment and modified atmosphere packaging on the physical and chemical changes of green asparagus Chairat Techavuthiporna,* , Panida Boonyaritthongchaib,c a b c
Division of Biological Science, Faculty of Science and Technology, Huachiew Chalermprakiet University, Samutprakarn 10540, Thailand Division of Postharvest Technology, School of Bioresources and Technology, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand Postharvest Innovation Center-KMUTT, Bangkhuntien, Bangkok 10150, Thailand
A R T I C L E I N F O
A B S T R A C T
Article history: Received 11 October 2015 Received in revised form 28 January 2016 Accepted 29 January 2016 Available online xxx
The effects of prestorage short-term Anoxia treatment combined with modified atmosphere packaging (MAP) on quality changes during the storage of green asparagus (Asparagus officinalis L.) spears were investigated. Two sets of asparagus were used in this study. The first set underwent short-term Anoxia treatment via the administration of gaseous N2 for 8 h at room temperature, while the second set was kept in ambient air at the same temperature. Consequently, treated and untreated spears were stored either freely or packaged in plastic bags with low density polyethylene, in which a passive modification of the atmosphere was allowed to develop. All samples were stored at 4 C for 8 days, followed by 8 days at 10 C. Samples treated with neither Anoxia nor MAP were used as a control. Our results show that treating the asparagus samples with Anoxia and MAP (Anoxia + PE) caused lower respiration, slowing the decrease in headspace O2. In the Anoxia + PE treated samples, spears lost <12% fresh weight after 8 days at 10 C. All treatments showed less increase in shear force while exposed at 4 C for 8 days, as compared with the significant increase found when transferred to 10 C. This increase in shear force was accompanied by the accumulation of fiber and lignin content. There was a positive relationship between toughening and fiber (R2 = 0.958) and toughening and lignin (R2 = 0.915). Moreover, the degradation of chlorophyll, sugar and ascorbic acid content under the Anoxia and MAP treatments were significantly reduced. The results of the present work indicate that Anoxia treatment, a non-chemical and simple postharvest technology, feasible for use in developing countries where food storage technologies are lacking. ã 2016 Elsevier B.V. All rights reserved.
Keywords: Asparagus Anoxia Modified atmosphere packaging Pretreatment Quality
1. Introduction In recent years, asparagus (Asparagus officinalis L.) has been increasingly consumed due to its nutritional value and flavor. However, it is a perishable commodity with a short shelf-life after harvest due to its high respiration rate that rapidly leads to senescence (Hennion and Hartmann, 1990; Lill et al., 1990; Irving and Hurst, 1993). Issues arising from the loss of quality in asparagus after harvest include the shriveling of spears, toughening as a result of lignification of pericyclic fibers (Bhowmik et al., 2001), chlorophyll degradation (Albanese et al., 2007), and changes in organic acid and sugar content (Baxter and Waters, 1991; Bhowmik et al., 2000). The perishable nature of asparagus poses a challenge to the development of effective methods to
* Corresponding author. E-mail address: [email protected] (C. Techavuthiporn). http://dx.doi.org/10.1016/j.postharvbio.2016.01.016 0925-5214/ ã 2016 Elsevier B.V. All rights reserved.
extend its postharvest consumption. The above undesirable effects can be reduced by quick cooling upon harvesting, refrigeration (below 5 C for long term storage), and storage in a modified atmosphere (Lipton, 1990). The storage of asparagus by controlled or modified the atmosphere may prevent or lessen postharvest changes such as texture, flavor, color and chemical composition (McKenzie et al., 2004; Villanueva et al., 2005; An et al., 2006, 2007; Sothornvit and Kiatchanapaibul, 2009). This method involves removing O2 and increasing the concentration of CO2. Because vegetables are living organisms, they require optimal concentrations of O2 and CO2 for respiratory activity. Below a threshold of O2 or above a threshold of CO2, cells undergo anaerobic respiration and produce lactic acid, acetaldehyde and ethanol (Peppelenbos and Oosterhaven, 1998). The extent of anaerobic activity depends on the amount of time cells are exposed to air. Treating fresh produce with an anaerobic atmosphere or anoxic conditions using pure N2 prior to storage slows the ripening of tomatoes (Kelly and Saltveit, 1988) and
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avocados (Pesis et al., 1993), delays skin browning in litchi (Jiang et al., 2004), and reduces the decrease in the firmness of kiwifruit (Song et al., 2009). Torres-Penaranda and Saltveit (1994) reported that short-term Anoxia treatment of asparagus for up to 6 h benefited its quality retention. Lill et al. (1990) reported that the rapid deterioration of stored asparagus was a major problem in retail display in supermarkets because stored spears had a shorter shelf-life after a simulated transit period. Bhowmik et al. (2000) indicated that the length of storage affected textural and compositional changes of asparagus after transfer in a simulation of retail sale. Although much research has focused on improving asparagus storage, few reports document the changes that usually occur during simulations of storage, transportation, and display in the supermarket. Additionally, modified atmosphere packaging (MAP) techniques have been extensively described. MAP improves quality and extends the shelf-life of many types of fresh produce, including asparagus. However, very little information exists regarding the application of MAP in combination with pre-storage treatment of asparagus spears. The objective of the present work was to evaluate the effect of Anoxia treatment and/or MAP application on the quality of green asparagus. This work also focused on physical and chemical changes in different portions of spears (upper and lower portions) during storage at 4 C and during an ensuing simulation of retail sale at 10 C. 2. Materials and methods 2.1. Plant material and handling Fresh green asparagus (A. officinalis L.) spears were obtained from commercial farms in the Nakhon Pathom province (Thailand) and transported to the laboratory. No damaged samples with closed bracts and 0.8–1.2 cm in diameter were selected. Spears were cut at 18 cm from the tip using a stainless steel knife. The asparagus was submerged in a 150 mg L 1 sodium hypochlorite solution for 2 min at 4 C and briefly air dried with ambient air at 25 C to remove surface liquid. 2.2. Sample treatments Two different sets (12 kg per set) of asparagus were prepared. The first set was subjected to short-term Anoxia treatment with gaseous N2. The asparagus was placed in a 10 L plastic chamber, then flushed with pure N2. The O2 concentration in the chamber was less than 0.05 kPa, as determined using a handheld Gas Analyzer (model: Oxybaby M + X, Germany). The samples were maintained in humidified N2 for 8 h at room temperature (approximately 25 C). The second set was kept in ambient air at the same temperature and 90–95% (Relative Humidity; RH) for 8 h. Consequently, both short-term Anoxia and ambient air treatments were established. N2-treated or untreated spears were placed in polystyrene trays measuring 13 20 cm, then either left unpackaged or packaged in plastic bags with 40 mm low density polyethylene (LDPE, 15 22 cm dimension), in which a passive modification of the atmosphere was developed. The O2 transmission rate was 187 mL m 2 h 1 at 23 C and standard pressure (Well Plas Co., Ltd., Thailand). Each tray contained samples, with an average weight of 120 5 g. One tray was performed for one replicate. All samples were refrigerated at 4 C and 90–95% RH for 8 days and then moved to simulate display at 10 C for 8 days. All analyses were performed at 0, 4 and 8 days of storage at 4 C and at 4 and 8 days of storage at 10 C, respectively. Each treatment was applied to four replicates in randomly of four trays.
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2.3. Gas headspace analyses The headspace gas concentrations in the sealed trays were measured in the same tray of each treatment at 0, 4 and 8 days of storage at 4 C and at 4 and 8 days of storage at 10 C. One milliliter of gas sample was withdrawn with a gastight syringe and then injected into gas chromatograph (Model GC-8A, Shimadzu, Japan) for measuring CO2 and O2. The injected gas sample was separated by a WG-100 column and analyzed with a thermal conductivity detector (TCD). Both gas concentrations were expressed in terms of partial pressure (kPa). 2.4. Weight loss Weight loss was measured periodically by weighing samples on a digital balance (model PA2102, OHAUS Corporation, USA). Weights were recorded on day 0, 4 and 8 at 4 C and day 4 and 8 at 10 C. The results are reported as a percentage loss based on the initial weight of the same package. 2.5. Physical and chemical analysis The asparagus spears, 0.8–1.2 cm in diameter and 18 cm in length and marked from the tip, were sectioned and separated into two cylindrical portions including the tip and the base at 9 cm intervals. The following determinations (physical and chemical changes) were made for each portion of the sample: texture, fiber, lignin, total chlorophyll, total sugar and total ascorbic acid. 2.5.1. Texture Texture or toughening was determined by taking nine spears from each tray. The texture of each sample was measured at the middle point of each spear section by performing a cutting test with a texture analyzer (TA-XT plus, Stable Microsystems) a method which was modified from Rodríguez et al. (2004). Values are expressed as maximum shear force (N) using a single blade (7 12 cm) that cut each sample at a cross-head speed of 2.0 mm s 1 over 12 mm. 2.5.2. Fiber content Fiber content was determined according to the AOAC (2000). Five grams of each fresh sample (tip and base) was individually heated in 25 mL of hot water and 6.25 mL of 50% (w/v) NaOH (Merck KGaA, Germany) for 5 min. The fiber was washed in running tap water through a size 30 mesh sieve containing the sample, then weighed to determine initial extracted weight. The extracts were dried at 100 C for 2 h and weighed again to calculate the percentage of fiber content. 2.5.3. Lignin content Lignin content was determined using the thioacidoglycolysis method, modified from Bruce and West (1989). Twenty-five grams of each fresh tissue (tip and base) was homogenized individually using 95% ethanol for 5 min then filtered using Whatman No. 4 filter paper under vacuum. The residue was washed with 17 mL of ethanol and dried at 50 C for 24 h. Approximately 0.25 g of the dried residue was mixed with 7.5 mL of 2 N HCl (Merck KGaA, Germany) and 0.5 mL of thioglycolic acid (Carlo Erba Reagenti SpA., Italy), then boiled in a water bath for 4 h. The mixture was centrifuged at 7500 g at 4 C for 15 min. The residue (lignin thioglycolate) was washed with 10 mL of water, resuspended in 10 mL of 0.5 N NaOH for 18 h at room temperature and centrifuged. 2 mL of concentrated HCl was added to the supernatant. The lignin thioglycolic acid complex was precipitated at 4 C for 4 h and centrifuged. The residue was then dissolved in 10 mL of 0.5 N NaOH. After performing appropriate dilutions, the absorbance was
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read at 280 nm using a spectrophotometer (UV-1600; Shimadzu Co., Japan). The lignin content was expressed as mg kg 1 on a fresh weight basis. 2.5.4. Chlorophyll content Chlorophyll content was separately analyzed in each portion of the spear. A fresh sample of outer tissue (0.25 g) was extracted in 10 mL of N,N-dimethylformamide (Riedel-de Haen, Germany) at 4 C for 24 h (Moran, 1982). The absorbance of each sample was measured at 645 and 663 nm to calculate total chlorophyll (g kg 1) using an estimation of the contribution of chlorophyll a and chlorophyll b content described by Inskeep and Bloom (1985). 2.5.5. Total sugar content Total sugar content was measured according to a modification from the method of Dubois et al. (1956). One gram of each spear portion was homogenized with 10 mL of 80% ethanol. The slurry was heated in a water bath at 60 C for 1 h, then filtered with filter paper (Whatman No. 4). One milliliter of the extract was mixed with 5% phenol (1 mL) and concentrated sulfuric acid (5 mL) to catalyze the reaction. After the mixture was cooled to room temperature, the absorbance at 490 nm was measured with a spectrophotometer. The concentration of sugar was determined using a standard curve with glucose and expressed as mg kg 1 of sugar on a fresh weight basis. 2.5.6. Ascorbic acid content Ascorbic acid content was analyzed according to the Roe et al. (1948) 2,4-dinitrophenol hydrazine method, in which 2 g samples are extracted with 5% metaphosphoric acid solution (Merck KGaA, Germany). The absorbance of the sample solution at 540 nm was measured with a spectrophotometer. A calibration curve was generated using standard ascorbic acid solutions (Carlo Erba Reagenti SpA., Italy). Values for ascorbic acid content were expressed as mg kg 1 on a fresh weight basis. 2.6. Statistical analysis The experimental data were the average of four replications from four independent trays. All experiments were performed using a completely randomized design. All results herein are presented as the mean S.D. Statistical significance was assessed using a 2-way ANOVA at the 99% confidence level. The sources of variations were treatments and storage period. Statistical analyses were performed by SAS Institute (1999).
Fig. 1. Changes in CO2 (upper) and O2 (lower) in packed green asparagus during 8 day at 4 C followed by 8 day at 10 C (PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
Saltveit (1994) found that the peak of relative respiration of spears after exposed to Anoxia condition. The possibility exists that accumulated products of anaerobic respiration may be responsible for the stimulation in respiration by spears exposed to Anoxia condition. Although the O2 level of Anoxia-treated sample was lower than to untreated sample, slightly higher level of CO2 between packaged spears was found. It probably due to a CO2:O2 permeability ratio of the bag being more than 1 (Silva et al., 1999). The CO2 accumulation in package of Anoxia-treated and untreated samples did not show a significant difference.
3. Results and discussion 3.1. Gas composition in package The evolution of CO2 and O2 of the headspace gas in the LDPE bags is shown in Fig. 1. An increase in CO2 concentration and a decrease in O2 content were found after packing. No significant differences in CO2 evolution were observed in packages during storage at 4 C in both Anoxia-treated and untreated samples. After transfer to the simulated retail temperature, the CO2 in samples subjected to Anoxia treatment was slightly higher than that of samples without Anoxia treatment. At equilibrium, the CO2 concentration of Anoxia-treated and untreated samples reached approximately 6.08 kPa and 5.07 kPa, respectively. In contrast, significant changes in O2 levels were found on day 8 at 4 C and when transferred to storage at 10 C (P < 0.01). The O2 concentrations at equilibrium were approximately 5.07 kPa and 11.15 kPa for Anoxia-treated and untreated samples, respectively. Although, low O2 conditions are well known to reduce the respiration of asparagus after harvest (Lipton, 1990), Torres-Penaranda and
Fig. 2. Weight loss percentage evolution of green asparagus during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
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3.2. Weight losses The percent of weight loss in green asparagus during storage at simulated temperatures (4 C and 10 C) is presented in Fig. 2. During storage at 4 C, the weight loss of the Anoxia + PE samples was significantly lower than that of other samples. This phenomenon was especially pronounced after the transfer of all samples to 10 C; the control sample had a maximum weight loss of 18%. In our experiment, the weight losses and also other analyses of control and Anoxia were measured and limited on another 4 days (8 + 4) after transferring to 10 C before deterioration such as a wilting and spoilage. In the Anoxia + PE samples, spears lost less than 12% after 8 days (8 + 8) at 10 C and wilting did not occur in this treatment. However, the difference in weight loss of packaged spears (PE and Anoxia + PE) was insignificant. Among all the treatments, storage period and interaction of treatments and storage period, the increase in weight loss was statistically significant with P-value < 0.01. It has been shown that storage temperature, postharvest treatment and storage duration have significant effects on the rate of weight loss (Javanmardi and Kubota, 2006). It is possible that the higher rate of transpiration and metabolism of nonpackaged spears in comparison to packaged spears could be the main cause for the acceleration of mass loss. In asparagus, weight loss is mainly attributed due to differences in the water vapor pressure of water between the spear surface area and atmosphere (Tzoumaki et al., 2009). Maintaining higher humidity in packages may minimize this change. In addition, the large difference loss of mass between control and Anoxia spears in this experiment is probably considered to be due to a loss of moisture via stomata. In tomato plant, the stomata begin to close after the condition of oxygen deprivation with a parallel decrease in
Fig. 4. Changes in fiber content of green asparagus (Tip; upper and Base; lower) during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
transpiration (Else et al., 1995). With short-term Anoxia treatment, therefore, closing of stomata may help treated spears to decrease transpiration. 3.3. Texture, fiber and lignin content
Fig. 3. Changes in texture of green asparagus (Tip; upper and Base; lower) during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
In determining the marketability of asparagus, the most important factor is spear toughness. Changes in texture, fiber and lignin content after harvest are of primary interest. Fig. 3 represents the textures of each asparagus portion using the different treatments (measured as maximum cutting force). Force increased in both the tip and base throughout the experimental period. Although the development followed the same patterns, the shear force was greater in the base than in the top portion. The rates of increase in shear force were slightly higher at 4 C and increased further when transferred to 10 C. However, this increase was not as great in samples treated with Anoxia prior to packaging in LDPE bags (Anoxia + PE). Anoxia pretreatment was found to have a significant impact on fiber content. Additionally, asparagus stored in LDPE bags exhibited significant fluctuations in fiber content. As shown in Fig. 4, the fiber content of each asparagus spear portion changed with storage conditions. The fiber content in the top portions was approximately half that in the bottom portions. All treatments were significantly effective in maintaining fiber content during storage at 4 C. Individual treatment of asparagus with Anoxia was much less effective but still significant compared to storage in air. Moreover, combining Anoxia and packaging significantly maintained the content of fiber in the basal section of spears and slightly increased fiber content in the tip portion compared to other samples, especially the control spears. The biosynthesis of lignin in green asparagus is controlled by multiple enzymes, including phenylalanine ammonialyase (PAL)
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Fig. 7. Correlation between shear force and lignin content of green asparagus (tip and base) during 8 day at 4 C followed by 8 day at 10 C.
Fig. 5. Changes in lignin content of green asparagus (Tip; upper and Base; lower) during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
which is a key enzyme in the synthesis of flavonoids such as anthocyanins and lignin (Flores et al., 2005; Tzoumaki et al., 2009). The lignin content of both the top and bottom portions of green asparagus are shown in Fig. 5. The initial lignin content was approximately 10.95 and 45.94 mg kg 1 in the tip and basal portions, respectively. An increase in lignin content was observed in untreated asparagus during the change in storage from 4 C to 10 C. Both Anoxia and MA treatments significantly maintained the lignin content of green asparagus at 4 C and delayed lignin formation after transfer to 10 C. Moreover, slight changes in lignin were detected in combination treatments, indicating that pretreatment with Anoxia and MA treatments prevented the accumulation of lignin during postharvest refrigeration and retail simulation temperature. Li and Zhang (2006) have also found that under hypobaric conditions, the increase in lignin and cell structure can be retarded, effectively helping to inhibit the
Fig. 6. Correlation between shear force and fiber content of green asparagus (tip and base) during 8 day at 4 C followed by 8 day at 10 C.
senescence of asparagus. Among all the treatments, storage period and interaction of treatments and storage period, the change in fiber and lignin contents were statistically significant with P-value < 0.01. We found a positive correlation between toughening and the production of fiber and lignin content in green asparagus, as shown in Figs. 6 and 7 (R2 = 0.958 and 0.915, respectively). Texture is one of the most critical parameters that consumers use to assess asparagus quality (Barrett et al., 2010; Siomos et al., 2000). During refrigeration in this experiment, fiber and lignin content increased gradually over time and increased sharply after the temperature was increased to 10 C, especially in the control. Fibrousness and the process of hardening are correlated, occurring after harvesting and accompanied by lignification of the sclerenchyma. In addition, these results are consistent with the mass loss of green asparagus. Changes in texture may also reflect losses of tissue water (Rodríguez et al., 2004; Tzoumaki et al., 2009). Modified atmosphere packaging with green asparagus has generally been reported to improve the rigidity of spears (Villanueva et al., 2005). Herein, slower changes in texture were observed upon combining Anoxia pre-treatment with MAP, which is likely linked to the accumulation of fermented compounds such as ethanol and acetaldehyde in anaerobic conditions (Polenta et al., 2005), as well as the inhibition of ethylene synthesis (Saltveit and Mencarelli, 1988). The exact mechanisms of the delay in textural changes using Anoxia treatment are still unclear. Pre-storage anoxic treatment might slow the metabolism of green asparagus and also inhibit textural changes. 3.4. Chlorophyll, total sugar and ascorbic acid content Chlorophyll is the pigment that causes the green color in asparagus. At the beginning of storage, the top spear portions contained slightly higher total chlorophyll than the bottom portion (2.39 and 2.14 g kg 1, respectively) (Fig. 8). Visually, the green color gradually faded during storage. A significant loss of chlorophyll was observed during the storage period at 4 C and after moving to 10 C in control samples compared with Anoxia and MAP treated samples. On the fourth day at 10 C, the total chlorophyll content at the top spear portions in the controls, Anoxia, PE, and Anoxia + PEtreated green asparagus were 1.29, 1.60, 1.72 and 1.88 g kg 1, respectively. In contrast, the total chlorophyll content at the bottom portions of the spears of control, Anoxia, PE, and Anoxia + PE-treated green asparagus were 1.01, 1.41, 1.58 and 1.63 g kg 1, respectively. Based on the above results, the combination treatment exhibited a significant beneficial effect on reducing chlorophyll changes in asparagus, which suppressed respiration during storage in LDPE bags. Additionally, there is a relationship
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Fig. 8. Changes in chlorophyll content of green asparagus (tip; upper and base; lower) during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
Fig. 9. Changes in sugar content of green asparagus (tip; upper and base; lower) during 8 day at 4 C followed by 8 d at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
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Fig. 10. Changes in ascorbic acid of green asparagus (tip; upper and base; lower) during 8 day at 4 C followed by 8 day at 10 C (Control, untreated samples; Anoxia, incubated with N2 gas for 8 h; PE, packaged samples with polyethylene (PE) bag; Anoxia + PE, incubated with N2 gas for 8 h and packaged with PE bag). Data are the average of four replicates standard deviation. The different letters denote significance among treatments.
between respiratory rate and chlorophyll degradation, according to Cantwell and Reid (1993). Fig. 9 shows the change in total sugar content at 4 C for 8 days and at 10 C for 8 days. The sugar content decreased in all samples toward the beginning of storage, decreasing from 112.63 mg kg 1 (tip portion) and 103.87 mg kg 1 (bottom portion). It has been reported that respiration is a major factor that contributes to postharvest losses (Brash et al., 1995; Uchino et al., 2004). Respiratory processes convert stored soluble solids, mainly sugar, into energy in the presence of oxygen (Nei et al., 2006). Our results clearly reflect a significant decrease in total sugar content over time in untreated samples and smaller decreases in spears treated with Anoxia, whether they be stored under MAP or non–MAP conditions. Significant changes were found in unpackaged samples after transfer to 10 C (P < 0.01). The percentage of sugar retention after 4 days of simulating resale temperature at 10 C for untreated and Anoxia samples were 41.49% and 49.64%, respectively. At the same temperature, the percentages detected for the MAP and combination samples were 68.51% and 71.70%, respectively. This demonstrates that total sugar content is mainly preserved in the latter two treatments when compared with unpackaged samples. At the end of storage (after 8 days at 10 C), the retention levels detected for MAP and combination samples were 47.85% and 65.17%, respectively. Initially, the ascorbic acid levels of the top spear portions were approximately 20% higher than in the bottom portion (Fig. 10). These results show that ascorbic acid content decreased significantly during storage in all samples analyzed. After transfer to 10 C, ascorbic acid retention percentages at the fourth day of refrigeration for untreated and Anoxia samples were 26.35% and 43.43%, respectively. At the same time, the percentages detected for the MAP and combination samples were 54.19% and 78.87%,
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respectively. The retention levels at the end of storage detected in MAP and combination samples were 42.02% and 66.54%, respectively. Among all the treatments, storage period and interaction of treatments and storage period, the change in sugar and ascorbic acid contents were statistically significant with P-value < 0.01, indicating that the deterioration rate varied depending upon the treatments applied. The highest rate was in non-treated spears, followed by samples treated individually with either Anoxia or MAP. Jiang et al. (2004) also found that exposure of litchi fruit to Anoxia environments preserved higher levels of ascorbic acid. 4. Conclusion The results of the present work show that treatment with Anoxia prior to packaging in slightly modified packages reduced postharvest losses of green asparagus. A combination of prepackaging Anoxia with packaging inhibited shear force increase, and fiber, and lignin formation. This combination treatment also better retained chlorophyll, total sugar, and ascorbic acid during storage and shelf life. Asparagus treated with Anoxia and packaging showed a minimal deterioration of the physical and chemical attributes compared to other treatments. As a nonchemical and facile postharvest technology, Anoxia treatment would benefit from further development, especially in developing countries where storage technology is currently inadequate. Acknowledgement This research work was financially supported by Postharvest Technology Innovation Center, Commission of Higher Education of Thailand. References Albanese, D., Russo, L., Cinquanta, L., Brasiello, A., Di Matteo, M., 2007. Physical and chemical changes in minimally processed green asparagus during cold-storage. Food Chem. 101, 274–280. An, J., Zhang, M., Lu, Q., Zhang, Z., 2006. Effect of a prestorage treatment with 6benzylaminopurine and modified atmosphere packaging storage on the respiration and quality of green asparagus spears. J. Food Eng. 77, 951–957. An, J., Zhang, M., Lu, Q., 2007. Changes in some quality indexes in fresh-cut green asparagus pretreated with aqueous ozone and subsequent modified atmosphere packaging. J. Food Eng. 78, 340–344. Association of Official Analytical Chemists (AOAC), 2000. Official methods of analysis of AOAC international, 17th ed. AOAC, Washington, DC, USA. Barrett, D.M., Beaulieu, J.C., Shewfelt, R., 2010. Color, flavor, texture, and nutritional quality of fresh-cut fruits and vegetables: desirable levels, instrumental and sensory measurement, and the effects of processing. Crit. Rev. Food Sci. Nutr. 50, 369–389. Baxter, L., Waters Jr., L., 1991. Quality changes in asparagus spears stored in flowthrough CA system or in consumer packages. HortScience 26, 399–402. Bhowmik, P.K., Matsui, T., Kawada, K., 2000. Textural and compositional changes of asparagus spears during storage at 1 C and subsequent senescence at 25 C. Pak. J. Biol. Sci. 3, 787–790. Bhowmik, P.K., Matsui, T., Kawada, K., Suzuki, H., 2001. Seasonal changes of asparagus spears in relation to enzyme activities and carbohydrate content. Sci. Hort. 88, 1–9. Brash, D.W., Charles, C.M., Wright, S., Bycroft, B.L., 1995. Shelf-life of stored asparagus is strongly related to postharvest respiratory activity. Postharvest Biol. Technol. 5, 77–81. Bruce, R.J., West, C.A., 1989. Elicitation of lignin biosynthesis and isoperoxidase activity by pectic fragments in suspension cultures of castor bean. Plant Physiol. 91, 889–897. Cantwell, M., Reid, M.S., 1993. Postharvest physiology and handling of fresh culinary herbs. J. Herbs Spices Med. Plants 1, 93–127. Dubois, M., Gilles, K.A., Hamilton, J.K., Rebers, P.A., Smith, F., 1956. Colorimetric method for determination of sugars and related substances. Anal. Chem. 28, 350–356.
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