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Development of food packaging materials containing calcium hydroxide and porous medium with carbon dioxide-adsorptive function
Food Packaging and Shelf Life 21 (2019) 100352
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Development of food packaging materials containing calcium hydroxide and porous medium with carbon dioxide-adsorptive function Hyun-Gyu Lee, Suyeon Jeong, SeungRan Yoo
T
⁎
World Institute of Kimchi, Gwangju 61755, Republic of Korea
A R T I C LE I N FO
A B S T R A C T
Keywords: Food packaging material Active packaging Carbon dioxide Adsorbent Kimchi
Kimchi packaging can be easily damaged by carbon dioxide generated during fermentation of kimchi, and adsorbents have been developed to overcome the problems of volume expansion and breakage of kimchi packaging caused by carbon dioxide. Here, we examined the applicability of calcium hydroxide and porous medium impregnation for improving adsorbent performance. The developed adsorbents were incorporated into low-density polyethylene to develop packaging materials for kimchi. Notably, packaging materials containing the adsorption powder impregnated with calcium hydroxide and porous medium showed improved mechanical properties and exhibited chemical and physical reactions, resulting in strong adsorptive power and reusability. The mechanical strength of the packaging was weak due to the agglomerative properties of the powder. In kimchi packaging, adsorption packaging did not affect kimchi ripening (p > 0.05). The optimal carbon dioxide concentration in kimchi packaging was 40–55%, and the carbon dioxide concentration could be controlled using the developed adsorption packaging materials.
1. Introduction The main function of traditional food packaging is to preserve and protect food from external physical, chemical, and microbiological factors (Manikantan & Varadharaju, 2011). These functions have enabled food to be stored and distributed for a long time, thereby improving human quality of life. In order to maintain better quality of food and extend shelf life, active packaging that protects food from the outside environment and interacts with the internal environment, including the food, has been developed (Park et al., 2012). Carbon dioxide is widely used in many fields and plays a beneficial role in food. Carbon dioxide inhibits the growth of microorganisms, resulting in hygienic management and prolonged shelf life. In addition, carbon dioxide prevents the oxidation of food by mixing with nitrogen, and imparts a carbonated flavor. Despite these positive effects, carbon dioxide can also have negative roles in food. For example, some agricultural products that are sensitive to carbon dioxide concentrations suffer from anaerobic respiration and accelerated decay in environments containing high carbon dioxide concentrations (Lee, 2016). Food that has not been sterilized may cause volume expansion and breakage of the packaging due to the generation of carbon dioxide during storage. As a result of volume expansion and breakage, food cannot be stored long term or distributed appropriately (Lee, Shin, Lee, Kim, &
⁎
Cheigh, 2001). Because carbon dioxide can have positive or negative roles, depending on the characteristics of the food, it is necessary to use an appropriate carbon dioxide concentration. For kimchi, carbon dioxide plays a beneficial role in improving the taste of kimchi, but makes it difficult to store kimchi for a long period due to volume expansion and breakage of kimchi packaging. Therefore, carbon dioxide should be controlled at an appropriate level. However, there is no clear standard for the optimal level of carbon dioxide concentration in kimchi packaging, thereby complicating the management of commercial kimchi. Active packaging for controlling carbon dioxide contains adsorbents, microholes, filters, and valves (Golestan, Ghosta, Pourmirza, & Valizadegan, 2015; Lee et al., 2012; Olmi, 2015). Most carbon dioxide control methods, except for adsorbents, involve the discharge of gas to the outside of the packaging. These methods are very effective at alleviating volume expansion and increases in pressure. However, these methods can be disadvantageous because the flavor of the food can escape to the outside environment, or the quality of the food can deteriorate due to the inflow of oxygen. In contrast, adsorbents effectively control the gas inside the food packaging without influx of external oxygen. However, because adsorbents are chemical substances, careful selection of the adsorbent material must be made. In food packaging, adsorbents are commonly used with sachets,
Corresponding author. E-mail addresses: [email protected] (H.-G. Lee), [email protected] (S. Jeong), [email protected] (S. Yoo).
https://doi.org/10.1016/j.fpsl.2019.100352 Received 1 February 2019; Received in revised form 25 April 2019; Accepted 27 June 2019 2214-2894/ © 2019 Elsevier Ltd. All rights reserved.
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which are easy to make and use; however, these materials are associated with several problems related to moisture and leakage, thereby affecting food safety. These problems can be overcome by mixing the adsorbent with a polymer, such as polyethylene, polypropylene, polyethylene terephthalate, and nylon. Among these materials, polyethylene is a commonly used food packaging material owing to its low price, low wettability, and outstanding mechanical properties (Hanani, Husna, Syahida, Khaizura, & Jamilah, 2018). Carbon dioxide adsorbents consist of chemical adsorbents (monoethanolamine, calcium hydroxide [CH], and sodium carbonate) and physical adsorbents (activated carbon [AC] and zeolite) (Wang, Jo, An, Rhim, & Lee, 2015). Among these chemical adsorbents, CH is the most common commercially available material. CH and physical adsorbents are food additives that are available under restricted conditions; they are suitable as food packaging materials based on safety (Lee, 2016). Chemical adsorbents have excellent performance but have a slow reaction rate, and reactions are typically irreversible. Physical adsorbents have the advantages of quick reaction and reversibility, but have weak adsorption power (Charles, Sanchez, & Gontard, 2006; Hauchhum & Mahanta, 2014; Lee, 2016; Rashidi, Yusup, & Loong, 2013). Many researchers have made great efforts to develop functionally improved substances to supplement the disadvantages of existing adsorbents. Additionally, impregnation has been used to supplement this approach (Liu, Teng, Zhang, Cao, & Pan, 2013; Yu, Huang, & Tan, 2012). However, studies on the use of this approach, including impregnation, in the field of food packaging have been insufficient. If substances that combine the advantages of chemical and physical adsorbents can be applied for food packaging, effective adsorption and the ability to reuse packaging may lead to consumer satisfaction and environmental protection. Accordingly, in this study, we aimed to develop a novel material for kimchi packaging to overcome the problems caused by carbon dioxide. We selected chemical and physical adsorbents and impregnated the chosen materials to develop adsorbents with improved performance. We then investigated the characteristics of the film with carbon dioxide adsorptive function and the effects of the developed materials on the carbon dioxide concentration and kimchi ripening in kimchi packaging. Our findings provide practical insights into the quality control of commercial kimchi.
2.2. Preparation of master batches and films
2. Materials and methods
2.3.3. Measurement of pressure, volume, and carbon dioxide concentration of kimchi packaging The pressure of the kimchi packaging was analyzed using a headspace pressure gauge (UTK-P5000; Ultra Tec, Seoul, South Korea). The volume of kimchi packaging was analyzed by measuring the volume of the overflowing water after immersing the kimchi packaging in a water tank. The carbon dioxide concentration was measured using a headspace gas analyzer (GS3 micro; Systech Illinois, Johnsburg, IL, USA). The carbon dioxide concentration was fiducially set to 0.3%.
Master batches and films were prepared by melt compounding with extruding powder and LDPE to confer the materials with carbon dioxide adsorptive function. The master batches and films were prepared using a twin screw extruder (BA-19; BauTek Co., Uijeongbu, South Korea) with a length/diameter ratio of 40:19. The extruder was set to 190 °C for the header, 190 °C for zones 1–5, 160 °C for zone 6, and 140 °C for the feed zone. The produced film had a thickness of 60 ± 10 μm. Importantly, 20% AC film was excluded from this study because it was not fabricated to a thickness of less than 90 μm. The powder contents of the master batches and films were calculated according to Eq. (1): Powder contents (Wp + Wr) × 100
of
master
batches
and
films
(%) = Wp/ (1)
where Wp is the powder weight (g), and Wr is the LDPE resin weight (g). 2.3. Application of packaging material (master batch) and film to kimchi packaging 2.3.1. Preparation of kimchi packaging A 500-mL aluminum pouch (SaeroPNL Co., Seoul, South Korea) and 150 g kimchi (Trechan Co., Gwangju, South Korea) were prepared for the kimchi experiment. The master batch (20 g) or film (0, 1, 3, 5, or 10 g) was sealed in a pouch with the kimchi and was then stored at 10, 4, or 0℃. The master batch was packed in a mesh pocket to prevent mixing with kimchi. 2.3.2. Measurement of pH and titratable acidity Before the measurements, the kimchi was homogenized with a hand blender (HR1372; Koninklijke Philips Electronics N.V., Amstelplein, Amsterdam, Netherlands) and then filtered through four layers of sterilized coarse gauze. Next, the pH of kimchi was measured using a digital pH meter (TitroLine Easy, SI Analytics; Xylem Inc., Rye Brook, NY, USA) after homogenization. The titratable acidity was measured by titrating 10 mL kimchi juice with 0.1 N sodium hydroxide to a pH of 8.3. Titratable acidity was calculated on the basis of lactic acid.
2.1. Adsorbent synthesis and optimization Environmental pollution caused by the use of plastics has raised concerns among the public. Although much effort has been made to replace plastics, no suitable substitute is available. However, if plastic is recycled and used for a long time, pollution can be reduced. In this study, CH and porous medium were synthesized for the reuse of adsorbent. Adsorption powders (CH + AC; CH + zeolite 13X [Z]) were prepared by impregnation. CH was dissolved in distilled water and stirred for 3 h. Then, a specific amount of AC or Z was added to the CH solution, and the resulting slurry was stirred for 30 min. After standing at room temperature for 4 h, the supernatant was discarded. Finally, the resulting slurry was dried at 105 °C overnight. Synthetic adsorbent was mixed with low-density polyethylene (LDPE, ASTM D1238 melt index: 2.8 g/10 min; Hanhwa Total Petrochemical Co., Ltd., Seosan, South Korea) and made into a master batch, and carbon dioxide adsorption was then evaluated to optimize the synthesis ratio. Fifty milliliters of distilled water was poured into a rectangular container (195 × 140 × 50 mm), and 20 g of the master batch on the petri dish was placed in the container. Then, carbon dioxide exchange packaging was evaluated to test the adsorptive power of the master batch. As a result of the experiment (Fig. 1), the ratio with the best adsorptive power was identified, and this ratio of synthetic adsorbent was used for the master batch and film production (CH:AC = 1:0.3; CH:Z = 1:0.15).
2.4. Analysis of film characteristics 2.4.1. Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) To characterize the chemical structure, FTIR spectroscopy spectra were recorded on a Nicolet iS50 FTIR instrument (Thermo Fisher Scientific Inc., Waltham, MA, USA), from 400 to 4000 cm−1, in attenuated total reflection mode. The surfaces and cross sections of the films were observed using SEM (Gemini 500; Zeiss, Oberkochen, Germany) after coating of the films with a thin layer of platinum. 2.4.2. Mechanical properties To evaluate the mechanical properties, the tensile stress at break and elongation at break were evaluated according to ISO 527-3 using an Instron 3366 (Instron Engineering Corp., Norwood, MA, USA). The tensile stress at break and elongation at break tests were conducted at a 2
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Fig. 1. Optimization of the impregnation ratio of calcium hydroxide and porous medium (activated carbon and zeolite 13X); a−dWithin samples (equivalent week), values with different lowercase letters are significantly different as per Duncan’s multiple range test (P < 0.05); A-DWithin weeks (equivalent sample), values with different uppercase letters are significantly different as per Duncan’s multiple range test (P < 0.05).
Fig. 2. Effects of the adsorption master batch (MB) on kimchi ripening and kimchi packaging during storage at 10 °C.
adsorptive function of the film, the carbon dioxide adsorption/desorption was analyzed using a thermogravimetry (TGA) analyzer (TGA/ DSC 1; Mettler Toledo, Columbus, OH, USA). The sample was heated under nitrogen at 100 ℃ for 30 min to remove impure gas. Carbon dioxide was then flowed at 25 ℃ for 1 h and heated under nitrogen at 100 ℃ for 30 min. This process was repeated to examine adsorption and desorption reactions. The speed of temperature increase and decrease was 20℃/min.
50 mm/min crosshead speed, 100 mm gauge length, and 10 mm width. The experiment was repeated for 10 specimens. 2.4.3. Measurement of water vapor permeability (WVP) WVP was measured according to ASTM 1249-90 using a PermatranW 3/33 (MOCON Inc., Minneapolis, MN, USA). In the instruments, the exposed surface area of the test film was 50 cm2. During measurements, experimental conditions were set as follows: temperature set point, 37.8 ℃; barometric pressure, 760 mmHg; flow rate, 10.67 SCCM; test time, 30 min; and relative humidity, 100%.
2.5. Statistical analysis
2.4.4. Carbon dioxide adsorption/desorption analysis of the film In order to investigate the effects of reuse on the carbon dioxide
Statistical analysis of data was performed using SPSS ver. 19.0 (SPSS Inc., Chicago, IL, USA). One-way analysis of variance and Duncan’s 3
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multiple range comparison tests were employed to determine the level of significance, and differences with P values of less than 0.05 were considered significant.
Ca(OH)2(s) ⇌ Ca2+(aq) + 2OH−(aq) −
3. Results and discussion 3.1. Application of packaging material (master batch) to kimchi packaging 3.1.1. Ripening index of kimchi Kimchi is fermented by metabolic processes of microorganisms derived from various food materials. In particular, lactic acid bacteria in kimchi produce metabolites during the growing process, and the produced metabolites are combined with the ingredients of kimchi to form a unique taste. Among the various factors that determine the quality of kimchi, the metabolites of lactic acid bacteria are the most important factors. Moreover, because metabolites of lactic acid bacteria acidify the kimchi, the pH and acidity can be regarded as indicators of the degree of kimchi ripening (Lee & Yoo, 2017). In this study, the chemical quality characteristics, which are indicators of the degree of kimchi ripening, were investigated when the master batch with carbon dioxide adsorptive function was packed with kimchi at 10℃ (Fig. 2). The pH decreased from 5.89 to 3.91, and the acidity increased from 0.34% to 1.65%, demonstrating that kimchi was acidified by metabolites of lactic acid bacteria during storage (Moon, Kim, & Chang, 2018). In particular, pH and acidity showed rapid changes until the first week, followed by slow changes. The results were similar to those of a study by Meng, Lee, Kang, and Ko, (2015)), which showed rapid changes until reaching the optimal ripening and gradual changes thereafter. Differences in pH and acidity according to the master batch were not clear. Because CH reacts with lactic acid and acetic acid (Teixeira, Levin, & Trope, 2005), which are major organic acids generated during the fermentation of kimchi (Shim et al., 2012), the master batch containing CH was expected to show delayed acidification of kimchi; however, these effects could not be confirmed in this study. This indicated that the CH in the master batch did not react with kimchi and did not affect the quality. In other words, CH was not eluted.
(2)
CO2(aq) + OH (aq) ⇌ HCO (aq)
(3)
HCO3−(aq) + OH-(aq) ⇌ H2O(l) + CO32-(aq)
(4)
Ca2+(aq) + CO32−(aq) ⇌ CaCO3(s)
(5)
Ca(OH)2(s) + CO2(g) ⇌ CaCO3(s) + H2O(l)
(6)
3-
Porous medium removes carbon dioxide by Van der Waals forces due to the interaction between the surface/pore space and carbon dioxide molecules (Thommes, 2010). Because the acid-base neutralization reaction (chemical adsorption reaction) is a stronger reaction than the Van der Waals physical adsorption reaction, impregnation of the porous medium with CH in this study significantly improved the adsorptive power of the master batch. 3.2. Film characteristics The master batch, as a raw material for plastic products, could be manufactured and used in various forms as needed. Kimchi packaging is mainly available in the form of pouches and containers. In this study, master batches were prepared into films, which were used as raw materials for the pouches. 3.2.1. FTIR spectra and SEM results The interactions between adsorption powder and LDPE were confirmed using the FTIR spectroscopy (Fig. 3). Interactions by physical or chemical bonding between two or more substances can be revealed by changes in spectral peaks (Fasihnia, Peighambardoust, Peighambardoust, & Oromiehie, 2018). As shown in Fig. 3, the peaks of LDPE film at 2918, 2851, 1468, and 718 cm−1 were assigned to CH2 asymmetrical stretching, CH2 symmetrical stretching, bending deformation, and rocking deformation, respectively (Rajandas, Parimannan, Sathasivam, Ravichandran, & Yin, 2012). Moreover, the peak of LDPE remained unchanged, even when the LDPE was mixed with the powder (CH, AC, Z, and impregnated powder) and made into a film. The CH/LDPE film was assigned a narrow peak of stretching of OeH at 3642 cm−1 and a vibration C–O of the carbonate group at 1091 cm−1 (Khachani, Hamidi, Halim, & Arsalane, 2014). The Z/LDPE film showed stretching of SieO and AleO vibrations from 974 to 670 cm−1 (Boroglu & Gurkaynak, 2011; Hu, Gao, Liu, Zhang, & Meng, 2017). The AC/LDPE film showed a sloped shape in the LDPE spectra because the AC was slanted without a specific peak. The FTIR spectrum of CH + Z/LDPE film showed an OeH peak and C–O peak from CH as well as an SieO peak from Z. The peaks of the powder between the LDPE polymers remained intact, indicating that the powder particles were embedded between the polymers without chemical bonding to the LDPE chains (Fasihnia et al., 2018). The appearance of embedded powder particles in LDPE was also confirmed by SEM. The surface and cross sections of the films were examined by SEM to visually observe the mixing of powder between LDPE polymers (Fig. 4). From images on the surface on the film, we confirmed that the powder was uniformly dispersed in the film. Additionally, powder has a tendency to agglomerate in the LDPE polymer. In particular, AC was found to be the most agglomerative in the film, and agglomeration of AC was alleviated by impregnating AC with CH. Agglomeration of powder in film generates voids and affects the mechanical properties of the film (Cao et al., 2016; Sarifuddin & Ismail, 2013). Indeed, voids in the film were confirmed in cross sectional images (Fig. 4).
3.1.2. Carbon dioxide adsorptive power in the master batch used for kimchi packaging Carbon dioxide produced by metabolism results in the carbonic taste of kimchi, but causes volume expansion and breakage of kimchi packaging, resulting in problems with storage and distribution (Lee et al., 2001). To overcome this problem, master batches with carbon dioxide adsorptive function were prepared and applied to kimchi packaging (Fig. 2). The control with the LDPE master batch burst after 2 weeks of fermentation due to the generation of carbon dioxide. At this time, the volume, pressure, and carbon dioxide concentration of kimchi packaging were 501 mL, 1049.50 mb, and 83.3%, respectively (Fig. 2). These findings confirmed that the kimchi packaging should be adjusted below this value in order to prevent breakage of the packaging during storage and distribution. Among the functional master batches, the master batch containing AC showed weak adsorptive power. Therefore, the packaging was broken after 2 weeks of storage, similar to the control sample. Additionally, the Z/LDPE master batch showed weak adsorptive power, resulting in increased volume, pressure, and carbon dioxide to 408 mL, 1021.98 mb, and 76.0%, respectively (Fig. 2). In contrast, the CH/LDPE master batch, CH + AC/LDPE master batch, and CH + Z/LDPE master batch did not show increased volume or pressure. These master batches maintained a carbon dioxide concentration of less than 50% in kimchi packaging, indicating that these materials had excellent adsorptive power. The main reason for this excellent adsorptive power may have been the presence of CH, which acts as a strong salt by forming calcium ions and hydroxyl groups in water (reaction (2)). The ionized hydroxyl group removes carbon dioxide by an acid-base neutralization reaction (reaction (3)). The overall reaction formula is given in reaction (6) (Han, Yoo, Kim, & Wee, 2011).
3.2.2. Mechanical properties and WVP The mechanical properties and WVP of the film are shown in Table 1. The tensile stress at break, elongation at break, and WVP of LDPE films were 24.98 MPa, 174.63%, and 8.36 g·m·mil/m2·day, respectively. Incorporation of the powder into the LDPE affected the 4
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Fig. 3. Analysis of Fourier-transform infrared spectra for adsorption powders and adsorption films.
reactions between the porous medium/LDPE film and the CH/LDPE film was related to differences in the reaction method with carbon dioxide. The porous medium/LDPE film chemically and physically reacted with carbon dioxide, but the chemical reaction was very weak, and the physical reaction predominated. The physical reaction rate was fast because of the low reaction energy; because the reaction energy was low, the desorption reaction easily occurred when heated to a high temperature. In contrast, CH reacts chemically, and the chemical reaction is advantageous in that the adsorption rate is slow but the adsorptive power is strong because of the large reaction energy (Charles et al., 2006; Hauchhum & Mahanta, 2014; Lee, 2016; Park, Kim, Cho, Kim, & Yang, 1998). In contrast to the results of our previous experiment with kimchi (Fig. 2), in which the porous medium had a weaker adsorptive power than the CH, the strong adsorptive power of the porous medium in Fig. 5 appeared to be caused by differences in the adsorption speed. In adsorption and desorption experiments using TGA, the physical adsorption reaction was fast and strongly adsorbed because it proceeded for a short time. As the reaction time with carbon dioxide increased, as in the kimchi experiment, the chemical adsorption reaction became stronger. Analysis of the impregnated powder/LDPE films showed that the physical and chemical reactions occurred simultaneously when the carbon dioxide was adsorbed. The impregnated powder/LDPE films slowly adsorbed carbon dioxide, similar to the CH/LDPE film, and the carbon dioxide was desorbed by heating, similar to the porous medium/ LDPE films. The characteristics of impregnated powder/LDPE films have not yet been optimized; however, if appropriately supplemented, these films may be reused many times, maintaining strong carbon dioxide adsorptive power and thereby reducing environmental pollution.
mechanical properties and WVP and varied up to 11.13–22.64 MPa, 47.60–98.21%, and 12.83–24.58 g m mil/m2 day. The increase in the powder content resulted in weak mechanical strength and increased WVP, similar to the results reported by Chollet, Swesi, Degraeve, and Sebti, (2009)). Incorporation of the powder changed the film owing to the interactions between powder particles and the LDPE. This interaction is not a chemical bond, it is a physical bond, and it exists in the form embedded in LDPE polymers. Embedded powder probably may result in reduced strength of the composite chain and could increase the mobility of water by securing space. The results of mechanical properties and WVP were also different depending on the type of powder. Inclusion of CH in LDPE yielded a higher tensile stress at break, higher elongation at break, and lower WVP than that of porous medium. The AC/LDPE films showed the lowest mechanical strength and highest WVP, and even 20% AC/LDPE film could not be prepared due to low mechanical strength. For impregnated powders of CH and porous medium, the results confirmed that impregnation improved the mechanical strength and WVP compared with single porous medium. In the future, low mechanical strength and high WVP can be improved by incorporation crosslinking agents and plasticizers and by bonding with other materials.
3.2.3. Carbon dioxide adsorption and desorption reaction As shown in Fig. 5, the porous medium/LDPE film rapidly adsorbed carbon dioxide, and the film was desorbed by heating. Among the porous media, Z had better adsorption and desorption capacities than AC, possibly because the specific surface area of Z was larger (Park, Hong, Kim, & Kang, 2013). In the CH/LDPE film, the desorption reaction was not induced by heating, and carbon dioxide adsorption occurred gradually. The difference in the adsorption and desorption 5
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Fig. 4. Scanning electron microscopy images of adsorption films.
3.3. Application of carbon dioxide adsorption film to kimchi packaging
Table 1 Analysis of the mechanical properties and water vapor permeability of films. Tensile stress at break (MPa)
LDPE 20% CH/LDPE film 20% Z/LDPE film 20% CH + AC/LDPE film 20% CH + Z/LDPE film 10% CH/LDPE film 10% AC/LDPE film 10% Z/LDPE film 10% CH + AC/LDPE film 10% CH + Z/LDPE film
24.98 18.74 19.61 12.51
± ± ± ±
2.03*a 1.92d 2.54cd 1.09e
18.68 ± 3.50d 22.64 11.13 19.66 12.52
± ± ± ±
2.31b 0.99e 4.30cd 1.58e
21.62 ± 1.30bc
Elongation at break (%)
Water vapor permeability (g m mil/m2 day)
174.63 ± 30.86a 84.10 ± 8.14c 57.44 ± 3.49de 48.39 ± 3.18e
8.36 ± 2.03e 13.48 ± 1.29cd 21.81 ± 0.39ab 24.58 ± 1.29a
64.44 ± 5.71d
19.78 ± 2.30b
98.21 47.60 81.07 84.53
± ± ± ±
5.05b 3.55e 8.03c 5.83c
82.25 ± 9.34c
12.83 23.43 14.07 16.38
± ± ± ±
3.3.1. Establishment of the optimal carbon dioxide concentration in kimchi packaging The best taste of kimchi is achieved through optimal ripening. Therefore, the optimal carbon dioxide concentration in the kimchi packaging was determined based on the optimal ripening period of kimchi. The optimal ripening period is reached when the acidity is 0.6–0.8% (Park, Kim, Kim, Kim, & Kim, 2003; Yun, Jeong, Moon, & Park, 2014). In this study, the optimal ripening period for each temperature was observed (Fig. 6). The optimal ripening period was from 4 to 6 days at 10 °C, from 10 to 17 days at 4 °C, and after 19 days at 0 °C. As the temperature was lowered, the time to reach the optimal ripening was increased, and the maintenance of the optimal ripening period was prolonged. The reason for the difference between the arrival time and maintenance period depending on the temperature is that the growth activity of lactic acid bacteria is decreased as the temperature is lowered. Although the arrival time and maintenance period of optimal ripening were different for each temperature, the optimal carbon dioxide concentration was similar (10 °C: 33–55%; 4 °C: 40–56%; 0 °C: over 40%). This is also because the carbon dioxide in kimchi is generated by
0.87d 3.15a 0.93cd 1.35c
16.04 ± 0.56c
a−e Within columns, values with different lowercase letters are significantly different as per Duncan’s multiple range test (P < 0.05). * Values are expressed as means ± SDs.
6
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Fig. 5. Adsorption and desorption curves of calcium hydroxide- and porous medium-incorporated LDPE films.
appropriate carbon dioxide concentration should be maintained. According to our findings, the optimal carbon dioxide concentration was approximately 55%. In order to investigate whether the carbon dioxide adsorption film maintained the optimal carbon dioxide concentration in the kimchi packaging, the performance of the carbon dioxide adsorption film in the kimchi packaging was evaluated (Fig. 6) by selecting the 20% CH + Z film, which was considered the best among the films. The rate of increase in the carbon dioxide concentration was delayed owing to adsorption by the film during storage. In samples containing 5 g or more of film for 4 weeks at 10℃, the level was maintained below the optimal carbon dioxide concentration (55%). Moreover, the concentration in samples with the 1 g films was
microbial metabolism (Jung et al., 2012). Therefore, although the arrival time and the maintenance period may be different depending on the temperature, the final carbon dioxide concentration was similar. In this study, the common overlapping carbon dioxide concentration range (40–55%) was set as the optimal concentration range at 10, 4, and 0 °C.
3.3.2. Maintenance of the optimal carbon dioxide concentration in kimchi packaging Carbon dioxide is responsible for the expansion of kimchi packaging, but plays a positive role in improving taste. Therefore, carbon dioxide should not be removed from the food during storage, and an
Fig. 6. Establishment of optimal carbon dioxide concentrations and evaluation of the carbon dioxide adsorptive capacities of 20% CH + Z films. 7
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The contents of organic acids, nucleotides and their related compounds in Kimchi prepared with salted-fermented fish products and their alternatives. Korean Journal of Food Science and Technology, 35(5), 769–776. Park, H. Y., Kim, S. J., Kim, K. M., You, Y. S., Kim, S. Y., & Han, J. (2012). Development of antioxidant packaging material by applying corn-zein to LLDPE film in combination with phenolic compounds. Journal of Food Science, 77(10), 273–279. Park, I. G., Hong, M. S., Kim, B. S., & Kang, H. G. (2013). Ambient CO2 adsorption and regeneration performance of zeolite and activated carbon. Journal of Korean Society of Environmental Engineers, 35(5), 307–311. Park, J. H., Kim, J. N., Cho, S. H., Kim, J. D., & Yang, R. T. (1998). Adsorber dynamics and optimal design of layered beds for multicomponent gas adsorption. Chemical Engineering Science, 53(23), 3951–3963. Rajandas, H., Parimannan, S., Sathasivam, K., Ravichandran, M., & Yin, L. S. (2012). A novel FTIR-ATR spectroscopy based technique for the estimation of low-density polyethylene biodegradation. Polymer Testing, 31, 1094–1099. Rashidi, N. A., Yusup, S., & Loong, L. H. (2013). Kinetic studies on carbon dioxide capture using activated carbon. Chemical Engineering Transactions, 35, 361–366. Sarifuddin, N., & Ismail, H. (2013). Comparative study on the effect of bentonite or feldspar filled low-density polyethylene/thermoplastic sago starch/kenaf core fiber composites. BioResources, 8(3), 4238–4257. Shim, S. M., Kim, J. Y., Lee, S. M., Park, J. B., Oh, S. K., & Kim, Y. S. (2012). Profiling of fermentative metabolites in kimchi: Volatile and non-volatile organic acids. Journal of the Korean Society for Applied Biological Chemistry, 55(4), 463–469. Teixeira, F. B., Levin, L. G., & Trope, M. (2005). Investigation of pH at different dentinal sites after placement of calcium hydroxide dressing by two methods. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology, 99(4), 511–516. Thommes, M. (2010). Physical adsorption characterization of nanoporous materials. Chemie Ingenieur Technik, 82(7), 1059–1073. Wang, H. J., Jo, Y. H., An, D. S., Rhim, J. W., & Lee, D. S. (2015). Properties of agar-based CO2 absorption film containing Na2CO3 as active compound. Food Packaging and Shelf Life, 4, 36–42. Yu, C. H., Huang, C. H., & Tan, C. S. (2012). A review of CO2 capture by absorption and adsorption. Aeroso and Air Quality Research, 12, 745–769. Yun, J. Y., Jeong, J. K., Moon, S. H., & Park, K. Y. (2014). Effects of brined baechu cabbage and seasoning on fermentation of kimchi. Journal of the Korean Society of Food Science and Nutrition, 43(7), 1081–1087.
maintained below the optimal carbon dioxide level (55%) at 4 and 0℃ after 4 weeks of storage. The carbon dioxide adsorption film developed in this study was found to be effective for carbon dioxide control when applied to kimchi packaging. In addition, varying the amount of the adsorptive film depending on the distribution period and distribution temperature may be effective for quality control of commercial kimchi. 4. Conclusion Food safety and long-term shelf life are important in food distribution and sales. In this study, CH and porous medium (AC and Z) were selected, and food packaging was developed to act as a safe adsorbent for food. In addition, an adsorptive powder was added to improve the functionality of the film. The adsorption powder was confirmed to be embedded in the polymer by physical bonding rather than chemical bonding, and the mechanical strength was found to be weakened, whereas the WVP was increased due to the agglomerative phenomenon. This phenomenon was alleviated by the synthesis of CH and porous medium, and the improvement of mechanical strength and WVP was confirmed. Additionally, the functional food packaging material containing adsorption powder had strong adsorptive power without affecting the ripening of kimchi, confirming the possible applications of this material to overcome problems related to volume expansion of kimchi packaging. In addition, the developed packaging material was expected to have applications in the development of reusable packaging because the chemical adsorption reaction and the physical adsorption reaction occurred at the same time. Finally, the optimal carbon dioxide concentration in kimchi packaging was set based on acidity as a ripening index, which will allow producers and sellers to efficiently manage the quality of commercial kimchi in distribution. Acknowledgement This research was supported by a research grant (KE1901-4) from the World Institute of Kimchi, and a High Value-added Food Technology Development Programs (318030-03-1-WT021), Ministry of Agriculture, Food and Rural Affairs, Republic of Korea. References Boroglu, M. S., & Gurkaynak, M. A. (2011). Fabrication and characterization of silica modified polyimide-zeolite mixed matrix membranes for gas separation properties. Polymer Bulletin, 66, 463–478. Cao, Z., Daly, M., Clémence, L., Geever, L. M., Major, I., Higginbotham, C. L., et al. (2016). Chemical surface modification of calcium carbonate particles with stearic acid using different treating methods. Applied Surface Science, 378, 320–329. Charles, F., Sanchez, J., & Gontard, N. (2006). Absorption kinetics of oxygen and carbon dioxide scavengers as part of active modified atmosphere packaging. Journal of Food Engineering, 72, 1–7. Chollet, E., Swesi, Y., Degraeve, P., & Sebti, I. (2009). Monitoring nisin desorption from a multi-layer polyethylene-based film coated with nisin loaded HPMC film and diffusion in agarose gel by an immunoassay (ELISA) method and a numerical modeling. Innovative Food Science & Emerging Technologies, 10, 208–214. Fasihnia, S. H., Peighambardoust, S. H., Peighambardoust, S. J., & Oromiehie, A. (2018). Development of novel active polypropylene-based packaging films containing different concentrations of sorbic acid. Food Packaging and Shelf Life, 18, 87–94. Golestan, M. N., Ghosta, Y., Pourmirza, A. A., & Valizadegan, O. (2015). Study on laser perforated films as gas permeable packaging for confused flour beetle (Tribolium confusum Jacquelin du Val.) control inside food packaging. Journal of Stored Products Research, 60, 54–59. Han, S. J., Yoo, M., Kim, D. W., & Wee, J. H. (2011). Carbon dioxide capture using calcium hydroxide aqueous solution as the absorbent. Energy and Fuels, 25, 3825–3834. Hanani, Z. A., Husna, A. B., Syahida, S. N., Khaizura, M. A. B., & Jamilah, B. (2018). Effect of different fruit peels on the functional properties of gelatin/polyethylene bilayer
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Food Packaging and Shelf Life journal homepage: www.elsevier.com/locate/fpsl
Development of food packaging materials containing calcium hydroxide and porous medium with carbon dioxide-adsorptive function Hyun-Gyu Lee, Suyeon Jeong, SeungRan Yoo
T
⁎
World Institute of Kimchi, Gwangju 61755, Republic of Korea
A R T I C LE I N FO
A B S T R A C T
Keywords: Food packaging material Active packaging Carbon dioxide Adsorbent Kimchi
Kimchi packaging can be easily damaged by carbon dioxide generated during fermentation of kimchi, and adsorbents have been developed to overcome the problems of volume expansion and breakage of kimchi packaging caused by carbon dioxide. Here, we examined the applicability of calcium hydroxide and porous medium impregnation for improving adsorbent performance. The developed adsorbents were incorporated into low-density polyethylene to develop packaging materials for kimchi. Notably, packaging materials containing the adsorption powder impregnated with calcium hydroxide and porous medium showed improved mechanical properties and exhibited chemical and physical reactions, resulting in strong adsorptive power and reusability. The mechanical strength of the packaging was weak due to the agglomerative properties of the powder. In kimchi packaging, adsorption packaging did not affect kimchi ripening (p > 0.05). The optimal carbon dioxide concentration in kimchi packaging was 40–55%, and the carbon dioxide concentration could be controlled using the developed adsorption packaging materials.
1. Introduction The main function of traditional food packaging is to preserve and protect food from external physical, chemical, and microbiological factors (Manikantan & Varadharaju, 2011). These functions have enabled food to be stored and distributed for a long time, thereby improving human quality of life. In order to maintain better quality of food and extend shelf life, active packaging that protects food from the outside environment and interacts with the internal environment, including the food, has been developed (Park et al., 2012). Carbon dioxide is widely used in many fields and plays a beneficial role in food. Carbon dioxide inhibits the growth of microorganisms, resulting in hygienic management and prolonged shelf life. In addition, carbon dioxide prevents the oxidation of food by mixing with nitrogen, and imparts a carbonated flavor. Despite these positive effects, carbon dioxide can also have negative roles in food. For example, some agricultural products that are sensitive to carbon dioxide concentrations suffer from anaerobic respiration and accelerated decay in environments containing high carbon dioxide concentrations (Lee, 2016). Food that has not been sterilized may cause volume expansion and breakage of the packaging due to the generation of carbon dioxide during storage. As a result of volume expansion and breakage, food cannot be stored long term or distributed appropriately (Lee, Shin, Lee, Kim, &
⁎
Cheigh, 2001). Because carbon dioxide can have positive or negative roles, depending on the characteristics of the food, it is necessary to use an appropriate carbon dioxide concentration. For kimchi, carbon dioxide plays a beneficial role in improving the taste of kimchi, but makes it difficult to store kimchi for a long period due to volume expansion and breakage of kimchi packaging. Therefore, carbon dioxide should be controlled at an appropriate level. However, there is no clear standard for the optimal level of carbon dioxide concentration in kimchi packaging, thereby complicating the management of commercial kimchi. Active packaging for controlling carbon dioxide contains adsorbents, microholes, filters, and valves (Golestan, Ghosta, Pourmirza, & Valizadegan, 2015; Lee et al., 2012; Olmi, 2015). Most carbon dioxide control methods, except for adsorbents, involve the discharge of gas to the outside of the packaging. These methods are very effective at alleviating volume expansion and increases in pressure. However, these methods can be disadvantageous because the flavor of the food can escape to the outside environment, or the quality of the food can deteriorate due to the inflow of oxygen. In contrast, adsorbents effectively control the gas inside the food packaging without influx of external oxygen. However, because adsorbents are chemical substances, careful selection of the adsorbent material must be made. In food packaging, adsorbents are commonly used with sachets,
Corresponding author. E-mail addresses: [email protected] (H.-G. Lee), [email protected] (S. Jeong), [email protected] (S. Yoo).
https://doi.org/10.1016/j.fpsl.2019.100352 Received 1 February 2019; Received in revised form 25 April 2019; Accepted 27 June 2019 2214-2894/ © 2019 Elsevier Ltd. All rights reserved.
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which are easy to make and use; however, these materials are associated with several problems related to moisture and leakage, thereby affecting food safety. These problems can be overcome by mixing the adsorbent with a polymer, such as polyethylene, polypropylene, polyethylene terephthalate, and nylon. Among these materials, polyethylene is a commonly used food packaging material owing to its low price, low wettability, and outstanding mechanical properties (Hanani, Husna, Syahida, Khaizura, & Jamilah, 2018). Carbon dioxide adsorbents consist of chemical adsorbents (monoethanolamine, calcium hydroxide [CH], and sodium carbonate) and physical adsorbents (activated carbon [AC] and zeolite) (Wang, Jo, An, Rhim, & Lee, 2015). Among these chemical adsorbents, CH is the most common commercially available material. CH and physical adsorbents are food additives that are available under restricted conditions; they are suitable as food packaging materials based on safety (Lee, 2016). Chemical adsorbents have excellent performance but have a slow reaction rate, and reactions are typically irreversible. Physical adsorbents have the advantages of quick reaction and reversibility, but have weak adsorption power (Charles, Sanchez, & Gontard, 2006; Hauchhum & Mahanta, 2014; Lee, 2016; Rashidi, Yusup, & Loong, 2013). Many researchers have made great efforts to develop functionally improved substances to supplement the disadvantages of existing adsorbents. Additionally, impregnation has been used to supplement this approach (Liu, Teng, Zhang, Cao, & Pan, 2013; Yu, Huang, & Tan, 2012). However, studies on the use of this approach, including impregnation, in the field of food packaging have been insufficient. If substances that combine the advantages of chemical and physical adsorbents can be applied for food packaging, effective adsorption and the ability to reuse packaging may lead to consumer satisfaction and environmental protection. Accordingly, in this study, we aimed to develop a novel material for kimchi packaging to overcome the problems caused by carbon dioxide. We selected chemical and physical adsorbents and impregnated the chosen materials to develop adsorbents with improved performance. We then investigated the characteristics of the film with carbon dioxide adsorptive function and the effects of the developed materials on the carbon dioxide concentration and kimchi ripening in kimchi packaging. Our findings provide practical insights into the quality control of commercial kimchi.
2.2. Preparation of master batches and films
2. Materials and methods
2.3.3. Measurement of pressure, volume, and carbon dioxide concentration of kimchi packaging The pressure of the kimchi packaging was analyzed using a headspace pressure gauge (UTK-P5000; Ultra Tec, Seoul, South Korea). The volume of kimchi packaging was analyzed by measuring the volume of the overflowing water after immersing the kimchi packaging in a water tank. The carbon dioxide concentration was measured using a headspace gas analyzer (GS3 micro; Systech Illinois, Johnsburg, IL, USA). The carbon dioxide concentration was fiducially set to 0.3%.
Master batches and films were prepared by melt compounding with extruding powder and LDPE to confer the materials with carbon dioxide adsorptive function. The master batches and films were prepared using a twin screw extruder (BA-19; BauTek Co., Uijeongbu, South Korea) with a length/diameter ratio of 40:19. The extruder was set to 190 °C for the header, 190 °C for zones 1–5, 160 °C for zone 6, and 140 °C for the feed zone. The produced film had a thickness of 60 ± 10 μm. Importantly, 20% AC film was excluded from this study because it was not fabricated to a thickness of less than 90 μm. The powder contents of the master batches and films were calculated according to Eq. (1): Powder contents (Wp + Wr) × 100
of
master
batches
and
films
(%) = Wp/ (1)
where Wp is the powder weight (g), and Wr is the LDPE resin weight (g). 2.3. Application of packaging material (master batch) and film to kimchi packaging 2.3.1. Preparation of kimchi packaging A 500-mL aluminum pouch (SaeroPNL Co., Seoul, South Korea) and 150 g kimchi (Trechan Co., Gwangju, South Korea) were prepared for the kimchi experiment. The master batch (20 g) or film (0, 1, 3, 5, or 10 g) was sealed in a pouch with the kimchi and was then stored at 10, 4, or 0℃. The master batch was packed in a mesh pocket to prevent mixing with kimchi. 2.3.2. Measurement of pH and titratable acidity Before the measurements, the kimchi was homogenized with a hand blender (HR1372; Koninklijke Philips Electronics N.V., Amstelplein, Amsterdam, Netherlands) and then filtered through four layers of sterilized coarse gauze. Next, the pH of kimchi was measured using a digital pH meter (TitroLine Easy, SI Analytics; Xylem Inc., Rye Brook, NY, USA) after homogenization. The titratable acidity was measured by titrating 10 mL kimchi juice with 0.1 N sodium hydroxide to a pH of 8.3. Titratable acidity was calculated on the basis of lactic acid.
2.1. Adsorbent synthesis and optimization Environmental pollution caused by the use of plastics has raised concerns among the public. Although much effort has been made to replace plastics, no suitable substitute is available. However, if plastic is recycled and used for a long time, pollution can be reduced. In this study, CH and porous medium were synthesized for the reuse of adsorbent. Adsorption powders (CH + AC; CH + zeolite 13X [Z]) were prepared by impregnation. CH was dissolved in distilled water and stirred for 3 h. Then, a specific amount of AC or Z was added to the CH solution, and the resulting slurry was stirred for 30 min. After standing at room temperature for 4 h, the supernatant was discarded. Finally, the resulting slurry was dried at 105 °C overnight. Synthetic adsorbent was mixed with low-density polyethylene (LDPE, ASTM D1238 melt index: 2.8 g/10 min; Hanhwa Total Petrochemical Co., Ltd., Seosan, South Korea) and made into a master batch, and carbon dioxide adsorption was then evaluated to optimize the synthesis ratio. Fifty milliliters of distilled water was poured into a rectangular container (195 × 140 × 50 mm), and 20 g of the master batch on the petri dish was placed in the container. Then, carbon dioxide exchange packaging was evaluated to test the adsorptive power of the master batch. As a result of the experiment (Fig. 1), the ratio with the best adsorptive power was identified, and this ratio of synthetic adsorbent was used for the master batch and film production (CH:AC = 1:0.3; CH:Z = 1:0.15).
2.4. Analysis of film characteristics 2.4.1. Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) To characterize the chemical structure, FTIR spectroscopy spectra were recorded on a Nicolet iS50 FTIR instrument (Thermo Fisher Scientific Inc., Waltham, MA, USA), from 400 to 4000 cm−1, in attenuated total reflection mode. The surfaces and cross sections of the films were observed using SEM (Gemini 500; Zeiss, Oberkochen, Germany) after coating of the films with a thin layer of platinum. 2.4.2. Mechanical properties To evaluate the mechanical properties, the tensile stress at break and elongation at break were evaluated according to ISO 527-3 using an Instron 3366 (Instron Engineering Corp., Norwood, MA, USA). The tensile stress at break and elongation at break tests were conducted at a 2
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Fig. 1. Optimization of the impregnation ratio of calcium hydroxide and porous medium (activated carbon and zeolite 13X); a−dWithin samples (equivalent week), values with different lowercase letters are significantly different as per Duncan’s multiple range test (P < 0.05); A-DWithin weeks (equivalent sample), values with different uppercase letters are significantly different as per Duncan’s multiple range test (P < 0.05).
Fig. 2. Effects of the adsorption master batch (MB) on kimchi ripening and kimchi packaging during storage at 10 °C.
adsorptive function of the film, the carbon dioxide adsorption/desorption was analyzed using a thermogravimetry (TGA) analyzer (TGA/ DSC 1; Mettler Toledo, Columbus, OH, USA). The sample was heated under nitrogen at 100 ℃ for 30 min to remove impure gas. Carbon dioxide was then flowed at 25 ℃ for 1 h and heated under nitrogen at 100 ℃ for 30 min. This process was repeated to examine adsorption and desorption reactions. The speed of temperature increase and decrease was 20℃/min.
50 mm/min crosshead speed, 100 mm gauge length, and 10 mm width. The experiment was repeated for 10 specimens. 2.4.3. Measurement of water vapor permeability (WVP) WVP was measured according to ASTM 1249-90 using a PermatranW 3/33 (MOCON Inc., Minneapolis, MN, USA). In the instruments, the exposed surface area of the test film was 50 cm2. During measurements, experimental conditions were set as follows: temperature set point, 37.8 ℃; barometric pressure, 760 mmHg; flow rate, 10.67 SCCM; test time, 30 min; and relative humidity, 100%.
2.5. Statistical analysis
2.4.4. Carbon dioxide adsorption/desorption analysis of the film In order to investigate the effects of reuse on the carbon dioxide
Statistical analysis of data was performed using SPSS ver. 19.0 (SPSS Inc., Chicago, IL, USA). One-way analysis of variance and Duncan’s 3
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multiple range comparison tests were employed to determine the level of significance, and differences with P values of less than 0.05 were considered significant.
Ca(OH)2(s) ⇌ Ca2+(aq) + 2OH−(aq) −
3. Results and discussion 3.1. Application of packaging material (master batch) to kimchi packaging 3.1.1. Ripening index of kimchi Kimchi is fermented by metabolic processes of microorganisms derived from various food materials. In particular, lactic acid bacteria in kimchi produce metabolites during the growing process, and the produced metabolites are combined with the ingredients of kimchi to form a unique taste. Among the various factors that determine the quality of kimchi, the metabolites of lactic acid bacteria are the most important factors. Moreover, because metabolites of lactic acid bacteria acidify the kimchi, the pH and acidity can be regarded as indicators of the degree of kimchi ripening (Lee & Yoo, 2017). In this study, the chemical quality characteristics, which are indicators of the degree of kimchi ripening, were investigated when the master batch with carbon dioxide adsorptive function was packed with kimchi at 10℃ (Fig. 2). The pH decreased from 5.89 to 3.91, and the acidity increased from 0.34% to 1.65%, demonstrating that kimchi was acidified by metabolites of lactic acid bacteria during storage (Moon, Kim, & Chang, 2018). In particular, pH and acidity showed rapid changes until the first week, followed by slow changes. The results were similar to those of a study by Meng, Lee, Kang, and Ko, (2015)), which showed rapid changes until reaching the optimal ripening and gradual changes thereafter. Differences in pH and acidity according to the master batch were not clear. Because CH reacts with lactic acid and acetic acid (Teixeira, Levin, & Trope, 2005), which are major organic acids generated during the fermentation of kimchi (Shim et al., 2012), the master batch containing CH was expected to show delayed acidification of kimchi; however, these effects could not be confirmed in this study. This indicated that the CH in the master batch did not react with kimchi and did not affect the quality. In other words, CH was not eluted.
(2)
CO2(aq) + OH (aq) ⇌ HCO (aq)
(3)
HCO3−(aq) + OH-(aq) ⇌ H2O(l) + CO32-(aq)
(4)
Ca2+(aq) + CO32−(aq) ⇌ CaCO3(s)
(5)
Ca(OH)2(s) + CO2(g) ⇌ CaCO3(s) + H2O(l)
(6)
3-
Porous medium removes carbon dioxide by Van der Waals forces due to the interaction between the surface/pore space and carbon dioxide molecules (Thommes, 2010). Because the acid-base neutralization reaction (chemical adsorption reaction) is a stronger reaction than the Van der Waals physical adsorption reaction, impregnation of the porous medium with CH in this study significantly improved the adsorptive power of the master batch. 3.2. Film characteristics The master batch, as a raw material for plastic products, could be manufactured and used in various forms as needed. Kimchi packaging is mainly available in the form of pouches and containers. In this study, master batches were prepared into films, which were used as raw materials for the pouches. 3.2.1. FTIR spectra and SEM results The interactions between adsorption powder and LDPE were confirmed using the FTIR spectroscopy (Fig. 3). Interactions by physical or chemical bonding between two or more substances can be revealed by changes in spectral peaks (Fasihnia, Peighambardoust, Peighambardoust, & Oromiehie, 2018). As shown in Fig. 3, the peaks of LDPE film at 2918, 2851, 1468, and 718 cm−1 were assigned to CH2 asymmetrical stretching, CH2 symmetrical stretching, bending deformation, and rocking deformation, respectively (Rajandas, Parimannan, Sathasivam, Ravichandran, & Yin, 2012). Moreover, the peak of LDPE remained unchanged, even when the LDPE was mixed with the powder (CH, AC, Z, and impregnated powder) and made into a film. The CH/LDPE film was assigned a narrow peak of stretching of OeH at 3642 cm−1 and a vibration C–O of the carbonate group at 1091 cm−1 (Khachani, Hamidi, Halim, & Arsalane, 2014). The Z/LDPE film showed stretching of SieO and AleO vibrations from 974 to 670 cm−1 (Boroglu & Gurkaynak, 2011; Hu, Gao, Liu, Zhang, & Meng, 2017). The AC/LDPE film showed a sloped shape in the LDPE spectra because the AC was slanted without a specific peak. The FTIR spectrum of CH + Z/LDPE film showed an OeH peak and C–O peak from CH as well as an SieO peak from Z. The peaks of the powder between the LDPE polymers remained intact, indicating that the powder particles were embedded between the polymers without chemical bonding to the LDPE chains (Fasihnia et al., 2018). The appearance of embedded powder particles in LDPE was also confirmed by SEM. The surface and cross sections of the films were examined by SEM to visually observe the mixing of powder between LDPE polymers (Fig. 4). From images on the surface on the film, we confirmed that the powder was uniformly dispersed in the film. Additionally, powder has a tendency to agglomerate in the LDPE polymer. In particular, AC was found to be the most agglomerative in the film, and agglomeration of AC was alleviated by impregnating AC with CH. Agglomeration of powder in film generates voids and affects the mechanical properties of the film (Cao et al., 2016; Sarifuddin & Ismail, 2013). Indeed, voids in the film were confirmed in cross sectional images (Fig. 4).
3.1.2. Carbon dioxide adsorptive power in the master batch used for kimchi packaging Carbon dioxide produced by metabolism results in the carbonic taste of kimchi, but causes volume expansion and breakage of kimchi packaging, resulting in problems with storage and distribution (Lee et al., 2001). To overcome this problem, master batches with carbon dioxide adsorptive function were prepared and applied to kimchi packaging (Fig. 2). The control with the LDPE master batch burst after 2 weeks of fermentation due to the generation of carbon dioxide. At this time, the volume, pressure, and carbon dioxide concentration of kimchi packaging were 501 mL, 1049.50 mb, and 83.3%, respectively (Fig. 2). These findings confirmed that the kimchi packaging should be adjusted below this value in order to prevent breakage of the packaging during storage and distribution. Among the functional master batches, the master batch containing AC showed weak adsorptive power. Therefore, the packaging was broken after 2 weeks of storage, similar to the control sample. Additionally, the Z/LDPE master batch showed weak adsorptive power, resulting in increased volume, pressure, and carbon dioxide to 408 mL, 1021.98 mb, and 76.0%, respectively (Fig. 2). In contrast, the CH/LDPE master batch, CH + AC/LDPE master batch, and CH + Z/LDPE master batch did not show increased volume or pressure. These master batches maintained a carbon dioxide concentration of less than 50% in kimchi packaging, indicating that these materials had excellent adsorptive power. The main reason for this excellent adsorptive power may have been the presence of CH, which acts as a strong salt by forming calcium ions and hydroxyl groups in water (reaction (2)). The ionized hydroxyl group removes carbon dioxide by an acid-base neutralization reaction (reaction (3)). The overall reaction formula is given in reaction (6) (Han, Yoo, Kim, & Wee, 2011).
3.2.2. Mechanical properties and WVP The mechanical properties and WVP of the film are shown in Table 1. The tensile stress at break, elongation at break, and WVP of LDPE films were 24.98 MPa, 174.63%, and 8.36 g·m·mil/m2·day, respectively. Incorporation of the powder into the LDPE affected the 4
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Fig. 3. Analysis of Fourier-transform infrared spectra for adsorption powders and adsorption films.
reactions between the porous medium/LDPE film and the CH/LDPE film was related to differences in the reaction method with carbon dioxide. The porous medium/LDPE film chemically and physically reacted with carbon dioxide, but the chemical reaction was very weak, and the physical reaction predominated. The physical reaction rate was fast because of the low reaction energy; because the reaction energy was low, the desorption reaction easily occurred when heated to a high temperature. In contrast, CH reacts chemically, and the chemical reaction is advantageous in that the adsorption rate is slow but the adsorptive power is strong because of the large reaction energy (Charles et al., 2006; Hauchhum & Mahanta, 2014; Lee, 2016; Park, Kim, Cho, Kim, & Yang, 1998). In contrast to the results of our previous experiment with kimchi (Fig. 2), in which the porous medium had a weaker adsorptive power than the CH, the strong adsorptive power of the porous medium in Fig. 5 appeared to be caused by differences in the adsorption speed. In adsorption and desorption experiments using TGA, the physical adsorption reaction was fast and strongly adsorbed because it proceeded for a short time. As the reaction time with carbon dioxide increased, as in the kimchi experiment, the chemical adsorption reaction became stronger. Analysis of the impregnated powder/LDPE films showed that the physical and chemical reactions occurred simultaneously when the carbon dioxide was adsorbed. The impregnated powder/LDPE films slowly adsorbed carbon dioxide, similar to the CH/LDPE film, and the carbon dioxide was desorbed by heating, similar to the porous medium/ LDPE films. The characteristics of impregnated powder/LDPE films have not yet been optimized; however, if appropriately supplemented, these films may be reused many times, maintaining strong carbon dioxide adsorptive power and thereby reducing environmental pollution.
mechanical properties and WVP and varied up to 11.13–22.64 MPa, 47.60–98.21%, and 12.83–24.58 g m mil/m2 day. The increase in the powder content resulted in weak mechanical strength and increased WVP, similar to the results reported by Chollet, Swesi, Degraeve, and Sebti, (2009)). Incorporation of the powder changed the film owing to the interactions between powder particles and the LDPE. This interaction is not a chemical bond, it is a physical bond, and it exists in the form embedded in LDPE polymers. Embedded powder probably may result in reduced strength of the composite chain and could increase the mobility of water by securing space. The results of mechanical properties and WVP were also different depending on the type of powder. Inclusion of CH in LDPE yielded a higher tensile stress at break, higher elongation at break, and lower WVP than that of porous medium. The AC/LDPE films showed the lowest mechanical strength and highest WVP, and even 20% AC/LDPE film could not be prepared due to low mechanical strength. For impregnated powders of CH and porous medium, the results confirmed that impregnation improved the mechanical strength and WVP compared with single porous medium. In the future, low mechanical strength and high WVP can be improved by incorporation crosslinking agents and plasticizers and by bonding with other materials.
3.2.3. Carbon dioxide adsorption and desorption reaction As shown in Fig. 5, the porous medium/LDPE film rapidly adsorbed carbon dioxide, and the film was desorbed by heating. Among the porous media, Z had better adsorption and desorption capacities than AC, possibly because the specific surface area of Z was larger (Park, Hong, Kim, & Kang, 2013). In the CH/LDPE film, the desorption reaction was not induced by heating, and carbon dioxide adsorption occurred gradually. The difference in the adsorption and desorption 5
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Fig. 4. Scanning electron microscopy images of adsorption films.
3.3. Application of carbon dioxide adsorption film to kimchi packaging
Table 1 Analysis of the mechanical properties and water vapor permeability of films. Tensile stress at break (MPa)
LDPE 20% CH/LDPE film 20% Z/LDPE film 20% CH + AC/LDPE film 20% CH + Z/LDPE film 10% CH/LDPE film 10% AC/LDPE film 10% Z/LDPE film 10% CH + AC/LDPE film 10% CH + Z/LDPE film
24.98 18.74 19.61 12.51
± ± ± ±
2.03*a 1.92d 2.54cd 1.09e
18.68 ± 3.50d 22.64 11.13 19.66 12.52
± ± ± ±
2.31b 0.99e 4.30cd 1.58e
21.62 ± 1.30bc
Elongation at break (%)
Water vapor permeability (g m mil/m2 day)
174.63 ± 30.86a 84.10 ± 8.14c 57.44 ± 3.49de 48.39 ± 3.18e
8.36 ± 2.03e 13.48 ± 1.29cd 21.81 ± 0.39ab 24.58 ± 1.29a
64.44 ± 5.71d
19.78 ± 2.30b
98.21 47.60 81.07 84.53
± ± ± ±
5.05b 3.55e 8.03c 5.83c
82.25 ± 9.34c
12.83 23.43 14.07 16.38
± ± ± ±
3.3.1. Establishment of the optimal carbon dioxide concentration in kimchi packaging The best taste of kimchi is achieved through optimal ripening. Therefore, the optimal carbon dioxide concentration in the kimchi packaging was determined based on the optimal ripening period of kimchi. The optimal ripening period is reached when the acidity is 0.6–0.8% (Park, Kim, Kim, Kim, & Kim, 2003; Yun, Jeong, Moon, & Park, 2014). In this study, the optimal ripening period for each temperature was observed (Fig. 6). The optimal ripening period was from 4 to 6 days at 10 °C, from 10 to 17 days at 4 °C, and after 19 days at 0 °C. As the temperature was lowered, the time to reach the optimal ripening was increased, and the maintenance of the optimal ripening period was prolonged. The reason for the difference between the arrival time and maintenance period depending on the temperature is that the growth activity of lactic acid bacteria is decreased as the temperature is lowered. Although the arrival time and maintenance period of optimal ripening were different for each temperature, the optimal carbon dioxide concentration was similar (10 °C: 33–55%; 4 °C: 40–56%; 0 °C: over 40%). This is also because the carbon dioxide in kimchi is generated by
0.87d 3.15a 0.93cd 1.35c
16.04 ± 0.56c
a−e Within columns, values with different lowercase letters are significantly different as per Duncan’s multiple range test (P < 0.05). * Values are expressed as means ± SDs.
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Fig. 5. Adsorption and desorption curves of calcium hydroxide- and porous medium-incorporated LDPE films.
appropriate carbon dioxide concentration should be maintained. According to our findings, the optimal carbon dioxide concentration was approximately 55%. In order to investigate whether the carbon dioxide adsorption film maintained the optimal carbon dioxide concentration in the kimchi packaging, the performance of the carbon dioxide adsorption film in the kimchi packaging was evaluated (Fig. 6) by selecting the 20% CH + Z film, which was considered the best among the films. The rate of increase in the carbon dioxide concentration was delayed owing to adsorption by the film during storage. In samples containing 5 g or more of film for 4 weeks at 10℃, the level was maintained below the optimal carbon dioxide concentration (55%). Moreover, the concentration in samples with the 1 g films was
microbial metabolism (Jung et al., 2012). Therefore, although the arrival time and the maintenance period may be different depending on the temperature, the final carbon dioxide concentration was similar. In this study, the common overlapping carbon dioxide concentration range (40–55%) was set as the optimal concentration range at 10, 4, and 0 °C.
3.3.2. Maintenance of the optimal carbon dioxide concentration in kimchi packaging Carbon dioxide is responsible for the expansion of kimchi packaging, but plays a positive role in improving taste. Therefore, carbon dioxide should not be removed from the food during storage, and an
Fig. 6. Establishment of optimal carbon dioxide concentrations and evaluation of the carbon dioxide adsorptive capacities of 20% CH + Z films. 7
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maintained below the optimal carbon dioxide level (55%) at 4 and 0℃ after 4 weeks of storage. The carbon dioxide adsorption film developed in this study was found to be effective for carbon dioxide control when applied to kimchi packaging. In addition, varying the amount of the adsorptive film depending on the distribution period and distribution temperature may be effective for quality control of commercial kimchi. 4. Conclusion Food safety and long-term shelf life are important in food distribution and sales. In this study, CH and porous medium (AC and Z) were selected, and food packaging was developed to act as a safe adsorbent for food. In addition, an adsorptive powder was added to improve the functionality of the film. The adsorption powder was confirmed to be embedded in the polymer by physical bonding rather than chemical bonding, and the mechanical strength was found to be weakened, whereas the WVP was increased due to the agglomerative phenomenon. This phenomenon was alleviated by the synthesis of CH and porous medium, and the improvement of mechanical strength and WVP was confirmed. Additionally, the functional food packaging material containing adsorption powder had strong adsorptive power without affecting the ripening of kimchi, confirming the possible applications of this material to overcome problems related to volume expansion of kimchi packaging. In addition, the developed packaging material was expected to have applications in the development of reusable packaging because the chemical adsorption reaction and the physical adsorption reaction occurred at the same time. Finally, the optimal carbon dioxide concentration in kimchi packaging was set based on acidity as a ripening index, which will allow producers and sellers to efficiently manage the quality of commercial kimchi in distribution. Acknowledgement This research was supported by a research grant (KE1901-4) from the World Institute of Kimchi, and a High Value-added Food Technology Development Programs (318030-03-1-WT021), Ministry of Agriculture, Food and Rural Affairs, Republic of Korea. References Boroglu, M. S., & Gurkaynak, M. A. (2011). Fabrication and characterization of silica modified polyimide-zeolite mixed matrix membranes for gas separation properties. Polymer Bulletin, 66, 463–478. Cao, Z., Daly, M., Clémence, L., Geever, L. M., Major, I., Higginbotham, C. L., et al. (2016). Chemical surface modification of calcium carbonate particles with stearic acid using different treating methods. Applied Surface Science, 378, 320–329. Charles, F., Sanchez, J., & Gontard, N. (2006). Absorption kinetics of oxygen and carbon dioxide scavengers as part of active modified atmosphere packaging. Journal of Food Engineering, 72, 1–7. Chollet, E., Swesi, Y., Degraeve, P., & Sebti, I. (2009). Monitoring nisin desorption from a multi-layer polyethylene-based film coated with nisin loaded HPMC film and diffusion in agarose gel by an immunoassay (ELISA) method and a numerical modeling. Innovative Food Science & Emerging Technologies, 10, 208–214. Fasihnia, S. H., Peighambardoust, S. H., Peighambardoust, S. J., & Oromiehie, A. (2018). Development of novel active polypropylene-based packaging films containing different concentrations of sorbic acid. Food Packaging and Shelf Life, 18, 87–94. Golestan, M. N., Ghosta, Y., Pourmirza, A. A., & Valizadegan, O. (2015). Study on laser perforated films as gas permeable packaging for confused flour beetle (Tribolium confusum Jacquelin du Val.) control inside food packaging. Journal of Stored Products Research, 60, 54–59. Han, S. J., Yoo, M., Kim, D. W., & Wee, J. H. (2011). Carbon dioxide capture using calcium hydroxide aqueous solution as the absorbent. Energy and Fuels, 25, 3825–3834. Hanani, Z. A., Husna, A. B., Syahida, S. N., Khaizura, M. A. B., & Jamilah, B. (2018). Effect of different fruit peels on the functional properties of gelatin/polyethylene bilayer
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