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Article

Sustainable Utilization Strategy of Organic Waste via Fabrication of Bioelastomer with Antibacterial and Antioxidant Activities Using Mandarin Peel Extracts

by
Kang Hyun Lee
1,†,
Youngsang Chun
2,†,
Ja Hyun Lee
3,
Jong Uk Lee
4,
Taek Lee
5,* and
Hah Young Yoo
1,*
1
Department of Biotechnology, Sangmyung University, 20, Hongjimun 2-Gil, Jongno-Gu, Seoul 03016, Republic of Korea
2
Department of Bio-Convergence Engineering, Dongyang Mirae University, 445-8, Gyeongin-ro, Guro-gu, Seoul 08221, Republic of Korea
3
Department of Convergence Bio-Chemical Engineering, Soonchunhyang University, 22, Soonchunhyang-ro, Asan-si 31538, Republic of Korea
4
Department of Chemical Engineering, Sunchon National University, 255, Jungang-ro, Suncheon-si 57922, Republic of Korea
5
Department of Chemical Engineering, Kwangwoon University, 20 Kwangwoon-Ro, Nowon-gu, Seoul 01897, Republic of Korea
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agriculture 2023, 13(1), 161; https://doi.org/10.3390/agriculture13010161
Submission received: 2 November 2022 / Revised: 28 December 2022 / Accepted: 5 January 2023 / Published: 9 January 2023
(This article belongs to the Special Issue Sustainable Utilization of Humic Substances and Organic Waste in Green Agriculture)
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Abstract

:
Mandarin peels (MPs), a food-processing residue, have several restrictions on their disposal and can cause serious environmental pollution. In this study, MP was used to fabricate a functional bioelastomer with antioxidant and antibacterial activities. Bioactive compounds were recovered from MPs in liquid form and added to the bioelastomer during fabrication to maintain the mechanical strength of the bioelastomer. The radical scavenging activities of the fabricated bioelastomer (B–MPE 15%) were 3.3% for DPPH and 20.8% for ABTS, respectively. In addition, B–MPE 15% exhibited antibacterial activity against gram-positive (Staphylococcus aureus), gram-negative (Escherichia coli), and antibiotic-resistant bacteria (Methicillin-resistant S. aureus and Vancomycin resistant Enterococcus). The chemical properties of B–MPE 15% were not significantly different from those of the control group (bare PDMS). Tensile strength, elongation at break, and water vapor transmission rate of B–MPE 15% were found to be 5.1 N/mm2, 649%, and 33.3 g/(m2 day), respectively. Therefore, the addition of MP extracts did not significantly affect the physical properties. The fabricated bioelastomer with antibacterial and antioxidant activities is expected to be utilized in the food packaging, pharmaceutical, and medical industries. Our research is expected to represent a future-oriented strategy for realizing carbon neutrality by upcycling food waste.

1. Introduction

Mandarin is one of the most popular fruits because of its sweet taste and ease of consumption, as well as its antioxidant, anticancer, antibacterial, and anti-adipogenic properties [1,2]. An estimated 630,000 tons of mandarins were produced in Korea [3], and it has been reported that approximately 50,000 tons of mandarin-processing residues are generated annually [4]. However, only 30% of the mandarin residues are used as medicinal herbs. While the remaining 70% used to be disposed of into the ocean [5], Korea has strictly forbidden this disposal method for food wastes since 2013 in accordance with the 1996 Protocol of the London Convention [6], as it leads to disruption of the marine food chain and loss of marine biodiversity [7]. Food waste is typically disposed of through landfilling, incineration, and composting [8]. However, in Korea, direct landfilling of food waste has been prohibited, by law, since 2005 to alleviate the shortage of landfills, protect groundwater and soil, and promote the conversion of food waste into value-added materials [9]. Meanwhile, incineration of food waste with a high moisture content can generate dioxins during combustion with other low-humidity wastes [10]. During composting, nitrate- and phosphorus-contacting leachates and greenhouse gases (GHGs) get generated, causing eutrophication and global warming, respectively [11]. As a result, various developed countries other than Korea, including the USA, EU, Japan, and China, are also suffering from social and environmental issues related to the disposal of food waste [12,13]. Therefore, it is necessary to propose a sustainable food-waste management plan that not only prevents environmental pollution but also converts food waste into value-added materials.
Traditionally, value-added materials, such as fuels and chemicals, have been produced in petroleum refineries [14]. However, these refineries are considered the main contributors to GHG emissions because they release carbon that was buried in the ground into the atmosphere. The CO2 emissions from this sector alone were estimated to be 1079 million tons in 2015 [15]. Many countries around the world are seriously concerned about environmental pollution caused by these GHG emissions, so they participated in the UN Framework Convention on Climate Change (UNFCCC) and adopted the Kyoto Protocol (1997), the Lima Call for Climate Action (2014), the Paris Agreement (2015), etc. [16]. Consequently, biorefineries, which utilize biomass as raw materials instead of petroleum-based materials, have been attracting attention as a strategy to achieve net-zero CO2 emissions [17]. In biorefineries, food waste is considered an ideal feedstock because it satisfies economic feasibility, owing to its low transport and storage costs, year-round availability, and ease of handling [18]. Mandarin peels (MPs), which account for approximately 7–11% of mandarins generated during juice processing, are mostly discarded because they are considered to have no economic value [19,20]. However, these residues contain cellulose, hemicellulose, pectin, essential oil, and flavonoid, which have the potential to be converted into value-added materials [21]. Although various studies have been carried out regarding the production of biofuels, such as ethanol [22] and methane [23], energy-based products have limitations that currently prevent them from completely replacing low-cost fossil fuels [24]. Therefore, in consideration of economic feasibility, it is necessary to produce bio-based products with high market values [25], such as flavonoids [26] and essential oil [27].
The predominant flavonoids in MP are hesperidin and narirutin [28], which have antioxidant [29], antibacterial [30], antidiabetic [31], and anti-inflammatory properties [32]. In addition, bioactive compounds derived from natural sources are in increasing demand, as alternatives to synthetic compounds, because of their safety and non-toxic effect on the human body [33]. Extraction techniques, including maceration, Soxhlet, microwave-assisted, ultrasound-assisted, and enzyme-assisted extraction, have been used to extract bioactive compounds from MP [34]. Among the various extraction methods, microwave-assisted extraction (MAE) has the distinct advantages of short extraction times, high extraction yields, and low solvent usage [35]. In addition, this technique is suitable for industrial-scale application [36]. The recovered bioactive substances are mixed with various polymers to fabricate bioelastomers that are used as functional materials in the food, pharmaceutical, and medical industries [37]. Dordevic et al. [38] produced edible chitosan films for food packaging using extracts of blueberries, red grapes, and parsley. Meanwhile, non-biodegradable synthetic polymers, such as polyethylene glycol (PEG), polyvinyl alcohol (PVA), polypropylene (PP), polyethylene (PE), and polydimethylsiloxane (PDMS), are also widely used in bioelastomer fabrication because they have stronger physicochemical properties than natural polymers [39].
Following these research trends, we previously fabricated a bioelastomer with antioxidant and antibacterial activities [40]. In our previous study [40], PDMS, which has higher flexibility, thermal stability, and biocompatibility, as well as lower toxicity than other synthetic polymers [41], was used as the polymer. In addition, by-products of aronia juice processing were used as the raw materials for natural bioactive compounds. However, the direct use of by-products in powder form dramatically reduced the mechanical strength of the fabricated bioelastomer. These barriers accentuate the disadvantage of PDMS, which is its relatively low mechanical strength due to its major structure composed of Si–O bonds, unlike the C–C bonds constituting PVA, PP, and PE [42]. Therefore, it is necessary to design a strategy for fabricating bioelastomers with antioxidant and antibacterial activities while maintaining their mechanical strength.
In this study, a strategy for the sustainable utilization of food processing residue was designed by fabricating a functional bioelastomer using bioactive compounds extracted from MPs. First, a mixing ratio of extraction solvents suitable for recovering the flavonoids, hesperidin and narirutin, from MP was selected. Microwave-assisted extraction was utilized to recover hesperidin and narirutin from MP with high efficiency in a short time. Furthermore, the effects of microwave power and irradiation time on flavonoid extraction were investigated. The recovered bioactive compounds were used to fabricate functional bioelastomers with antioxidant and antibacterial activities. Finally, the biological properties, chemical structure, and mechanical strength of the fabricated bioelastomer were compared with those of the control group. This study is the first attempt to produce a functional material by mixing flavonoid extracts obtained from MP, a waste resource, with PDMS to design a sustainable biorefinery.

2. Materials and Methods

2.1. Materials

Mandarin peels (MPs) were purchased from Cheongmyeongyagcho (Chungju-si, Chungcheongbuk-do, Korea). The MPs were ground with a blender and sieved to a size of 90 μm. Polydimethylsiloxane (PDMS; Elastosil E43) was obtained from Wacker (Munich, Germany). Hesperidin, narirutin, dimethyl sulfoxide (DMSO), 1,1-diphenyl-2-picryl-hydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), and potassium persulfate were purchased from Sigma-Aldrich (St. Louis, MO, USA). Methanol (MeOH), phosphoric acid, acetonitrile, and heptane were purchased from Samchun Chemical (Seoul, Republic of Korea). All reagents used in this study were of analytical grades.

2.2. Preparation of Mandarin Peel Extracts

To select the most efficient extraction solvent, 1 g of MP was immersed in 10 mL of a MeOH:DMSO solution mixed in different proportions (1:9, 3:7, 5:5, 7:3, and 9:1, v/v). MP, then, was extracted in an incubator at 40 °C, with a shaking speed of 150 rpm, for 24 h. To design the MAE process for maximum flavanone recovery from MP, MP was immersed in the selected extraction solvent (1:10, w/w) and extracted at various microwave powers (70, 210, 350, 490, and 630 W) and irradiation times (5, 10, 15, 20, and 30 s). Each extract was centrifuged at 13,000 rpm for 10 min to separate the supernatant and, then, analyzed and used for bioelastomer fabrication.

2.3. Fabrication of Bioelastomer

PDMS was poured into a square Petri dish (24.5 × 24.5 cm), and 20 mL of heptane and mandarin peel extracts (MPEs) were recovered under the determined MAE conditions were added and mixed uniformly. The bioelastomer manufacturing conditions are listed in Table 1. The Petri dish was transferred to a vacuum oven and dried at 40 °C until the moisture was completely removed.

2.4. Antioxidant Activity of Bioelastomer

2.4.1. DPPH Radical Scavenging Activity

DPPH radical scavenging activity was determined using the DPPH assay with a slight modification [43]. The DPPH stock solution was prepared by dissolving the DPPH reagent in MeOH to a concentration of 0.5 mM. The DPPH working solution was prepared by diluting the prepared DPPH stock solution with methanol until the absorbance at 517 nm reached 1.2. Each bioelastomer (size: 1 × 1 cm) was immersed in 1 mL of the DPPH working solution and reacted at 25 °C for 30 min. The bioelastomer was then removed, and the absorbance of the supernatant was measured at 517 nm using a spectrophotometer (DU 730, Beckman Coulter, Brea, CA, USA). The blank was 1 mL of methanol, and the control was 1 mL of DPPH working solution without bioelastomer added. All experiments were performed in triplicate to obtain the standard deviations. Radical scavenging activity was calculated using the following Equation (1):
Radical scavenging activity (%) = (1 − (ODsample/ODcontrol)) × 100

2.4.2. ABTS Radical Scavenging Activity

ABTS radical scavenging activity was measured using the ABTS assay with a slight modification [44]. An ABTS stock solution was prepared by reacting 7 mM ABTS solution and 2.45 mM potassium persulfate in a 1:1 ratio (v/v). ABTS working solution was prepared by diluting the prepared ABTS stock solution with methanol until the absorbance at 734 nm reached 1.0. Each bioelastomer (size: 1 × 1 cm) was immersed in 1 mL of the ABTS working solution and reacted at 25 °C for 30 min. The bioelastomer was then removed, and the absorbance of the supernatant was measured at 734 nm using a spectrophotometer; the blank was 1 mL of methanol, and the control was 1 mL of ABTS working solution without bioelastomer added. All experiments were performed in triplicate to obtain the standard deviations. The radical scavenging activity was calculated using Equation (1) above.

2.5. Antibacterial Activity of Bioelastomer

The antibacterial activity of the bioelastomer was determined following the method in our previous study [41]. Staphylococcus aureus was used as the gram-positive bacteria, Escherichia coli as the gram-negative bacteria, and methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) as the antibiotic-resistant bacteria. All the bacteria were cultured in a shaking incubator at 150 rpm, for 24 h, at 37 °C in 50 mL of nutrient broth. The bacteria were diluted to 106 CFU/mL and inoculated on nutrient agar plates. Bioelastomers (size: 1 × 1 cm) were placed in the center of the nutrient agar medium, inoculated with each bacterium, and then, incubated at 37 °C for 24 h. The antibacterial zone was determined using the Image J software (v1.52i, National Institutes of Health, Bethesda, MN, USA). All experiments were performed in triplicate to obtain the standard deviations.

2.6. Characterization of Bioelastomer

The chemical structures of the bioelastomers were investigated using Fourier-transform infrared spectroscopy (FT-IR; JASCO FTIR-4600, Jasco, Japan). Tensile strength and elongation at break were determined, according to ASTM D412, using a universal testing machine (Instron 3367; Norwood, MA, USA). Water vapor transmission rate (WVTR) was determined, according to ASTM F1249, using a Permatran-W 3/33 MA (Mocon, Minneapolis, MN, USA). The morphology of both bioelastomers was characterized using scanning electron microscopy (SEM, SNE-3000M, SEC Inc., Suwon, Republic of Korea) at a scanning voltage of 5 kV.

2.7. Analytical Methods

The hesperidin and narirutin contents in MPE were determined using high-performance liquid chromatography (HPLC). The analytical conditions were as follows: INNO column C18 (5 μm, 4.6 mm × 250 mm, Young Jin Biochrom, Seongnam-si, Republic of Korea); diode array detector (DAD); wavelength, 250 nm; temperature, 25 °C; injection volume, 5 μL; flow rate, 0.8 mL/min. The gradient elution conditions were as follows: acetonitrile for solvent A and 0.03% (v/v) phosphoric acid in DW for solvent B; 0 min, 10% A; 0–15 min, 20% A; 15–28 min, 40% A; 28–36 min, 75% A; 36–38 min, 10% A; 38–50 min, 10% A. Standard curves for quantification were prepared using hesperidin and narirutin as the standard reagents.

3. Results and Discussion

3.1. Selection of Extraction Solvent for Flavanone Recovery from Mandarin Peels

To maximize flavanone recovery from MPs, appropriate mixing ratios of the extraction solvents were investigated. A MeOH:DMSO mixture was used to extract total flavonoids from MP [45]. Similarly, Magwaza et al. [46] demonstrated that a mixed MeOH:DMSO solution (1:1, v/v) effectively and rapidly extracts phenolic compounds, such as flavanone glycosides and phenolic acid, from mandarin rinds. Figure 1 shows the effects of the mixing ratio of MeOH:DMSO on the flavanone (hesperidin and narirutin) recovery from MPs. The extraction solvent was mixed with solutions of MeOH and DMSO that had MeOH:DMSO ratios of 1:9, 3:7, 5:5, 7:3, and 9:1 (v/v). The resulting flavanone recovery with each solution was 26.6, 31.9, 43.7, 28.0, and 18.4 mg/g-biomass for hesperidin and 5.2, 6.3, 8.7, 6.1, and 5.3 mg/g-biomass for narirutin, respectively. These results agree with those of a previous study [46], which showed that the MeOH:DMSO solution mixed in the same ratio is the most effective extraction solvent for recovering flavanone from MPs. Therefore, a 5:5 ratio (v/v) of the MeOH:DMSO mixture was selected as the extraction solvent for recovering flavanone from MPs (Figure A1).

3.2. Determination of Microwave-Assisted Extraction Conditions

The MAE process was designed to recover high yield of flavanone from MP in a short time. However, high microwave power and extended irradiation time can cause the thermal degradation of these phenolic compounds [47]; extraction conditions should be determined based on the maximum energy that can be input without causing thermal degradation to reduce the consequent loss of bioactive compounds. Therefore, the effects of microwave power and irradiation time on flavanone extraction from MPs were investigated (Figure 2). Figure 2a shows the results of hesperidin recovery from MPs. At a microwave power of 70 W, hesperidin recovery was not significantly affected by irradiation time, and it only slightly increased from 49.0 mg/g-biomass at 5 s to 53.2 mg/g-biomass at 30 s. At a microwave power of 210 W, hesperidin recovery steadily increased from 49.5 mg/g-biomass at 5 s to 66.8 mg/g-biomass at 30 s, but the maximum recovery was not achieved. At microwave powers of 350, 490, and 630 W, hesperidin recovery steadily increased for 20 s, after which it decreased with increasing irradiation time. The reduction significantly increased as the microwave power increased, which was presumed to be because of thermal degradation caused by excessive energy input. This phenomenon was confirmed by Ahmad and Langrish [48], who extracted phenolic acids from MPs. Finally, the maximum hesperidin recovery was found to be 71.6 mg/g-biomass at 490 W and 20 s. Recovery of narirutin from MPs showed a similar tendency to that of hesperidin (Figure 2b). At microwave powers of 350, 490, and 630 W, narirutin recovery steadily increased for 20 s, after which it decreased with increasing irradiation time. The maximum narirutin recovery was found to be 16.3 mg/g-biomass at 490 W and 20 s. At 490 W and 20 s, the energy input was approximately 9600 J (W × s); as it was estimated that energies higher than 9600 J caused thermal degradation of flavanones, 490 W and 20 s were chosen as the extraction conditions for flavanone recovery from MPs.

3.3. Antioxidant Activity of Bioelastomer

Measuring the antioxidant activity of bioelastomers is important for preventing the negative effects of free radicals in biological and food packaging applications [49]. Table 2 shows the radical scavenging activity of the fabricated bioelastomer. The radical scavenging activity of the bioelastomer increased in proportion to the content of MP-derived flavanone extract (MPE). The DPPH radical scavenging activity of the bioelastomer increased sharply by 1.8-fold when 15% MPE was added, but it was still a low 3.3 ± 0.2%. The ABTS radical scavenging activity exceeded 20% at 15% MPE and reached 26.7 ± 1.2% at 20% MPE. The DPPH and ABTS radical scavenging activities of the hesperidin standard (100 ppm) were found to be 3.5 ± 0.4% and 17.8 ± 0.6%, respectively. These results imply that the ABTS assay is more sensitive than the DPPH assay for evaluating the antioxidant activity of the bioelastomers and hesperidin, a major component of MPE. Floegel et al. [50] reported that the DPPH assay is appropriate for hydrophobic systems, and the ABTS assay is suitable for hydrophilic, lipophilic, and highly pigmented systems. Flavonoid glycosides, such as hesperidin, are hydrophilic because the presence of sugars increases their polarity [51]. In addition, MPE recovered using a MeOH:DMSO mixture is hydrophilic and is presumed to contain high amounts of pigments such as flavonoids, carotenoids, and chlorophylls [52].

3.4. Antibacterial Activity of Bioelastomer

S. aureus can cause food poisoning and toxic shock syndrome, while E. coli can cause septicemia and cholecystitis [53]. In addition, infections of antibiotic-resistant bacteria, such as methicillin-resistant S. aureus (MRSA) and vancomycin-resistant Enterococcus (VRE), threaten human safety to the extent that the World Health Organization (WHO) has selected it as one of the top 10 threats to global public health [54]. Therefore, bioelastomers that exhibit antibacterial activity are expected to be highly useful in the food packaging, pharmaceutical, and medical fields.
B–MPE 0–10% did not exhibit antibacterial activity against any bacteria (data not shown). However, B–MPE 15% showed antibacterial activity against gram-positive (S. aureus), gram-negative (E. coli), and antibiotic-resistant bacteria (MRSA and VRE) (Figure 3). The antibacterial zone of B–MPE 15% was determined to be 20.4 ± 1.5 cm2 for S. aureus, 16.0 ± 1.2 cm2 for E. coli, 9.4 ± 0.4 cm2 for MRSA, and 14.8 ± 1.0 cm2 for VRE. The antibacterial zone of 50 ppm ampicillin, an antibiotic used as a positive control, was found to be 19.3 ± 0.6 cm2 for S. aureus and 12.5 ± 0.5 cm2 for E. coli. The antibacterial activity of B–MPE 15% was presumed to be due to the flavonoids present in MPE: flavonoids can cause bacterial cell death by inhibiting the metabolism and synthesis of DNA and RNA [55]. The antibacterial effect of B–MPE 15% was more sensitive against gram-positive bacteria (S. aureus) than against gram-negative bacteria (E. coli). Alexandre et al. [56] reported that gram-positive bacteria are more sensitive to interactions with phenolic compounds because they lack an outer membrane, causing the compounds to diffuse into them more quickly than in gram-negative bacteria. Similarly, Choi et al. [57] demonstrated that hesperidin, a major flavonoid in MPE, has lower values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for S. aureus than for E. coli.
Therefore, the bioelastomer with antioxidant and antibacterial activity was determined to be B–MPE 15%, and the contents of hesperidin and narirutin added to the bioelastomer were estimated to be 53.7 mg/50 g-B–MPE 15% and 12.2 mg/50 g-B–MPE 15%, respectively.

3.5. IR Analysis of Bioelastomer

The chemical structures of B-MPE 0% (control, PDMS) and B-MPE 15% were measured using FTIR. In the FT-IR spectra (Figure 4), the peak was at 797 cm–1, corresponding to the symmetric stretching of Si–O–Si, the peaks at 1020 cm–1 and 1100 cm–1 corresponded to the asymmetric stretching of the Si–O–Si of the PDMS backbone, the peak at 1257 cm–1 corresponded to the asymmetric stretching of CH3, and 2926 cm–1 corresponded to the symmetric bending of the CH3 of the PDMS side chain. The same peaks appeared for both PDMS layers, indicating that the PDMS monomers with MPE were completely cured. Furthermore, this proves that there are only physical interactions between the filler and the matrix without the formation of covalent bonds [58]. These results agreed with those of Shivangi et al. [59], who found that the addition of bioactive extracts did not significantly affect the surface chemical properties of the fabricated biofilm.

3.6. SEM Image of Bioelastomer

Scanning electron microscopy (SEM) was used to observe the surface of the fabricated bioelastomer (Figure 5). The B–MPE 0% film was transparent with a smooth surface (Figure 5a). In contrast, the B–MPE 15% film exhibited a yellowish porous surface (Figure 5b). The difference in the morphology of the samples was attributed to the presence of insoluble flavonoid matter that was left behind after the evaporation of the extraction solvent [60]. In addition, the addition of the extracts changed the optical properties of the bioelastomer, resulting in differences in color and transparency.

3.7. Mechanical Strength of Bioelastomer

To evaluate the applicability of the selected B–MPE 15%, the mechanical properties of the fabricated bioelastomer, namely its tensility and flexibility, were investigated by measuring its tensile strength and elongation at break, respectively [61]; the results are shown in Table 3. There was no significant difference between the tensile strengths of B–MPE 0% (5.2 N/mm2) and B–MPE 15% (5.1 N/mm2). This indicated that the MPEs were uniformly mixed with the well-cured PDMS layer without reducing the mechanical strength of the fabricated bioelastomer. Meanwhile, the elongation at break of B–MPE 15% (694%) was significantly higher than that of B–MPE 0% (551%); these results are consistent with those reported by da Rosa et al. [62], who showed that phenolic compounds, derived from plant extracts, can increase elongation at break.

3.8. Water Vapor Transmission Rate of Bioelastomer

The water vapor transmission rate (WVTR) refers to the amount of water vapor that can permeate per unit area of a material per unit time. In the food packaging industry, lower values are considered advantageous [63]. Bourakadi et al. [64] reported that barrier properties, including the WVTR, are significantly affected by the chemical properties of the additives. From the WVTRs of B–MPE 0% and 15%, which were found to be 26.6 g/(m2 day) and 33.3 g/(m2 day), respectively (Table 3), it can be seen that the addition of MPE slightly increased the WVTR of the bioelastomers. This was probably due to the presence of polar compounds in the MPE: in general, extracts containing polar compounds, such as flavonoids and phenolic acids, improve the hydrophilicity of film materials, leading to an increase in their water vapor permeability [65].

4. Conclusions

Here, we proposed a biorefinery strategy based on the extraction of useful substances prior to the saccharification process of MPs, as well as the utilization of the extracted compounds. In this study, we recovered hesperidin and narirutin from MP and used them to fabricate bioelastomers. These bioelastomers that were fabricated using extracts exhibited significantly improved mechanical strength compared to bioelastomers that directly utilized biomass in powder form. In addition, the fabricated bioelastomer exhibited significant antioxidant and antibacterial activities and, thus, shows great potential for use in the food packaging, pharmaceutical, and medical industries. Our biorefinery strategy is expected to provide future direction for the realization of a sustainable society and carbon neutrality.

Author Contributions

Conceptualization, K.H.L. and Y.C.; methodology, J.H.L.; software, J.H.L.; validation, J.U.L. and T.L.; formal analysis, K.H.L. and Y.C.; investigation, J.U.L.; data curation, K.H.L. and Y.C.; writing—original draft preparation, K.H.L. and Y.C.; writing—review and editing, T.L. and H.Y.Y.; visualization, J.H.L.; supervision, H.Y.Y.; project administration, T.L. and H.Y.Y.; funding acquisition, T.L. and H.Y.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (MSIT) (NRF-2020R1C1C1005060 and RS-2022-00165814).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A

Agriculture 13 00161 g0a1a 550Agriculture 13 00161 g0a1b 550
Figure A1. HPLC chromatogram for hesperidin standard (a); narirutin standard (b); mandarin peel extracts (c).
Figure A1. HPLC chromatogram for hesperidin standard (a); narirutin standard (b); mandarin peel extracts (c).
Agriculture 13 00161 g0a1aAgriculture 13 00161 g0a1b

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Agriculture 13 00161 g001 550
Figure 1. Effects of the mixing ratio of MeOH:DMSO solution on flavanone (hesperidin and narirutin) recovery from MPs.
Figure 1. Effects of the mixing ratio of MeOH:DMSO solution on flavanone (hesperidin and narirutin) recovery from MPs.
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Figure 2. Effect of microwave power and irradiation time on the hesperidin (a) and narirutin (b) recovery from MPs.
Figure 2. Effect of microwave power and irradiation time on the hesperidin (a) and narirutin (b) recovery from MPs.
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Figure 3. Antibacterial activity of Bioelastomer–MPE 15% against gram-positive (S. aureus), Gram-negative (E. coli), and antibiotic-resistant bacteria (MRSA and VRE).
Figure 3. Antibacterial activity of Bioelastomer–MPE 15% against gram-positive (S. aureus), Gram-negative (E. coli), and antibiotic-resistant bacteria (MRSA and VRE).
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Figure 4. Fourier transform infrared (FT-IR) spectra of the Bioelastomer–MPE 0% (control, PMDS, black) and the Bioelastomer–MPE 15% (red).
Figure 4. Fourier transform infrared (FT-IR) spectra of the Bioelastomer–MPE 0% (control, PMDS, black) and the Bioelastomer–MPE 15% (red).
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Figure 5. SEM images of B–MPE 0% (a) and B–MPE 15% (b) (inset: film-type product).
Figure 5. SEM images of B–MPE 0% (a) and B–MPE 15% (b) (inset: film-type product).
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Table
Table 1. Detailed manufacturing conditions of bioelastomers.
Table 1. Detailed manufacturing conditions of bioelastomers.
SamplePDMS (g)MPE (g)
B–MPE 0% (control, PDMS)500
B–MPE 1% (w/w)49.50.5
B–MPE 3%48.51.5
B–MPE 5%47.52.5
B–MPE 7%46.53.5
B–MPE 10%455
B–MPE 15%42.57.5
B–MPE 20%4010
Table
Table 2. Radical scavenging activity of the fabricated bioelastomer.
Table 2. Radical scavenging activity of the fabricated bioelastomer.
SampleRadical Scavenging Activity (%)
DPPHABTS
B–MPE 0% (control, PDMS)00
B–MPE 1%1.0 ± 0.013.1 ± 0.3
B–MPE 3%1.1 ± 0.116.8 ± 0.4
B–MPE 5%1.2 ± 0.117.3 ± 0.6
B–MPE 7%1.5 ± 0.118.8 ± 0.3
B–MPE 10%1.8 ± 0.119.8 ± 0.6
B–MPE 15%3.3 ± 0.220.8 ± 0.8
B–MPE 20%4.8 ± 0.326.7 ± 1.2
Hesperidin 100 ppm3.5 ± 0.417.8 ± 0.6
Table
Table 3. Physical properties of Bioelastomer–MPE 0% (control, PMDS) and Bioelastomer–MPE 15%.
Table 3. Physical properties of Bioelastomer–MPE 0% (control, PMDS) and Bioelastomer–MPE 15%.
SampleTensile Strength
(N/mm2)		Elongation at Break
(%)		Water vapor Transmission Rate
(g/(m2 day))
B–MPE 0%5.255126.6
B–MPE 15%5.164933.3
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Lee, K.H.; Chun, Y.; Lee, J.H.; Lee, J.U.; Lee, T.; Yoo, H.Y. Sustainable Utilization Strategy of Organic Waste via Fabrication of Bioelastomer with Antibacterial and Antioxidant Activities Using Mandarin Peel Extracts. Agriculture 2023, 13, 161. https://doi.org/10.3390/agriculture13010161

AMA Style

Lee KH, Chun Y, Lee JH, Lee JU, Lee T, Yoo HY. Sustainable Utilization Strategy of Organic Waste via Fabrication of Bioelastomer with Antibacterial and Antioxidant Activities Using Mandarin Peel Extracts. Agriculture. 2023; 13(1):161. https://doi.org/10.3390/agriculture13010161

Chicago/Turabian Style

Lee, Kang Hyun, Youngsang Chun, Ja Hyun Lee, Jong Uk Lee, Taek Lee, and Hah Young Yoo. 2023. "Sustainable Utilization Strategy of Organic Waste via Fabrication of Bioelastomer with Antibacterial and Antioxidant Activities Using Mandarin Peel Extracts" Agriculture 13, no. 1: 161. https://doi.org/10.3390/agriculture13010161

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