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Article

Novel Poly(butylene succinate-dilinoleic succinate) Films in Packaging Systems for Fresh Cut Chicory

by
Szymon Macieja
1,
Małgorzata Mizielińska
1,
Mirosława El Fray
2 and
Artur Bartkowiak
1,*
1
Center of Bioimmobilisation and Innovative Packaging Materials, Faculty of Food Sciences and Fisheries, West Pomeranian University of Technology, 71-270 Szczecin, Poland
2
Department of Polymer and Biomaterials Science, Faculty of Chemical Technology and Engineering, West Pomeranian University of Technology, 71-311 Szczecin, Poland
*
Author to whom correspondence should be addressed.
Coatings 2025, 15(9), 1095; https://doi.org/10.3390/coatings15091095
Submission received: 18 August 2025 / Revised: 13 September 2025 / Accepted: 15 September 2025 / Published: 18 September 2025
(This article belongs to the Special Issue Preparation and Applications of Bio-Based Polymer Coatings)
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Abstract

Ready-to-eat products, such as mixed-cut leafy vegetables, require packaging that provides adequate mechanical protection, a barrier against UV radiation, gases, and water vapor, as well as microbiological safety. In this study, thin films made of polybutylene succinate (PBS) and poly (butylene succinate-dilinoleic succinate) (PBS-DLS) copolyester were prepared by casting a film-forming solution onto a glass plate and spreading it with a roller. These films were compared to commercial thin films made of oriented polypropylene (OPP). OPP films exhibited ten times higher tensile strength than PBS films (104.36 ± 10.03 MPa for OPP, 10.96 ± 0.68 MPa for PBS, and 6.36 ± 0.62 MPa for PBS-DLS). Incorporation of co-monomeric units of dilinoleic succinate (DLS) into PBS structure significantly improved elongation at break, increasing from 38.16% ± 12.36% for PBS to 132.30% ± 25.08% for PBS-DLS. However, commercial OPP had the highest elongation at break, reaching 231.84% ± 20.30%. OPP films exhibited the highest transparency in the visible light range but also in the UV range. In contrast, PBS and PBS-DLS films provided better UV radiation blocking. The films were used to create sachets by heat sealing, into which freshly cut chicory leaves were placed. The packaged product was stored under refrigerated conditions for 48 h and 120 h. While OPP and PBS-DLS films provided good protection against moisture loss in chicory, leaves packed in PBS sachets lost significant weight during storage. The packaged product contained considerable microbial contamination, but the type of packaging did not influence its reduction or increase. Ultimately, the PBS-DLS copolymer exhibited higher elongation at break and greater water vapor barrier properties than PBS. Protection against moisture loss in packaged chicory for PBS-DLS packaging was similar to that for commercial OPP. Despite their weaker mechanical properties, PBS-DLS films appear to be a promising alternative to OPP films for packaging fresh food products.

1. Introduction

Conventional packaging, primarily produced from petroleum-based polymers (e.g., polyethylene, poly(ethylene terephthalate), polypropylene) generates vast amounts of waste due to the widespread use of single-use materials and their long degradation time [1]. It is estimated that plastics account for approximately 40% of global packaging waste [2], with their decomposition in natural environments taking years [3]. This leads to their accumulation in ecosystems, ocean pollution, and the formation of microplastics, which pose risks to human and animal health [4].
Bio-based polymers (bioplastics), such as poly (lactic acid) (PLA), poly (butylene succinate) (PBS) and polyhydroxyalkanoates (PHA), offer a promising alternative as they are derived from renewable resources and are biodegradable or compostable under controlled conditions, significantly reducing long-term environmental impact [5]. Compared to conventional plastics, some bio-based polymers have a lower carbon footprint due to CO2 sequestration by plants used in their production [6]. However, their mechanical and barrier properties (e.g., moisture resistance) are often inferior, which may limit food shelf life [7,8]. Additionally, higher production costs and insufficient composting infrastructure remain key challenges [9].
Despite these limitations, bio-based polymers provide a crucial advantage in the context of sustainable development: reducing non-degradable waste while minimizing reliance on fossil resources. However, to serve as an effective alternative, further technological optimization and the development of circular economy systems are required [9].
Packaging for cut chicory, particularly ready-to-eat products, must meet stringent requirements: providing protection against moisture loss, oxidation, and microbial growth while allowing for proper respiration. Conventional solutions, such as polypropylene (PP) trays or polyethylene (PE) films, often utilize modified atmosphere packaging (MAP) to extend chicory freshness [10]. However, these materials generate significant waste, as they are typically single-use and challenging to recycle due to contamination with organic residues [11]. Additionally, when improperly disposed of, they release toxic substances and microplastics, which can infiltrate soil and water systems [12].
Poly (butylene succinate) (PBS), a bio-based polymer derived from renewable resources (e.g., succinic acid obtained via sugar fermentation), presents a promising alternative for this sector. Unlike some more rigid bio-based polymers such as poly (lactic acid) (PLA), PBS exhibits high flexibility and moisture resistance [13]—key properties for chicory packaging, where water vapor condensation can accelerate spoilage. PBS can be processed into thin, transparent films or trays with barrier properties comparable to PE [14], effectively regulating O2 and CO2 exchange in MAP systems. Notably, PBS biodegrades under industrial composting conditions, reducing landfill waste [15].
Despite its advantages, the use of PBS presents challenges. Its production cost remains higher than that of conventional plastics [16], and optimizing its barrier properties (e.g., oxygen permeability) often requires modifications such as nanoparticle additives or blending with other polymers [17,18]. Moreover, effective PBS biodegradation depends on the availability of composting infrastructure, which remains insufficient in many regions [19]. Nevertheless, from a life-cycle perspective, PBS offers significant carbon footprint reduction and aligns with circular economy principles, particularly when derived from agricultural waste [15]. For the ready-to-eat industry, this represents not only an eco-friendly alternative but also an opportunity to enhance brand image through sustainable development initiatives.
One of the effective methods of modifying the structure and properties of PBS is the synthesis of copolymers using various comonomers [20,21]. Recently developed aliphatic PBS copolymers containing long chain (C36) biobased glycol as soft segments were successfully synthesized using a two-step polycondensation technique [22]. Novel poly (butylene succinate-dilinoleic succinate) (PBS-DLS) of variable segmental composition show lower melting point and higher elasticity with increasing DLS soft segments content. It was shown in previous research [23], that as DLS content in copolymer increases, it becomes harder for microorganisms to adhere to the surface of the films. As demonstrated in a previous study, both PBS and PBS-DLS films obtained by solvent casting exhibit micro-beaded microstructure [23]. Nevertheless, as the DLS proportion to PBS increases, the surface becomes smoother and the irregularities are smaller and less observable. Moreover, polymer is becoming less amorphous compared to PBS homopolymers what may affect the gases and water vapor permeability of the films.
In this study, new thin films based on poly (butylene succinate-dilinoleic succinate) (PBS-DLS) containing 50 wt.% of soft segments were developed through a method of pouring a film-forming solution onto a glass panel with roller spreading. The properties of the obtained films were compared with those of films made of commercial PBS and oriented polypropylene. The OPP films were used as control material since the chicory purchased for this study was packaged in this polymer. Sealed sachets in which chicory was packed were made from the films. It should be underlined that it was first attempt ever to test this non-commercial copolymer as food packaging material. Microbiological and physical changes in the chicory were studied after 48 and 120 h.

2. Materials and Methods

2.1. Materials

Chicory (Endywia frisee and Endywia escarola)—ready to eat pre-washed and pre-cut mix was bought at local market. Poly (butylene succinate)—PBS (FZ91PM BioPBS™) was purchased from Mitsubishi Chemical (Tokyo, Japan). Oriented polypropylene was provided by MarDruk Opakowania (Andrychów, Poland). Chloroform and Methanol was supplied by Chempur (Piekary Śląskie, Poland). Plate Count Agar, Sabouraud Dextrose Agar, Violet Red Bile Glucose Agar, Glutaraldehyde, Sodium Cacodylate buffer and buffered peptone water were purchased from Merck (Darmstadt, Germany). PBS-DLS copolyester containing 50 wt.% of soft segments (PBS-DLS 5:50) was synthesized according to procedure described in [22]. All the chemicals were of analytical grade.

2.2. Films Preparation

Film-forming solutions were prepared by introducing 20 g of a polymer (commercial PBS (FZ92PM BioPBS™), or a PBS-DLS 50:50) into 200 mL of chloroform. The solutions were stirred using a magnetic stirrer (Ika, Warsaw, Poland) until all of the polymer was dissolved. Thin films were obtained using a Unicoater 409 coating machine (Erichsen, Hemer, Germany) equipped with a 100 µm diameter roller. A volume of 10 mL of the film-forming solution was applied to a glass plate and evenly spread using the roller. The dimensions of films obtained through spreading the film-forming solutions on glass plates were 20cm × 20 cm. The films were left on the glass surface to allow for solvent evaporation (approximately 5 min). To reduce polymer adhesion to the glass, the film surface was gently moistened with a slightly damp paper towel. Finally, the films were manually peeled off the glass plate and placed between sheets of paper to protect them before further analysis or use in chicory packaging. Peeled films were conditioned for 3 days at 25 °C and 50% relative humidity in a climate room prior to any tests to ensure full solvent evaporation.

2.3. Characterization of Films Properties

2.3.1. Thickness and Mechanical Properties of the Films

The thickness of the film was measured using a digital micrometer (Dial Thickness Gauge 7301, Mitoyuto Corporation, Kanagawa, Japan, with an accuracy of 0.001 mm). Ten measurements were taken at random spots around each film sample and expressed as the mean ± standard deviation. The average values were used to determine the mechanical properties.
The mechanical tests were conducted using a Zwick/Roell Z2.5 tensile tester (Ulm, Germany) following ASTM D822-02. The films were cut into strips with a width of 10 mm, the starting gauge was 25 mm, and the crosshead speed was 10 mm/min. No less than six replicate samples were examined. Elongation at break (EB), maximum tensile strength (TS), and Young’s modulus (YM), along with standard deviations, were computed using TestXpert III software (v1.61).

2.3.2. UV-Vis Spectroscopic Analysis

To measure the UV-Vis spectra (absorbance in the 200–800 nm range) of the film samples, a Thermo Scientific Evolution 220 UV-Vis spectrophotometer (Fisher Scientific, Waltham, MA, USA) was used.

2.3.3. Color and Opacity Measurements

In order to identify the color of the obtained films, a colorimeter (CR-5, Konica Minolta, Tokyo, Japan) was used with the CIELab color scale. The films were repeatedly sampled 10 times at random spots on each of the tested films. Films were measured for opacity using an EE Model 12 opacity meter (Diffusion Systems LTD, London, UK). The opacity meter was pre-calibrated using a standard white plate (value 100 ± 1, Diffusion Systems LTD, London, UK), and readings were carried out ten times for each film and expressed as mean ± standard deviation.

2.3.4. Water Vapor Transmission Rate Measurements

The WVTR was determined using the ISO 2528:2017 gravimetric cup method [24] at a temperature of 25 °C and a relative humidity of 75% for 24 h. A 68-3000 EZ-Cup vapor pressure tester (Thwing-Albert Instrument Company, West Berlin, NJ, USA) was used for the measurements. Granular silica gel was selected as the desiccant, and no less than three replicates were tested. Before determining the WVTR, the films were conditioned at 25 °C and 75% relative humidity for 24 h. The parameter calculations were based on the slope/sample diameter × 24 h.

2.3.5. Water Contact Angle Measurement

The water contact angle of the film surface was evaluated using a contact analyzer (Phoenix-Mini, PM-041807, Surface Electro Optics, Suwon, Republic of Korea). The water contact angle values were computed using Surfaceware software (v9.9) after a drop of distilled water was applied on the film surface.

2.3.6. Microscopic Evaluation of Films

The surfaces of OPP, PBS, and PBS-DLS films were examined using SEM (scanning electron microscope). First, the films (both top and bottom sides) have been positioned on pins and coated with a gold thin film in a sputter coater at room temperature (Quorum Technologies Q150R S, Laughton, East Sussex, UK). SEM microrographs were then obtained using a Vega 3 LMU microscope (Tescan, Brno-Kohoutovice, Czech Republic). A tungsten filament with an accelerating voltage of 10 kV was used for the microscopic examination.

2.4. Sachets Preparation

Prior to contact with chicory, commercial oriented polypropylene (OPP) film (of the same diameters to films obtained in Section 2.2), poly (butylene succinate) (PBS), and a PBS-DLS 50:50 copolymer were exposed to UV light for 15 min to ensure sterilization. The films were folded in half, and two edges were sealed using a thermal sealer (HSE-3, RDM Test Equipment, Hertfordshire, UK) to form an open sachet measuring 10 cm × 20 cm. Each polymer sachet was filled with 5.0 ± 0.1 g of chicory leaves and subsequently sealed by heat-sealing the open edge. The sealing parameters were set as follows: sealing time—1 s, pressure—2.5 kN, and temperature—110 °C for OPP, 65 °C for PBS, and 60 °C for the PBS-DLS 50:50, respectively.
The 18 bags (6 of each bag) containing chicory were then kept at 5 °C. The 9 samples were analyzed after 48 h (three sachets of each kind of sachet/polymer material) and last 9 samples were analyzed after 120 h of storage. Representatives of each sachet before storage are shown in Figure 1.

2.5. Microbial Quality Investigation

Chicory microbiological quality was examined both before and after storage. In each test, 1 ± 0.1 g of the sample was transferred under aseptic conditions to a sterile Stomacher bag containing the physiological peptone saline (PPS: 0.1% w/v peptone; 0.85% w/v NaCl (Merck, Darmstadt, Germany)). The chicory was then homogenized using a bag mixer (Interscience, Saint-Nom-la-Brèteche, France) for 60 s. Next, appropriate decimal dilutions were prepared in PPS solution. The total number of bacteria (psychrophilic and mesophilic) was determined in accordance with PN-EN ISO 4833-2:2013-12 [25], the total coliforms bacteria count was determined according to PN-ISO 4832:2007 [26] while yeast and mold counts were analyzed according to the PN-ISO 21527-2:2009 standard [27].

2.6. Moisture Content and Relative Humidity Investigation

The moisture content of chicory before being stored and after 48 and 120 h of storage was measured using a dryweight scale (Radwag, Warsaw, Poland). Two samples from each package were tested. In order to measure the relative humidity inside the chicory packaging, data loggers (DS1923-F5# Hygrochron Temperature and Humidity Data Logger, Mouser Electronics, Mansfield, TX, USA) were placed separately in each package to maximize integration. Relative humidity was measured hourly during 120 h of storage.

2.7. Microscopic Analysis of Chicory Leaves

The microscopic analysis of the chicory leaves was made prior to packaging and after 48 and 120 h of sample storage. The experiment was conducted using a Zeiss SteREO Discovery V20 stereomicroscope (Carl Zeiss MicroImaging GmbH, Göttingen, Germany). As the next step, the chicory leaves (the same leaves that were analyzed using the stereomicroscope) were fixed at 4 °C in 2% glutaraldehyde prepared in 0.1 M sodium cacodylate buffer (pH 7.4) for 18 h. After incubation, the samples were washed with 0.1 M sodium cacodylate and dehydrated in a series of ice-cold solutions of methanol in water (−20 °C; 20%, 40%, 60%, 80%, and 100% v/v) at intervals of 2-h. The leaves were then placed on a Petri dish for 5 min before being mounted on pin stubs. A thin gold film was applied as described in Section 2.3.6. The leaves were examined by applying the same protocol as was described for film samples in Section 2.3.6. All specimens were viewed from above at magnifications of 1000×.

2.8. Statistical Analysis

The statistical analyses were performed using Statistica version 13 (StatSoft Polska, Krakow, Poland). Significant differences between means were identified using analysis of variance (ANOVA), followed by Fisher’s LSD post hoc test at a significance threshold of p < 0.05.

3. Results and Discussion

3.1. Thickness and Mechanical Properties of the Films

Table 1 shows the results of testing the thickness and mechanical properties of the films. The obtained PBS films were not statistically different in thickness from those made of commercial OPP (p > 0.05). However, the addition of DLS to the PBS matrix significantly increased the thickness of the obtained films (p < 0.05). Nevertheless, the obtained films had similar TS values regardless of the presence or absence of DLS soft segments. These values were 10.96 ± 0.68 MPa for PBS and 6.36 ± 0.62 for films with PBS-DLS, respectively. Commercial OPP showed much higher TS values of 104.36 ± 10.03 MPa, which may be related to a different preparation method, probably blow molding, which causes the polymer chains to orient in a specific way and therefore results in an increase in the mechanical parameters of the film. Incorporation of co-monomeric units of DLS into PBS polymer structure, on the other hand, affected changes in the EB of the films. While the EB value for the PBS films was 38.16% ± 12.36 %, the PBS-DLS films showed a significantly higher value (p < 0.05) of 132.30% ± 25.08 %. This is due to the plasticizing properties of amorphous DLS segments. For commercial OPP film, EB was 231.84% ± 20.30 %, which was the highest value. That is in line with data provided in previous articles on PBS modification [28,29].

3.2. UV-Vis Spectroscopic Analysis

Figure 2 shows the UV-Vis transmittance of the films tested. The highest transmittance for radiation in the visible light range (wavelength 380–800 nm) was exhibited by films made of OPP transmitting more than 80% of this radiation. Also, for UVA (wavelength 320–380 nm) and UVB (wavelength 280–320 nm) radiation, the films were highly transparent. It was only for UVC radiation (wavelengths below 280 nm) that a sharp decrease in transparency could be observed with decreasing wavelength. For PBS films, much weaker transmittance was observed for both visible and UV light. The addition of DLS to the polymer matrix resulted in increased transmittance of radiation from the visible range (for the PBS films tested)-DLS showed greater transmittance of radiation from the Vis range despite the greater thickness of the films). PBS-DLS films showed a transmittance for radiation in the Vis range of more than 20%. This value gradually decreased with shortening wavelength until an observed sharp decrease at 290 nm and a second decrease at 240 nm, first to 8% and then to 0%. This phenomenon may be due to the presence of carbonyl groups in PBS polymer, which is even greater in the PBS-DLS copolymer. Carbonyl groups are one of chromophores commonly believed to be involved in the photodegradative mechanisms for numerous hydrocarbon polymers [30]. Higher transmittance of PBS-DLS films can also be explained by more amorphous character compared to semi-crystalline PBS [22].

3.3. Color and Opacity Measurements

Table 2 presents the measurements of color, opacity, and transparency at wavelengths of 660 nm and 280 nm, which serve as indicators of transparency for the human eye and barrier properties against UV light, respectively. All films exhibited similar values in terms of brightness (L* parameter), a* (green-red balance), and b* (blue-yellow balance). The PBS films stood out in terms of opacity. The value of this parameter was determined to be 16.30 ± 0.91, while for OPP and PBS-DLS, it was 7.20 ± 0.12 and 7.74 ± 0.09, respectively.
Despite the similar opacity values of PBS-DLS and OPP films, the highest transparency for human vision, measured at a wavelength of 660 nm, was observed for OPP films, with a value of 89.33%. PBS-DLS films exhibited significantly lower transparency at 27.58%, while PBS films had the lowest transparency, with a value of 17.60%.
From the perspective of food storage, UV radiation barrier properties are an important parameter, as they help protect packaged products from degradation caused by this high-energy radiation. The highest barrier properties were observed for PBS films, which allowed only 6.95% of the 280 nm wavelength radiation to pass through. PBS-DLS films transmitted slightly more—10.14%. The weakest UV barrier was provided by OPP films, which transmitted 81.56% of this radiation.

3.4. WVTR and Water Contact Angle Analysis

Table 3 shows the results of WVTR and average contact angle analysis of the commercial OPP film and the obtained PBS and PBS-DLS films. OPP films are known for their high water vapor barrier properties. Seok-Hoon et al. reported WVTR of OPP films at 5.9 g/m2·day [31].
Water Contact Angle measured for OPP films was 68 ± 2° which is typical value for this polymer after plasma activation [32].
It is worth mentioning at this point that another important factor from the food preservation point of view is the oxygen barrier properties of the packaging. PBS is known for its relatively high oxygen permeability, but this can be reduced by copolymerization with DLS [33]. Unfortunately, due to the low thickness of the films produced (as shown in Table 1) and their microstructure (shown in Figure 3), we were unable to determine the OTR using our equipment (OX-TRAN Model 2/10 (Mocon, Minneapolis, MN, USA) in accordance with ASTM D3985).

3.5. Microscopic Evaluation of Films

Figure 3 shows SEM images of the surface microstructure of commercial OPP films and the developed PBS and PBS-DLS films from the top and bottom sides. The commercial OPP film has a uniform structure with minor imperfections. Such a structure has been previously described for OPP [30].
The PBS and PBS-DLS thin films obtained by spreading the film-forming solution on the surface of the glass sheet differed in microstructure depending on the side (top or bottom) tested. The PBS film from the top side (the side of solvent evaporation/not in contact with the glass) had a micro-beaded, heterogeneous structure. On the other hand, from the bottom side (adjacent to the glass during solvent evaporation), the film has a uniform structure, but with holes present.
The PBS-DLS film had a homogeneous structure on its top side, looking like interconnected cells or a leathery material. The interconnected structures of heterogeneous shapes and sizes form a uniform surface with no observable holes. From the bottom side of the film, one can see a completely homogeneous surface devoid of any imperfections.
The large number of free spaces between interconnected micro beads in the PBS film may affect the properties of the resulting material. In previous work, it was shown that depending on the proportion of soft DLS segments in the copolymer matrix, the susceptibility of the films to the formation of bacterial and fungal biofilms on them changed. As the proportion of soft DLS segments in the copolymer matrix increased, the film structure became more uniform, and thus the specific surface area available for adhesion by microorganisms decreased [23].
Comparing the WVTR results with SEM micrographs it can be noted that higher WVTR [g/m2·day] value for PBS-DLS than for PBS was observed (Table 3). The results contradict the SEM images presented in Figure 3. As was noticed, the bottom side of the PBS-DLS film was smooth and in contrast to the bottom side of PBS, neither pinholes nor porosity were seen on it. However, the top side of the PBS-DSL film was not completely smooth and had some irregularities and small, deep holes, what combined with the low thickness of the film, this might have affected the WVTR result.

3.6. Moisture Content Investigation

Table 4 shows the changes in moisture content of the packaged chicory. The initial water content of the packaged product was 94.66 ± 0.95 percent. After 48 h, there were slight decreases in the values of this parameter, but the differences were not significant (p > 0.05). At the next measurement, after 120 h, a significant decrease in the moisture content of chicory packaged in sachets with PBS was noted. The value was 59.73 ± 13.62%. This result is in agreement with WVTR results. The moisture content of chicory packed in sachets made of the other two polymers (OPP and PBS-DLS) was not significantly different from the control (p > 0.05).
Observations made by Kim et al. [34], who packaged chicory in three different types of packaging (a paper carton, a paper box with endive wrapped in high-density polyethylene (HDPE) film, and a plastic box container covered with high-density polyethylene (HDPE) film), showed that the use of HDPE packaging effectively prevents moisture loss. The weight loss of the product protected by films was similar to the results obtained in this study.
PBS modified with zinc oxide nanoparticles was previously used for packaging freshly cut apple pieces [35]. The presence of nanoparticles in the polymer matrix led to an increased rate of weight loss in apples during storage.
Figure 4 shows the changes in relative humidity inside OPP, PBS and PBS-DLS sachets containing chicory during 120 h of storage. As can be seen in the graph, packaging made of commercial OPP provided constant relative humidity during 120 h of storage. The sachet made of PBS-DLS let in small amounts of water vapor for the first 20 h after which the relative humidity remained about the same until the end of storage. Packaging made of PBS provided the worst moisture retention inside the package. The value dropped from an initial 91% relative humidity 1 h after packaging to 40% relative humidity after 120 h under refrigeration. These results are in line with those obtained for moisture content stored in chicory sachets. The differences in providing protection against loss of product moisture and moisture inside the package can be explained by the microstructure of the package. As shown in previous work [23], films obtained by the solvent method are characterized by a microstructure of micro beads, which results in the formation of free spaces. Nevertheless, chemical modification of PBS using hydrophobic DLS results in changes in surface morphology − it becomes smoother and irregularities occur less frequently. Consequently, the barrier to moisture in such a film increases.

3.7. Microbial Quality Investigation

Figure 5 presents the microbial counts (log CFU/g) of coliform bacteria (cultured on Violet Red Bile Glucose Agar) in samples taken immediately before packaging (C) and after 48 h and 120 h of refrigerated storage. The number of coliform bacteria remained at a similar level (106–107 CFU/g) for control sample (C, fresh chicory) and throughout the storage period, regardless of the polymer used for packaging. The only exception was chicory packed in sachets made of OPP, analyzed after 48 h of storage. In this case, the microbial count was more than 10 times lower. However, for the sample tested after 120 h, this difference was no longer statistically significant compared to the other packaging types and the control sample of fresh chicory.
Figure 6 presents the fungal and mold counts (log CFU/g) in fresh chicory and chicory packaged in sachets made of OPP, PBS, or PBS-DLS before packaging (C) and after 48 h or 120 h of storage. Both for fresh chicory and for chicory stored for 120 h, the CFU/g count of fungal and mold cells was around 105.
For samples analyzed after 48 h, these values were 7 times lower for the sample packed in OPP and 5 times lower for the sample packed in PBS-DLS. However, these results are not significantly different from those for fresh chicory (p > 0.05), and the result for fresh chicory is not statistically different from the results after 120 h of storage (p > 0.05).
Figure 7 presents the total microbial cell count (log CFU/g) obtained on Plate Count Agar incubated at 37 °C. Both for fresh chicory and for chicory analyzed after 48 or 120 h of storage in packaging, a similar total microbial count was observed, regardless of the type of packaging used.
These results ranged from 1.55 × 106 ± 4.46 × 105 for fresh chicory (C) to 1.07 × 107 ± 1.59 × 106 [CFU/g] for chicory packaged in PBS-DLS after 120 h of storage. However, these differences were not statistically significant (p > 0.05). Similar results were shown by Sun, Y. et al. [36], who noted that the total bacterial count detected on fresh lettuce/chicory leaves exceeded 5 log CFU/g. However, after washing, cutting, disinfecting, and dewatering, it was reduced to approximately 4 log CFU/g. The authors indicated that at the beginning of storage, the total bacterial count was the lowest (around 3 log CFU/g), but gradually increased after 24 h of storage. For leaves stored for 72, 96, 144, and 192 h, the total bacterial count again exceeded 5 log CFU/g. The researchers explained that the decrease in the number of bacterial cells at the beginning of storage might have been due to the inhibitory effect of low temperature on microbial growth. The higher number of mesophilic bacteria (8.51 log CFU/g) was detected from fresh lettuce leaves by Chamorro J.C. et al. [37]. The authors used plasma activated water (PAW) treatment to reduce the total count of mesophilic bacteria. The researchers observed that the number of these microorganisms was significantly reduced from day 1 to day 3 of storage, probably due to PAW treatment, and then increased for day 7. Changes in the quality of chicory during storage in a polyvinyl chloride (PVC) film and in a mono-oriented polypropylene (OPP) film at 4 °C were studied by Lavelli V. et al. [38]. The maximum limit of 5 × 107 CFU/g for the total count of mesophilic aerobic bacteria was observed by the authors after 4 days using the PVC film and after 4.5 days using the OPP film. The maximum limit of mesophilic bacterial cells observed in this study was reached after 5 days of chicory leaves storage in OPP and PBS-DLS bags. The authors mentioned that total coliform, yeast and mold populations also increased during storage, but the increases were four to five orders of magnitude lower than the mesophilic bacteria count.
Figure 8 presents the count of psychrophilic microorganisms (log CFU/g) present in the analyzed chicory samples before packaging and after refrigerated storage, obtained on PCA incubated at 5 °C. These counts ranged from 1.75 × 106 ± 5.24 × 105 for fresh chicory (C) to 3.81 × 107 ± 1.17 × 107 [CFU/g] for chicory packaged in PBS-DLS sachets after 120 h of storage. This represented a significant increase in the number of microorganisms (p < 0.05). However, when comparing the results for different polymers (OPP, PBS, and PBS-DLS), the differences between them were not statistically significant (p > 0.05). The higher number of psychrophilic bacteria (8.95 log CFU/g) was detected from fresh lettuce leaves by Chamorro J.C. et al. [37]. The researchers treated the samples of leaves with plasma-activated water. Their results—specifically, the observed counts of meso- and psychrophilic bacteria—showed that the plasma-activated water treatments on the third day of storage exhibited stronger inactivation efficiency than the same treatments performed on day one. This indicates that microorganisms subjected to the lethal dose of plasma-activated water were unable to repair themselves during three days of refrigerated storage. However, psychrophilic bacterial cells inactivation efficiency was maintained for up to seven days.
As it was shown recently, modification of PBS with long chain hydrophobic DLS has an impact on the microstructure of films. Solvent-cast PBS films have micro beaded structure [28] and as the DLS content in PBS-DLS copolymer increases, the surface becomes progressively smoother, with less observable holes [23]. Similar results were obtained in SEM investigation in this study. This phenomenon alters the film permeability to gases and water vapor, which in turn might influence microbial growth in products packed in polymer-based packaging. Differences in microbial counts can be attributed to differences in dry mass of plant material used for microbial test (1 g of product taken to analysis) or differences in conditions inside sachets (for example relative humidity). While the studied films do not provide any noticeable antimicrobial activity on their own, further studies involving polymers modified with antimicrobial additives should be implemented to investigate the possibility of obtaining biopolymer-based food packaging with additional beneficial characteristics.
As demonstrated by Miceli et al. [39], who studied the evolution of shelf-life parameters of ready-to-eat escarole (Cichorium endivia var. latifolium) subjected to different cutting operations, chicory sourced from the local market and subjected to processes typical for the fresh-cut, ready-to-eat industry still contained a significant number of CFU/g. After undergoing industrial processing, the total psychrotrophic microorganisms and total mesophilic microorganisms counts were approximately 105 CFU/g. The number of coliform bacteria was 103 CFU/g, while fungi counts were 102 CFU/g. Over the course of storage, these values increased to 107, 107, 104, and 105 CFU/g for psychrotrophic microorganisms, mesophilic microorganisms, coliform bacteria, and fungi, respectively.
The limitation of microbial growth in packaged products can be achieved by incorporating antimicrobial additives into the polymer matrix. Naknaen P., 2014 used zinc oxide nanoparticles in the production of blown PBS, which was then used to package freshly cut apples [35]. Due to the presence of nanoparticles in the polymer matrix, a slowdown in the growth rate of aerobic bacteria was observed during product storage.

3.8. Microscopic and Scanning Electron Microscopic Evaluation

Figure 9 presents images from an inverted optical microscope and scanning electron microscope (SEM), showing the appearance and structure of leaves before packaging and after 48 and 120 h. In the optical microscope images, the fresh leaf displays a smooth surface and an undamaged central rib. The SEM image shows a more irregular leaf structure with visible stomata that are closed or partially open, indicating its freshness.
After 48 h of storage in sachets, clear changes can be observed. In each sample, the stomata are open, indicating high transpiration and water loss. While microscopic images of leaves packed in OPP and PBS-DLS sachets still show smooth surfaces with minor changes in color and structure, the leaf stored in a PBS sachet has undergone significant changes. It has become wrinkled, and browning of the leaf veins is visible.
After 120 h of storage, leaves packed in OPP and PBS-DLS sachets begin to lose color intensity, with slight browning appearing at the leaf edges. Chicory packed in PBS sachets is completely wrinkled, and its vascular structures are browned. In SEM images, stomata remain open in all observed leaves. However, in the case of leaves packed in PBS, the leaf structure is highly irregular, and the stomata are difficult to distinguish.
Observed changes in the micro- and nanostructure of leaves are in line with the results of moisture content analysis. Similar observations were performed previously for chicory (Lactuca sativa L.) packed in polyethylene packaging and stored at refrigerated temperature [40]. As Ru et al. mentioned [41], a major problem limiting the shelf-life of ready-to-eat chicory leaves is enzymatic browning, caused by the oxidation of phenol compounds to quinones in the presence of oxygen or peroxidase, followed by polymerization resulting in browning pigments formation. This process can be slowed down by packaging the chicory leaves in sachets that may limit the transmission rate of oxygen into the package.

4. Conclusions

Before concluding the results obtained, it should be noted that the films produced in this study were manufactured using methods other than those used in industry. This is due to the fact that the amounts of polymer obtained as a result of PBS-DLS synthesis are too small to be used in industrial-like conditions. Therefore, it was decided to conduct the tests using a solvent casting method, which allowed thin films to be obtained while small amounts of polymer were used. Further tests are required to confirm the results obtained using industrial methods.
Commercial OPP films exhibited ten times higher tensile strength than biodegradable PBS films. However, modification of the biopolymer by incorporation of co-monomeric units of dilinoleic succinate (DLS) into the PBS matrix significantly improved mechanical properties of the biopolymer. Additionally, OPP films exhibited the highest transparency in the visible light range, but also in the UV range. On the other hand, PBS and PBS-DLS films were noticed to have UV radiation blocking properties. The obtained films were used as packaging materials (sachets) for freshly cut chicory leaves. The chicory leaves were then stored in these sachets under refrigerated conditions for 48 h and 120 h. While OPP and PBS-DLS films provided good protection against moisture loss in chicory, leaves packed in PBS sachets lost significant weight during storage. It has to be mentioned that the type of packaging did not influence the microbial purity of leaf samples. However, the total count of mesophilic, psychrophilic or/and coliform bacteria detected for fresh chicory (before storage) was high. To decrease the growth of microorganisms which may be responsible for the decrease in chicory shelf-life, the antimicrobial coating can be applied on the packaging material. Additionally, to decrease browning of leaves, antioxidant coating could be applied on the described packaging. Summarizing, despite their weaker mechanical properties, biodegradable PBS-DLS films appear to be a promising alternative to synthetic OPP films as packaging for fresh, ready-to-eat food products. In their current state, the presented films are not yet as good as commercial OPP films, but the aim was to show that by modifying the matrix, it is possible to obtain PBS-DLS films with certain properties similar to those of commercial films. Further research shall focus on further improvement of PBS-DLS films so that their properties surpass those of commercial films. It may be carried out by the modification of PBS-DLS films with the active (antimicrobial and antioxidant) coatings, that may provide even better protection/preservation and significantly extend the shelf-life of food products.

Author Contributions

Conceptualization, S.M. and M.M.; methodology, M.M.; validation, S.M. and M.M.; formal analysis, S.M. and M.M.; investigation, S.M. and M.M.; data curation, S.M. and M.M.; writing—original draft preparation, S.M. and M.M.; writing—review and editing, M.E.F.; visualization, S.M. and M.M.; supervision, A.B. and M.E.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
CFUColony forming units
EBElongation at break
OPPOriented polypropylene
PBSPoly Butylene Succinate
PBS-DLSPoly butylene succinate-co-dilinoleic succianate
PCAPlate Count Agar
SEMScanning electron microscope
TSTensile strength

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Coatings 15 01095 g001
Figure 1. Chicory packed in prepared sachets. OPP on the left, PBS-DLS in the middle, PBS on the right.
Figure 1. Chicory packed in prepared sachets. OPP on the left, PBS-DLS in the middle, PBS on the right.
Coatings 15 01095 g001
Coatings 15 01095 g002
Figure 2. UV-Vis spectra of OPP, PBS and PBS-DLS films.
Figure 2. UV-Vis spectra of OPP, PBS and PBS-DLS films.
Coatings 15 01095 g002
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Figure 3. SEM photos of OPP, PBS and PBS-DLS films. Magnification 1000 times and an accelerating voltage of 10 kV.
Figure 3. SEM photos of OPP, PBS and PBS-DLS films. Magnification 1000 times and an accelerating voltage of 10 kV.
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Figure 4. Relative humidity inside prepared OPP, PBS and PBS-DLS sachets containing chicory.
Figure 4. Relative humidity inside prepared OPP, PBS and PBS-DLS sachets containing chicory.
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Coatings 15 01095 g005
Figure 5. The total coliforms bacteria count detected from fresh chicory and stored samples.
Figure 5. The total coliforms bacteria count detected from fresh chicory and stored samples.
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Figure 6. The total yeast and mold count detected from fresh and stored chicory leaves.
Figure 6. The total yeast and mold count detected from fresh and stored chicory leaves.
Coatings 15 01095 g006
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Figure 7. The total count of mesophilic bacteria detected from fresh and stored chicory leaves.
Figure 7. The total count of mesophilic bacteria detected from fresh and stored chicory leaves.
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Figure 8. Total count of psychrophilic bacteria detected from fresh and stored chicory leaves.
Figure 8. Total count of psychrophilic bacteria detected from fresh and stored chicory leaves.
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Figure 9. Microscopic and SEM photos of chicory leaves before and after storage.
Figure 9. Microscopic and SEM photos of chicory leaves before and after storage.
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Table 1. Thickness and mechanical characteristics of OPP, PBS and PBS-DLS films.
Table 1. Thickness and mechanical characteristics of OPP, PBS and PBS-DLS films.
SampleThickness (mm)Tensile Strength (MPa)Elongation at Break (%)
OPP0.025 ± 0.003 a104.36 ± 10.03 b231.84 ± 20.30 c
PBS0.024 ± 0.002 a10.96 ± 0.68 a38.16 ± 12.36 a
PBS-DLS0.035 ± 0.004 b6.36 ± 0.62 a132.30 ± 25.08 b
Values are means ± standard deviation. Means with different letters (a–c) in columns are significantly different at p < 0.05.
Table 2. Color (L*, a*, b*), opacity and transmittance of OPP, PBS and PBS-DLS films.
Table 2. Color (L*, a*, b*), opacity and transmittance of OPP, PBS and PBS-DLS films.
SampleL*a*b*OpacityT660 (%)T280 (%)
OPP53.29 ± 0.54 a20.41 ± 0.16 a42.11 ± 1.72 a7.20 ± 0.12 a89.3381.56
PBS53.93 ± 0.71 b20.28 ± 0.30 a41.83 ± 0.38 a16.30 ± 0.91 b17.606.95
PBS-DLS53.69 ± 0.31 a,b20.08 ± 0.14 b40.43 ± 1.43 b7.74 ± 0.09 a27.5810.14
Values are means ± standard deviation. Means with different letters (a,b) in columns are significantly different at p < 0.05.
Table 3. WVTR and Average Water Contact Angle of Films.
Table 3. WVTR and Average Water Contact Angle of Films.
SampleWVTR [g/m2·day]Average Water Contact Angle [°]
OPP6 ± 4 c68 ± 2 a
PBS1350 ± 294 a51 ± 4 b
PBS-DLS288 ± 26 b71 ± 5 a
Values are means ± standard deviation. Means with different letters (a–c) in columns are significantly different at p < 0.05.
Table 4. Moisture content of fresh chicory leaves and after 48 and 120 h refrigerated storage.
Table 4. Moisture content of fresh chicory leaves and after 48 and 120 h refrigerated storage.
SampleMoisture Content [%]
0 hControl94.66 ± 0.95 a
48 hOPP92.19 ± 1.93 a
PBS90.12 ± 0.62 a
PBS-DLS92.71 ± 2.26 a
120 hOPP91.63 ± 2.71 a
PBS59.73 ± 13.62 b
PBS-DLS91.88 ± 0.35 a
Values are means ± standard deviation. Means with different letters (a,b) in columns are significantly different at p < 0.05.
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MDPI and ACS Style

Macieja, S.; Mizielińska, M.; El Fray, M.; Bartkowiak, A. Novel Poly(butylene succinate-dilinoleic succinate) Films in Packaging Systems for Fresh Cut Chicory. Coatings 2025, 15, 1095. https://doi.org/10.3390/coatings15091095

AMA Style

Macieja S, Mizielińska M, El Fray M, Bartkowiak A. Novel Poly(butylene succinate-dilinoleic succinate) Films in Packaging Systems for Fresh Cut Chicory. Coatings. 2025; 15(9):1095. https://doi.org/10.3390/coatings15091095

Chicago/Turabian Style

Macieja, Szymon, Małgorzata Mizielińska, Mirosława El Fray, and Artur Bartkowiak. 2025. "Novel Poly(butylene succinate-dilinoleic succinate) Films in Packaging Systems for Fresh Cut Chicory" Coatings 15, no. 9: 1095. https://doi.org/10.3390/coatings15091095

APA Style

Macieja, S., Mizielińska, M., El Fray, M., & Bartkowiak, A. (2025). Novel Poly(butylene succinate-dilinoleic succinate) Films in Packaging Systems for Fresh Cut Chicory. Coatings, 15(9), 1095. https://doi.org/10.3390/coatings15091095

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