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Article

Beer Bagasse as Filler for Starch-Based Biocomposite Films for Food Packaging Applications

by
Paula Gómez-Contreras
,
Maite Cháfer
,
Amparo Chiralt
and
Chelo González-Martínez
*
Instituto Universitario de Ingeniería de Alimentos FoodUPV, Universitat Politècnica de València, 46022 València, Spain
*
Author to whom correspondence should be addressed.
Biomass 2025, 5(3), 46; https://doi.org/10.3390/biomass5030046
Submission received: 30 June 2025 / Revised: 4 August 2025 / Accepted: 5 August 2025 / Published: 12 August 2025
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Abstract

Development of biodegradable packaging materials and valorization of agri-food waste are necessary to produce more sustainable materials while reducing the environmental impact. Starch-based biocomposite films reinforced with beer bagasse fractions with different purification degrees were developed and characterized in structural, mechanical, thermal and optical properties. To this aim, 5% and 10% (w/w) of either beer bagasse (BB) or its lignocellulosic-rich fibers (LF), obtained by subcritical water extraction at temperatures between 110 and 170 °C, were incorporated into starch matrices. Elastic modulus and tensile strength values increased by up to eight-fold and 2.5-fold, respectively, compared to the control film. The incorporation of BB or LF significantly enhanced the mechanical resistance of the films. In general, the increment in the filler:polymer ratio significantly increased the EM values (p < 0.05), while decreasing the stretchability of the films around 80–85%, regardless of the type of filler. This effect suggests a good interfacial adhesion between the fillers and the polymeric matrix, as observed by FESEM. The biocomposite films exhibited a dark reddish appearance, reduced transparency, light blocking barrier capacity and remarkable antioxidant activity due to the presence of phenolic compounds in the fibers. The water vapor and oxygen barrier properties were better preserved when using the more purified LF obtained at 170 °C. Overall, starch films reinforced with beer bagasse fractions showed strong potential for the development of biodegradable food packaging materials.

1. Introduction

Packaging plays an essential role in the food industry, ensuring products’ preservation, quality and safety until consumption, protection and transport. In recent years, the development of eco-friendly packaging has become key to reducing waste generation and minimizing plastic-related pollution without compromising functionality or efficiency in food preservation [1,2]. Approximately one-third of environmental pollution is generated by packaging used in everyday consumption, particularly in the food industry [3]. Therefore, innovation in biodegradable and renewable materials is a priority to promote a more environmentally responsible production and consumption model [4].
Among biodegradable materials, starch is particularly attractive as a film-forming agent and has gained significant interest as a viable alternative due to its renewability and cost-effectiveness. However, its inherent limitations, such as brittleness and sensitivity to moisture, limit its application [1,2,3,4]. To address these challenges, researchers have explored the reinforcement of starch-based films with different fillers, usually based on cellulose and its derivatives. For example, lignocellulose fibers, lignin, cellulose nanofibrils and nanocrystals have been reported to improve the mechanical resistance of any given polymer, which strongly depend on the type and fraction of the cellulose filler and the dispersion and adhesion between the matrix and the filler. The interest in using lignocellulosic fibers as fillers for packaging applications has increased over the last years due to the environmental pollution and high cost of cellulose extraction [5,6,7]. Thus, different lignocellulose fibers (LF) from sugar cane bagasse, wheat straw rice straw, wood, flax and hemp have been already incorporated into polymeric films as reinforcement agents [5]. These LF can be also obtained from agri-food waste, thus allowing these residues to be processed and transformed into high-value biomaterials, offering a viable alternative for producing eco-friendly packaging. Furthermore, the sustainable management of agri-food waste and byproducts represents a key strategy to reduce the environmental impact of the food industry [8].
Brewer spent grain or beer bagasse (BB) is the insoluble and solid part of the malted barley brewer spent grain produced during beer production, and accounts for 85% of the total waste generated by the brewing industry. It is composed of approximately 73% lignocellulose fibers (on a dry weight basis), being around 17% cellulose, 28% hemicellulose, 28% lignin and 20% proteins [6]. In addition, BB is also a rich source of phenolic compounds such as hydroxycinnamic acids (p-coumaric, ferulic, sinapic, and caffeic acids), with proven antioxidant and antimicrobial activity [7]. Owing to its composition, this lignocellulosic waste has high potential to be used as a filler for the development of biodegradable food packaging materials, while promoting a circular economy model, optimizing the use of resources and reducing the generation of solid waste [8]. Lin et al. developed cast films based on poly(vinyl alcohol) (PVA), glycerol, BB and hexamethoxymethylmelamine as a cross-linking agent [9]. The films exhibited acceptable mechanical resistance with up to 40% BB content, which significantly decreased when using greater concentrations. Castanho et al. incorporated different sizes and contents of BSG (1–5%) into starch-based films. The composite films showed a slightly improved tensile strength and thermal stability compared to pure TPS films, thus acting as a promising filler due to the compatibility with the polymer matrix and increased polymer crystallinity [10]. Revert et al. found that the incorporation of BB particles into polypropylene (PP) matrix using maleated polypropylene as compatibilizer agent reduced costs and provided higher thermal stability to the neat PP films, although their mechanical properties were worsened [11]. Ferreira et al. investigated BB-based food-packaging trays made from BB, incorporating chitosan and glyoxal [12]. However, to the best of our knowledge, no studies have specifically focused on the use of lignocellulosic fibers from BB as fillers in biodegradable packaging materials.
The main objective of this study is to develop biocomposite packaging materials for food applications, using starch modified films with PCL and beer bagasse (BB) or its lignocellulose fibers (LF). The effect of filler content (5% and 10%) and type (BB or its LFs) on the film functional properties was evaluated. The lignocellulose fibers from BB, with different cellulose purities, were obtained by subcritical water extraction at four temperatures (110, 130, 150, and 170 °C). Films were obtained by melt-blending of the components and thermo-compression. The functional properties of the films, such as optical, tensile, barrier and thermal properties were analyzed together with the microstructure and potential antioxidant capacity.

2. Materials and Methods

Cassava starch (9% amylose) was supplied by Quimidroga S.A. (Barcelona, Spain), glycerol (99.5% purity), phosphorus pentoxide (P2O5, 98.2% purity) and magnesium nitrate (Mg(NO3)2, 98% purity) were from Panreac Química, S.A. (Castellar del Vallès, Barcelona, Spain) and polycaprolactone (PCL), with a molecular weight between 70,000–90,000 daltons from Aldrich Chemistry (Sigma–Aldrich Co., LLC, Madrid, Spain).
Beer bagasse (BB), kindly supplied by a brewery factory located in Valencia, was previously dried, milled and defatted as reported in a previous study [13]. The defatted powder was submitted to subcritical water extraction (SWE) using a ratio solids–water of 1:8 in a pressure reactor (Model 1-TAP-CE, 5 L capacity, Amar Equipment PVT. LTD, Mumbai, India) at different temperatures (110, 130, 150, 170 °C) and the corresponding pressures, which were optimized in a previous study [13]. After each extraction step, the dispersions were filtered with a pore size less than 0.5 mm (Filterlab, Barcelona, Spain) and the solid and liquid fractions were separated. The insoluble lignocellulosic fraction (LF) was enriched to a different extent in cellulose due to the selective extraction of non-cellulosic components. The chemical composition of the raw BB and the different LFs obtained at each temperature is shown in Table 1.

2.1. Film Preparation

The different components were melt-blended in an internal mixer (Haake PolyLab QC, Thermo Fisher Scientific, Dreieich, Germany) at 160 °C and 50 rpm for 10 min. The blend sample consisted of previously dried cassava starch (60 °C for 24 h in a vacuum oven), 35% (w/w) glycerol with respect to the starch, as plasticizer, and 10% (w/w) PCL with respect to the starch, incorporating or not 5% and 10% (w/w) of the defatted BB or the LF obtained at different temperatures (LF110, LF130, LF150, and LF170). The ratio of glycerol was selected as the minimal amount that promoted the formation of thermoplastic starch by thermal processing, without reducing the film performance [14]. The different formulations (Table 1) were named SP, SP-xBB and SP-xLFy, where x = mass fraction of beer bagasse or LF incorporated (5 or 10%) and y = extraction temperature. Once melt-blended, the formulations were cold ground with N2 and conditioned in a desiccator with an oversaturated Mg(NO3)2 solution (53% relative humidity (RH)) for one week. The films were obtained by thermo-compressing 8 g of each pre-conditioned formulation by means of a hot plate hydraulic press (LP20, Labtech Engineering, Bangkok, Thailand) by preheating for 1 min at 160 °C, compressing for 6 min at 160 °C (2 min at 30 bars and 4 min at 100 bars) and cooling for 3 min at approximately 70 °C. For the characterization of microstructure and thermal analysis, the films were previously conditioned at 0% RH (using P2O5).

2.2. Characterizations of the Films

2.2.1. Tensile, Barrier and Optical Properties

The tensile properties of the films, such as tensile strength at break (TS), elongation at break (E) and elastic modulus (EM), were measured in eight replicates for each formulation according to ASTM D882 [15] using a universal testing machine (TA.XTplus, model, Stable Micro Systems, Haslemere, England). The 25 mm × 100 mm conditioned film samples were gripped by two jaws initially 50 mm apart and stretched at a crosshead speed of 50 mm min−1.
The water vapor permeability (WVP) of the films was obtained gravimetrically according to ASTM E96/E96M [16], with some modifications [17]. Thus, 3.5 cm diameter film samples (conditioned at 53% RH and 25 °C) were sealed in Payne permeability cups (Elcometer SPRL, Hermelle/s Argenteau, Belgium) containing 5 mL of distilled water (100% RH) and placed into desiccators at 25 °C with 53% RH. The cups were weighed periodically (ME36S, Sartorius, ±0.00001 g, Fisher Scientific, Hampton, NH, USA) every 2 h for 30 h. The WVP of the films was determined from the water vapor transmission rate, which was determined from the slope of the weight loss vs. time curve. For each film, the analysis was performed in triplicate.
The oxygen permeability (OP) of the films was determined in conditioned films, according to ASTM D3985-05 [18] methodology using an Oxygen Permeation Analyzer (Model 8101e, Systech Illinois, IL, USA) at 25 °C and 53% RH, once the equilibrium was reached and using an exposure area during the tests of 50 cm2 for each formulation. The OP of the films was calculated in duplicate according to Equation (1):
O P = O T R ∆ p   ×   l
where OTR is the oxygen transmission rate (cm3/m2 s), l is the thickness of the material (m), ∆ p is the difference in partial pressure of oxygen between the two sides of the film (Pa).
The optical properties of 53% RH conditioned films were measured in triplicate using a Minolta spectrocolorimeter (Model CM-3600d, Tokyo, Japan), following the Kubelka–Munk theory. Thus, the infinite reflection spectra (R∞) and internal transmittance (Ti) of the films (in the range of 400 to 700 nm, including the specular component) were obtained by measuring the films’ reflectance on white and black backgrounds (Rg and R0, respectively) as proposed by [19]. Additionally, the CIELab color coordinates, luminosity (L*), hue (h*) and chroma (C*) were also calculated from the reflectance of a theoretically infinitely thick material layer using D65 illumination and a 10° observer.

2.2.2. Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA)

DSC measurements of samples (5–10 mg) in aluminum crucibles were carried out in duplicate under a flow of nitrogen (10 mL/min) in a differential scanning calorimeter (DSC 1 StarSystem, Mettler Toledo, Schwarzenbach, Switzerland). The temperature scan profile was the following: the sample was heated from −25 °C to 230 °C at 10 °C/min, held for 5 min at 230 °C, cooled down to −25 °C and heated up again from −25 to 230 °C at 10 °C/min.
A thermogravimetric analyzer (TGA 1 Stare System analyzer, Mettler-Toledo, Switzerland) was used to obtain the mass loss vs. temperature (TG) curve and its derivative (DTG) of the P2O5 conditioned samples. To this end, approximately 8–10 g of sample was placed into an alumina crucible and heated from 25 °C to 700 °C at 10 °C/min under nitrogen flow. The measurements were taken in duplicate for each film.

2.2.3. Infrared Spectroscopy (FTIR) and Microstructural Analysis

The Attenuated Total Reflectance–Fourier Transform Infrared Spectroscopy (ATR–FTIR) of films was determined in duplicate using a Bruker spectrophotometer (Bruker, Germany) in the spectra range between 4000 to 500 cm−1. The spectra were averaged over 32 scans using a spectral resolution of 2 cm−1.
Microstructural analysis of the surface and cross sections of the films was performed by means of a Field Emission Scanning Electron Microscope, FESEM (Supra™ 25-Zeiss, Oberkochen, Germany) using an accelerating voltage of 2 kV after being gold coated with an EM MED020 sputter coater (Leica BioSystems, Barcelona, Spain).

2.2.4. Antioxidant Activity

The antioxidant capacity of the films was evaluated using the ABTS method [19]. The ABTS∙+ radical was generated by reacting an ABTS solution (7 mM) with potassium persulfate (2.45 mM) for 16 h in the dark. The ABTS∙+ solution was then diluted in ethanol until an absorbance of 0.700–0.800 was reached at 734 nm. Film fragments (1 cm2) were incubated with 5 mL of this solution and shaken at 80 rpm in the dark. The absorbance (Af) was measured at 734 nm after different reaction times (10, 30, 60, 90, and 120 min), using a solution without a sample as a blank (Ab) [20]. The assay was performed in triplicate, and the antioxidant activity was expressed as percentage inhibition using Equation (2).
I n h i b i t i o n   % = 100 × A b − A f A b

2.2.5. Statistical Analysis

Statgraphics Plus for Windows 5.1 (Manugistics Corp., Rockville, MD, USA) was used to carry out the statistical data analysis through a variance analysis (ANOVA). To distinguish the samples, Fisher’s least significant difference (LSD) was used at the 95% confidence level.

3. Results and Discussion

Table 2 shows the composition and the white index of the defatted beer bagasse (BB) and the lignocellulosic fibers (LF) obtained by SWE at different temperatures, as reported in a previous study [13]. This composition could affect the fibers properties (interphase area, shape, structure and uniformity) which, in turn, could affect the adhesion forces and compatibility with the polymer matrix, thus affecting the functional properties of the films. As can be observed, the BB and the LF treated at the lower temperatures showed higher hemicellulose content than the other fillers, in agreement with its selective removal by SWE [13]. The residue with the greatest lignin, protein content and cellulose purity and lowest hemicellulose content was the LF at 170 °C. This is due to the high extraction yield of SWE at this temperature (41 g extract/100 g BB) previously reported [13], which promoted the enrichment of LF in cellulose and other non-soluble compounds. Furthermore, this lignocellulosic fiber exhibited the lowest white index, in agreement with the increasing purification degree of the fibers when the extraction temperature rose. The SWE treatment could also affect fiber morphology, i.e., shape, structure and uniformity [19,21].

3.1. Morphological Characteristics of Films

Figure 1 and Figure 2 show the FESEM images of the cross-section of the composites incorporating or not the different fillers (BB and the LF obtained at the different temperatures). The filler free films showed a continuous and homogeneous phase, which corresponded to the starch matrix, and very small, dispersed domains of PCL that were not completely miscible with starch, as described in previous studies [22,23]. The PCL particles appeared evenly distributed and exhibited the typical cryofracture with thread-like formations due to their high stretchability. Small cavities were also observed, corresponding to voids left by the PCL particles upon cryofracture of the sample.
Both the starch continuous phase and the dispersed PCL domains were also observed in the films containing the different fillers (Figure 1 and Figure 2), but other dispersed particles can also be observed, corresponding to the BB or LF immiscible components, such as cellulose. Likewise, the size of dispersed particles, including the PCL domains, were greater as the filler content rose. This suggests the poor dispersion of PCL in the starch matrix when BB or LF are present in the blend. Some BB and LF components, such as phenols, lignin or carbohydrates, could be totally or partially miscible within the starch continuous matrix, modifying their composition, whereas other components appeared dispersed as solid irregular particles.
The films incorporating the LF fillers, where some of the BB compounds were eliminated, exhibited dispersed particles embedded within the continuous matrix, fully coated by a dense polymer layer covering their surface, regardless of the type of filler. This suggests a good integration and compatibility of the LF within the polymeric matrix. It is remarkable that at 5% the LF were well dispersed in the matrix, whereas at 10% filler concentration, the presence of large agglomerates or clusters was noticeable. The different LF composition, depending on the SWE temperature, had not a marked effect on the film microstructure, which was markedly affected by the filler ratio. These differences in the microstructure of the different films could affect their functionality, mainly barrier and mechanical performance.

3.2. Mechanical and Barrier Properties

Table 3 shows the values of the elastic modulus (EM), tensile strength and deformation at the break point (E%) of the different formulations. The values of the mechanical parameters of the blend starch-PCL films agree with those found by Ortega-Toro et al. [21] for similar blends. The presence of PCL in starch films exerted a positive effect on the mechanical properties of the neat starch films, leading to more rigid and stretchable samples with greater resistance to break [21,22].
The incorporation of the beer bagasse and its lignocellulosic fibers obtained at the different temperatures significantly increased (p < 0.05) the mechanical strength of the films, leading to a reinforcement effect. Thus, the filler-loaded films were up to 177% stiffer and 150% more resistant to break (greater EM and TS values, respectively) and around 37–97% less extensible (lower E%) than the control film (SP) (p < 0.05). BB and LF composition mainly consist of lignocellulosic material (cellulose, hemicellulose and lignin) and proteins that could favor the compatibility with starch components during the melt-blending step, as has been observed in the FESEM micrographs. Furthermore, the presence of filler-polymer interactions, i.e., between the cellulose and the amylopectin chains, could enhance the inter-chain forces and favor a good interfacial adhesion, thus leading to more mechanically resistant films, as has been previously reported by other authors working with different fibers [24,25,26]. Moreover, the crystallinity associated with the hydrogen bonds of the cellulosic fraction could also contribute to the increment in the rigidity of the matrix [26]. On the other hand, the reduction in the E% values can be attributed to the discontinuities introduced within the polymer matrix and the limitations in the polymer chain mobility due to the presence of fibers [20]. Similar trends were observed in other studies based on starch films incorporating different fillers such as rice straw fibers [27] or microcrystalline cellulose [28,29].
The type of filler and the filler content significantly affected the mechanical performance of the films. In general, the incorporation of BB into SP films promoted a lower increment in the mechanical resistance and lower extensibility of the films than those incorporating LF. This can be attributed to the greater cellulose content and enhanced surface roughness of the thermally treated LF, which increases the surface area available for interaction with the matrix, thus contributing to a more improved surface adhesion and better integration of fibers [30]. Although no notable effect of the LF extraction temperature on the films mechanical response was found, the composite films with the LF obtained at 170 °C exhibited the greatest stretchability (p < 0.05), regardless of the ratio filler:polymer used. The high cellulose and lignin contents of this LF and its very low hemicellulose concentration (2%) due to its selective dissolution under subcritical water conditions could facilitate its integration into the polymeric matrix, thus leading to a greater film stretchability. Moreover, the increment in the filler:polymer ratio significantly increased the EM values (p < 0.05), while decreasing the stretchability of the films around 80–85%, regardless of the type of filler. Therefore, these results showed the reinforcing capacity of beer bagasse fillers when incorporated into starch-based films, likely due to the good compatibility and surface adhesion of the fillers within the TPS matrix, which depended on the filler content and composition.
Table 4 shows the thickness, moisture content and permeabilities values of the different formulations. No significant differences were observed in the thickness and moisture content of the films. The mean moisture content of the films was around 9.5–10.7%, slightly greater for starch films incorporating the different fillers (BB or LF). As can be observed in Table 3, the incorporation of the filler and the increment in the filler:polymer ratio worsened the gas barrier capacity of the SP films, especially when using 10% BB. Thus, the water vapor permeability values significantly increased, up to 64%, in the SP-10BB film in comparison with the control (SP), this increment being only around 17% in films loaded with the LF obtained at the highest temperature (170 °C), thus suggesting a better compatibility of this filler with the matrix, as commented on above. On the other hand, all the composite films exhibited similar or higher oxygen barrier capacity than the control film. In general, the use of the non-treated BB and the increment in the filler:polymer ratio worsened the gas (water and oxygen) barrier capacity of the films. Although an increase in the effective tortuosity factor is expected with the filler addition leading to a greater barrier capacity of the composite films, the effect of other factors on the film’s permeability, such as dispersion degree of the particles in the polymer matrix and their interfacial adhesion force, filler chemical composition, morphology and crystallinity degree, among others, would also contribute to modifying the transport of the water and oxygen molecules through the films [31]. Thus, films incorporating non-treated fillers (BB) richer in hydrophilic hemicellulose could promote the transport of water molecules through the filler, while this effect was less marked in film incorporating the fiber LF170 with lower hemicellulose and more lignin content. Moreover, the increment in the filler content could promote the filler aggregation, leading to an uneven distribution of the fibers in the starch matrix, which favored the preferential path for water, thus increasing the WVP values. Similar results were obtained by other studies when increasing the microcrystalline cellulose (MCC) content from 6 to 9% in starch-based films [32]. Among the filler-loaded films, the SP films incorporating LF170 (5 or 10%) showed the best water and oxygen barrier properties.

3.3. Optical Properties and Appearance of Starch Films

Table 5 shows the optical properties of the different films, in terms of luminosity, hue, and chroma and internal transmittance at 550 nm, and Figure 3 displays the internal transmittance values spectra together with the film’s appearance. Control films (SP) were colorless and highly transparent, in agreement with their high Ti values. As can be observed, the incorporation of the fillers significantly modified the appearance of the films, which became opaquer with a reddish-brown, darker and more saturated color compared to control films, except SP-LF170, which exhibited lower C*ab values (less saturated). These changes could be attributed to the intrinsic color of the initial fillers (beer bagasse and fibers). Furthermore, the filler-loaded films exhibited strong light absorption below 550 nm wavelength (Figure 3), blocking up to 100% of light compared to the control film, thus acting as an effective light barrier. This enhanced light-blocking capacity could be attributed to the strong absorbance of aromatic structures and functional groups present in the polyphenolic compounds linked to the vegetal lignocellulosic fibers, the so-called insoluble-bound or non-extractable polyphenols. In fact, Saura-Calixto et al. reported that the polyphenols associated with fibers accounted for 30 to 60% of total polyphenols in red wine [33]. All the mentioned effects were significantly more pronounced (p < 0.05) in films incorporating LF compared to those containing non-treated BB, particularly in formulations with higher LF content (10%) and those obtained at elevated temperatures (150 and 170 °C).
The phenolic compounds associated with the cell wall materials exhibit functional specific properties such as prebiotic and antioxidant effects [34,35,36,37]. Thus, the presence of phenolic compounds in the composite films was confirmed through their antioxidant capacity measured via the ABTS∙+ radical scavenging capacity assay. Figure 4 shows the percentage of ABTS∙+ inhibition by the filler-loaded films, as a function of the film contact time with the radical solution. A progressive release of active compounds was observed, especially during the first 30 min, thus reflecting their capacity to scavenge ABTS∙+ radical. The release of phenolic compounds was notably higher in films containing the higher filler content (10%) and those incorporating LF extracted at 170 °C, which were also those exhibiting the greatest light-blocking capacity. The SWE process promoted the autohydrolysis of antioxidant compounds from the plant matrix, which favors their release and reaction with the radical. Additionally, the formation of new antioxidants, such as Maillard compounds, during SWE can contribute to the antioxidant capacity of the films [38]. Both autohydrolysis and neoformation of antioxidant compounds increased as the temperature rose.

3.4. Thermal Stability of the Films

The TGA and their derivative curves (DTGA) for the different starch-based films with and without fillers, conditioned at 0% RH, are shown in Figure 5. SP films exhibited a small mass loss step that occurred between 150–220 °C, attributed to the bonded water and glycerol. After this, two differentiated degradation stages were observed, at 314 °C and 400 °C, corresponding to the maximum degradation rate temperatures of plasticized-starch and PCL, respectively [39,40]. From about 220 °C, thermal degradation of SP occurred in several steps, associated to scission of glycosidic bonds and the formation of glycosidic radicals and starch depolymerization. On the other hand, the thermal degradation of PCL has been demonstrated to proceed through a combination of radical-mediated cleavage driven by the decomposition of hydroxy end-groups and random chain scission [41]. The last degradation step of the films, between 470 and 640 °C, was attributed to the degradation of the first step fragmentation products.
The presence of fillers hardly modified the degradation pattern of the films, due to their relatively low mass ratio in the composites (5 and 10%). The overlapping of the degradation steps of the filler components slightly modifies de TGA curves. The degradation temperatures of the main filler’s components are 150–350 °C, 275–350 °C, and 160–900 °C, for hemicellulose, cellulose and lignin, respectively. This agrees with that observed in other studies carried out with starch and PVA based films loaded with cellulose fibers [21,39]. The major weight losses in the TGA curve of composite films (around 50%) took place between 260 and 340 °C, which corresponds to the starch degradation, with no notable changes with respect to the filler free film. However, the incorporation of the fillers into SP films reduced the main peak in DGTA curves, while slightly increased the temperature peak, especially for fillers obtained at high temperature in SWE treatment, which were richer in cellulose and lining. This greater richness makes their effect on the thermal degradation curve more noticeable, since the degradation of these major compounds overlapped to a greater intensity with the polymer curve. Other authors have also observed a decrease in the DTGA peak of the polymer when incorporating different natural fibers into polymeric matrices [41,42]. Chanthavong et al. reported a thermal stability enhancement of the composite film when incorporating microcellulose fibers with higher thermal stability. Furthermore, an increment in the residual weight mass in the composites in comparison with the control films was observed, which can be attributed to the contribution of the fiber components [43].
The thermal properties of the neat PCL films and SP films incorporating or not the fillers were analyzed by DSC. Figure 6 shows the typical thermogram for PS and two PS incorporating lignocellulosic fibers (LF) as a filler, where the only thermal events observed were those corresponding to the PCL. As can be deduced from the thermal behavior in DSC analyses, PCL crystallization in the films was greatly inhibited. In some samples, a very small melting enthalpy was observed during the heating step (melting temperature around 60 °C), while cold crystallization (crystallization temperature around 56 °C) was observed before the subsequent melting endotherm in other cases. The crystallinity degree of PCL deduced from the melting enthalpy (corrected with the cold crystallization enthalpy when this occurred) ranged between 0% in films without fillers and 25% in filler-loaded films. Therefore, the small ratio of PCL and its potential interactions with starch chains led to amorphous PCL in the blend films, but the incorporation of fibers promoted the PCL crystallization to some extent. The nucleating effect of different fibers and cellulose nanocrystals for the PCL crystallization has also been described by other authors [44,45,46,47,48,49].

3.5. FTIR Analysis

FTIR spectra curves show absorbance peaks corresponding to the characteristic functional group of the film components. Figure 7 displays the spectra of the control SP films and those containing 10% filler, as the films incorporating 5% exhibited similar FTIR profiles. The FTIR spectra of SP films exhibited a characteristic broad absorption band around 3600–3000 cm−1, corresponding to the -OH stretching vibrations of plasticized starch, attributed to hydrogen-bonded hydroxyl groups. The peak at 2918 cm−1 was associated with the aliphatic saturated C-H stretching vibration of CH2 groups. Additionally, an absorption band at 1725 cm−1 was observed, corresponding to the carbonyl groups (C=O) characteristic of PCL [49,50]. The peak at 1632 cm−1 could be due to the O-H bending vibrations from absorbed water and free water, whereas the peak at 1078 cm−1 is characteristic of thermoplastic starch (TPS), corresponding to C–O bonds of starch C–O–H groups [51]. The bands at 1144, 1078 and 1013 cm−1 are related to the ordered structures of starch, whereas the band at 995 cm−1 is associated with its amorphous regions.
The FTIR spectra of the filler-loaded films were similar to those of the SP films. Nevertheless, a slight shift of the peak at 3274 cm−1 towards lower wavenumbers (ranging between 3272 to 3268 cm−1) was observed. This shift suggests that the newly formed hydrogen bonds between the fillers and starch are stronger than the intra- and intermolecular hydrogen bonds between the hydroxyl groups of starch chains. Similar results were reported by Boudiema et al. working with thermoplastic starch and natural cellulose fibers [52]. Furthermore, a change in the relative intensity of the bands at 1013 and 995 cm−1 was detected in the filler-loaded films compared to PS films. Thus, the 995:1011 absorbance ratio (Figure 7), which has been proven to positively correlate with a greater structural organization of starch [53,54], significantly decreased in the composite films. Thus, the obtained results suggested that the formation of ordered starch structures into the PS films was more inhibited when the fillers were incorporated.

4. Conclusions

The incorporation of beer bagasse (BB) and its lignocellulosic fibers (LF) obtained at the different temperatures by subcritical water extraction into starch-based films promoted changes in their functional properties, mainly in terms of mechanical resistance, gas and light barrier capacity and antioxidant activity. Thus, these fillers significantly increased the stiffness and the mechanical strength of the films, leading to a reinforcement effect due to good interfacial adhesion among components, as confirmed by FESEM observations. The FTIR spectral modifications observed in the FTIR spectra of the filler-loaded films suggested the presence of molecular interactions between starch and the incorporated fillers, and a decrease in the starch molecular order. Furthermore, the incorporation of the filler and the increment in the filler:polymer ratio worsened the water vapor barrier capacity of the SP films. All the filler-loaded films exhibited strong light absorption at wavelength range of 400–550 nm, blocking up to 100% of light, thus acting as an effective light barrier. This strong light barrier effect is particularly relevant for active packaging applications requiring protection against light-induced oxidation. Moreover, these formulations exhibited significantly enhanced antioxidant activity, likely due to the presence of phenolic compounds and lignin structures retained in the fibers. The barrier and antioxidant capacity of the films was better promoted when LFs were used in composites, especially when obtained at 170 °C, whereas BB is most cost-effective due to its direct incorporation in the film. These findings highlight the potential use of beer bagasse or its lignocellulosic fibers as film fillers for the development of biodegradable packaging materials with improved functionalities.

Author Contributions

Conceptualization, A.C. and C.G.-M.; Methodology, M.C. and P.G.-C.; Formal Analysis, P.G.-C.; Writing—Original Draft Preparation, P.G.-C. and M.C.; Writing—Review & Editing, A.C. and C.G.-M.; Funding Acquisition, C.G.-M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by MCIN/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR (project TED2021-132295B-I00). The authors also thank the Generalitat Valenciana (GVA) for the grant received through the GRISOLIA program (CIGRIS/2021/033).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

References

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Figure 1. FESEM micrographs (×1000) of the cross-section of starch and PCL blend films (SP) incorporating or not different contents of beer bagasse (5%: SP-5BB, 10%: SP-10BB).
Figure 1. FESEM micrographs (×1000) of the cross-section of starch and PCL blend films (SP) incorporating or not different contents of beer bagasse (5%: SP-5BB, 10%: SP-10BB).
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Figure 2. FESEM micrographs (×2000) of the cross-section of starch-based films loaded with 5% or 10% of beer bagasse lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
Figure 2. FESEM micrographs (×2000) of the cross-section of starch-based films loaded with 5% or 10% of beer bagasse lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
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Figure 3. Visual appearance and vis spectra of the starch-based films loaded with 5% or 10% of beer bagasse (BB) or its lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
Figure 3. Visual appearance and vis spectra of the starch-based films loaded with 5% or 10% of beer bagasse (BB) or its lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
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Figure 4. Inhibition of the ABTS∙+ radical by the starch-based films loaded or not with the different fillers: beer bagasse (BB) or its lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C) at 5% content (a) and 10% content (b).
Figure 4. Inhibition of the ABTS∙+ radical by the starch-based films loaded or not with the different fillers: beer bagasse (BB) or its lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C) at 5% content (a) and 10% content (b).
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Figure 5. Thermogravimetric analysis (TGA) curves (above) and first derivative curves (DTG) curves (below) of starch-based films loaded or not with 5% or 10% of beer bagasse (BB) or its lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
Figure 5. Thermogravimetric analysis (TGA) curves (above) and first derivative curves (DTG) curves (below) of starch-based films loaded or not with 5% or 10% of beer bagasse (BB) or its lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
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Figure 6. Typical DSC thermograms (1st heating scan) of SP and SP films incorporating 5 and 10% of lignocellulosic fibers (LF) obtained at 110 °C.
Figure 6. Typical DSC thermograms (1st heating scan) of SP and SP films incorporating 5 and 10% of lignocellulosic fibers (LF) obtained at 110 °C.
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Figure 7. FTIR spectra of (a) SP films incorporating or not 10% of different fillers (beer bagasse, BB or its lignocellulosic fibers (LF)) obtained by SWE at different temperatures (110, 130, 150, 170 °C) and (b) SP and PS films incorporating 10% LF170 in the 900–1200 cm−1 range.
Figure 7. FTIR spectra of (a) SP films incorporating or not 10% of different fillers (beer bagasse, BB or its lignocellulosic fibers (LF)) obtained by SWE at different temperatures (110, 130, 150, 170 °C) and (b) SP and PS films incorporating 10% LF170 in the 900–1200 cm−1 range.
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Table 1. Mass fraction of the different components (g/100 g film) in starch-based films.
Table 1. Mass fraction of the different components (g/100 g film) in starch-based films.
FormulationsXSXGlyXPCL (%)XBB or LF
SP0.690.240.07-
SP-5BB0.660.230.070.05
SP-10BB0.620.220.060.10
SP-5 LF1100.660.230.070.05
SP-10LF1100.620.220.060.10
SP-5LF1300.660.230.070.05
SP-10LF1300.620.220.060.10
SP-5LF1500.660.230.070.05
SP-10LF1500.620.220.060.10
SP-5LF1700.660.230.070.05
SP-10LF1700.620.220.060.10
Table 2. Chemical composition and white index (WI) of the defatted beer bagasse (BB) and its lignocellulosic fibers (LF) obtained at different temperatures.
Table 2. Chemical composition and white index (WI) of the defatted beer bagasse (BB) and its lignocellulosic fibers (LF) obtained at different temperatures.
SampleProtein
(%)		Ash
(%)		Lignin
(%)		Cellulose
(%)		Hemicellulose
(%)		WI (%)
BB22 ± 2 a3.71 ± 0.01 c9.5 ± 1.6 ab17 ± 2 a17.9 ± 0.6 d43
LF11028 ± 2 b3.12 ± 0.11 b9.1 ± 0.4 a16 ± 2 a15 ± 2 c45
LF13026.2 ± 0.2 ab2.79 ± 0.04 b11.6 ± 0.1 b20 ± 2 a14.9± 1.2 c42
LF15026 ± 2 b2.27 ± 0.11 a14.6 ± 0.5 c21 ± 2 a7.8 ± 1.2 b35
LF17035.7 ± 0.2 c3.10 ± 0.20 b19.6 ± 0.3 ᵈ30 ± 3 b2.01 ± 0.08 a27
a, b, c… different superscript letters within the same column indicate significant differences among films (p < 0.05).
Table 3. Mechanical parameter in terms of elastic modulus (EM), tensile strength at break (TS) and elongation at break (E) of starch-based films loaded with 5% or 10% of beer bagasse (BB) or its lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
Table 3. Mechanical parameter in terms of elastic modulus (EM), tensile strength at break (TS) and elongation at break (E) of starch-based films loaded with 5% or 10% of beer bagasse (BB) or its lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
FilmEM (MPa)TS (MPa)E (%)
SP80 ± 14 a5.96 ± 1.13 a69 ± 2 e
SP-5BB500 ± 71 e,f13 ± 2 d,e,f12± 2 b
SP-10BB544 ± 63 f8.43± 1.15 b2.2 ± 0.7 a
SP-5LF110380 ± 60 c,d14.71 ± 1.11 f33 ± 6 c
SP-10LF110643 ± 88 g13.4 ± 1.3 d,e,f4.83 ± 1.08 a
SP-5LF130443 ± 86 d,e14.4 ± 1.3 e,f29 ± 6 c
SP-10LF130697 ± 84 g15 ± 3 f5 ± 1.12 a
SP-5LF150322 ± 52 c12.6± 1.6 d,e29 ± 7 c
SP-10LF150500 ± 145 e,f11.3 ± 0.5 c,d6 ± 2 a
SP-5LF170226 ± 62 b13 ± 3 d,e44 ± 8 d
SP-10LF170 342 ± 59 c10.5 ± 1.7 c14 ± 6 b
a, b, c… different superscript letters within the same column indicate significant differences among films (p < 0.05).
Table 4. Thickness, water content (Xw), water vapor permeability (WVP), and oxygen permeability (OP) values of starch-based films loaded or not with 5% or 10% of beer bagasse (BB) or its lignocellulosic fibers /LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
Table 4. Thickness, water content (Xw), water vapor permeability (WVP), and oxygen permeability (OP) values of starch-based films loaded or not with 5% or 10% of beer bagasse (BB) or its lignocellulosic fibers /LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
FilmThickness (µm)Xw (%)WVP·1011
(g/Pa s m)		OP·1014
(cm3/m s Pa)
SP312.05 ± 0.03 c9.7 ± 0.2 a,b350 ± 11 a12 ± 2 b,c
SP-5BB293.73 ± 0.02 a,b,c9.9 ± 0.3 a,b436 ± 66 b,c19.4 ± 1.7 d
SP-10BB277.43 ± 0.02 a9.5 ± 0.1 a572 ± 41 c27.1 ± 1.2 f
SP-5LF110285.13 ± 0.02 b,c9.9 ± 0.1 a,b492 ± 35 b,c10.1 ± 0.6 a,b
SP-10LF110284.8 ± 0.01 a,b,c9.7 ± 0.3 a,b497 ± 81 b,c10.4 ± 0.8 a,b
SP-5LF130272.9 ±0.02 a,b10.0 ± 0.2 a,b417 ± 74 a,b9 ± 1 a
SP-10LF130312.05 ±0.03 a,b,c9.5 ± 0.4 a499 ± 40 b,c23.1 ± 0.1 e
SP-5LF150285.08 ± 0.02 a,b,c9.8 ± 0.1 a,b492 ± 25 b,c11.1 ± 0.2 a,b
SP-10LF150280.3 ± 0.02 a,b10.1 ± 0.5 a,b418 ± 34 a,b17.2 ± 0.8 d
SP-5LF170288.75 ± 0.01 a,b,c11 ± 2 b433 ± 59 a,b11.6 ± 0.8 b,c
SP-10LF170275.53 ± 0.01 a,b,c9.6 ± 0.3 a,b419 ± 63 a,b13.7 ± 0.9 c
a, b, c… different superscript letters within the same column indicate significant differences between films (p < 0.05).
Table 5. Optical properties in terms of lightness (L*), hue angle (Hab*), chroma (C*) and internal transmittance values (Ti) at 550 nm of starch-based films loaded or not with 5% or 10% of beer bagasse (BB) or its lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
Table 5. Optical properties in terms of lightness (L*), hue angle (Hab*), chroma (C*) and internal transmittance values (Ti) at 550 nm of starch-based films loaded or not with 5% or 10% of beer bagasse (BB) or its lignocellulosic fibers (LF) obtained by SWE at different temperatures (110, 130, 150, 170 °C).
FilmL*Hab*C*abTi (550 nm)
SP76 ± 9 c72.4 ± 0.2 g14.4 ± 0.1 d0.82 ± 0.01 g
SP-5BB52 ± 9 b64.2 ± 0.2 f19.3 ± 0.1 h0.63 ± 0.01 f
SP-10BB47 ± 9 a,b60.3 ± 0.5 e17.4 ± 0.2 f0.53 ± 0.01 e
SP-5LF11052 ± 9 b63.3 ± 0.4 f18.9 ± 0.2 g,h0.62 ± 0.01 f
SP-10LF11046 ± 9 a,b59.5 ± 0.8 e17.3 ± 0.5 f0.52 ± 0.02 e
SP-5LF13051 ± 8 b63.2 ± 0.4 f18.6 ± 0.2 g0.61 ± 0.02 f
SP-10LF13043 ± 9 a,b56.9 ± 0.3 d15.8 ± 0.3 e0.46 ± 0.01 d
SP-5LF15044 ± 9 a,b57.9 ± 1.5 d,e14.2 ± 0.9 d0.47 ± 0.04 d
SP-10LF15039 ± 9 a,b45.6 ± 0.3 c8.9 ± 0.2 c0.27 ± 0.01 c
SP-5LF17035 ± 9 a42.4 ± 1.2 b5.5 ± 0.2 b0.18 ± 0.01 b
SP-10LF17034 ± 9 a18.7 ± 4 a1.2 ± 0.2 a0.05 ± 0.01 a
a, b, c… different superscript letters within the same column indicate significant differences between films (p < 0.05).
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Gómez-Contreras, P.; Cháfer, M.; Chiralt, A.; González-Martínez, C. Beer Bagasse as Filler for Starch-Based Biocomposite Films for Food Packaging Applications. Biomass 2025, 5, 46. https://doi.org/10.3390/biomass5030046

AMA Style

Gómez-Contreras P, Cháfer M, Chiralt A, González-Martínez C. Beer Bagasse as Filler for Starch-Based Biocomposite Films for Food Packaging Applications. Biomass. 2025; 5(3):46. https://doi.org/10.3390/biomass5030046

Chicago/Turabian Style

Gómez-Contreras, Paula, Maite Cháfer, Amparo Chiralt, and Chelo González-Martínez. 2025. "Beer Bagasse as Filler for Starch-Based Biocomposite Films for Food Packaging Applications" Biomass 5, no. 3: 46. https://doi.org/10.3390/biomass5030046

APA Style

Gómez-Contreras, P., Cháfer, M., Chiralt, A., & González-Martínez, C. (2025). Beer Bagasse as Filler for Starch-Based Biocomposite Films for Food Packaging Applications. Biomass, 5(3), 46. https://doi.org/10.3390/biomass5030046

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