Innovative Agrowaste Banana Peel Extract-Based Magnetic Iron Oxide Nanoparticles for Eco-Friendly Oxidative Shield and Freshness Forti�cation

This study presents the synthesis of agrowaste banana peel extract-based magnetic iron oxide nanoparticles (BPEx-MIONPs), emphasizing antioxidant capacity and food preservation. Using iron (III) chloride hexahydrate (FeCl 3 · 6 H 2 O) as a precursor and a reducing agent from agrowaste peel extract, a precisely controlled process yielded BPEx-MIONPs. Characterization involved X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). XRD revealed tetragonal Fe 2 O 3 , cubic magnetite structure, and monoclinic FexOy-NPs with an average size of 14.8 nm. TEM and SEM showcased diverse morphologies—cubic, quasi-spherical, and elongated microdomains. FTIR con�rmed Fe–O bonds (1000 − 400 cm -1 ). Antioxidant assessment showed robust DPPH free radical scavenging; BPEx achieved 100% inhibition at 18 min, and BPEx-MIONPs had an IC 50 of ~ 136 µg/mL. BPEx-MIONPs, stabilized with banana-based bioplastic, effectively preserved grapes, reducing weight loss to 6.2% on day 3, compared to the control (19.0%). This pioneering study combines banana peel antioxidants with magnetic iron oxide nanoparticles, providing sustainable solutions for food preservation and nano-packaging. Ongoing research aims to re�ne conditions and explore broader applications of BPEx-MIONPs.


Introduction
Nanoscience, focusing on materials with dimensions ranging from 1 to 100 nm, has witnessed signi cant growth in recent years [1].The synthesis of nanomaterials has become an area of intense interest due to their diverse applications across various industrial sectors [2,3].Iron oxide nanoparticles (IONPs) have emerged as a subject of considerable attention among these nanomaterials due to their exceptional thermal, optical, electronic, and superparamagnetic properties [4].These nanoparticles, occurring naturally and synthesized through various methods, exhibit distinct crystal structures and iron valence states, with magnetic properties such as saturation magnetization, coercivity, and remanence being of particular interest [5].
Magnetic iron oxide nanoparticles (MIONPs), one of the most commonly used nanoparticles, have found widespread applications due to their unique characteristics, including speci city, magnetism, and biocompatibility [6].While physical and chemical methods have traditionally been employed for nanoparticle synthesis, their complexity and environmental impact have led to an increasing interest in green synthesis methods [7].Green synthesis, mainly using plant-based materials, has gained prominence for its simplicity, cost-effectiveness, and ability to produce crystalline nanoparticles with various shapes and sizes [8].Various techniques are used for the preparation of IONPs, among which the hydrothermal method stands out for its exibility in adjusting processing parameters.This method allows the synthesis of nanostructures with different dimensions, including 1D, 2D, and 3D structures [9].Iron oxide nanoparticles exhibit superior chemical stability, low toxicity, and superparamagnetic behavior, making them valuable for supplementary treatment tools, for example in a very promising cancer treatment known as magnetic hyperthermia [10].The eco-friendly green synthesis of iron oxide has gained popularity due to its effectiveness, low cost, non-toxicity, and environmentally friendly nature.
Plant-based materials, rich in phenolic compounds, act as reducing agents for metal salts, resulting in the production of nanoparticles with unique properties [11].Biosynthesis, utilizing microorganisms and plant extracts, has emerged as green and bene cial.Thus, plant-based methods offer advantages such as reduced reaction times and elimination of the cell culture step [12].However, the majority of these green methods use high quality fruits, which can make them unpro table due to their high consumption and consequent loss of nutritional value.Therefore, the importance of exploring alternatives becomes evident.
Agrowastes continue to represent an opportunity, offering abundant bioactive compounds that may act as both bioreducing and capping agents.However, further research is needed to fully exploit their potential.[13].
Simultaneously, the escalating global plastic crisis has resulted in severe environmental repercussions, with plastic waste polluting oceans, harming wildlife, and contributing to long-lasting ecological damage [14].Conventional plastics, primarily derived from non-renewable fossil fuels, pose a signi cant challenge due to their non-biodegradable nature [15].In response to these pressing issues, the demand for sustainable alternatives is on the rise.Bioplastics, derived from natural sources such as plant-based materials, offer a promising solution.Unlike traditional plastics, bioplastics have the advantage of being biodegradable and, in some cases, compostable [16,17].
The production of bioplastics encompasses the use of renewable resources, including corn starch [18], potato starch [19], sugarcane [20], wheat [21], and soybeans [22], as well as speci c bioplastics like PLA derived from corn or sugarcane, and innovative sources such as algae [23], hemp [24], and wood pulp cellulose [25].These resources not only contribute to mitigating environmental impacts, but also reduce dependence on nite fossil fuel reserves.[17].This shift towards bioplastics represents a crucial step in fostering a more environmentally conscious and sustainable approach to material usage.Banana-based biopolymers, with their diverse chemical compositions including proteins, polysaccharides, lipids, ashes, etc., are suitable candidates for developing bioplastics for nano-packagings [26,27].
The novelty of the present research lies in its innovative approach, utilizing agrowaste from Honduran banana peels for the synthesis of iron oxide nanomaterials.This unique methodology takes advantage of the rich availability of bioactive compounds in this kind of agrowaste, which can serve as effective agents in the synthesis process.Therefore, the study aims to contribute to the eld of food nanopackaging by offering sustainable and environmentally friendly materials, with a speci c focus on the development of bioplastic-based nano-packaging solutions.The results obtained from this research are anticipated to have a substantial impact, introducing new possibilities for the development of more sustainable materials in the eld of food preservation and packaging.
The research introduces a pioneering method for recycling a common agricultural waste such as banana peel and synthesize magnetic iron oxide nanoparticles (BPEx-MIONPs) using banana peel extract.
The study focuses on converting banana peels into useful nanomaterials with antioxidant capacity, enabling the development of bioplastics with potential for food preservation, and thus contributing to environmental conservation and bioeconomy.Employing advanced techniques such as X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy, the investigation provides a comprehensive understanding of the magnetite structure and various morphologies of BPEx-MIONPs.This research enhances our knowledge of novel nanocomposites, opening up exciting possibilities for sustainable food preservation and packaging applications in the expanding eld of nanotechnology.
Fresh agrowaste banana peels and grapes were supplied form a loca market in Danli Honduras.

Banana peel extract preparation
In the initial phase of our experimental procedure, we focused on the meticulous preparation of banana peel extract for subsequent nanoparticle synthesis.Fresh agrowaste banana peels, selected with care and free from damage, were meticulously washed to remove any potential physical contaminants.The peels were manually removed, cut into smaller pieces, and evenly spread on stainless steel trays.After a 24hour drying process at a constant temperature of 90°C, the peel pieces were ground into a nely powdered form using a manual mill.This material was then further processed to achieve the desired particle sizes of 250 − 63 µm through the utilization of a standard test sieve.

BPEx-MIONPs synthesis
Following the successful extraction of banana peel powder, our focus shifted to synthesizing magnetic iron oxide nanoparticles (BPEx-MIONPs) in the second stage.The process commenced with maceration extraction, involving the dissolution of 50 g of fruit powder in 100 mL of water at 80°C for 24 h.After ltration, the extract's concentration in g/mL was determined.Essential reagents, a 1M solution of FeCl 3 •6H 2 O, and a 5M solution of NaOH were prepared.The synthesis was initiated by mixing 100 mL of fruit extract with 100 mL of the FeCl 3 •6H 2 O solution, stirred with a magnetic stirrer.pH adjustment to 7.5 using NaOH (5M) was crucial.The mixture underwent a 3-hour reaction at 60-80°C, followed by cooling, centrifugation, washing, and drying of the resulting iron oxide nanoparticles for subsequent analysis.

BPEx-MIONPs characterization
In this section, the various methods employed to characterize the nanoparticles were detailed.Our approach involves utilizing X-ray diffraction (XRD) and transmission electron microscopy (TEM).For XRD analysis, patterns were obtained (measured on a Bruker D8 Advance A25 diffractometer with a Cu anode) to con rm the crystalline phase and crystal systems, allowing for the calculation of size and crystallinity of the BPEx-MIONPs, as outlined in a previous study [28].Diffractograms were generated within the 2θ range of 15-70 degrees.The morphology and particle size of BPx-MIONPs were analyzed using a Zeiss EVO scanning electron microscope for scanning electron microscopy (SEM).Further analysis of nanoparticle morphology and size was performed through TEM using a Talos S200 microscope (FEI, USA) operating at 200 kV.Additionally, Fourier transform infrared spectroscopy (FTIR) was employed to glean insights into the structure of the BPEx-MIONPs by examining vibrational modes in the range of 4000 to 400 cm -1 .

Antioxidant activity
During the preparation of banana peel extract (BPEx) and banana peel extract-based magnetic iron oxide nanoparticles (BPEx-MIONPs), an assessment of their antioxidant capacity was conducted using the Disc Diffusion technique against the DPPH free radical [29].In this approach, approximately 7 mg of DPPH was dissolved in ethanol, and a 25 mL DPPH free radical solution was spread onto a 10 cm diameter aluminum plate.Subsequently, 0.5 mL of the respective extracts (BPEx and BPEx-MIONPs) was applied at the center of the plate containing the DPPH solution, resulting in an immediate color change to clear yellow.The evaluation of antioxidant activity involved measuring the areas of color change using ImageJ software.The assessment method, validated by recording the area, utilized the formula for inhibition percentage: where represents the total area of inhibited DPPH with violet color, and represents the remaining areas without a change in color over time.A complete color change to yellow is recorded as 100% inhibition.This technique serves as a valuable tool for quantifying the antioxidant capacity of BPEx and BPEx-MIONPs, providing crucial insights into their potential applications, including in the synthesis of iron oxide nanoparticles.

Bioplastic solution preparation
Based on the results of a previous study [27], banana agrowaste from Mesa SAN R11 El Paraíso, Honduras, was subjected to a meticulous process to transform it into our.After peeling and slicing, the material was dried, tempered, and milled to achieve desired characteristics.The presented protocol revealed banana composition: moisture (1.50%), ashes (7.81%), lipids (0.22%), proteins (2.25%), and polysaccharides (59.2%).An aqueous banana water solution (1-3) was prepared, where 1 gram dissolved in 30 mL of water, followed by stirring for approximately 10 min at 100°C.After ltration using coffee ltration paper, the resulting solution was collected as the liquid, and approximately 7 mg of glycerin was thoroughly mixed in for forming the bioplastic [30].Given the nutrient-rich composition of grapes and their susceptibility to microbial decay, we selected them to assess the feasibility of using BPEx-MIONPs stabilized with banana-based bioplastic as a bio-coating for food nanopackaging.Approximately 7 mg of BPEx-MIONPs were introduced into the solution forming the bioplastic, manually mixed with the banana solution until a visually homogeneous dispersion was achieved.Subsequently, grapes were immersed in the resulting solutions-both with and without BPEx-MIONPs-for 3 min.The samples were then left at room temperature (28 ± 7°C) with an average relative humidity (RH) of ≈ 87% for a 6-day shelf-life test.At three-day intervals, images were captured, and the weight loss rate (WLR, %) was calculated as follows [31]:

Dip coating of grapes
where and are the weights of fresh and preserved grapes, respectively.

Statistical Analysis
Measurements from three replicates were subjected to one-way ANOVA to identify signi cant differences using OriginLab software.
The calculated crystallinity index is 99.9%, highlighting the high degree of crystallinity in the synthesized nanoparticles.Individual peaks exhibit varying crystallinity percentages, with the peak at 31.68° (202) corresponding to monoclinic Fe 3 O 4 [35] (Reference Code: 00-153-2800), demonstrating 10.4% crystallinity.These results con rm the well-de ned crystalline structure of BPEx-MIONPs, providing essential insights into their physical and chemical properties in the context of agrowaste-based nanoparticle synthesis.The average crystalline size, calculated using the Debye-Scherrer formula, is determined to be 14.8 nm.Magnetic responses of these structures are depicted in Fig. 1.b, illustrating the correlation between the different systems and their magnetic behavior.

Nanoparticle visualization (TEM)
Figure 2 illustrates the TEM analysis of BPEx-MIONPs, revealing a diverse array of morphologies, including both spherical and elongated nanoparticles.In Fig. 2.a, distinctive spherical shapes ranging from 5 to 39 nm, with an average diameter distribution of 8.47 ± 0.56 nm, are evident, as depicted in Fig. 2.b.These spherical nanoparticles hold signi cant promise for applications in elds such as medicine, electronics, and nanotechnology owing to their compact form and magnetic properties [36].
Contrastingly, Fig. 2.c shows thin brillar shapes ranging from ultra ne nano brils to elongated nanorods of diameter ranging from 1 to 62 nm, with a total average diameter distribution of 2.61 ± 0.1 nm (Fig. 2.d).
These nano brils exhibit unique characteristics, such as a larger surface area and a more robust interaction with their environment.Consequently, they emerge as potentially intriguing candidates for applications in sensors, catalysts, and optoelectronic devices [37].It is crucial to note that the size and shape of nanoparticles or nano brils play a pivotal role in in uencing their properties and behavior.While the average diameter serves as a valuable metric for characterizing the size of nanoparticles within a sample, the consideration of size distribution is equally essential.This distribution can vary, ranging from highly uniform nanoparticles/nano brils to those with more dispersed sizes.Similar spherical morphologies have been reported in [40,41], and elongated shapes have been reported in [37].

SEM
Figure 3 provides an image of the intricate particle assembly of the synthesized BPEx-MIONPs, displaying an interplay of shapes and structures.SEM image shows an array predominantly made up of spherical nanoparticles, which resemble coral reef formations (Fig. 3.a).The nanoparticle assemblies presented in this study emulate the collaborative dynamics observed in coral reefs, wherein colonies of particles intricately coalesce through a synergistic interaction between phytochemicals and magnetic ions, giving rise to agglomerates and aggregates.SEM images were meticulously processed using the ImageJ software's image calculator, incorporating thresholding and Gaussian blur lters [38].The analyzed particles were subjected to Gauss t analysis using OriginLab, revealing a nanoparticle diameter of 7.9 ± 1.5 nm, as illustrated in Fig. 3.b.Notably, this size aligns well with ndings from XRD and TEM techniques, with minor discrepancies attributed to variations in each technique's setup [39].
Moreover, the SEM particle agglomerate size distribution, depicted in Fig. 3.c, unveils a diverse range spanning from 10 to 1200 nm, with an average size of approximately 487.9 nm.This broad distribution underscores the versatility in particle sizes within the assembly, encompassing smaller individual nanoparticles to larger agglomerates.The observed range signi es a well-de ned and controlled synthesis process, enabling the formation of nanoparticles with varied sizes and con gurations.
The distinctive coral reef-like assembly observed in Fig. 3.a not only highlights the innovative synthesis approach but also underscores the potential applications of these BPEx-MIONPs.The combination of unique shapes, sizes, and magnetic properties enhances their adaptability for various uses, from biomedical applications to environmental remediation [42].This intricate particle assembly contributes to the overall understanding of the synthesized nanoparticles, emphasizing their potential as multifunctional materials with diverse applications.

Chemical signature (FTIR)
As can be seen in Fig. 4, The FTIR spectrum of the synthesized magnetic iron oxide nanoparticles using banana peel extract (BPEx-MIONPs) reveals a rich tapestry of functional groups contributing to their physicochemical properties.The prominent peaks at 3165 cm -1 , 3066 cm -1 , and 3039 cm -1 in Fig. 4.a signify O-H stretching vibrations, indicative of hydroxyl groups, possibly originating from water molecules or hydroxyl molecules linked by hydrogen bonds [43,44].The presence of C ≡ C stretching vibrations at 2646 cm -1 and 2621 cm -1 (Fig. 4.a) suggests the involvement of alkynes or acetylene groups [45,46].
Additionally, the peak at 2357 cm -1 (Fig. 4.a) could be attributed to the presence of carbon dioxide (CO 2 ) during analysis.The peak at 2166 cm -1 (Fig. 4.a) may indicate the presence of cyanide groups (CN), suggesting nitrogen-containing compounds.Moving to the lower wavenumber range in Fig. 4.a, the peaks at 2006 cm -1 and 1774 cm -1 are characteristic of C = O stretching vibrations, with the former possibly associated with ketones or aldehydes and the latter suggesting ester groups [44].The peak at 1572 cm -1 corresponds to C = C stretching vibrations, indicative of unsaturated carbon-carbon bonds.Further analysis in Fig. 4.a reveals the presence of methylene (CH 2 ) bending vibrations at 1425 cm -1 , while the peak at 1211 cm -1 suggests C-O stretching vibrations, characteristic of ether groups or alcoholic functionalities [47,48].Transitioning to Fig. 4.b, the peaks at 1059 cm -1 are associated with C-N stretching vibrations, suggesting the presence of amines.Finally, the peaks at 877.5 cm -1 , 773.3 cm -1 , and 698.1 cm -1 in Fig. 4.b are attributed to metal-oxygen (Fe-O) stretching vibrations, con rming the presence of iron oxide (Fe 3 O 4 ) in the synthesized nanoparticles [47,48].The peaks at 557.3 cm -1 and 441.6 cm -1 in Fig. 4.b indicate metal-oxygen (Fe-O) bending vibrations (α-Fe 2 O 3 ), further supporting the identi cation of iron oxide [49].This intricate network of functional groups signi es the complex composition of BPEx-MIONPs, showcasing the diverse interactions contributing to the stabilization and functionalization of these magnetic nanoparticles.

Assessing antioxidant properties
The evaluation of antioxidant activity in banana peel extract (BPEx) through the DPPH free radical assay demonstrated remarkable results, as outlined in Table 1.The initial inhibition, starting at 9.89% after 5 s (T2), progressively increased, reaching 65.61% at 6 min (T3), 89.98% at 12 min (T4), and ultimately achieving a complete inhibition of 100% at 18 min (T5).This temporal trend signi es the dynamic enhancement of antioxidant properties within the banana extract over the assessment period.The outstanding antioxidant properties of the banana peel extract were further evidenced by a noticeable color change during the DPPH free radical assay.The extract exhibited an initial yellow hue, intensifying to a clearer yellow over time, as evidenced by the color change, indicating an increase in the inhibition percentage, as can be seen in Table 1.This distinct color transformation, correlated with the temporal progression of the assay, aligns with the concurrent increase in inhibition percentage, as illustrated in Table 1.The dynamic shift in color serves as a visual con rmation of the escalating antioxidant activity, providing additional support to the quantitative results obtained through the DPPH assay.
Banana peels boast robust antioxidant properties, primarily attributed to polyphenolic compounds like catechins, epicatechins, and gallocatechins.Flavonoids such as quercetin and rutin, along with tannins, amplify the antioxidant and other capabilities.The presence of dopamine, dietary ber, vitamins (especially vitamin C), and carotenoids like beta-carotene further enhances these health-promoting qualities [46,50,51].
The assessment of antioxidant activity in BPEx-MIONPs, as revealed by the IC 50 value of 129.1 µg/mL (Fig. 5), underscores the substantial antioxidant potential embedded within these magnetic nanoparticles.This high antioxidant activity can be attributed to the synergistic effects arising from the unique combination of banana phytochemicals and the structural attributes of magnetic ions [52,53].
Table 1: Antioxidant activity of banana peel extract (BPEx) over time in the DPPH free radical assay con rmed by visualized photographs depicting color change.
The observed size of BPEx-MIONPs, as determined by TEM (approximately from 2.1 to 8.5 nm) and XRD (14.8 nm), is a crucial factor contributing to their enhanced antioxidant capacity.The nanoparticles' nanoscale dimensions amplify their surface area, facilitating increased interactions between the nanoparticles and free radicals, thereby increasing their scavenging capability [54].This phenomenon is further supported by the distinct shapes observed in TEM images, showing both spherical and elongated forms.The diverse morphologies indicate a heterogeneous distribution of particle shapes, potentially leading to varied reactivity towards free radicals [55].Moreover, the magnetic ions present in the nanoparticles contribute to their antioxidant activity [56].The magnetic properties inherent in the structure of BPEx-MIONPs may facilitate electron transfer reactions, playing a role in the reduction of free radicals and, consequently, enhancing their antioxidant e cacy.This characteristic provides an additional dimension to their antioxidant activity, distinguishing them from conventional antioxidant agents.
The simultaneous presence of banana phytochemicals and magnetic ions creates a multifaceted antioxidant system within BPEx-MIONPs, where the various components act synergistically to e ciently neutralize free radicals [57].This innovative amalgamation of natural plant-derived compounds and magnetic nanoparticles not only enhances antioxidant capabilities but also holds promise for diverse applications, including elds such as biomedical or environmental.The versatility in shape, size, and structural attributes demonstrated by TEM and XRD collectively contribute to the superior antioxidant performance of BPEx-MIONPs, marking them as promising candidates for further exploration in nanotechnology and antioxidant applications.

Dip coating of grapes
In the context of grape preservation with bioplastic coating, our observations in the control group (coated in the absence of BPEx-MIONPs) revealed a signi cant reduction in water content, with a 19% loss by day 3 and a substantial 34.8% loss by day 6 (Fig. 2).In stark contrast, the grape samples coated with banana peel extract-based magnetic iron oxide nanoparticles (BPEx-MIONPs) exhibited remarkable preservation e ciency, showing only a 6.2% water loss on day 3 and a comparatively lower 23.6% loss on day 6.
These ndings distinctly demonstrate the superior preservation capacity of the banana nanoparticles in food, emphasizing their potential as a valuable and eco-friendly solution for extending the shelf life of perishable produce [58].The controlled release properties and stabilizing effects of BPEx-MIONPs contribute to reducing water loss and maintaining the freshness of preserved grapes over an extended period.

Conclusions
This study represents a signi cant step forward in harnessing the potential of agrowaste banana peels for the synthesis of magnetic iron oxide nanoparticles (BPEx-MIONPs), showing their dual functionality in antioxidant capacity and food preservation.The diverse morphologies revealed through XRD, TEM, and SEM analyses, combined with the con rmation of Fe-O bonds through FTIR, support the successful fabrication of nanoparticles with unique structural characteristics.The robust antioxidant activity observed against DPPH free radicals, along with the preservation e ciency demonstrated in grape storage, underscores the practical applications of BPEx-MIONPs in sustainable food packaging.
Nevertheless, it is crucial to acknowledge certain limitations in our study.While improvements in preservation capacity have been observed, there is a need to enhance laboratory experiments by accounting for variations in humidity, temperature, and other environmental factors.These conditions could have in uenced the results, suggesting that an extended shelf life of the preserved food might be achievable under ideal circumstances.Furthermore, the study primarily focused on the characterization of BPEx-MIONPs.Future research should address the imperative need for advanced toxicity studies and in vivo evaluations, ensuring the safety and e cacy of these nanoparticles in real-world applications.
Moving forward, re ning experimental conditions, incorporating advanced characterization techniques, and expanding the scope to include comprehensive toxicity assessments will be crucial in unlocking the full potential of BPEx-MIONPs.Moreover, exploring broader applications across various contexts will contribute to the development of innovative and sustainable solutions in the elds of nanotechnology and food preservation.Figure 3 SEM images depicting the coral reef-like assembly of BPEx-MIONPs, formed by spherical nanoparticles (a).Nanoparticle diameter distribution, calculated by Gaussian tting and ranging from 0 to 100 nm, with an average size of ca.7.9 nm (b).Size distribution of particle assembly (agglomerates), ranging from 10 to 1200 nm, with an average size of ca.487.9 nm (c).

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