The berry industry has experienced considerable growth in recent years owing to increasing consumer demand for nutrient-rich and functional foods. Berries are widely recognized for their high bioactive compound content—including polyphenols, anthocyanins and dietary fibers—which contribute to their antioxidant, anti-inflammatory and antimicrobial properties (Yadav, 2021). However, industrial processing of berries generates substantial quantities of pomace, a byproduct comprising the skins, seeds and residual pulp of the processed berries, accounting for 20–30 % of the total fruit weight (Struck et al., 2016). Currently, berry pomace is often discarded or used as low-value animal feed, despite its rich content comprising polysaccharides, polyphenols and other phytochemicals (Radha et al., 2024). Recent studies have demonstrated that berry pomace, particularly from blackberries, blueberries and raspberries, retains high concentrations of antioxidants and antimicrobial agents, making it a promising raw material for value-added applications (Raczkowska & Serek, 2024). Blackberry pomace is a notable source of anthocyanins and dietary fibers. (Čechovičienė et al., 2024). Blackberry pomace contains a large amount of bioactive compounds from which anthocyanin pigments, seed oil, plant fibers and other finely processed products can be extracted. Reusing this agricultural by-product can yield antioxidant extracts. Četojević-Simin et al. (2015) showed that ‘Meeker’ and ‘Willamette’ red raspberry pomace is rich in phenolic antioxidants, with effects such as free radical scavenging, anti-inflammation, anti-proliferation and antibacterial properties. Strawberry pomace is also a promising source of antioxidants and trace nutrients (Jaroslawska et al., 2011). Cranberry pomace contains a large amount of dietary fiber, with content ranging from 58.7 % to 71.2 % (White et al., 2010). For example, blueberry pomace contains at least 18 identified polyphenols (Lončarić et al., 2020). However, the high moisture content and perishability of fresh pomace can pose challenges for their storage and direct utilization, necessitating sustainable strategies to convert them into functional materials. Given these considerations, the development of advanced materials derived from berry pomace, such as carbon-based nanomaterials, has emerged as a viable method of repurposing agricultural waste while enhancing its functional properties.

Carbon dots (CDs) are zero-dimensional carbon nanomaterials with a size of less than 10 nm (Bian et al., 2023; Ornelas-Hernández et al., 2022), which were accidentally discovered during the separation and purification of single-walled carbon nanotubes, and were initially thought to be fluorescent carbon nanoparticles, later referred to as ‘carbon quantum dots.’ The structure of CDs is quasi-spherical, comprising nanocrystalline sp2 hybridized carbon cores and amorphous sp3 hybridized carbon shells (Xie et al., 2022). Since its discovery in 2004, CDs has attracted widespread attention owing to its many advantages—including its tunable radiation wavelength, easy surface functionalization modification, and good biocompatibility (Guo, Liu, Wei, et al., 2022). CDs can be synthesized via two typical strategies—that is, top-down methods, which fragment bulk carbon materials (e.g., graphite, carbon nanotubes) into nanoscale particles through electro-oxidation, laser ablation, or harsh chemical treatment, and bottom-up methods, which assemble small molecular precursors (e.g., citric acid, biomass) into CDs under mild conditions (Du et al., 2020). Whereas top-down methods often require energy-intensive processes and expensive equipment, bottom-up methods—such as hydrothermal, solvothermal, or microwave-assisted synthesis methods—offer cost-effective and eco-friendly alternatives (Chernyak et al., 2020; Mahat & Shamsudin, 2020). Among these, hydrothermal treatment stands out for its simplicity, scalability and compatibility with diverse biomass-derived precursors, providing an ideal route to convert nitrogen- and oxygen-rich berry pomace into functional CDs while staying consistent with the principles of green chemistry and agricultural waste valorization.

As a representative class of biomass-derived carbon dots (BCDs), pomace-based CDs inherit the intrinsic advantages of their sustainable precursors, including the abundant surface functional groups (e.g., -OH, -COOH, -NH₂) derived from natural polyphenols and polysaccharides (P. Zhang, Gao, et al., 2025). The unique composition of berry pomace endows these BCDs with enhanced photoluminescence, antioxidant capacity, and antimicrobial properties compared to their synthetic counterparts (Kanwal et al., 2022). Notably, their intrinsic biocompatibility and multifunctionality have encouraged their application in active food packaging, where BCDs serve dual roles—that is, as optical sensors for real-time food freshness monitoring via fluorescence response (Kousheh et al., 2020), and antimicrobial or antioxidant agents to extend the shelf life of fresh agricultural products (Han et al., 2022; Hao et al., 2023). The unique chemical composition of plant-derived precursors multifunctional properties of the resulting CDs (K. Huang et al., 2025). Natural antimicrobial substances in the precursors, such as catechins, may be partially retained in the CDs or influence their surface chemistry, thereby enhancing antibacterial effects. For instance, CDs derived from oolong tea waste demonstrate stronger antibacterial activity against Gram-positive bacteria (Ye et al., 2025). The chromophore structures from anthocyanins and flavonoids in precursors may be partially retained or transformed during carbonization, directly contributing to the luminescent centers of the CDs. S and N co-doped CDs derived from red onion skins exhibit visible color changes under different pH conditions (Tohamy, 2025). Furthermore, agricultural wastes rich in cellulose and hemicellulose, such as lemon peels, potato peels and sugarcane bagasse, can produce CDs that are abundant in hydroxyl and carboxyl groups. These functional groups facilitate interactions with biopolymers, enabling the CDs to act as effective nanofillers and matrix enhancers (K. Huang et al., 2025). Despite these advances, systematic comparisons of BCDs derived from different berry pomace—particularly regarding their structure-activity relationships and performance in packaging systems—remain unexplored. Recent research on modifying biodegradable polymers for food packaging has emphasized the important role of nanoscale additives and interfacial compatibilizers in developing multifunctional composites. Taking polylactic acid (PLA) composites as an example, incorporating CDs as multifunctional nanofillers not only provides inherent ultraviolet (UV) shielding due to the strong absorption properties but also significantly enhances the mechanical and barrier properties. These improvements result from the formation of a uniformly dispersed nano-reinforced structure that creates tortuous diffusion pathways for gas molecules. Interfacial adhesion is primarily regulated by hydrogen bonds between the functional groups of CDs and the polymer chains, which is crucial for effective stress transfer and performance improvement (Sun et al., 2025). Similarly, incorporating gelatinized starch acetate-functionalized montmorillonite into PLA/starch blends allows this functionalized clay to act as both a compatibilizer and a nanobarrier. This integration improves mechanical properties, thermal stability and barrier performance through synergistic effects (Chen et al., 2023). In addition, to address the inherent incompatibility of polymer blends, biodegradable epoxy-based terpolymers have been employed as reactive compatibilizers for PLA/PBAT blends, leading to substantial improvements in both mechanical and thermal properties (Niu et al., 2025). Overall, research shows that precise interfacial design, from physical hydrogen bonding to chemical covalent bridging, is crucial for developing high-performance multifunctional packaging materials that can overcome the limitations of single biopolymers.

This study selected the residues from five typical berries including blackberry, blueberry, cranberry, raspberry and strawberry as carbon sources for CDs synthesis. These berries are recognized as rich sources of antioxidants, particularly polyphenols and anthocyanins. These aromatic compounds, serving as excellent carbon precursors, possess conjugated structures and abundant functional groups that facilitate the formation of CDs with unique optical properties during carbonization. Additionally, they may introduce inherent surface functional groups, thereby reducing the need for post-modification steps (Aslandaş et al., 2015). Berries are also rich in fructose, glucose, citric acid and ascorbic acid. Sugars can serve as the core carbon framework of CDs, while organic acids not only function as reaction media but also potentially introduce functional groups such as carboxyls on CDs surface, enhancing their water solubility and reactivity (Zhi et al., 2018). Although these five berries share similarities in their macroscopic composition, they differ significantly in the specific types of polyphenols, the ratio of sugars to acids and their vitamin content. This combination of shared characteristic and distinct compositional differences provides an excellent comparative research system for systematically studying how the chemical composition of different biomass precursors affects the physicochemical properties of the derived CDs.

Develop a sustainable hydrothermal method for synthesizing fluorescent CDs from five types of berry pomace (blackberry, blueberry, cranberry, raspberry and strawberry) as a valorization strategy for forestry byproducts.

Systematically compare their antioxidant and antimicrobial properties to identify the optimal candidate; and

Fabricate functional polylactic acid (PLA) nanocomposite films by incorporating CDs for postharvest packaging applications of blackberries.

The study followed a three-phase design, namely CDs synthesis and optimization, CDs-incorporated nanofiber films fabrication and characterization, as outlined in Fig. 1. The stages included CDs synthesis and optimization, preparation and characterization of CDs composite nanofiber films, and post-harvest preservation of blackberries. The successful implementation of this method demonstrates a closed-loop solution that simultaneously addresses the challenges of agricultural waste management and food preservation, thereby providing great potential for extending the shelf life of fresh agricultural products.