Nano-Encapsulation of Natural/Bio-Based Materials as Bio-Adsorbents for Detoxification of Food Contaminants

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Nano-Encapsulation of Natural/Bio-Based Materials as Bio-Adsorbents for Detoxification of Food Contaminants

Food safety has emerged as a critical global concern, driven by the increasing detection of toxic pollutants in the food chain. These contaminants—including heavy metals like cadmium and lead, persistent pesticides, carcinogenic polycyclic aromatic hydrocarbons (PAHs), mycotoxins produced by mold, and ubiquitous microplastics—threaten public health through long-term exposure and bioaccumulation. The World Health Organization (WHO) has underscored the need for innovative solutions to mitigate these risks, as traditional remediation methods often fall short in terms of efficiency, sustainability, or compatibility with food systems.

Natural and bio-based materials, repurposed as bio-adsorbents, offer a promising alternative. Derived from renewable sources such as agricultural waste, seaweed, and microbial biomass, these materials possess inherent properties that enable them to bind and remove pollutants. When combined with encapsulation technology—an approach that encloses bio-adsorbents within protective matrices—their effectiveness is significantly enhanced, addressing limitations like instability, poor selectivity, and environmental sensitivity. This synergy of natural materials and advanced engineering is reshaping the landscape of food safety.

Sources, synthesis and modification of bio-adsorbents.Fig 1. Sources, synthesis and modification of bio-adsorbents. (Shamloo, E., et al., 2025)

Bio-adsorbents: Sources and Mechanisms of Action

Bio-adsorbents are diverse in origin, each with unique structural and chemical features that determine their pollutant-removal capabilities. Plant-based materials, including fruit peels, crop residues, and polyphenol-rich extracts, are abundant and cost-effective. For example, orange peels and rice husks, often discarded as agricultural waste, contain high levels of cellulose, lignin, and functional groups (hydroxyl, carboxyl) that interact with heavy metals through ion exchange and chelation. Polyphenols, found in berries, tea, and dark chocolate, exhibit a strong affinity for organic pollutants like PAHs and mycotoxins via hydrogen bonding and π-π stacking.

Animal-derived bio-adsorbents, such as chitosan from crustacean shells and collagen from animal tissues, offer distinct advantages. Chitosan's amino and hydroxyl groups make it highly effective at binding metal ions and dyes, while its biocompatibility ensures safety in food applications. Bone char, produced by heating animal bones, is particularly adept at removing fluoride and heavy metals from water used in food processing.

Microbial biomass, including bacteria, algae, and fungi, adds another layer of versatility. Algae, for instance, can accumulate heavy metals through intracellular uptake, while fungal mycelia secrete extracellular enzymes that break down pesticides. Aquatic sources like brown seaweed provide alginate, a polysaccharide that forms hydrogels capable of trapping microplastics and organic contaminants.

The adsorption process relies on multiple mechanisms: physical interactions (van der Waals forces), chemical bonding (covalent or ionic), ion exchange, and surface complexation. The efficiency of these interactions depends on factors such as the bio-adsorbent's surface area, porosity, and functional group density—properties often enhanced through processing steps like grinding, chemical activation, or thermal treatment. For example, treating cellulose with phosphoric acid increases its porosity and introduces phosphate groups, boosting its capacity to adsorb metals.

Encapsulation Technology: Enhancing Performance and Stability

Encapsulation transforms bio-adsorbents from promising materials into robust tools for food safety. By enclosing bio-adsorbents within protective matrices—typically polymers, lipids, or natural gums—this technology addresses key limitations: vulnerability to environmental stress (moisture, temperature fluctuations), poor reusability, and non-specific interactions with food components.

Key Encapsulation Techniques

Several techniques are employed to encapsulate bio-adsorbents, each tailored to specific applications:

  • Spray drying: A cost-effective method where a liquid containing the bio-adsorbent is atomized into heated air, forming dry, stable microcapsules. This technique is widely used for heat-stable bio-adsorbents, such as probiotics and antioxidant-rich extracts, and is effective for removing volatile organic compounds (VOCs) from food.
  • Ionic gelation: Utilizes natural polymers like chitosan and alginate, which form gels in the presence of ions (e.g., calcium). This mild process preserves heat-sensitive bio-adsorbents and is ideal for targeting dyes and metal ions.
  • Layer-by-Layer (LbL) assembly: Builds thin, tunable shells by alternating layers of oppositely charged polymers. This precision technique allows for the selective removal of specific pollutants, such as heavy metals and pesticides, by modifying shell thickness and composition.
  • Electrospinning: Produces nanofibrous matrices using electric fields, creating high-surface-area structures that excel at capturing microplastics and nano pollutants. The fibrous morphology enables rapid adsorption and easy separation from food matrices.

Advantages of Encapsulation

Encapsulation enhances stability by shielding bio-adsorbents from harsh conditions, such as acidic environments in processed foods or high temperatures during cooking. For example, encapsulated probiotics can survive stomach acid to reach the intestines, but in food safety, this same protection allows bio-adsorbents to retain functionality in pasteurized or fermented products.

Selectivity is another critical benefit. By modifying the encapsulation matrix with specific functional groups, researchers can design bio-adsorbents to target pollutants while avoiding interactions with beneficial food components. This prevents unintended changes to food texture, flavor, or nutritional value. For instance, LbL-assembled capsules with amine-functionalized shells preferentially bind heavy metals without affecting vitamins or minerals.

Reusability is improved through encapsulation, as the protective matrix reduces structural degradation during adsorption-desorption cycles. Supercritical fluid encapsulation, which uses solvent-free processes, produces matrices resistant to chemical leaching, enabling repeated use in water treatment for food processing.

Targeting Pollutants: Applications in Food Safety

Encapsulated bio-adsorbents have demonstrated efficacy across a range of food contaminants, making them versatile tools in food safety:

Heavy Metals

Heavy metals like cadmium, lead, and nickel accumulate in crops grown in contaminated soil and in seafood, posing risks of neurotoxicity and organ damage. Graphene oxide/Fe3O4/polyaniline nanocomposites, encapsulated via electrospinning, exhibit a maximum adsorption capacity of 142.8 mg/g for cadmium, outperforming many synthetic adsorbents. Chitosan-alginate capsules, modified with ethylenediaminetetraacetic acid (EDTA), effectively remove lead and nickel from drinking water used in beverage production, reducing concentrations to safe levels (below 10 μg/L as per WHO standards).

Pesticides and Mycotoxins

Pesticide residues, such as organophosphates and pyrethroids, persist in fruits, vegetables, and grains. Mesoporous molecularly imprinted polymers (MIPs), encapsulated in silica nanoparticles, selectively bind pesticides like pyriproxyfen and deltamethrin in apple juice, achieving removal efficiencies above 90%. For mycotoxins—such as aflatoxin B₁, a carcinogen found in nuts and oils—dopamine-grafted chitosan-Fe3O4 composites show exceptional performance, with adsorption capacities of 3.44 mg/g and high specificity, ensuring no impact on oil quality.

Microplastics

Microplastics, ubiquitous in water and processed foods, are a growing concern due to their potential to carry toxins and accumulate in the body. Superhydrophobic Fe3O4 nanoparticles, encapsulated in a lipid shell, exhibit remarkable affinity for microplastics like polystyrene and polyethylene, with an adsorption capacity of 809.29 mg/g. These nanoparticles can be easily separated from liquid foods (e.g., bottled water, juice) using a magnet, ensuring complete removal.

Dyes and PAHs

Synthetic dyes (e.g., tartrazine, ponceau 4R) and PAHs (e.g., benzo(a)pyrene) contaminate processed foods and edible oils. ZnS/CuO-decorated carbon nanotubes, encapsulated via hydrothermal synthesis, remove over 98% of these dyes from water, while vitamin C-reduced graphene oxide/Fe3O4 composites effectively target PAHs in vegetable oils, with a maximum adsorption capacity of 0.356 mg/g for benzo(a)pyrene.

Safety, Regulation, and Future Directions

The safety of encapsulated bio-adsorbents is paramount for food applications. Natural polymers like chitosan and alginate are generally recognized as safe (GRAS), with low cytotoxicity confirmed through in vitro tests (e.g., MTT assays) and in vivo studies. However, rigorous evaluation is required for modified bio-adsorbents, particularly those involving synthetic polymers or nanoparticles, to ensure they do not leach harmful substances into food.

Regulatory frameworks for bio-adsorbents in food are evolving. While organizations like the FDA and EFSA provide guidelines for food contact materials, specific standards for encapsulated bio-adsorbents are lacking. Harmonizing regulations to address safety, efficacy, and labeling will be critical for commercial adoption.

Future research will focus on enhancing scalability, selectivity, and sustainability. Innovations include developing biodegradable encapsulation matrices (e.g., polylactic acid, PLA) that degrade naturally after use, and multi-functional bio-adsorbents capable of removing multiple pollutants simultaneously. For example, combining chitosan (for heavy metals) with activated carbon (for organics) in a single LbL capsule could streamline pollutant removal in complex food matrices.

Advancements in nanotechnology, such as nano emulsions and electrospun nanofibers, will further boost adsorption efficiency by maximizing surface area and improving target specificity. Additionally, exploring underutilized bio-adsorbent sources—such as invasive plant species or industrial by-products—could reduce costs and environmental impact.

Conclusion

Encapsulated bio-adsorbents represent a paradigm shift in food safety, merging nature's ingenuity with engineering precision. By leveraging renewable resources and advanced encapsulation techniques, these materials offer a sustainable, effective solution to removing toxic pollutants from the food chain. As research continues to refine their performance and address regulatory challenges, encapsulated bio-adsorbents are poised to become a cornerstone of global efforts to ensure safer, healthier food for all. Their potential to protect public health while minimizing environmental harm underscores the power of harmonizing technological innovation with natural systems.

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Reference

  1. Shamloo, Ehsan, et al. "Encapsulation of natural/bio-based materials as nano bio-adsorbents for removal of toxic pollutants from food products: A review." Carbohydrate Polymer Technologies and Applications (2025): 100870.

This article is for research use only and cannot be used for any clinical purposes.

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