A fruit coating made from kitchen ingredients harvests electricity from humid air to power sensors while suppressing bacteria and extending shelf life up to 3.4 times.
(Nanowerk Spotlight) One-third of all food produced globally spoils before anyone eats it. Edible fruit coatings can slow decay by retaining moisture and inhibiting bacteria, but they remain passive layers that cannot signal when something goes wrong. Researchers have now built a coating from kitchen staples that does both: it actively suppresses bacterial growth while harvesting enough electricity from humid air to power environmental sensors. Made from gelatin, glycerol, and citric acid, paired with thin edible gold foil electrodes, the film extends fruit shelf life 2.5 to 3.4 times.
The approach builds on a 2015 discovery that certain materials generate electricity by absorbing atmospheric moisture, releasing ions that flow directionally to create current. First demonstrated in graphene oxide films, this phenomenon suggested that food-grade ingredients might serve as edible power sources.
Two obstacles slowed progress. Most moisture-sensitive materials investigated for power generation contain components unsuitable for consumption. Food-based materials, meanwhile, delivered electrical output too weak for practical use, with voltages often below 0.1 V. Tangled molecular chains and dense hydrogen bonding networks in natural food polymers trap ions and impede their movement.
A study published inAdvanced Functional Materials (“Edible Electronics for Energy Harvesting and Antibacterial Preservation via Moisture‐Induced Ion Migration”) overcame both barriers. Researchers at Donghua University and affiliated institutions in China developed what they call “E-aspic,” named after the traditional savory jelly dish made from meat stock. The active film uses only edible components: gelatin (the protein in aspic), glycerol (a food-grade fat), and citric acid (a familiar seasoning).
Concept of edible E-aspic. a) Preparation of aspic-based edible electronics with properties for fruit preservation and energy harvesting. b) Edible raw materials are derived from a wide range of biological products. c) The energy-harvesting and antibacterial mechanisms of E-aspic originate from the moisture-induced generation and migration of free ions. d) Self-powered and preservative fruit coating. The integration of E-aspic on the fruit surface enables power supply to external electronic devices. e) Miniaturized E-aspic unit voltage performance exceeds 12 h (the upper and lower electrodes are gold foil). f) Designing flexible edible electronics. E-aspic can be fabricated in various shapes and incorporates other edible ingredients whilemaintaining its self-powered capability. (Image: Reproduced with permission from Wiley-VCH Verlag) (click on image to enlarge)
Exposed to humid air, E-aspic generates electricity through moisture-induced ion migration, achieving a peak power density of 0.45 mW cm⁻³, sufficient to directly power environmental sensors without requiring rectification and with minimal power management. Active-metal electrodes such as aluminum or zinc boost electrical output through redox reactions but are unsuitable for direct ingestion; fully edible configurations use gold foil electrodes instead.
Controlling how hydrogen ions move through the material proved central to the design. In ordinary gelatin, polymer chains entangle and form extensive hydrogen bonds, trapping ions and limiting mobility. Glycerol restructures this network by weakening interactions between molecular chains, allowing ions to migrate freely. Molecular dynamics simulations confirmed increased diffusion rates in the modified system.
Citric acid raises the concentration of free ions available for transport through its three carboxyl functional groups, while its hygroscopic nature enhances moisture absorption. Together, these modifications produce nearly a fourfold increase in moisture uptake at 60% relative humidity.
Quantum chemistry calculations confirmed that gelatin donates electrons to hydrogen ions more readily than the other components, channeling ion movement along the polymer backbone rather than through the surrounding matrix.
Environmental conditions affect device output. At 25% humidity, voltage remains stable but current drops. At 90% humidity, current reaches 3.94 mA cm⁻³. The operating range spans −4 to 40 °C and 25% to 90% relative humidity, covering typical food storage conditions, though performance depends on maintaining adequate moisture levels.
Applied as a fruit coating, E-aspic forms a thin, transparent film that enhances surface gloss while preserving natural appearance. In mechanical testing, a representative film measuring approximately 0.025 cm thick exhibited 153.4% strain capacity (meaning it can stretch to more than 2.5 times its original length without breaking), with 6.6 MPa fracture strength, and bent without cracking.
The ion migration that powers the device also suppresses bacterial growth. The acidic environment within the coating affects cellular metabolism, while hydrogen ions migrating toward the fruit surface adsorb electrostatically onto negatively charged bacterial membranes. This disrupts the transmembrane potential bacteria need for nutrient transport and metabolism, ultimately compromising membrane integrity.
Tests against Escherichia coli and Staphylococcus aureus showed near-complete elimination of bacterial colonies at 15% and 20% E-aspic concentrations. Electron microscopy revealed cell shrinkage, membrane damage, and leakage of contents.
Preservation results varied by fruit type but consistently extended shelf life by 2.5 to 3.4 times. Uncoated loquats began rotting on day 2; coated ones remained viable after 17 days. Bananas extended from 4 to 10 days, cherries from 5 to 17, and blueberries from 5 to 15.
The system scales readily. Just 1.5 g of raw materials yields 100 E-aspic units at an estimated materials cost of 0.867 cents. Connected in series, 100 units generate 81.5 V of direct current. In parallel, they produce a peak current of 6.1 mA.
The researchers demonstrated the concept by coating cherry tomatoes with E-aspic wired into a 3×3 array. The edible circuit powered temperature and humidity sensors throughout storage, tracking conditions that would otherwise require conventional batteries containing toxic materials like lithium.
Limitations remain. Electrical output varies significantly with humidity and temperature, and electrode selection involves tradeoffs between performance and edibility. The technology has yet to be tested in commercial supply chains.
A coating that extends shelf life, suppresses bacteria, and powers its own monitoring system from humid air nonetheless offers a practical path toward smarter food logistics. The raw materials derive from industrial biomass byproducts and low-value agricultural waste, fabrication requires only a water bath and household dryer, and in its fully edible configuration the system is water-soluble and safe to consume. For an industry losing one-third of its product to spoilage, the appeal extends well beyond novelty.
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Chengyi Hou (Shanghai Jiao Tong University School of Medicine)
, 0000-0003-4142-2982 corresponding author
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