It is well known that active packaging extends the shelf life of food thanks to the antimicrobial and antioxidant properties of its components, which are typically essential oils and nanomaterials (silver, zinc oxide and titanium dioxide). Recently, attention has been shifting from conventional nanomaterials to ‘carbon quantum dots’ (CQDs), a term that refers to carbon nanoparticles with a size of less than 10 nanometres, where one nanometre is one thousandth of a millimetre. These particles are so small that it would be possible to line up thousands of them across the width of a human hair. CQDs are already used in a variety of fields, from biomedicine for drug delivery to solar cells. At present, CQDs have received less research attention than silicon quantum dots or quantum dots based on other semiconductors, which are used in transistors, solar cells, cancer detection techniques and LED lighting. A method for preparing CQDs from fruit waste , which is a renewable biomass, has recently been developed. A review by D. Gupta et al. (2025) described the relevant preparation processes, the properties of CQDs and their applications in food packaging.

Preparation of DQFs from fruit waste

The fruit processing industry generates a large quantity of inedible waste (peels, husks and seeds), which accounts for 30–40% of the total weight of the fruit and can be used as cost-effective and sustainable raw materials for the production of DRCs:

⦁ Peels from oranges, lemons, pineapples, pomegranates, watermelons, mangoes, bananas, papayas and kiwis;

⦁ Peanut, lychee, walnut and passion fruit husks;

⦁ Papaya, avocado and apple seeds.

Using these waste materials as a starting point, DQCs can be synthesized through both top-down and bottom-up approaches. Specifically, top-down approaches involve the decomposition of carbohydrates and carbon fibres into DQCs through the following processes:

⦁ Laser ablation, which is rapid and produces highly pure DQCs, but requires specialised equipment;

⦁ Electrochemical oxidation, which produces DQCs in high yields, but also requires specialised equipment;

⦁ Combustion, which is a simple process but yields low yields and produces particles of uneven size, which therefore do not deliver optimal performance.

Active food packaging made from fruit waste

Bottom-up approaches, however, produce CQDs from smaller carbon units through the following processes and are generally preferred over top-down processes due to their environmental friendliness and cost-effectiveness:

⦁ Microwave synthesis, which is simple, fast, and environmentally friendly, but allows limited control over the size of the CQDs, making them unlikely to be uniform;

⦁ Pyrolysis, which is a simple, high-yield method;

⦁ Hydrothermal synthesis, which is simple, economical, high-yield, allows size control, and is environmentally friendly, but is slow and requires high temperatures and pressures.

This type of synthesis is among the most widely used to prepare CQDs from fruit waste because it can be conducted on a large scale.

Properties of CQDs for food packaging

CQDs produced from fruit waste have the following important properties for food packaging:

• non-toxicity and safety;
• excellent antimicrobial properties, important for delaying the spoilage of packaged foods and ensuring food safety. The antimicrobial properties of CQDs derive both from their small size, which allows them to pass through microbial cell membranes and reach the interior of the cell, and from their ability to be engineered specifically to interact with target microorganisms;
• excellent antioxidant activity, derived from the fact that fruit waste is rich in polyphenols. These are powerful antioxidants capable of neutralizing the action of free radicals, which are known to be responsible for the oxidation of all organic molecules;
• UV blocking: the incorporation of CQDs into food packaging creates a protective UV barrier that shields foods from harmful UV radiation, thus preserving the organoleptic properties, nutritional content, and color stability of food products.