In the light of the facts: a review on photoactivable nanomaterials applied on fruit

In recent years, scientist involved in the food sector started to look at nanotechnologies with growing interest. Nanostructures can convey different types of substances, such as antibacterial and anti-maturation ones, allowing for their gradual and controlled release. Furthermore, they can release their content when in contact with a certain target or after a certain event, such as a photo-activation inductor. Paradoxically, nanostructures are widely studied and used in medicine, as vectors of drugs against cancers and other diseases while, on the contrary, food applications are still at the embryonic stage, due to possible harm to consumers. Indeed, the European Food Safety Authority (EFSA) prohibited the use of nanocarriers smaller than 100 nm of food because they could be a risk for health. This review aims to analyse which photosensitive compounds can be used in the form of nanostructures to increase shelf life of fruits. In particular, we focus our attention on berries, which have a short shelf life, a very delicate and thin peel and also a high added value. Photoactivation generates reactive oxygen species (ROS) elicited by illumination with visible (in general blue light) or ultraviolet (UV) light. Such ROS generation leads to the inactivation of many bacterial strains, especially Gram-positive ones, included multi-drug-resistant pathogens as Enterococcus faecium, Staphylococcus aureus and Enterobacter. Many natural substances are photosensitive, i.e., curcumin, melatonin, hypericin, and essential oils. Among them, curcumin, a component of Curcuma longa L., was very effective to improve the shelf life of berries because its antioxidant properties and its antibacterial affects Gram-negative bacteria. Moreover, new formulations of nanostructures proposed as coatings for berries will be investigated, showing their strengths and weaknesses.