Abstract: A method of marking fruits includes an incision in a fruit piece surface with a laser beam and the deposition in the superficial incision of a contrast agent comprising salts or oxides of iron or copper at a concentration between 0.001% and 1% of the total weight. The salts or oxides are capable of reacting with any of the phenolic and/or polyphenolic compounds present in the superficial tissues of the fruit. This contrast agent may also include other additives: acidity regulators, emulsifiers, antioxidants and complexing.

Abstract: The present invention relates to a process for obtaining nanocrystalline corundum, characterised in that it comprises a first step of thermal treatment of the raw material used in the process at standard pressure, to a temperature greater than that of the last endothermic accident of the differential thermal analysis record of the raw material, performed to 925° C.; and a second step of fast cooling from the maximum temperature reached in the preceding step to room temperature. Moreover, the present invention relates to the nanocrystalline corundum obtainable from the process described, as well as to multiple uses of said corundum. Furthermore, this material may be disaggregated, for example by means of high-energy grinding, to produce a fine aggregate that may be used as an abrasive or as a functional load in plastic polymers or other types of materials.