Mechanical investigation to assess the peel contribution in apple fruit

• Peel strength of apple was assessed by a texture analyzer.
• Peel mechanical features were characterized by five novel parameters.
• Fruit peel contributes up to more than 60% to penetrometer firmness.
• Peel mechanical properties varied considerably within an apple germplasm collection.

Fleshy fruits are generally stored before consumption, especially apple, during which several diseases and disorders can occur. Mechanical handling and transportation may cause general wounding, leading to dramatic quality decay and fruit loss, thus to a negative economic impact. Although the majority of the research addressing fruit quality has mainly focused on the flesh, the multi-layered peel tissue complex represents the first natural barrier of a fruit. In this study, a texture analyzer was employed to investigate the peel contribution on the general fruit firmness of apple, assessing a germplasm collection composed by 65 accessions after two months of cold storage. This device generated a mechanical force–displacement profile from which a set of analytical parameters was derived. A comparative analysis between intact and peeled portions performed on each single fruit, enabled the characterization of the contribution of the peel on fruit firmness. By analysing the phenotypic variance of these analytical parameters within the apple collection by a multivariate statistical approach, two clusters were identified, amongst which a specific set of apple cultivars was distinguished by a superior peel contribution. The parameters here isolated and employed are finally proposed as novel traits with a potential impact for breeding, and suitable for the characterization and selection of novel accessions with an enhanced postharvest potential due to an improved mechanical performance of the peel.