Physical and mechanical properties of lemon (Citrus lemon) seeds

The objective of this study was to determine some geometric, gravimetric, and mechanical properties of lemon seeds and how these were influenced by moisture content under a range of post-storage processing conditions. The skin, pulp, and seed fractions of lemon fruits were determined. The seed fraction had a value of 1.86% with an average hull/seed ratio of 38.92%. Seed moisture content was varied by drying with hot air from the storage condition (8.28% d.b.) to a minimum moisture condition (1.31% d.b.). The drying kinetics were adequately described using a two-term exponential model, which suggested the presence of two distinct internal seed resistances to moisture transfer related to its composition. Furthermore, with the exception of thickness, all geometric properties evaluated tended to decrease as moisture content decreased, especially at the driest level evaluated. Within these, the most important variations were found in theoretical volume (24.20%) and width (22.28%), for a moisture content change of 84%. Gravimetric and mechanical properties exhibited the same tendency, with the exception of true density, which increased, and bulk density and bulk porosity which did not change significantly. It is noteworthy that rupture energy decreased by approximately 50% as the moisture content was reduced from 8.28 to 4.62%. In conclusion, drying lemon seeds generated smaller and more fragile structures that could benefit subsequent processes such as dehulling or milling, among others, but could also negatively affect seed movement through undesirable breaking. Therefore, knowledge of the properties studied in this work will be useful for the design of manufacturing and storage equipment, as well as handling and process operations.