Impact of storage period and conditions on mechanically harvested olives (Olea europaea L.)

• Phenolics changed even in visually undamaged fruit. • Oleuropein degraded faster in riper fruits under uncontrolled conditions. • Metabolic changes were more intense in fruits that were more mature at harvest. • Cold storage reduces maturing and oxidation during storage. In this study, changes in visual, physical and biochemical parameters of mechanically harvested olive fruit cultivar 'Istrska belica' were evaluated during 23 days of storage under cold (C) and uncontrolled (U) conditions over two years. At harvest, the fruit of both years had a similar maturity index (0.62 and 0.76) and fruits weight (2.75 g and 2.85 g) but different firmness (5.98 N and 5.77 N) and phenolic content. In 2022, fruit at harvest were softer and had more damaged spots after mechanical harvest, which resulted on a greatest decrease in antioxidant capacity during storage (for 12 % in U and 9 % in C). Although, firmness and fruit weight decreased while the maturity index increased, the changes during storage were more evident in phenolic content, from which oleuropein decreased the most (in 2021 for 30 % in U and 18 % in C, in 2022 for 31 % in U and 15 % in C). Consequently, the content of its degradation products, including demethyloleuropein glucoside, elenolic acid, and verbascoside, increased over time under both storage conditions. On the other hand, an increase in oleuropein degradation was observed under uncontrolled storage conditions, which was also confirmed by the faster increase in the final products (elenolic acid glucoside, hydroxytyrosol glucoside and oleoside). Changes in phenolic contents, physical parameters and damage propagation were slower at the lowest storage temperature. The initial quality of the fruit, such as ripeness, firmness and damage, also had a strong influence on changes during storage. The results suggest that fruit should not be overripe before storage and should be cooled as soon as possible for the shortest time necessary to minimise oxidation and phenolic degradation.