Impact of harvest time on chemical composition and antioxidant activity of fresh and dried plum fruits

The aim of this study is to establish the impact of harvest time on the chemical composition and antioxidant activity of fruits. A two-year research (2011 and 2012) was conducted on fruits of the 'Čačanska Rodna' cultivar, collected by selective picking at three 7-day intervals during the season and dried in the experimental dryer at air temperature of 90°C. Chemical composition was determined in both fresh and dried fruits using standard methods. The antioxidant activity was established using the ABTS method, while the content of total phenols and flavonoids was determined by the spectrophotometric methods with Folin-Ciocalteu reagent and aluminium-chloride, respectively. Using high-performance liquid chromatography (HPLC), it was revealed that the major phenolic compound in fresh plums and prunes is neochlorogenic acid, followed by caffeic acid. The obtained results reveal that prunes possess a higher antioxidant activity than fresh plum fruits, in all harvest times, which is determined by the phenol and flavonoids contents. Despite the fact that fruits were picked selectively for the drying purposes, later harvest caused an increase in the dry matter content and a decrease in total acids, accompanied by a decrease in the content of caffeic acid on the other side. Changes in the content of all the other parameters in the fresh plum fruits and prunes show no regular patterns in correlation with the harvest time.