Chemical compositions of raspberry leaves influenced by growth season, cultivars and leaf position

Raspberry leaves with high polyphenols have high utilization value, but the accumulation trend of phenolics in raspberry leaves in different growing seasons, cultivars, and leaf positions, is not clear. The utilization of leaves and raspberry comprehensive income are limited due to the uncertain factors. Therefore, the content changes of chlorophyll a, chlorophyll b, carotenoids, total phenolic content (TPC), total flavonoids content (TFC), saponins, hydrolyzed tannins and condensed tannins of raspberry leaves from May to October, in annual-fruiting (AF) raspberry (cv. Heritage) and biennial-fruiting (BF) raspberry (cv. Reveille, cv. Tulameen and cv. Australian Red), and three leaf positions were investigated. Eighteen phenolic compounds were identified in which quercetin-3-glucuronide, kaempferol-3-rutinoside, ellagic acid, chlorogenic acid, epicatechin and procyanidin B1 were quantitatively analyzed by HPLC-MS. The results showed that chlorophyll a, chlorophyll b, carotenoids showed a parabolic trend of rising first and then falling, while TPC, TFC, hydrolyzed tannins, condensed tannins and saponins showed a gradual increase trend from May to October. The total accumulation of secondary metabolites was the Heritage, Australian Red, Tulameen and the Reveille from high to low. The apical leaves accumulated TPC, TFC and quercetin-3-glucuronide, kaempferol-3-rutinoside, ellagic acid, while the basal leaves accumulated condensed tannins and saponins. Overall, growth season was the main factor affecting the accumulation of secondary metabolites, followed by cultivar and leaf positions. Therefore, according the properties of cultivars, it can be recommended that AF and BF cultivar leaves can be harvested twice in early summer and late autumn after reproductive shoot preservation, while the leaves of BF cultivar without fruiting shoots can be extensively harvested once in late autumn.