ORCHARD WASTE AS A VALUABLE BIO-RESOURCE: A CHEMICAL COMPOSITION ANALYSIS

A significant volume of biomass is burned or abandoned during apple production as a result of cultural practices such as spring and summer pruning and thinning of excess fruitlets. As a part of investigations for possible alternative uses of valuable natural products present in orchard waste, the occurrence of phenolic compounds in spring pruning twigs of ‘Cortland’ and ‘Bishop Pippin’, summer pruning leaves and stems of ‘Northern Spy’ and hand-thinned immature ‘Honeycrisp’ fruit was determined and compared with mature ‘Idared’ fruit. For the identification of phenolic compounds, liquid chromatography coupled to triple quadruple mass spectrometry (LC-MS/MS) in tandem mode was used. The dehydrated plant tissues were ground into a fine powder and the compounds were extracted using acidified methanol. Identification and quantification of 25 selected phenolic compounds was performed by comparing their retention times with those of authentic standards and their mass spectra in multiple reaction monitoring (MRM) mode. Among the 16 major phenolic compounds detected in spring pruning branches, dihydrochalcones (137 mg/100 g dry weight [DW]) and flavonols (130 mg/100 g DW) were the most abundant and represented 80% of total phenolics. Leaves of summer pruning branches of ‘Northern Spy’ contained 3.8-fold higher total phenolics than that of their stems. Approximately 66% phenolics of leaves of summer pruning branches were represented by three quercetin (q) glycosides: q-3-galactoside, q-3-glucoside, and q-3-rhamnoside. The major phenolics of immature ‘Honeycrisp’ apples were epicatechin, phloritin, phloridzin, cyanidin-3-galactoside, and q-3-glucoside. Overall, among the tested orchard waste, abundance of total phenolics based on DW was distributed in the order of: summer pruning leaf > spring pruning stem > immature fruit > summer pruning stem > mature fruit.