Electroactive Phenolic Contributors and Antioxidant Capacity of Flesh and Peel of 11 Apple Cultivars Measured by Cyclic Voltammetry and HPLC-DAD-MS/MS.

In this study, 11 apple cultivars were characterized by their total phenolic content (TPC) and total flavonoid content (TFC) and antioxidant, reducing, and chelating capacity by 2,2-diphenyl-1-picrylhydrazyl (DPPH) test, cyclic voltammetry (CV), and ferric reducing antioxidant power (FRAP) assays; and ferrous ion chelating capacity. The phenolic compounds in flesh and peel were determined by liquid chromatography coupled to mass spectrometry and diode array detector (HPLC-DAD-MS/MS) and their electroactivity by CV. The results showed higher TPC, TFC, and antioxidant capacity by DPPH test in the peels of all apple cultivars as compared to the respective flesh. The peel extracts also showed two-fold higher FRAP values as compared to the flesh extracts. The reducing capacity of the peel and flesh determined by CV measurements confirmed the results achieved by spectrophotometric methods of evaluating antioxidant capacity. There was no significant difference in chelating capacity in the peel and flesh. The HPLC-DAD-MS/MS analysis showed the presence of 11 phenolic compounds in the peel and flesh which varied in antioxidant, reducing, and chelating activity. The order of the phenolic compound content in flesh and peel in Quinte cultivar, which showed the highest antioxidant capacity, was as follows: epicatechin > chlorogenic acid > quercetin 3-arabinoside > quercetin 3-glucoside > cyanidin 3-galactoside > quercetin 3-rhamnoside > catechin > phloridzin > rutin > phloretin = quercetin. CV results were highly correlated with those obtained by spectrophotometry and HPLC-DAD-MS/MS, providing evidence to support the use of cyclic voltammetry as a rapid method to determine the phenolic profile and reducing the power of apple flesh and peel. The association between antioxidant assays and phenolic compound content showed that the highest contribution to the antioxidant capacity of apple peel and flesh was provided by catechin, epicatechin, and cyadinin-3-galactoside, while phloretin, phloridzin, and chlorogenic acid were the main contributors to chelating activity. Results from this study clearly indicate that removing the peel from apples may induce a significant loss of antioxidants.

Evaluation of flavonoid contents and antioxidant capacity of the aerial parts of common and tartary buckwheat plants.

The analysis of major and minor flavonoids, and antioxidant capacity of stems, leaves, flowers, unripe seeds and ripe seeds of common and tartary buckwheat plants collected during different growth periods was addressed in this study. The highest rutin contents were observed in flowers and leaves collected from common and tartary buckwheat at early flowering as well as flowering and seed formation states. A low quercetin contents were found in all studied aerial part of buckwheat plants. Quercitrin (quercetin-3-rhamnoside) was only found in flowers collected at different growth periods while flavone C-glucosides were accumulated preferentially only in unripe seeds collected from common buckwheat at an early flowering state. The rank of antioxidant capacity provided for aerial parts of common and tartary buckwheat at early flowering state was as follows: flowers > leaves > stems. The highest contribution of rutin to the antioxidant capacity of the aerial parts of common and tartary buckwheat was found for stems followed by leaves, flowers and unripe seeds. The results demonstrate that flowers from common and tartary buckwheat collected at early flowering as well as flowering and seed formation states have the future potential to be a useful food ingredient.