Antioxidant capacity of four polyphenol-rich Amazonian plant extracts: A correlation study using chemical and biological in vitro assays

Many plants used in Amazonian folk medicine present a high antioxidant activity. In this study, the antioxidant activities of four largely used plants, namely Byrsonima crassifolia, Davilla kunthii, Davilla rugosa and Inga edulis, were evaluated, using methanolic extracts of their leaves, fruits and bark and several different in vitro tests, based either on the capacity to scavenge free radicals (ORAC, TRAP) or on the ability to protect biological structures (LDLs, erythrocytes). The total phenolics (TP), flavanoids (TFA) and flavonols (TFO) were also measured. Almost all extracts performed well in all assays of antioxidative capacity, with best activities found in leaves (compared to fruits and bark). Most antioxidative performance indicators (ORAC, TRAP, LDL protection) correlated well with the TP and TFA content of the extracts. Conversely, correlation was lower between TFO and these indicators, reflecting a lower involvement of these compounds in antioxidant processes. Erythrocyte protection against oxidant-triggered haemolysis showed no correlation with any of the phenolic content indicators, suggesting that most of these compounds have a low ability to protect lipid targets in the erythrocyte membrane. On the other hand, protection of erythrocytes against haemolysis correlated positively with LDL protection. The extract of I. edulis leaves contained average amounts of polyphenols but ranked first in the majority of the tests, indicating the occurrence of particularly efficient compounds with very important antioxidant properties, which could be used for medicinal and other applications.