Variation of phenolic profile and antioxidant activity of North American highbush blueberry leaves with variation of time of harvest and cultivar

The phytochemical composition of leaves varies with the stages of growth of a plant. Hence, during this study, moisture content, total phenolic content, total monomeric anthocyanins and antioxidant activity in terms of DPPH inhibition activity and FRAP in highbush blueberry leaves of two different cultivars Nelson and Elliot, harvested in May, July, September and October, were analysed and quantified using microwave assisted extraction with a solvent combination of ethanol and citric acid. Colour indices for respective powdered leaf samples were also analysed. It was observed that leaves of both the cultivars had a high amount of total phenolics in October (for Nelson 152.356 ± 3.369 and for Elliot 155.830 ± 2.103 mg GAE/g dry matter respectively). However, the blueberry leaves of the Nelson variety had the highest content of monomeric anthocyanins (1.202 ± 0.080 M 3-G equiv./g dry matter). The DPPH inhibition activity and FRAP for Elliot leaves were much higher than the Nelson leaves collected during May, July and September. However, Nelson leaves collected in October had higher DPPH inhibition activity and FRAP than the Elliot leaves. Total phenolic contents of the leaves were found to be strongly correlated to both DPPH inhibition activity and FRAP. Also strong positive correlation was observed between colour index “a” and total monomeric anthocyanin content, which implied an increase in redness of the leaves with an increase in the monomeric anthocyanin content which is experienced in the Fall season.