Antioxidant Capacity and Polyphenolic Content of Blueberry (Vaccinium corymbosum L.) Leaf Infusions

Antioxidant capacity and polyphenolic content of leaf infusions prepared from six highbush blueberry cultivars (Vaccinium corymbosum L.), one wild lowbush blueberry cultivar (Vaccinium myrtillus L.), and one commercially available mix of genotypes were determined. In order to simulate household tea preparation conditions, infusions were prepared in water heated to $95^{\circ}C$. The dynamics of extraction of polyphenolic antioxidants were monitored over the course of 30 minutes. Extraction efficiency, quantified in terms of the total phenol (TP) content, and antioxidant capacity of infusions, evaluated by the ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,20-azinobis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging assays, were compared with cultivar type and extraction time. The 30-minute infusions exhibited the highest TP content and antioxidant capacity according to all three assays. Wild blueberry infusion had the highest TP content (1,879 mg/L gallic acid equivalents [GAE]) and FRAP values ($20,050\;{\mu}M$). The range of TP values for 30-minute infusions was 394.1,879 mg/L GAE with a mean of 986 mg/L GAE across cultivars; FRAP values fell between 3,015 and $20,050\;{\mu}M$ with a mean of $11,234\;{\mu}M$ across cultivars. All 30-minute infusions exhibited significant scavenging capacity for $DPPH^{\cdot}$ and $ABTS^{\cdot+}$ radicals, comparable to different concentrations of catechin, gallic acid, and 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid. Overall, tested infusions showed significant reducing capacity as well as radical scavenging potential, which places blueberry leaf tea high on the list of dietary sources of antioxidants.