Hydrothermal extraction, a promising method for concentrating phenolic antioxidants from red osier dogwood () leaves and stems.

Red osier dogwood (ROD) () is a popular ornamental shrub in most parts of North America. It has a record of ethnopharmacological uses by native North Americans. With increasing awareness about the health benefits of natural antioxidants, efforts are needed to develop methods for producing plant-based antioxidants as sources of nutraceuticals or functional food ingredients. This study aimed at establishing an optimum temperature for hydrothermal extraction of phenolic compounds from the leaves and stems of ROD. Spray-dried extracts obtained from hydrothermal extraction at four different temperatures, as well as their raw materials and spent residue were analyzed for moisture content and water activity. The samples were extracted with organic solvent and their total phenolic content, phenolic composition and antioxidant activity were also determined. Moisture content was below 10% and the water activity was below 0.6 inclusive, which are recommended for storing dry plant products. Glucogallic acid, ellagic acid, rutin, quercetin 3--malonylglucoside and quercetin were the phenolic compounds identified in all the samples. Rutin was the predominant compound. As expected, all the spray-dried extracts had higher phenolic content and antioxidant activity than the raw materials and spent materials. Among the temperatures studied, 98 °C was the most effective in extracting the phenolic compounds. The spray-dried extracts may find application in high-value antioxidant-rich products such as functional food ingredients and nutraceuticals. The spent materials retained a considerable amount of phenolic antioxidants and can therefore be useful in preparing antioxidant-rich animal feed.