Mārcis Dzenis

Assessment of Alder Tree Bark Potential as a Renewable Source of Proanthocyanidins in Latvia

Abstract With the purpose to assess potential of alder tree bark as a renewable source of bioactive polyphenolic compounds, antioxidant properties of hydrophilic extracts and proanthocyanidins (PAC) isolated from bark of two alder species (grey alder and black alder) growing in Latvia have been examined employing two test systems, ABTS●+, DPPH● assays. In the tests the high free radical scavenging capacities of the PAC were demonstrated. The polyphenolic nature of the bark PAC opens the possibility of its application as food additive. The PAC has good potential as an antioxidant for mayonnaise.

CHARACTERIZATION OF BARK RICH-IN-TANNINS EXTRACTS FROM DECIDUOUS TREES WITH EMPHASIS ON THEIR ANTIOXIDANT ACTIVITY

The barks of deciduous trees spread over a wide area of Northern Europe, were sequentially extracted using solvents of increasing polarity. The highest yields of hydrophilic extractives were found for ash tree and goat willow (23.6% and 23.8%, respectively). The highest total contents of polyphenols were found for black alder and goat willow bark (0.18 GAEg-1 and 0.12 GAEg-1, respectively). Hydrophilic extract from the both grey and black alder barks contained high amount (up to 7% on bark dry mass) of condensed tannins (CT) or oligomeric proanthocyanidins (OPC). In tests with free radicals (ABTS•+, DPPH•), the high radical scavenging capacities of the hydrophilic extracts enriched with OPC were demonstrated. The antioxidant efficiency of the hydrophilic extracts and purified OPC from alder barks was tested by their influence on thermo-oxidative destruction of model polyurethane (PU) films. The hydrophilic extracts enriched with tannins have good potential as a technical antioxidant for polyurethanes, with the most prominent activity for the hydrophilic extract from black alder and goat willow bark.