Evaluation of potential applications for chestnut (Castanea sativa) shell and eucalyptus (Eucalyptus globulus) bark extracts

The potential of chestnut shell and eucalyptus bark extracts as phenol substitutes in the formulation of adhesives, as chrome substitutes in leather tanning and as a source of antioxidants compounds has been studied. The influence of extraction conditions, type and concentration of alkaline compounds (NaOH, Na2SO3 and Na2CO3) and temperature, on extraction yield and on extract characteristics: Stiasny number, tannin content, total phenols content, FRAP (ferric reducing/antioxidant power) antioxidant capacity and molecular weight distribution was analysed. Chestnut shell extracts had much better properties than eucalyptus bark extracts and significantly higher extraction yields were obtained. The increase of temperature from 70 to 90 °C not only increased the extraction yield but also improved the quality of the extracts. For both materials, the 2.5% Na2SO3–90 °C extract, together with the 2.5% NaOH–2.5% Na2SO3–90 °C extract for chestnut shell, showed high extraction yields and the best properties for all the applications proposed.