Recovery of added value compounds from cork industry by-products

•Recovery of tannins from cork granulate and powder was studied by RSM.•Extraction efficiency increases using cork powder by using 60% acetone, 9h30.•Twenty-three ellagitannins were tentatively identified by HPLC-DAD/ESI-MS.•Dimer of gallocatechin linked to ellagitannins tentatively identified by MALDI-TOF.•Cork powder is a potential raw material for the recovery of high valuable compounds. The generated residues from cork industry are granulated and reused for the production of agglomerates, yet there is a percentage of those residues not valorised due to the small granulometry size denominated as cork powder. The extraction of high valuable compounds such as ellagitannins and condensed tannins from these cork residues were studied using different experimental approaches. For the extractions, a response surface methodology (RSM), using aqueous solutions of two green solvents such as acetone and ethanol, was used. Acetone was the best organic solvent due to the high yield of extraction achieved and less results variability. Using cork powder the extraction efficiency increased due to the increase on the yield of extraction (5.8 ± 1.0 mg ellagic acid equivalents/ g cork powder and 4.3 ± 0.8 mg proanthocyanidin fraction equivalents/ g cork powder) by using less solvent concentration (60% acetone) and extraction time (9h30). Twenty-three ellagitannins were tentatively identified by HPLC-DAD/ESI-MS in the tannin-rich extract of both corks granulate and powder, five of them being reported for the first time in cork extracts: vescalin, castalin, guajavin B/ eugenigrandinin A, vescavaloninic and castavaloninic acids. Other complex ellagitannins such as glycosylated structures up to DP3 of acutissimin A/B and guajavin B/ eugenigrandinin A, other oligomeric ellagitannins and a glycosylated dimer of gallocatechin linked to vescalagin/castalagin were tentatively identified by MALDI-TOF. These compounds recycled from undervalued cork industry residues may be further used in technological applications in different industrial fields, hence contributing for a circular economy. The results indicate that the recovery of these high valuable compounds using this methodology can add value and sustainability to this cork transformation chain.