Chlorogenic acid (CQA), the ester of caffeic acid with quinic acid, has been one of the most studied polyphenols due to its potential biological activity and usefulness in pharmaceutical treatment. We found that in an aqueous solution of each chlorogenic acid isomer, 3-, 4- and 5-CQA, its two complexes with water are formed. In the RP chromatographic system, these CQA-water derivatives differ in retention data from that of their precursors and do not decompose, which indicates their considerable stability. The formation of CQA-water complexes has not been reported yet. Comprehensive NMR research of CQA-water derivatives complexes shows that their significant stability results from the formation of hydrogen bonds between water and CQA isomer – e.g., between water and OH3, OH4 and ester groups of CQA molecule in the case of 5-CQA-water derivative. The existence of CQA-water derivatives in CQA containing food products was in the paper shown. It should be noted that the stable CQA-water complexes may exhibit a different biological activity than CQA. This issue requires separate biomedical research.

The valorisation and management of agri‐food waste are currently hot investigation topics which probe the recovery of valuable compounds, such as polyphenols. In this study, high‐pressure/high‐temperature extraction (HPTE) and ultrasound‐assisted extraction (UAE) have been used to study the recovery of phenolic compounds from grape marc and olive pomace in hydroalcoholic solutions. The main phenolic compounds in both extracts were identified by HPLC‐DAD. Besides extraction yield (total polyphenol and flavonoid content) and the antiradical power, polyphenol degradation under HPTE and UAE has also been studied. HPTE with ethanol 75% gave higher phenolic extraction yields: 73.8 ± 1.4 mg of gallic acid equivalents per gram of dried matter and 60.0 mg of caffeic acid equivalents per gram of dried matter for grape marc and olive pomace, respectively. In this study, the efficient combination of ethanol/water mixture with HPTE or UAE has been used to enhance the recovery of phenolic compounds from grape marc and olive pomace. HPLC‐DAD showed that UAE prevents phenolic species degradation damage because of its milder operative conditions.