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Highlights • The transformation of curcumin during its extraction in different systems. • The influence of extraction method on curcumin transformation was examined. • The influence of extractant type and pH on curcumin transformation was examined. • Formation of hydroxy and alkoxy adducts of different curcumin isomers. • MS2, HRMS and NMR analysis of curcumin transformation products. Abstract Curcumin is a phenolic compound produced by some plants, among which Curcuma longa is the reachest in this principal curcuminoid. Curcumin is known from its lability, however, the structural curcumin transformations and the formation of hydroxy and alkoxy adducts has not been reported yet. The formation of the mentioned derivatives is favoured by an alkaline environment. The presented results are important both from the analytical and food processing point of view as curcumin transformation products can be mistakenly treated as new components naturally present in turmeric, while in fact they may be formed during food products preparation, causing consumer misinformation about their bioactivity. In this context, an attempt has been made to investigate this problem. The present paper shows that curcumin easily transforms into ketonic/enolic structural isomers and forms adducts with water and alcohols. All structures of these compounds were confirmed by MS n , HRMS and partly also by NMR data. [ABSTRACT FROM AUTHOR]