Stability of chlorogenic acid as model system after household microwave treatment

Several health benefits have been associated with the consumption of foods and drinks rich in chlorogenic acid [1]. However, besides the properties of this phenolic secondary metabolite, named also as 5-caffeoylquinic acid (5-CQA), an important issue is represented by its low stability during food processing or extraction procedures which result into isomerization to neochlorogenic acid (3-CQA) and cryptochlorogenic acid (4-CQA) as well as in the formation of further products [2]. Figure 1 shows the structure of the three main CQA isomers. According to a recent study [3], a notable reduction of 5-CQA content in Lycium barbarum leaf extracts after household preparation by microwave was observed, in respect to the more traditional decoction and infusion procedures. Based on this evidence, the 5-CQA reactivity in water was evaluated by simulating the domestic microwave procedure in the more drastic conditions, using as model system aqueous solutions of standard 5-CQA. Specifically, the results obtained by the use of commercial waters, characterized by a different fixed residue, were compared with those obtained by the use of analytical grade waters. An optimized HPLC-UV method allowed to monitor the 5-CQA conversion to its main isomers, while the identification and structural elucidation of further transformation products was performed by LCHRMS/MS. The results highlighted a different 5-CQA isomerization degree depending on the specific water sample, and the formation of oxidation derivatives of CQA isomers. The study highlights the importance of the analytical control to monitor 5-CQA transformation during microwave treatment. This represents a first stage which could allow minimizing CQA decomposition while preserving the potential health promoting effects of such bioactive constituent in foods and beverages.