Green coffee beans are rich in polyphenol chlorogenic acids (CGAs), which are decomposed to give caffeic acid (CFA) and quinic acid (QNA) upon roasting. CGA, CFA and QNA primarily confer the bitterness, astringency and acidity to the coffee brew. Aiming at the structural and thermodynamic insights into the β-cyclodextrin (β-CD) encapsulation of key compounds in coffee (CGA 1, CFA 2, and QNA 3), a systematic, comprehensive study using single-crystal X-ray diffraction and DFT calculation has been undertaken. Scrutinizing the X-ray-derived inclusion structures of 1-3 reveals that the CFA moiety plays a determinant role in complexation, in agreement with the DFT-derived relative thermodynamic stabilities. The guest molecules gain stability through OH⋯O hydrogen bonding with β-CD and are well shielded in the β-CD wall. The three stable β-CD inclusion complexes with coffee key compounds suggest the implications of CDs as encapsulating agents for improving bioactivities and masking bitter taste in foods.
Keywords: Caffeic acid; Caffeic acid (PubChem CID: 689043); Chlorogenic acid; Chlorogenic acid (PubChem CID: 1794427); DFT calculation; Ethanol (PubChem CID: 702); Quinic acid; X-ray analysis; d-(−)-Quinic acid (PubChem CID: 24278290); β-Cyclodextrin; β-Cyclodextrin (PubChem CID: 444041).
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