Improved stability of (+)-catechin and (−)-epicatechin by complexing with hydroxypropyl-β-cyclodextrin: Effect of pH, temperature and configuration

•The thermodynamic parameters of CA (EC) + HP-β-CD complexes were obtained.•The inclusion interactions were enthalpy-driven process.•HP-β-CD showed a stronger protection effect on CA than that on EC.•1H NMR provided conclusive evidence regarding the formation of inclusion complexes.

The stability and bioavailability of catechins, a kind of tea polyphenols with health benefit, could be improved by complexing with cyclodextrins. The aim of this study was to investigate the complexation of two geometrical isomers, (+)-catechin and (−)-epicatechin, with hydroxypropyl-β-cyclodextrin (HP-β-CD) in tris–HCl buffer solutions at pH 6.8–8.0 using isothermal titration calorimetry, fluorescence and proton nuclear magnetic resonance spectroscopy. Experimental results showed that these inclusion interactions are primarily enthalpy-driven processes. The complexation constant (KC) of EC + HP-β-CD complex was less than that of CA + HP-β-CD at the same temperature and pH value. Temperature and pH studies showed that the KC value decreased with the rise of temperature and pH. Stability study indicated that HP-β-CD showed a stronger protection effect on CA than that on EC. The different inclusion modes between CA and EC were discussed in terms of the discrepancy in their molecular structures.