Extraction of chlorogenic acids from hibiscus (Hibiscus syriacus L.) by subcritical-water

Chlorogenic acids are formed from hibiscus (Hibiscus syriacus L.) by ester bonding of caffeic acid and quinic acid, and they have isomers named neochlorogenic acid (NCGA) and cryptochlorogenic acid (CrCGA) that are esterified on different sites of caffeic acid. Subcritical-water extraction (SWE) is an ecofriendly and highly efficient technique because it utilizes a nontoxic solvent and has a very short extraction time. Twenty different SWE conditions were applied to hibiscus, with extraction times of 10–40 min, and extraction temperatures of 110–190 °C. The concentrations of chlorogenic acid, NCGA, and CrCGA were maximal for extraction conditions of 190 °C/10 min, 110 °C/10 min, and 130 °C/40 min, respectively. The extraction efficiency varied with the extraction conditions among the three isomers due to the hydrophilicity of the hydroxyl residue depending on the steric structure, the stability of the steric structure varying with the position of the acyl group, and the isomerization caused by the reversible movement of the acyl group.