Extraction characteristics and kinetic studies of oleanolic and ursolic acids from Hedyotis diffusa under ultrasound-assisted extraction conditions

• OA and UA were extracted from H. diffusa using an ultrasound-assisted process.
• The hyphenated process is an efficient alternative to conventional liquid extraction.
• OA and UA extractions were analyzed using a second-order kinetic model.
• The extraction rates of OA and UA could be modelled by the Arrhenius equation.
• H. diffusa may be an important source of OA and UA.

We report a hyphenated procedure for the extraction of oleanolic acid (OA) and ursolic acid (UA) from Hedyotis diffusa. The hyphenated ultrasound-assisted extraction (HUAE) procedure consists of heat-reflux extraction (HRE) followed by ultrasound-assisted extraction (UAE). This hyphenated technique uses a lower temperature, consumes less solvent and is faster than previous methods. Compared to heat-reflux and traditional ultrasound-assisted extractions, HUAE gave a 12% higher yield of OA and UA from H. diffusa and required less severe operating conditions. Thus, mild operating conditions can be used, which results in a higher quality product. HUAE is an effective and selective method for the extraction of OA and UA. Additionally, the HUAE of OA and UA from H. diffusa were interpreted using a second-order kinetic model to predict the extraction parameters at various temperatures. Furthermore, the activation energies for the extractions of OA and UA were 9.073 and 10.575 kJ/mol, respectively, based on the second-order extraction rate constants used to build the models. By fitting the main parameters of the model, we could compare the effects of the extraction parameters on the H. diffusa material and better understand the extraction process.

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