From Plant Bioresources and Agro-Industrial Bioresidues to Health-Oriented Bioproducts: Green Recovery and Valorization of Oleanolic Acid

Oleanolic acid (OA) is a pentacyclic triterpenoid recoverable from several plant-processing residues, but its usefulness as a bioproduct feedstock depends on more than botanical occurrence. Olive leaves, olive pomace, grape pomace, and peel-rich fruit residues differ markedly in OA content, co-triterpenoid profile, moisture, handling requirements, and realistic product route. This review compares these feedstocks quantitatively where comparable data are available and examines extraction and purification as connected processing steps. Dimethyl carbonate has shown high OA selectivity in grape pomace. Microwave-assisted extraction studies report the amount of OA recovered per unit of dry biomass together with laboratory-scale energy data for residual olive skin, while supercritical CO2 is suitable for lipophilic matrices but may still require extensive downstream separation. DES and ionic-liquid systems remain less developed because solvent recovery, residual solvent control, and product compatibility have not been demonstrated for complete OA processes. Techno-economic and life-cycle studies on the same residue classes show that drying, transport, solvent recycling, energy integration, and co-product recovery can determine process performance; a complete OA-specific TEA or LCA was not identified. Product development also depends on whether the output is purified OA, a standardized triterpenoid-rich fraction, or a formulated matrix. Human evidence is most developed for OA-enriched olive oil, whereas most other health-related applications remain preclinical. No complete source–process–product dataset was identified that links feedstock composition, OA recovery, final specification, exposure, safety, and economic and environmental performance.