Valorisation of Nigerian Medicinal Plant Waste Biomass: Bioactive Compound Recovery, Antioxidant Activity, and Potential for Nutraceutical Application

The commercial processing of medicinal plants in Nigeria generates substantial biomass waste streams from juice extraction, oil pressing, and decoction residues that currently represent lost pharmacological and economic value. A circular economy approach to Nigerian medicinal plant processing demands systematic valorisation of these by-products through recovery of residual bioactive compounds and their development into nutraceutical applications. This PhD research characterises the bioactive compound profiles, antioxidant activities, and nutraceutical feasibility of waste biomass from the industrial-scale processing of five commercially important Nigerian medicinal plants: Hibiscus sabdariffa calyces, Moringa oleifera seeds, Garcinia kola seeds, Adansonia digitata fruit pulp, and Zingiber officinale rhizomes. Processing residues were collected from herbal product manufacturers in Lagos, Kano, and Enugu. Residual phytochemical content was quantified by UHPLC-HRMS following optimised extraction. Total phenolic, flavonoid, and anthocyanin content were compared to primary extracts. Antioxidant capacity was evaluated by DPPH, ABTS, FRAP, and ORAC assays. Functional properties including water-holding capacity, oil absorption capacity, and prebiotic fermentation potential were assessed. Safety evaluation included heavy metal screening, mycotoxin detection, and microbial load assessment. Significant residual bioactive content was demonstrated in all five waste streams, with H. sabdariffa residues retaining 42% of primary extract polyphenol content. Nutraceutical feasibility scores were calculated based on bioactive density, safety profile, and processing adaptability. The Zingiber and Moringa seed waste fractions were identified as highest-priority candidates for nutraceutical development. Economic valorisation modelling projected 23-38% revenue increase for participating processors. Keywords: valorisation, medicinal plant waste, nutraceutical, antioxidant, circular economy