Phenotypic, bioactive and metabolomic diversity among indigenous Southern African underutilised monkey orange (Strychnos spinosa Lam.) fruit accessions

Strychnos spinosa Lam. is an indigenous African fruit tree with considerable phenotypic diversity, yet the extent to which visible fruit morphotypes correspond to biochemical and metabolic variation remains poorly resolved. This study integrated fruit morphology, physicochemical traits, spectrophotometric bioactive-compound assays, antioxidant capacity and untargeted LC-QTOF-MS profiling across 32 accessions collected in KwaZulu-Natal, South Africa. Large pyriform fruits (fresh weight: 1103-1328 g) exhibited elevated carotenoid content (632.50 mg β-carotene/100 g) and lipid-rich metabolite profiles dominated by phosphatidylcholines. Small roundish purple fruits demonstrated higher titratable acidity (1.20-1.83%) and phenolic content (3.72 mg GAE/g), correlating with superior antioxidant activity (DPPH: 1.82 μmol TE/g; positive correlation with TPC, r = 0.65 ). Smooth green fruits displayed balanced total soluble solids (14-16 °Brix) and titratable acidity (1.50-1.80%) with diverse metabolite clusters. Multivariate analysis showed that external morphotype captured only part of the underlying biochemical variation, indicating that morphology alone is insufficient for selecting chemically distinct germplasm. Untargeted metabolomics further resolved accession-dependent chemical variation and highlighted lipid-like, terpenoid-like and other discriminatory ions; structural assignments are treated as putative pending confirmation with reference standards and diagnostic MS/MS evidence. Five accessions (GvRR-GRO, GRP-dGEO, PRxCP-GEF, PRR-dGEF and GSR-dGRF) were identified as contrasting candidates for subsequent validation of digestive stability and bioaccessibility. These findings expand knowledge of intraspecific diversity in S. spinosa and provide an evidence base for germplasm characterization, conservation, selection and future domestication of this underutilized southern African fruit tree.