Valorisation of Marula Fruit Peel: Polyphenols, Bioactivity and Food Applications

Marula fruit peel (MFP) is an underutilised processing by-product with considerable potential as a source of food-relevant phenolic compounds. This structured narrative review critically synthesises peel-specific evidence on phytochemical composition, extraction, biological properties, safety and food applications using a four-level framework that distinguishes direct peel studies from indirect evidence. Peel-specific high-performance liquid chromatography (HPLC) studies have identified caffeic, vanillic, ferulic, p-hydroxybenzoic and p-coumaric acids, together with p-hydroxybenzaldehyde. Recent exocarp research also indicates a broader phenolic and flavonoid profile, with solvent-dependent differences in phenolic recovery and measured antioxidant activity. Food-application evidence is currently strongest for vinegar produced from mixed peel–pulp residues and the use of peel extract to retard lipid oxidation in salad dressing. Although direct peel studies report chemical antioxidant activity and preliminary cellular and preclinical responses, these findings do not establish health benefits in humans. Overall, MFP has potential as a value-added food ingredient, but standardised food-grade preparations, product-level validation and safety assessment are needed before its functionality can be established.