Potato Peel Waste as a Candidate Substrate for Streptomyces Fermentation Toward Antifungal Antibiotic Production: A Review of Evidence, Constraints and a Research Framework

Abstract

Potato processing generates peel equal to roughly 15–40% of tuber mass, and this moist, starch-containing residue is mostly diverted to animal feed, fertiliser or biogas. Streptomyces species are leading bacterial producers of antibiotics, and low-cost agro-industrial residues are increasingly tested as fermentation media. Objective. To appraise whether potato peel waste (PPW) can support the production of antifungal metabolites by Streptomyces, and to define the evidence still needed to show this. Narrative review on peel composition and pretreatment, Streptomyces fermentation optimisation and waste-derived media. Values were extracted as printed, and second-hand data were flagged. Sources were gathered without a systematic search, and each claim is labelled as direct evidence on peel, evidence on whole tubers or other substrates, or hypothesis. Findings. PPW composition is highly variable (starch 44.9–52% and ash 7.7–14.6%, reported on differing bases; glycoalkaloids 6.7–3,580 µg/g dry weight), and drying, pesticide residues and endogenous phenolics and glycoalkaloids shape its suitability. The only directly relevant study identified used discarded whole potatoes rather than peel, and transfer of its result to peel remains a hypothesis. In that study, Streptomyces sp. SO6 formed diffusible antifungal metabolites (0.96 mg/g) and pigments (1.75 mg/g) in submerged culture on 16 g/L potato powder, with an extract inhibiting Botrytis cinerea (19 mm at 100 µg/disc); pigment yield was a separate readout, and the active compounds were not identified. Optimisation studies on other media associate antifungal output with starch or other slowly assimilated carbon, low nitrate, initial pH 6.5–8.7, 25–30 °C, 3–9 days and dissolved oxygen above 20% saturation. No reviewed study reports antifungal production on peel itself with statistical optimisation, matrix-controlled bioassays and compound identification. PPW is a plausible but unproven substrate for antifungal production. A five-stage framework is proposed: standardise and decontaminate the peel, compare raw and hydrolysed forms, optimise by response surface design, include uninoculated-peel controls in bioassays, and report yields per kilogram of dry peel.