Evaluation of 3,4-Dihydroxybenzaldehyde, Dopamine and Its Oxidation Products as Inhibitors of Colletotrichum musae (Berk. & Curt.) Arx in Green Banana Fruits

Abstract

Standard ethanolic extracts prepared from green banana peel without oxidation control inhibited C. musae in vitro. 3,4-Dihydroxybenzaldehyde, previously reported as an antifungal compound in green banana peel [RPP 48, 1251], was not located on chromatograms of extracts and was not regarded as a major contributor to antifungal activity. Fungal inhibitors separated from extracts were identified as oxidation products of dopamine and were also produced by the action of tyrosinase on dopamine. Extracts prepared with oxidation control had little or no antifungal activity. Although dopamine oxidation products in standard extracts were regarded as artefacts of the extraction procedure, it is suggested that these products may form during hypersensitive reactions in cells of green bananas and inhibit subcuticular hyphae which develop from hyaline appressoria. Dopamine itself was extracted from peel in antifungal concn but appeared to be confined within specialized cells. Changes in its concn were not synchronized with changes in the activity of dark-coloured appressoria which act as latent structures of the fungus.