Unripe wood apple fruit is generally free from visible fungal growth before and at harvest but a succession of fungi appears on the fruit shell, and sometimes in the pulp, during ripening. A TLC‐Cladosporium bioassay of the chloroform extract taken from unripe fruit shell demonstrated three inhibition areas. Similar extracts from stem‐bark and root‐bark produced these three, and one additional, inhibition areas. The four compounds responsible for inhibition were identified as psoralene, xanthotoxin, 2,6‐dimethoxybenzoquinone and osthenol.

Concentrations of the three antifungal compounds on unripe fruit shell increased during the first 4 days after harvest and then declined. They remained much below those required to inhibit the development of three fungi on TLC plates. Titratable acidity of the unripe fruit pulp was high but decreased by about 50% during ripening. Levels of reducing sugars were very low in the unripe fruit pulp but increased by about five times during ripening. Levels also increased in the fruit shell and its washings. The possible role of these factors in restricting fungal growth in unripe fruits is discussed.