EXPERIMENTAL PRODUCTION OF AFLATOXIN ON INTACT CITRUS FRUIT1

Abstract

Surfaces of intact citrus fruits were inoculated with spores of Aspergillus parasiticus and the fruits were incubated at 24–30 C in an atmosphere with 13–93% relative humidity (RH). With 13–20% RH, no mold growth occurred on limes and growth was not observed on grapefruits until 7 days of incubation. After 14 days, mold growth was noted only on a portion of grapefruits, lemons, and oranges. Although surface areas of fruits without mold growth were dry and brittle, they failed to achieve equilibrium with the atmosphere. When fruit was incubated in an atmosphere of 66–93% RH, fungal growth was considerably faster and more prolific. Generally, one-third to one-half of the surface of each inoculated fruit was covered with mycelium after 4 days of incubation. Sporulation by the mold began at this time. After 7, 10, and 14 days of incubation all fruits were totally covered with mycelium and spores. Relative humidity values between 66 and 93% caused no appreciable difference in amount of aflatoxin present in peels of various fruits. The edible portion (endocarp) of grapefruit contained aflatoxins B1, B2, G1, and G2 after only 4 days of incubation. In another sample of grapefruit, aflatoxin penetrated 26–33 mm into the endocarp after 7 days. After 7 and 10 days, aflatoxin was recovered from samples of lemon and lime endocarp, respectively. In one lemon, after 7 days, aflatoxin appeared in endocarp 20–26 mm below the surface. The amount of aflatoxin in endocarp became less as the distance from the surface (peel) increased.