Effects of Nutrients and Inhibitors in Olives on Aflatoxigenic Molds

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Growth and aflatoxin production by Aspergillus parasiticus NRRL 2999 and Aspergillus flavus NRRL 6555 were studied on fresh olives, fresh olives supplemented with nutrients, and fresh olives treated with heat, lye, and freezing temperatures. Studies were also done on yeast extract sucrose agar (YESA) either mixed with chopped fresh olives or made with aqueous extracts of fresh and treated olives. Samples were incubated at 25°C for 7 d. Olive paste supplemented with zinc and sucrose supported little growth and no aflatoxin B1 production. Amino acids, yeast extract, and a combination of zinc, carbohydrate, and amino acids exhibited extensive growth and moderate amounts of aflatoxin. Fresh and frozen olive pastes supported poor growth and no aflatoxin production. Heat- and lye-treated olives supported extensive growth and little aflatoxin production. Heavy growth and moderate amounts of aflatoxin B1 were supported by YES A mixed with olive pastes. YES A made with aqueous extracts of olives supported extensive growth and moderate toxin production, except on YES A made with extract from frozen olives which exhibited poor growth and low toxin amounts. A. flavus grew similarly to A. parasiticus but was unable to produce any aflatoxin except on heat- and lye-treated olives, where traces were detected. Olives are a poor substrate for mold development and may contain inhibiting substances against growth and aflatoxin production.