When I volunteered at the San Francisco Food Bank with other food bloggers on Saturday (an outing organized by Amy and Sam), one of our tasks was to transfer oranges from huge crates to smaller boxes. As we moved the oranges, we ran across quite a few that had patches of white, green and blue mold. This got me thinking about the mold on oranges. What is it? Is it useful to humans, or just a pest?
After a bit of research, I found a short report from the Indian River Research and Education Center (PDF) about oranges that identified the green mold as Penicillium digitatum and the blue mold as Penicillium italicum. Although it is not so pleasant to grab a mold-covered orange, the color can be quite lovely, and as I’ll explain below, molds in the Penicillium genus are quite important to humans. The light green reminds me of the classic celeste green of a Bianchi road bicycle, which then leads to thoughts of the open road.
I didn’t discover any useful applications of the orange molds, but the Penicillium genus has some important species. Foremost, of course, is the antibiotic drug, penicillin, which was initially derived from Penicillium notatum and has more recently been replaced by Penicillium chrysogenum (according to the McGraw Hill Science and Technology Encyclopedia). Several cheeses are inoculated with a Penicillium species during production, including Roquefort (P. roqueforti), Gorgonzola (P. glaucum), and Camembert (P. camemberti).
George Barron’s website on Fungi has some more information about Penicillium fungi and great picture.
At Green Car Congress I ran into yet another use for spoiled oranges and orange peels: making ethanol to use as a transportation fuel. The post states that “[c]itrus waste is rich in pectin, cellulose and hemicellusic polysaccharides, which can be hydrolyzed into sugars and fermented into ethanol.” The proposed project will use waste material (instead of real food) as the feedstock and the ethanol plants will be near the citrus facilities: “Citrus Energy notes that the 5 million tons of citrus waste produced annually from Florida’s 100 million citrus trees is available on a continuous basis for 8 months a year with no transportation costs to ethanol plants co-located with citrus producers. Existing road and rail transportation systems servicing the citrus plant would take the ethanol to market.” No details about whether the mold has any special properties in the ethanol process…