Soil molds were screened for their ability to produce antioxidants and synergists with tocopherol (Toc), and a fungus (strain 32-1), belonging to Penicillium sp., was isolated. It has been found that citrinin in the culture filtrate of strain 32-1 shows a potent antioxidative activity. The AOM stability of lard increased with an increase of the amount of citrinin added, and its AOM value obtained when 0.1 % citrinin was added was 215 h. The 1H-NMR spectrum of citrinin shows that a proton in the

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... hydroxyl group forms hydrogen bond to adjecent oxygen atom. The facts that citrinin has an antioxidative activity suggest, however, that the activity is mediated by conformational changes of the molecule and that the carboxylic group may be defined as proton-donor.