A variety of fungi are reported to be capable of producing patulin in defined media including Aspergillus clavatus, A. giganteus, A. terreus, Byssochlamys fulva, B. nivea, Paecilomyces variotii, Penicillium carneum, P. clavigerum, P. concentricum, P. coprobium, P. dipodomyicola, P. expansum, P. glandicola, P. griseofulvum (formerly known as P. patulum, P. urticae), P. roqueforti, P. sclerotigenum, and P. vulpinum [61-66]. However, P. expansum is considered the major producer of patulin in food, and, in particular, pome fruits such as apples. In pure culture, P. expansum is reported to produce over 59 secondary metabolites including patulin, citrinin, cyclopiazonic acid, chaetoglobosins A and C, roquefortine C, penicillic acid, and ochratoxin. However, only some of these metabolites (patulin, citrinin, chaetoglobosins, roquefortine) were actually detected in apples and apple products [61-66].
Reviews on the physiology and growth characteristics of P. expansum and other fungi that produce patulin have been published [67,68]. In addition, Doores  wrote a comprehensive review of the microbiology of apples and apple products. Pénicillium expansum is a psychrophile . The optimum growth temperature for this species is near 25° C, but there are reports of growth of the organism at —3°C . Minimum water activities for spore germination are 0.82 to 0.83 . Pénicillium expansum has a very low requirement for oxygen; the organism was found to grow at atmospheric oxygen levels of less than 2%. Carbon dioxide concentrations of up to 15% have been found to stimulate growth of the organism . The growth characteristics of the fungus help explain the finding of P. expansum and patulin in apples stored under modified atmosphere conditions .
Although patulin is typically not destroyed during pasteurization of juices, P. expansum and its spores typically do not survive this thermal treatment. However, other species of patulin-producing fungi (B. fulva and B. nivea) produce spores that are resistant to processing at temperatures of 90°C . Consequently, there is a possibility of patulin production in stored juices if spores of these fungi germinate. At present, it is unclear if heat-resistant ascospores contribute significantly to the patulin content of apple juice products.
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