Penicillium expansum is one of the most pervasive and destructive postharvest pathogens of pome fruits such as apples and pears, but it can affect other fruits including tomatoes, strawberries, avocados, bananas, mangoes, grapes, peaches, and apricots [3,68]. The primary habitat of P. expansum is in fruit storage and packinghouse facilities, but it can also be found in orchard soil, seeds of various plants, and on the surface and in the core of unblemished fruit. The fungus is primarily a wound pathogen, gaining entrance through fresh mechanical injuries such as stem puncture, bruises and insect injuries, hail or weather-related damage, and fingernail scratches caused by fruit pickers . There are also reports of the fungi entering apple fruits through open calyx canals, at the point of attachment of stem to fruit, and through skin lenticels . The infection often occurs while apples are still on the tree, but it remains latent until the fruit is harvested and stored . The appearance of the decay caused by P. expansum is characterized by rotten areas that are soft, watery, and light brown in color. The surface of older lesions may be covered by bluish-green spots that initially are white in color .
Although P. expansum can be isolated from the surface of a wide variety of fruits, patulin has only been detected in apples, pears, blueberries, cherries, peaches, plums, strawberries, raspberries, and mulberries . The organism is rarely isolated from vegetables . The mere presence of P. expansion does not necessarily imply that patulin will be present since mycotoxin production is influenced by many factors including environmental conditions, cultivar and nutritional status of the fruit, the microbial load on the fruit, and strain of the fungus [3,74].
Patulin is found with greater incidence and concentration in apples than in other fruit, and they contribute the vast majority of patulin in the human diet . The toxin has been detected in intact fruit, juice, cider, applesauce, and apple puree. Whole apples (table fruit) are not believed to contribute significantly to human exposure since contaminated fruit is often discarded or trimmed to remove moldy areas before it is eaten. The greatest exposure to patulin comes from consumption of apple juice and cider pressed from moldy fruit .
Numerous surveys have been published on the incidence and concentration of patulin in apples and apple products [5-7,75-82]. Harwig et al.  surveyed 61 samples of whole apples from different orchards in Canada. Pénicillium expansun was isolated from 42 of the samples, while patulin was found in 28 samples of expressed juice at levels up to 240 mg/l. Wilson and Nuovo  analyzed 100 samples of freshly pressed apple cider and detected high levels of patulin (up to 45,000 mg/l) in several samples of cider produced from organically grown fruit. The authors concluded that cider samples with the highest patulin concentrations were made from ground-harvested and rotten fruit. In contrast to these results, Malmauret et al.  and Riteni  reported no significant difference in patulin levels from fruit grown organically compared to conventionally grown fruit. In surveys of apple products obtained in Turkey and New South Wales, Australia, Yurdun et al.  and Burda  reported that >25% of juice samples contained > 50 mg patulin/l, and several samples contained 500 to 1000 mg patulin/l. Watkins et al.  analyzed apple juice purchased in Victoria, Australia, and found that >65% of samples were contaminated with patulin, and > 33% had levels over 50 mg patulin/l. In contrast, Ritieni , Leggott and Shephard , and Lai et al.  reported that patulin levels in almost all tested apple products purchased in Italy, South Africa, and Taiwan, respectively, were < 50 mg/l. A survey conducted of apple juices purchased between 1994 and 2000 in the U.S. revealed that 12.6% of juices had patulin levels over 50 mg/l, and approximately 6% had levels > 100 mg/l . Overall, surveys of apple products indicate that, although the incidence of patulin contamination is fairly high, levels of contamination are typically less than 50 mg patulin/l.
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