Apples provide favourable conditions for growth of various fungi, due to their high water activity and sugar content. Most commonly mentioned mould is Penicillium expansum, the cause of so called blue mould. On apples these fungi are able to synthesize secondary metabolites called mycotoxins. The most commonly present mycotoxin in apples and apple products is patulin, which is immunotoxic and neurotoxic to humans if ingested at high concentrations. The limit for maximum level of patulin in apple products is 50 µg/kg. Mould enters the fruit through the damaged surface, which occurs in case of heavy rain, insect attack or careless manipulation. However, mould infections often occur only in storage rooms. The most recommended way to storage apples is in refrigerated chambers and refrigerated chambers with controlled atmosphere, where the levels of CO₂ and O₂ are adjusted to slow down the ripening of the fruit. Despite low temperatures and low level of O₂ the growth of P. expansum is only slowed down and patulin can still be produced. Therefore, patulin can be present in various apple products. Since patulin is also thermostable, its removal is very difficult. Effective reduction of patulin has been demonstrated by certain food processing technologies, such as washing, pasteurization and fermentation. There are also several physical, chemical and biological processes of removing patulin from apple products. This includes heat treatment, light UV treatment, electroporation, use of high pressures, ozone and microorganisms. Some procedures function on patulin adsorption, while others provoke its degradation. Even with these processing technologies, the removal of patulin from apple products is not entirely possible, and there may also be negative changes in sensory quality and nutritional value of foods.
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