Moulds are categorised as fungi that develop in the form of multi-cellular filaments, namely hyphae. They reproduce via the production of large quantities of small spores. Mould spores can be formed either by asexual or sexual methods.
Moulds are responsible for biodegradation in foods by breaking down the complex organic matter into simpler substances which can result in food spoilage. The undesirable decay of the foods progressively develops after the ripening stage or when the food is physically damaged (such as bruised fruits as a result of poor handling/delivery). The growth of moulds is detected when distinctive blue/green “fur” or orange spots develop on the affected foods.
Sometimes the growth of certain types of moulds can offer beneficial vaules in the food industry. For example, Penicillium spp exert desirable effects on the ripening of specific cheeses. The enzymes of the moulds are able to break down the fats and proteins which results in generating characteristic flavours of the cheese. Mould species such as Penicillium candidum and Penicillium camemberti are used in the production of Brie and Camembert which develop white moulds on the outside of the cheese. The application of Penicillium spp in Danish Blue and Stilton produce blue moulds through the inside of the cheese. Furthermore, Penicillium spp provide medical applications; e.g. Penicillium notatum and Penicillium chrysogenum produce penicillin that has long been used for its antibacterial activity.
The following are the most commonly species of moulds that highly contribute to the food spoilage:
Rhizopus nigricans is commonly known as the bread mould as it prevalently develops in this type of food. It is also able to attack vegetables which contain sugar at relatively low PH and develops unpleasant mushy texture. Beans, carrots, potatoes, cabbages, sprouts, cauliflower, turnips, cucumbers and tomatoes are likely to be degraded by Rhizopus nigricans. In addition, Rhizopus rot occurs in fruits such as grapes, blackberries, strawberries, oranges, lemons, peaches, plums, pears.
Aspergillus species are widely distributed in foods. They are able to grow in oilseeds, edible nuts and cereals. Predominantly, they produce green moulds on the surface of the affected foods.
Aspergillus spp can develop numerous types of food spoilage. Aspergillus niger causes black mould rot in fruits including grapes, cherries, peaches, apricots, plums and prunes. Fresh meats, bacon, nuts, bread, butter and pickles also undergo the spoilage by the activity of Aspergillus niger. Penicillium species are also contributory to the food spoilage. They attack a wide range of fruits and exhibit blue mould rot. Penicillium corylophilum which is tolerant to the cold temperature can grow on the chilled meats such as beef. Refrigerated bacon, butter and pickles are also prone to be invaded by Penicillium spp. Mucor species widely develop in foods such as deteriorating vegetables. The incubated colonies can quickly flourish at 25-30ºC.