166 Chilled foods can grow in atmospheres with a low oxygen level and/or high carbon dioxide concentration and so may cause problems in vacuum-packed or modified- atmosphere-packed meat products. In vacuum-packed sliced meats, this microorganism produces an objectionable pungent 'cheesy'odour micrococcus species are Gram-positive cocci which can grow in the presence of high salt concentrations. They tend not to grow well at chill temperatures but can cause souring and slime production on cured meats and in curing brines should temperature abuse occur( Gardner 1983 ). Other microorganisms that may cause spoilage problems in cured meats and/or vacuum-packed meat products are Corynebacterium, Kurthia and Arthobacter species( Gardner 1983, Gould nd Russell 1991) 6. Yeasts and moulds Compared with bacteria, both yeasts and moulds grow more slowly in foods permitting good growth and so are generally out-competed. Therefore this group is seldom responsible for the spoilage of fresh proteinaceous foods. If, however the conditions in the food are altered to limit bacterial growth, the role of yeasts and moulds may become more significant. Many yeasts can grow at temperatures less than 0C (Michener and Elliott 1964). Furthermore, yeasts and moulds are generally more resistant than bacteria to low pH, reduced a values and the presence of preservatives (Jay 1978). Moulds tend to require oxygen for growth whereas many yeasts can grow in the presence or absence of oxygen. Most yeasts and moulds are not heat-resistant and are readily destroyed by a thermal process. The mould genus Byssochlamys however, may produce relatively heat-resistant ascospores(Bayne and Michener 1979) Freshly collected meat, poultry, fish and dairy products rarely contain yeasts or moulds but they rapidly become contaminated from the environment. In particular, air movements may be an important vector of transmission, especially with mould ascospores. Typical spoil myces, Hansenula, Kluveromyces, Rhodotorula, Saccharomyces, Torula and Zygosaccharomyces species(Walker and Stringer 1990, Pitt and Hocking 1985) Moulds that may be isolated from spoiled chilled foods include Aspergillus, Cladosporium, Geotrichum, Mucor, Penicillium, Rhizopus and Thamnidium species(Pitt and Hocking 1985, Filtenborg et al. 1996). Fungal spoilage may be characterised by the production of highly visible, often pigmented, growth, slime, fermentation of sugars to form acid, gas or alcohol, and the development of off-odours and off-flavours odours and flavours have been described as yeasty, fruity, musty, rancid and ammoniacal As with the lactic acid bacteria, yeasts and moulds are sometimes deliberately added to food products. For example, the development of Penicillium camembertii on the surfaces of brie and camembert cheeses is essential for the desired flavour, odour and texture characteristics. This mould growing on other types of cheeses would be described as a spoilage defectcan grow in atmospheres with a low oxygen level and/or high carbon dioxide concentration and so may cause problems in vacuum-packed or modified￾atmosphere-packed meat products. In vacuum-packed sliced meats, this microorganism produces an objectionable pungent ‘cheesy’ odour. Micrococcus species are Gram-positive cocci which can grow in the presence of high salt concentrations. They tend not to grow well at chill temperatures but can cause souring and slime production on cured meats and in curing brines should temperature abuse occur (Gardner 1983). Other microorganisms that may cause spoilage problems in cured meats and/or vacuum-packed meat products are Corynebacterium, Kurthia and Arthobacter species (Gardner 1983, Gould and Russell 1991). 6. Yeasts and moulds Compared with bacteria, both yeasts and moulds grow more slowly in foods permitting good growth and so are generally out-competed. Therefore this group is seldom responsible for the spoilage of fresh proteinaceous foods. If, however, the conditions in the food are altered to limit bacterial growth, the role of yeasts and moulds may become more significant. Many yeasts can grow at temperatures less than 0ºC (Michener and Elliott 1964). Furthermore, yeasts and moulds are generally more resistant than bacteria to low pH, reduced aw values and the presence of preservatives (Jay 1978). Moulds tend to require oxygen for growth whereas many yeasts can grow in the presence or absence of oxygen. Most yeasts and moulds are not heat-resistant and are readily destroyed by a thermal process. The mould genus Byssochlamys however, may produce relatively heat-resistant ascospores (Bayne and Michener 1979). Freshly collected meat, poultry, fish and dairy products rarely contain yeasts or moulds but they rapidly become contaminated from the environment. In particular, air movements may be an important vector of transmission, especially with mould ascospores. Typical spoilage yeasts include Candida, Debaryo￾myces, Hansenula, Kluveromyces, Rhodotorula, Saccharomyces, Torula and Zygosaccharomyces species (Walker and Stringer 1990, Pitt and Hocking 1985). Moulds that may be isolated from spoiled chilled foods include Aspergillus, Cladosporium, Geotrichum, Mucor, Penicillium, Rhizopus and Thamnidium species (Pitt and Hocking 1985, Filtenborg et al. 1996). Fungal spoilage may be characterised by the production of highly visible, often pigmented, growth, slime, fermentation of sugars to form acid, gas or alcohol, and the development of off-odours and off-flavours. Odours and flavours have been described as yeasty, fruity, musty, rancid and ammoniacal. As with the lactic acid bacteria, yeasts and moulds are sometimes deliberately added to food products. For example, the development of Penicillium camembertii on the surfaces of Brie and Camembert cheeses is essential for the desired flavour, odour and texture characteristics. This mould growing on other types of cheeses would be described as a spoilage defect. 166 Chilled foods