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Microbial growth and rancidity are the primary causes of quality deterioration in dairy products. The type of breakdown depends on the characteristics of the particular product. Hard cheeses with relatively low water activity are normally affected by the growth of moulds, whereas products with high water activity such as cream and soft cheeses are more susceptible to fermentation and rancidity.
Lactobacillus, which is widely used in the dairy industry, can also pose a problem as it turns products sour by lowering their pH value. This may be further intensified by incorrect packaging atmospheres with excessive levels of carbon dioxide (e.g. cottage cheese packages).
Preventing mould formation with carbon dioxide
Carbon dioxide (CO2) is the main gas used to package hard cheeses. It effectively stops/reduces microbial activity and helps to retain texture. Carbon dioxide concentrations of as low as 20% strongly inhibit the growth of mould fungi. Lactic acid bacteria, a natural constituent of cheese, is hardly affected by the surrounding atmosphere.
Soft cheeses are also packaged in atmospheres with higher levels of carbon dioxide and lower levels of oxygen to inhibit bacterial growth and rancidity.
Carbon dioxide levels of up to 100% are used for hard cheeses. This is usually restricted to between 20 and 40% in the case of soft cheeses. The reason for this is to prevent the package from collapsing under atmospheric pressure as the carbon dioxide dissolves into the water.
Value added cheese, such as grated or sliced cheddar, are also packaged in modified atmospheres. Grated cheese is normally packed in an atmosphere of 70% nitrogen and 30% carbon dioxide. By limiting carbon dioxide to 30%, manufacturers can avoid package collapse.
Cultured products present new window of opportunity
In the past, cultured products such as cottage cheese and yoghurt were not packaged in modified atmospheres. This however, is changing, in order to meet market demands for longer shelf lives. Carbon dioxide extends the shelf life of cottage cheese by one week, for example.
Cream stays fresh
Cream and dairy products containing cream rapidly turn sour in carbon dioxide atmospheres. By replacing oxygen with nitrogen, manufacturers can prevent rancidity and the growth of aerobic bacteria.