SAFE FOOD AND WATER

PROVIDING SAFE MILK

Milk is highly vulnerable to microbial contamination during collection and storage. Once contaminated, it provides an excellent medium for growth and reproduction of a considerable range of microorganisms. Various means of treatment are used to reduce the risk to humans, the most common of which is flash pasteurisation. Milk is heated to 72°C for 15 seconds and then cooled rapidly to 3°C. The heating process kills many pathogenic organisms (e.g. Mycobacterium tuberculosis, Listeria, Campylobacter and Salmonella) and spoilage organisms (e.g. Lactobacillus spp) whilst the rapid cooling prevents organisms which can survive the heat treatment (e.g. Enterococcus spp and spore-forming Bacillus spp) from dividing rapidly. Mycobacterium bovis, which can be carried by cows and cause bovine tuberculosis in humans, is also destroyed. It is fortunate that spore-forming pathogens do not normally occur in milk. The limited heat treatment does not adversely affect either the flavour or the nutritional value of milk.
Pasteurisation extends the keeping time of milk to several days if it is refrigerated.

Background

Alternative treatments of milk

• Sterilisation Milk is heated to 43 °C, filtered, homogenised and bottled. The bottles are then autoclaved at 115 °C for 20 minutes. Kills all microorganisms apart from some spores. Sterilised milk keeps for months, but the taste is altered and some vitamins are destroyed.

  
  

• UHT treatment Milk is heated to 132.2 °C for 1 second and placed in cartons. UHT milk is virtually sterile and keeps for many months. The flavour and nutritional value are hardly changed.

PROVISION OF CLEAN WATER AND SANITATION

During the last century, far-reaching and dramatic improvements to human health, with consequent dramatic reduction in the mortality rate, occurred in Britain. This is due to the provision of safe food and water, and hygienic means of disposal of urine, faeces and other wastes. Very significant also was the move to less crowded housing conditions, reducing the incidence of transmission of pathogens and their vectors. Such measures were crucial to the elimination of some of the most ravaging and lethal infectious diseases such as cholera, typhus and typhoid. These improvements have made a much greater impact on mortality than the advances in medical techniques and procedures, which tend to have a much higher profile.

Before the existence of drainage systems connected to sewage works, human urine and faeces ended up in streets, or in streams and rivers which were often used as a source of drinking water This was particularly the case when piped water supplies were not freely available and when such supplies were not effectively purified.

In the UK, the mains water supply is drawn from reservoirs, rivers and subterranean aquifers. To secure the high quality needed for the maintenance of public health, various purification procedures are adopted. Chemical treatments and filtration are used to achieve the required levels of colour, clarity and taste, followed by disinfection (e.g. by chlorine or ozone) to improve microbiological quality.