The use of high temperature short time heat treatment (HTST) of milk (72°C for 15 seconds) to destroy pathogenic bacteria, reduce the number of spoilage organisms and increase shelf life is well established (Juffs and Deeth, 2007).
The history of pasteurization (pasteurisation is also valid) is fascinating and is notable for its public health success and for the insights of many scientists and engineers. Prior to the introduction of pasteurization, consumption of raw cow milk was a major source of infection by bacteria causing tuberculosis. Pasteurization has eliminated heat-treated-milk as a source of infection. Regrettably raw milk and raw milk products remain a major source of new cases of bovine tuberculosis.
Learn more about heat treatment and survival of MAP
Model probability of detecting a pathogen in food.
Despite the global use of HACCP systems and a legal requirement for the use of HACCP in many jurisdictions' food poisoning remains an endemic problem and large numbers of people continue to be hospitalised, die and as a result companies either face substantial legal costs and / or in many cases are forced to cease trading.
While the use of HACCP systems significantly reduces the need for microbiological end point testing of foods, sampling schemes and microbial analysis have important roles in system validation and quality assurance.
Further information on the mathematics of microbial sampling
Growth and acid production by starter cultures may be inhibited by bacterial viruses, bacteriophages, or added substances including antibiotics, sterilant and detergent residues, or free fatty acids produced by or as a result of the growth of microorganisms, and natural often called indigenous antimicrobial proteins.
Milk should not contain antibiotic residues. Milk production in the UK is regulated by the Dairy Products (Hygiene) Regulations 1995. These regulations include the standards for raw milk. Prior to 1990 milk was deemed to be contaminated if an antibiotic concentration of > 0.01 international units (iu) /ml was present, the standard has now been increased to 0.006 iu/ml. Manufacturers buying milk from producers impose stringent financial penalties on farmers producing contaminated milk and have procedures to exclude this from the food chain. Despite legislation and financial penalties, there is evidence to suggest that residues occasionally still cause problems. In a survey of the causes of slow acid production by cheese starters in the UK (Boyle and Mullan, 2000, unpublished results) found that, some 28 % of respondents attributed slow acid problems to antibiotics.
More about starter-inhibitors
This article discusses the origins and role of starters in dairy fermentations, the ecology of starter bacteria, the classification of starter bacteria, the types of starter culture used and concludes with some observations on artisanal cultures. The author has provided a broader perspective on the use of starter cultures in food fermentations in the Encyclopedia of Food Microbiology. The chapter can be downloaded from Elsevier Ltd. This article should be read in conjunction with the article discussing the major functions of starters in dairy fermentations and the relative importance and effectiveness of the antimicrobial agents produced by starters.
More about the microbiology of starters
The effect of modified atmosphere packaging (MAP) on dairy products, raw meat, raw poultry , cooked meat and fruit and vegetables is discussed.
Dairy products
MAP has the potential to increase the shelf life of a number of dairy products. These include fat-filled milk powders, cheeses and fat spreads. In general these products spoil due to the development of oxidative rancidity in the case of powders and or the growth of micro-organisms, particularly yeasts and moulds, in the case of cheese.
Whole milk powder is particularly susceptible to the development of off-flavours due to fat oxidation. Commercially the air is removed under vacuum and replaced with N2 or N2/CO2 mixes and the powder is hermetically sealed in metal cans.
Due to the spray drying process air tends to be absorbed inside the powder particles and will diffuse into the container over a period of 10 days or so. This typically will raise the residual O2 content to 1%-5% or higher. Because some markets require product with low levels of residual O2(<1%) some manufacturers re-pack the cans after 10 days storage. Use of O2 scavenging may also be useful.
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