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Ultra High Temperature (UHT) - Articles and news items

Advanced microbial modelling techniques and risk-based management applied to aseptic-UHT process

Issue 1 2014  •  5 March 2014  •  Laure Pujol and Jeanne-Marie Membré, INRA, UMR1014 Secalim and LUNAM Université, Oniris

Ultra High Temperature (UHT)-type products are ambient stable products, with a long shelf life (three to six months). Since they do not require any cold chain storage and can be consumed immediately, they are consumed extensively everywhere on the globe. They are defined as commercially sterile meaning that the product “must be free of microorganisms capable of growing under normal non-refrigerated conditions of storage1.” Basically, the challenge in a UHT process is to fill a ‘sterile’ product in a ‘sterile’ container in order to achieve commercial sterility…

New thoughts on a time-tested technology: milk pasteurisation

Issue 4 2012  •  5 September 2012  •  Daina Ringus and Kathryn Boor, College of Agriculture and Life Sciences, Food Science Department, Cornell University

The commercial adoption of milk pasteurisation was a major boon for urban public health in the first half of the 20th century. Before the widespread use of pasteurisation, the proliferation of diseases such as bovine tuberculosis and brucellosis among humans was frequently linked with consumption of unpasteurised (raw) milk15. Pasteurisation remains an important public health measure since raw milk can transmit pathogens associated with animals. For example, in the past year in the United States, human foodborne outbreaks caused by Salmonella and Campylobacter jejuni have been linked to consumption of raw milk.

Pasteurisation is a heat treatment applied to inactivate all non-spore-forming human pathogens associated with milk. Pasteurisation is not intended to sterilise milk, but rather to inactivate harmful bacteria. Current processing time and temperature requirements are designed to destroy Coxiella burnetii, the causative agent of Q fever. This organism is considered to be the most heat-resistant human pathogen associated with milk6. Continuous high temperature, short time (HTST) pasteurisation is the most commonly used method for pasteurising fluid milk in the US. HTST pasteurisation requires heating to 72°C for 15 seconds, as recommended by the Grade ‘A’ Pasteurised Milk Ordinance (PMO), the basis for dairy regulatory programs in the US1. The same HTST time/temperature requirements are applied in Australia3, with a similar combination, 71.7°C for 15 seconds, in Europe4. Milk can become contaminated with microorganisms before or after pasteurisation.

UHT processing of milk

Issue 3 2012  •  4 July 2012  •  Hilton Deeth, Emeritus Professor, University of Queensland

Milk is a highly perishable food so to enable it to be stored and distributed for consumption without spoilage, and without being a health risk through growth of pathogenic bacteria, it is heat treated. The most common type of heat treatment in many parts of the world is pasteurisation, which is performed at a minimum of 72°C for 15 seconds. This is the least heat treatment needed to destroy most pathogenic microorganisms and it also destroys most spoilage organisms. However, a small number of bacteria remain after pasteurisation and packaging, and can grow during storage. Such growth is slow at low temperature and consequently pasteurised milk is always kept refrigerated. Even under refrigeration, pasteurised milk only keeps for about two weeks1.

One way of extending the shelf-life of milk is to heat it at temperatures high enough to destroy almost all microorganisms, and then store it in sealed containers without contamination by bacteria. There are two ways in which this can be carried out: in-container sterilisation and ultrahigh- temperature (UHT) processing. Both produce a ‘commercially sterile’ product which means the milk does not contain micro – organisms which can grow under the normal conditions of storage which, in this case, is room temperature2,3.

In-container sterilisation, which uses canning technology, is a batch operation which involves heating the final containers of milk in an autoclave at 110-120°C for 10-20 minutes. By contrast, UHT processing involves heating the milk in a continuous flow system at about 140°C for a very short time – around five seconds.

Emerging challenges and trends in UHT processing of milk and other dairy products

Issue 4 2011  •  6 September 2011  •  Marina Witthuhn, Jörg Hinrichs and Zeynep Atamer, Universität Hohenheim, Institute of Food Science and Biotechnology, Department of Dairy Science and Technology

In order to obtain safe dairy products with a long shelf-life, heating processes have been designed to ensure the necessary inactivation of the indigenous microbial flora. One of the methods is the ultra-high temperature (UHT) processing of milk which has become widespread since the implementation of aseptic packaging processes1. Nowadays, this method is not only used for milk, but it is also applied to a whole range of dairy products with different microbial, physical and chemical properties. Therefore, new challenges for the manufacturers arise as these products require a different treatment to guarantee the safety and quality. UHT processing in general as well as emerging trends and challenges in processing of milk and milk products will be discussed in this article.

UHT processing of milk generally refers to processes that are conducted at 135 to 150°C for 10 to one seconds1,2. In production plants working with direct steam injection, even higher temperatures of 150 to 152°C are used for up to 13 seconds3. In contrast to this, sterilisation of milk is realised at temperatures varying from 109 to 120°C for 40 to 20 minutes2. These two processes are designed in such a way that the destruction of microorganisms of importance (bacterial spores) is the same in both cases as this is essential for the sterility of the final product. However, the effects on vitamins and other substances (e.g., lactose, amino acids) can differ greatly3. Nowadays, with the emerging application of UHT treatments to dairy products other than milk, such as products containing functional ingredients (e.g., infant food), new processing conditions have to be defined.

 

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