Pasteurisation - Articles and news items
Industry news • 11 July 2014 • The Food Standards Agency
The FSA Board is being asked to consider new proposals for the sale of raw, or unpasteurised, milk…
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.
Issue 5 2011 • 1 November 2011 • Dr. Seamus O’Mahony, School of Food and Nutritional Sciences, University College Cork
Pasteurisation is a relatively mild heat treatment designed to inactivate vegetative pathogenic microorganisms in milk. Pasteurisation, coupled with refrigerated storage of pasteurised product, makes milk safe for human consumption and also extends the shelf-life of the product. Pasteurised milk is not sterile, with refrigerated storage inhibiting / retarding the growth of thermophilic spore-forming bacteria which survive pasteurisation. Pasteurised milk typically contains low numbers of psychrotrophic bacteria, which eventually limit shelf-life. The process of pasteurisation is named after the French microbiologist Louis Pasteur, who discovered that wine could be preserved by inactivating bacteria by heating at a temperature below boiling. This approach was later applied to milk, with the first systems for commercial pasteurisation of milk being introduced in the last decade of the nineteenth century.
The early systems relied on heating of milk to approximately 63-65°C and holding for approximately 30 minutes in batch vessels, followed by rapid cooling to less than 12°C (i.e., low-temperature-long-time (LTLT) pasteurisation). While some plants (e.g., farmhouse dairy product manufacturers) may still employ this LTLT approach to pasteurisation, it has largely been superseded by highthroughput, continuous-flow plate heat exchanger (PHE)-based pasteurisers, in which milk is heated to 72-74°C and held for at least 15 seconds in a process called hightemperature- short-time (HTST) pasteurisation.
Issue 3 2011 • 7 July 2011 • Silvia Monfort, Santiago Condón, Javier Raso & Ignacio Álvarez Tecnología de los Alimentos, Facultad de Veterinaria, Universidad de Zaragoza
In literature, there are many publications related to the microbial inactivation by PEF in LWE. However, there is not yet an answer to the question: is it possible to pasteurise liquid whole egg with pulsed electric fields? This could be due to the difficulties in comparing results since different treatment conditions have been used by authors, the narrow range of microbial species investigated, or the study of PEF lethality by the end-point method, among other reasons. This article summarises the results obtained by the group ‘New technologies of food preservation’ at the University of Zaragoza (Spain) carried out in order to answer that question.
Eggs and egg products are a nutritious part of our diet and a useful ingredient in foods due to their functional properties. Unfortunately, they are responsible for a large number of foodborne illnesses each year, constituting an obstacle to the well-being of populations and a source of high economic losses. In 2006, from a total of 5,710 outbreaks in Europe, egg and egg products were the most common food vehicle, responsible for 11.7 per cent of these outbreaks. Salmonella – mainly serovars Salmonella Enteritidis and Salmonella Typhimurium – was the microorganism responsible in most of the cases1.
Agronomic foods are often naturally contaminated with harmless and pathogenic microorganisms. In most cases, agronomic goods are freshly processed, or appropriately processed to preserve and increase shelf stability. Common preservation techniques include heat pasteurisation or sterilisation, irradiation, disinfestations with gaseous substances etc. In particular, the two latter techniques are rarely used nowadays due to legal restrictions as well as safety and nutritional concerns.
This article introduces the use of radio frequency (RF) and ohmic (OH) heating for meat pasteurisation and gives a brief overview of some UCD Dublin findings on the quality of OH and RF cooked meats.
RF and OH vs. conventional pasteurisation of meat
In pasteurising meat, the aim is to eliminate pathogens and reduce the level of spoilage organisms to give a reasonable shelf life under subsequent refrigerated storage conditions. Another important reason for cooking meat is to induce certain chemical reactions in a product which produce the flavour, colour and texture a consumer expects in a cooked meat. Conventional industrial pasteurisation of larger meat products is generally performed in a batchwise fashion either by placing products in steam ovens or alternatively by immersion in tanks of hot water. The difficulty with solids such as meat is that heat transfer within these products is predominantly by conduction which is relatively slow. The net effect is that it is necessary to leave the product in the heating media for a relatively long period of time for the interior to heat to an appropriate temperature. Meanwhile the outer surface of the product will have reached a high temperature at a much earlier stage which can lead to overheating in this area. Both OH and RF are forms of electro heating in which electrical energy is applied to products via a series of electrodes. In contrast to conventional heating, OH and RF generate heat within the product predominantly by internal ionic friction (although in RF a certain amount of heat will also be generated by friction induced by dipole rotation). These technologies differ from each other in a number of respects including the fact that in OH, electrical energy is passed directly into a food while in RF, electrical energy is first converted to electromagnetic radiation which is then applied to the food. The practical implications of this is that RF radiation will penetrate through conventional plastic packaging (metal clips cannot be used) without any requirement for direct contact with electrodes, while in OH, the product needs to be either unpackaged, in direct contact with the electrodes and subsequently packaged, or alternatively be in a sealed pack which has conductive regions which allow electrical current into the meat. Meat products have a certain amount of ionic compounds present naturally (e.g. calcium) with others (e.g. salt, phosphates etc.) added during product manufacture. These ions are dispersed around the product relatively uniformly. Essentially what happens in an RF or OH heating system is that an electrical field with positive and negative regions is formed. Under these conditions positive ions in the product move towards negative regions of the field and negative ions move towards positive regions of the field. Heating occurs in the case of OH because this field is not static with polarity continually changing, generally at low frequencies (50 Hz in Europe or 60 Hz in USA). In RF, polarity changes at much higher frequencies (e.g. 27.12 MHz). Therefore, no sooner have ions started to move than the polarity of the electrodes swaps and ions have to move again. The net effect of all of this is that heat is generated internally by friction (thereby avoiding the lag between the surface and the centre of the product).
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