Christian James

Salmonella, Campylobacter and Escherichia coli 0157:H7 decontamination techniques for the future

Raw meat, particularly poultry meat, remains an important, and probably the major source of human infection with campylobacters and salmonellas. In spite of decades of effort it has so far proved extremely difficult to raise food animals free of these pathogens. For the foreseeable future, therefore, the most effective approach must be to decontaminate the final raw product. In this way numbers of these pathogens entering kitchens and commercial food processing premises will be reduced substantially, and hence opportunities for cross-contamination onto ready-to-eat foods or for survival during cooking or other processes will be much lower. The ideal method of decontamination will have the following attributes: it will not change appearance, smell, taste or nutritional properties; it will leave no residues; it will pose no threat to the environment; it will encounter no objections from consumers or legislators; it will be cheap and convenient to apply; it will improve the shelf life by inactivating spoilage organisms as well as pathogens. Various techniques will be listed and their potential assessed (see Table 1).

Microbial contamination of food refrigeration equipment

Refrigeration systems in chilled rooms in 15 plants processing a variety of foods were studied. These included plants processing raw meat and salads, Chinese ready meals, dairy products, slicing and packing of cooked meats and catering establishments. An initial survey of total numbers of microbes at a total of 891 sites on evaporators, drip trays and chilled room walls was followed up with a more detailed examination of 336 sites with high counts, selecting for Listeria spp., coliforms, enterococci, Staphylococcus aureus and Bacillus cereus. Temperatures (particularly air on and air off, maximum and near defrost heaters) relative humidity, airflow, layout and cleaning regimes were surveyed. In general, no correlation could be found between any of the physical measurements and the numbers and types of bacteria detected. Maximum mean temperatures in the chilled rooms varied from -1 to +16.9 °C and few chilled units were regularly cleaned. Twenty five percent of sites examined had more than 105 colony-forming units per cm2, although, very few pathogens or faecal indicator bacteria were detected. Listeria spp. were not found and coliforms were found only once, in low numbers. Low numbers of S. aureus or B. cereus were present in 9 of the 15 plants, B. cereus was found on evaporators and associated drip trays in two catering plants and two plants processing cooked meat. Enterococci and S. aureus were found most frequently in a raw red meat slaughterhouse (always in low numbers). In general, microbial contamination was lower in rooms where wrapped rather than unwrapped products were stored. The type of product also affected the degree of contamination, with raw red meat and poultry or dry ingredients giving highest counts, and raw vegetables and cooked products lowest. The work demonstrated that bacteria were present on evaporator cooling coils in all factory cold rooms visited. Although evaporator-cleaning procedures were carried out in some factories as part of routine maintenance these were not shown to be effective at maintaining low levels of bacteria on evaporators. To maintain evaporator hygiene it is suggested that more regular cleaning procedures, possibly by means of automated cleansing systems, should be considered.

The effect of short-time microwave exposures on inoculated pathogens on chicken and the shelf-life of uninoculated chicken meat

Abstract Fresh skin-less chicken breasts were inoculated with Escherichia coli K12 and Campylobacter jejuni (5–6 log 10 cfu cm −2 ) and exposed to microwaves (2450 MHz) in an experimental microwave oven at full power (IEC 1138.8 W) for 10, 20 or 30 s. All three exposures had only a minimal effect on bacterial numbers, in some cases counts were higher after treatment, irrespective of treatment time. Exposure to microwaves for 20 and 30 s had some effect on meat appearance (signs of partial cooking were observed). Further trials were carried out using uninoculated skin-on breasts to determine if 30 s exposure had any effect on subsequent microbial growth and hence shelf-life. There was found to be no difference between the shelf-life of treated and untreated samples stored at 3±1°C. Overall, the results indicate that short time exposure of microorganisms on chicken meat to microwaves has no significant effect on numbers or growth.

Surface pasteurisation of poultry meat using steam at atmospheric pressure

Abstract The effects of various steam treatments on the appearance, shelf-life and microbiological quality of chicken portions were investigated. Application of steam at atmospheric pressure (100°C for 10 s) on naturally contaminated chicken breast portions resulted in a 1.65 log 10 cfu cm−2 (S.D. 1.06) reduction in the numbers of total viable bacteria. However, in comparison with untreated controls, this treatment did not extend the shelf-life. Steam treatment for up to 10 s on chicken portions inoculated with a nalidixic acid resistant strain of Escherichia coli serotype O 80 resulted in a maximum reduction of 1.90 log 10 cfu cm−2 (S.D. 0.63). Overall, results indicate that significant reductions in microbiological numbers can be achieved on chicken meat using steam. However, such reductions have little effect on the shelf-life of portioned chicken.

Surface pasteurisation of shell eggs

Microbial and visual contamination of eggs during production and processing is of concern to the consumer and to the egg industry for both health and economic reasons. While egg washing has the potential to reduce significantly the amount of visual and microbial contamination of eggs, there are substantial concerns as to the effectiveness of current egg washing technology. It is also unclear whether the use of egg washing results in salmonella moving from the exterior of the egg shell through the shell into the contents of the egg where they may grow to high levels. A short investigation was carried out on the applicability of four different heat treatments (hot air, hot water, infra-red radiation, and atmospheric steam) for the surface pasteurisation of shell eggs. The aim of this work was to assess temperatures on the outside and interior of the shell to identify the highest surface temperatures that could be achieved without damaging the contents of the egg. Initial results show that temperatures sufficient to achieve significant reductions in salmonella numbers can be attained on the outside of an egg without raising interior temperatures to those that would cause coagulation of the egg contents.

Non-Uniformity of Surface Temperatures After Microwave Heating of Poultry Meat

Microwave energy has the potential to raise the surface temperatures of meat rapidly for a short period of time sufficient to reduce bacterial numbers significantly without causing physical changes to the meat. Studies have investigated the ability of a standard domestic microwave oven (2450 MHz; IEC 1191 W), an experimental repeatable microwave cavity (2450 MHz; IEC 1139 W) and a number of shielding techniques to achieve uniform surface temperature distributions on pieces of poultry meat. In the domestic oven temperature differences of up to 60 and 80 degrees C were found between different points on the surface of the same sample after 30 s and 3 minutes of heating respectively. The use of a standard cavity and shielding resulted in a difference of less than 5 degrees C between the average surface temperature on the edge and middle of regular slabs of chicken after 30 s exposure. Results show that microwave heating, using 2450 MHz, is unlikely to produce consistently uniform enough surface temperatures on meat to reduce bacterial numbers without surface damage.

A Review of Novel and Innovative Food Freezing Technologies

Freezing is a very well-established food preservation process that produces high quality nutritious foods with a long storage life. However, freezing is not suitable for all foods, and freezing can cause physical and chemical changes in some foods that are perceived as reducing the quality of either the thawed material or the final product. This paper reviews the many innovative freezing processes that are currently being researched and developed throughout the world to improve freezing conditions and product quality. Some innovative freezing processes (impingement and hydrofluidisation) are essentially improvements of existing methods (air blast and immersion, respectively) to produce far higher surface heat transfer rates than previous systems and thus improve product quality through rapid freezing. In these cases, the advantages may depend on the size of the product, since the poor thermal conductivity of many foods limits the rate of cooling in large objects rather than the heat transfer between the heat transfer medium and the product. Other processes (pressure shift, magnetic resonance, electrostatic, microwave, radiofrequency, and ultrasound) are adjuncts to existing freezing systems that aim to improve product quality through controlling the way that ice is formed in the food during freezing. Another alternative is to change the properties of the food itself to control how ice is formed during freezing (such as in dehydrofreezing and the use of antifreeze and ice-nucleation proteins).

A Critical Review of Dehydrofreezing of Fruits and Vegetables

Freezing is a very well established food preservation process that produces high-quality nutritious foods that offer the advantage of a long storage life. However, freezing is not suitable for all foods, and freezing does cause physical and chemical changes in many foods that are perceived as reducing the quality of the thawed material. Many innovative freezing processes are currently being researched and developed throughout the world to overcome these problems. One of these is dehydrofreezing. Dehydrofreezing is an adjunct to freezing in which a food is first dehydrated to a desirable moisture content and then frozen. It is particularly suited to fruits and vegetables. Since fresh fruits and vegetables contain more water than meat, and their cellular structure is less elastic, they are prone to more damage during freezing than meat. Removing some of the water prior to freezing theoretically allows the ice crystals to form and expand without damaging the cellular structure. Reducing the water content prior to freezing also has the potential to reduce the freezing time, the initial freezing point, and the amount of ice formed within the product. Despite being often cited as a new, novel or emerging technology, the concept of dehydrofreezing was developed in the 1940s. However, it has remained a niche process being commercially applied to products such as potatoes, carrots, and onions. In recent years there has been renewed interest in dehydrofreezing, and this review looks at the most recent innovations in dehydrofreezing research.

The heat pipe and its potential for enhancing the freezing and thawing of meat in the catering industry

Abstract The rate of freezing and especially thawing of meat is limited by its poor thermal conductivity. Providing a high conductivity path to the thermal centre of the meat is a potential method of overcoming this problem. The aim of this research was to investigate the feasibility of using heat pipes to increase freezing and thawing rates in meat joints. Two sizes of heat pipe were used on a number of assorted joints of varying weights under catering conditions of freezing and thawing. It was found that by using a heat pipe a saving in time of up to 42% could be produced when freezing and up to 55% when thawing.

Minimal Processing of Ready Meals

There is a large, and ever-growing, domestic and catering market for chilled and frozen ready meals. A chilled or frozen ready meal is a fully prepared meal that will ultimately be heated in a conventional domestic, or microwave, oven. Consumers expect a meal with an eating quality that is at least as good as if they had cooked and prepared it themselves. There is a growing demand for new “fresh-like”, “clean-labelled”, “minimally processed” products positioned on a more wholesome, fresh, and naturalness platform. This chapter reviews both current technologies for manufacturing chilled and frozen ready meals, and the novel and alternative processing options that are emerging for manufacturers, such as microwave, radiofrequency, ohmic, and high-pressure technologies.