Stephen J. 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).

Measurement and prediction of air movement through doorways in refrigerated rooms

Reducing the amount of air infiltration through the doorways of food storage rooms would improve temperature control and the overall economics of food storage. In the UK a joint government/industry supported LINK project has been set up to look at methods of reducing air infiltration. The project is combining direct experimental measurement with computational fluid dynamics (CFD) modelling. A CFD model of air movement through a doorway has been developed and verified against conventional and laser Doppler anemometry (LDA) measurements. The CFD model has been shown to be generally accurate, however, there are areas where the accuracy is less than perfect. For example the CFD model predicted the shape of the vertical profile accurately, although it under-predicted the maximum velocity by 0.1 m s−1 and it predicted the height at which the airflow changed direction to be 40 mm lower than was measured by the LDA.

The ultra rapid chilling of pork

Pork carcasses and sides were ultra rapidly chilled in air at -30°C and 1 m/s for 4 h and compared with controls chilled in air at 0°C and 0·5 m/s for 24 h. All the required heat was removed during the 4-h process, there was a 1% saving in evaporative weight loss, the pork could be cut and packed immediately and there were no important differences in appearance and bacteriological quality. The loin from sides, but not carcasses, froze during chilling and showed a fourfold increase in drip loss. Loins from both sides and carcasses were tougher than the controls.

Consumer handling of chilled foods: Temperature performance

Abstract Chilled foods are stored for periods of between a few hours and many days in domestic refrigerators. However, there are little published data on the temperature performance of domestic refrigerators within the home. A survey has been taken in 252 households in the UK and some of the results are presented in this paper. The refrigerators investigated in the survey were found to have an overall mean temperature of approximately 6°C, which ranged from 11.4 to −0.9°C. Temperature ranges over the whole refrigerator varied from 4.5 to 30.5°C with 3.7% of the total being warmer than 20°C. On average 29.9% of refrigerators operated below 5°C and 66.7% operated below 7°C. Few refrigerators (7.3%) ran, on average, above 9°C. No refrigerator characteristic (apart from type) could be related to temperatures or temperature distribution in the refrigerators investigated.

Chilling of recipe dish meals to meet cook—chill guidelines

Abstract Within Europe the most severe cooling guidelines for cook-chill products are those produced by the Department of Health in the United Kingdom. These guidelines recommend that 80-mm trays of product should be chilled to below 10°C in 2.5 h and that the smaller 40- and 10-mm trays should be chilled below 3°C in 1.5 h/ Trials were carried out to determine whether 10-, 40- or 80-mm deep trays of bolognese sauce could be cooled to below 3°C within the guidelines. Assuming that surface freezing was to be avoided and a simple single-stage operation used, only the 10-mm tray could be chilled within these limits. A computer model was developed that produced predictions that were in good agreement with the experimental data. The program demonstrated that other foods, such as beef curry and chicken Italian, had similar cooling responses to those experimentally measured for bolognese sauce.

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.

Electrical stimulation and ultra-rapid chilling of pork

Six pigs were stimulated at 5 min post mortem and six remained unstimulated. All the pigs were split hot and one side from each pig was rapidly chilled in two stages (air at -40°C and 1 m/s for 80 min followed by 0°C and 0·5 m/s for 130 min) and the other side was conventionally chilled (air at 0°C and 1 m/s for 24 h). The weight loss from rapidly chilled sides was approximately 1% less than that from conventionally chilled controls. Cooked samples of Longissimus dorsi were tougher from unstimulated rapidly chilled sides (0·23 J) than from unstimulated conventionally chilled sides (0·18 J), whilst samples from both stimulated treatments were significantly more tender (0·15 J). These differences in toughness are thought to be due to a combination of cold shortening and lack of conditioning. The average pH in the longissimus dorsi of both rapidly and conventionally chilled stimulated sides at 50 min post mortem was 5·57 and samples from these muscles were slightly paler and more watery than the unstimulated controls.

Experimental verification of analytical and CFD predictions of infiltration through cold store entrances

Measurements of infiltration through different size entrances of a cold store at two different cold store temperatures were taken and compared against established analytical models and computational fluid dynamics (CFD) models. The analytical and CFD models generally tended to over predict the infiltration. The analytical model developed by Gosney et al. [Proc. Inst. Refrig. 72 (1975) 31] provided the closest comparison with the various experiments. The CFD models were more accurate than the fundamental analytical models but less accurate than those based on a semi-empirical approach. For the experimental configurations examined, CFD offered no real advantage over these empirical analytical models. If the conditions were such that the infiltration rate changed with time or if door protection devices (e.g. air curtains) were used, CFD would become much more advantageous in predicting infiltration.

The chill chain "from carcass to consumer".

To provide safe meat and meat products of high organoleptic quality, attention must be paid to every aspect of the chill chain. The process commences with the initial chilling of the freshly slaughtered carcass and continues through to the storage of the chilled retail portion within the home. Within the chill chain are two different categories of refrigeration processes. In the first group are those such as primary and secondary chilling, where the aim is to change the average temperature of the meat. In the others, such as chilled storage, transport and retail display, maintaining the initial temperature of the meat or meat product is the prime aim. Failure to understand the needs of each process results in excessive weight loss, higher energy use, reduced shelf life or a deterioration in product quality.

The temperature performance of domestic refrigerators

Abstract The domestic refrigerator is one of the most common household appliances, but little data have been published on its temperature performance. Investigations made under controlled conditions have shown that temperature distributions within empty storage compartments vary between different types of refrigerator. In some types loading with products substantially changes the temperature distribution. Data are provided on the influence of loading and door openings on the temperature performance.