Modelling of food transportation systems - a review

In 2002, over a million refrigerated road vehicles, 400,000 refrigerated containers and many thousands of other forms of refrigerated transport systems are used to distribute chilled and frozen foods throughout the world. All these transportation systems are expected to maintain the temperature of the food within close limits to ensure its optimum safety and high quality shelf life. Increasingly, modelling is being used to aid the design and optimisation of food refrigeration systems. Much of this effort has concentrated on the modelling of refrigeration processes that change the temperature of the food such as chilling, freezing and thawing. The purpose of a refrigerated transport system is to maintain the temperature of the food and appears to have attracted less attention from modellers. This paper reviews the work that has been carried out specifically on the modelling of food temperature, microbial growth and other parameters in the transportation of food. © 2006 Elsevier Ltd and IIR

Temperature and energy performance of refrigerated retail display and commercial catering cabinets under test conditions

An analysis of the performance of well freezers, chest freezers, frozen and chilled door cabinets (solid or glass door) and open fronted chilled cabinets under EN441 test conditions demonstrated that maximum temperatures in cabinets were generally in the most exposed (to ambient) areas and that minimum temperatures were located in the least exposed areas. Detailed positions of maximum and minimum temperature varied between cabinet types. In chest freezers 95% of the maximum temperature positions were located in the top layer and 95% of the minimum temperature positions were located in the middle layer of the cabinets. In full door frozen cabinets the maximum temperature position was in the majority of cases on the top shelf (64%) with most maximum packs being at the front of the top shelf (53%). In the chilled full door cabinets 94% of the maximum temperature packs were situated at the front of the cabinet. In open fronted cabinets the majority of maximum temperature packs (97%) were located at the front of the cabinet, the largest number (60%) being at the front of the base of the cabinet. In well cabinets the majority of maximum temperature packs (81%) were located in the top layer of the cabinet and the majority (91%) of minimum temperature packs were located in the bottom of the cabinet. Large differences in energy consumed by cabinets of similar size and temperature performance were found indicating that large reductions in energy and CO2 emissions could be achieved by selection of the most efficient cabinets. © 2006 Elsevier Ltd and IIR

Development of a novel multi-capillary, multi-temperature commercial refrigerator cabinet with common low-pressure receiver

A multi-temperature 4 drawer catering cabinet was designed to operate using a low-pressure receiver with capillary expansion to the separate evaporator in each drawer. Low-pressure receivers have been shown to be an effective way of allowing evaporators to operate in a fully flooded mode thus enabling more efficient use of the evaporator surface for heat transfer. If a low-pressure receiver is used in a refrigeration circuit the control of refrigerant flow into the evaporator is less critical as the expansion device is not responsible for preventing liquid returning to the compressor. Therefore, a capillary expansion device can be used effectively over a range of operating pressures. The system was shown to be effective at maintaining temperatures in the storage drawers during chilled, frozen and mixed storage temperature tests carried out to the EN441 test standard. The cabinet operated successfully at all conditions except when the heat load in each drawer was excessive (>400 W above base level heat load). In this case, refrigerant was found to back up in the condenser and the low-pressure receiver was empty of liquid refrigerant. A solution to this would be to allow controlled flow of refrigerant from the condenser to the low-pressure receiver at high condensing pressures

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. © 2003 Elsevier Ltd. All rights reserved

Viability of calanoid copepod eggs from intertidal sediments: A comparison of three estuaries

Calanoid copepod nauplii hatched from intertidal sediment samples from 3 British estuaries, the Exe, the Humber and the Mersey. The Exe Estuary is exposed to low levels of urban and agricultural pollution but the Humber and Mersey are subject to more extensive urban and industrial pollution. Samples were taken from the Humber and the Exe in April and November 1995 and from the Mersey and the Exe in June and October 1995. The concentrations of polycyclic aromatic hydrocarbons (PAH) in the sediments were measured as an index of pollution. The PAH concentrations in sediment were lowest in the Exe (mean 200 mu g/g dry weight in the Humber and some >300 mu g/g dry weight in the Mersey. Many more nauplii hatched from incubated sediments from the Exe than from the more polluted estuaries in April, June and November but larger numbers of nauplii hatched from the samples from the Mersey than from the Exe in October. Eggs were extracted from the samples taken in October and November and incubated; 92% of those from the Exe, 48% of those from the Humber and 14% of those from the Mersey hatched. This is consistent with reduction in viability of eggs with increased pollution. The viability of copepod eggs from sediments appears to have potential as a technique for in situ bioassay of fine sediments

Vascular perfusion chilling of red meat carcasses - A feasibility study.

Meat carcasses must be chilled to below 7°C before leaving the slaughterhouse. Typically this is done by passing cold air over the surfaces of eviscerated and de-hided carcasses. This surface cooling can take many hours to reduce centre temperatures to below 7°C. In vascular perfusion chilling (VPC), a cold fluid is circulated through the intact vascular system, offering significant reductions in cooling time. This paper describes a small feasibility study to evaluate vascular perfusion techniques for rapid chilling of lamb carcasses using a proprietary Flo-ice(™) system. This produces pumpable ice slurries containing very fine ice particles, suitable for circulating through vascular systems. VPC was found to be capable of rapid initial reduction of carcass temperatures in comparison with air chilling (mean times to 20°C in deep legs were reduced from 2.6 to 1.3h, which was significantly different at P<0.05). In all cases however, uptake of perfusate into the carcasses occurred. This limited the duration of the perfusion treatment and as a result restricted the period of enhanced cooling. Samples from carcasses treated with VPC were lighter (P<0.05, with mean measured L value increasing from 43.4 to 46.8) and more yellow (P<0.05, with mean measured b value increasing from 6.7 to 7.9) than samples from conventionally chilled carcasses, and had lower shear force values when cooked (P<0.05, with mean force reducing from 10.0 to 6.8kg). This was most probably due to the added water in the meat. Microbial quality of the meat was not significantly affected by the perfusion treatments

Feasibility Of Using Vascular Perfusion Chilling For Red Meat Carcasses

Meat carcasses must be chilled to below 7°C before leaving the slaughterhouse. Typically cold air is circulated over the surfaces of the carcasses, which can take many hours to reduce centre temperatures to below 7°C. In vascular perfusion chilling (VPC), a cold fluid is circulated through the intact vascular system, offering significant reductions in cooling time. This paper describes a small feasibility study to evaluate VPC for rapid chilling of lamb carcasses. VPC was found to be capable of rapid initial reduction of carcass temperatures, but uptake of perfusate into the carcasses limited the time for which perfusion treatment could be applied. Samples from carcasses treated with VPC were lighter and more yellow than samples from conventionally chilled carcasses, and had lower shear force values when cooked. This was most probably due to the added water in the meat. Microbial quality of the meat was not significantly affected

Ivory from early Anglo-Saxon burials in Lincolnshire – a biomolecular study

Ivory bag rings have been found in more than 70 cemeteries across southern, central, and eastern England dating to between the late-5th and 7th centuries AD. These rings are most frequently found in richly furnished female graves, and would have served as the framework for bags that hung at the waist. Debate over the source of this ivory has prevailed since the 19th century, with walrus and mammoth ivory considered as possible contenders to elephantid ivory. Recent excavations at an early Anglo-Saxon cemetery in Scremby, Lincolnshire revealed a number of elaborate female burials containing such bag rings. Using radiocarbon dating this study aimed to establish whether the rings were contemporary with the burials before seeking to identify the species of ivory through Zooarchaeology by mass spectrometry (ZooMS). Strontium analysis was also used to identify the place of residence of the elephantids at the time of tusk formation. Through a multi-methodological approach, we have established that the ivory used for the Scremby bag rings came from elephants living in an area of young volcanic rocks in Africa at some point during the 5th and 6th centuries AD. This preliminary evidence allows us to consider the networks and socio-economic factors that facilitated the distribution of ivory from Africa to the British Isles at this time

Application of Vacuum Insulation Panels in the cold chain - Analysis of viability

© 2014 Elsevier Ltd and IIR.Vacuum Insulation Panels (VIPs) have already found application in some specialist applications where minimal energy consumption is important and space is at a premium. This paper investigates the feasibility of widespread application of VIPs in the cold chain by embedding them into the polyurethane (PU) foamed walls of traditional refrigerator and freezer cabinets. Thermal modelling of the insulation of a range of typical refrigerator and freezer cabinets as used throughout the cold chain was carried out both with and without VIPs embedded in the insulating walls. The potential energy savings and payback times were then calculated; for refrigerators the average payback was 9.7 years, for freezers it was 4.5 years