A Cold Chain, is a network of temperature-controlled links involved in moving a product from supplier to consumer. The products moving across this chain, must remain within a temperature range until these reach their final destination. The chain is considered broken when the product is exposed to temperatures outside the acceptable range.
The internal biological and chemical processes of fresh produce continue after harvesting. Produce is a living, breathing commodity which emits heat and carbon dioxide. There are four environmental conditions that can be managed to get good-quality product to market (Thompson, 1998):
Temperature is the most important of the four; therefore, the risk of a failure in the cold chain could cause excessive ripening, weight loss, softening, color and texture changes, physical degradation, bruising, and attack by rot and molds. These factors affect freshness, desirability, and marketability. Temperature is also a factor that can be easily and promptly controlled, although in some regions of the globe, especially in tropical and subtropical regions, postharvest losses of horticultural crops can be unavoidable (Emond, 2008). Another aspect of temperature control is that while for most foods temperature ought to be maintained at a minimum, some fruits and vegetables of tropical and subtropical origin such as papaya, mango, tomato, banana, oranges, guava, cucumber, and bell pepper display sensitivity to low temperature and may develop symptoms of chilling injury at temperatures below a certain threshold, usually below 10°C. Chilling injury is damage due to changes in the physiology of the fruit that often becomes visible after transferring a chilling-sensitive crop to non-chilling temperatures. Therefore, it is very important to transport and store chilling-sensitive crops at temperatures high enough to prevent chilling injury. Similarly, heat-sensitive fruits and vegetables should be handled at temperatures low enough to extend their postharvest life (i.e., usually around 0°C to 1°C)
Temperature control is the key point in cold chain operation and the most important factor when prolonging the shelf life of fresh fruit and vegetables and to prevent the growth of microorganisms and deterioration of biological products during processing, storage, and distribution. Each stage crossed by a temperature-sensitive product is related to the preceding one and has an impact on the following one. Thus, when a link of this “cold chain” fails, it inevitably results in a loss of quality and revenue, and, in many cases, leads to spoilage or even safety problems.. Cold chain temperature control is important in maintaining freshness and extending the storage life of fresh fruits and vegetables or their derivative fresh-cut products. It is a vital component for a complete cold chain to deliver fresh produce from field to consumers. Quality loss in one link of the cold chain adds to the loss sustained in the previous links. Product condition at market reflects the cumulative quality losses at each step in handling. Variation in temperature may also cause condensation on the inside of the package. It is not easy to maintain appropriate conditions over the whole chain; negligence or mishandling in the logistics of perishable food products is very common, including goods being poorly or excessive cooled.During postharvest handling and storage of horticultural products, modified atmosphere (MA), controlled atmosphere (CA), or ultra-low oxygen (ULO) is commonly used to complement the refrigerated storage. However, it is to be noted that the success in the application of these new technologies is subordinated to good temperature management practices: it influences both the respiration rate of fresh produce and the permeability of the film for O2 , CO2 , and H2 O of a package product. One of the main problems is that produce respiration is more sensitive to temperature changes than —normally— the permeability of a packaging film. With increasing temperatures, more O2 will be consumed by fresh produce thandiffused through the packaging film, resulting inevolution of the atmosphere toward anoxia. Therefore, a film that produces a favorable atmosphere at the temperature for which the package was designed may cause excessive accumulation of CO2 and depletion of O2 at higher temperatures, caused by an increased respiration rate. This anoxic situation could lead to metabolic disorders such as fermentation with production of ethanol, acetaldehyde, off flavors, and odors. On the other hand, lower temperatures will lead to reduced respiration that will accumulate O2 above an optimal atmosphere, thereby rendering MAP packaging measures less effective. Package design under those conditions is a difficult compromise, where concern for efficient cooling, proper cool storage, and resistance to temperature fluctuations is paramount. For example, a larger vent area in the packaging increases the cooling efficiency, but the strength of the package should be taken into account.
The maintenance of a constant optimal temperature throughout the postharvest handling chain is one of the most difficult tasks and is far from being universally attained. Even when transport by truck or sea can provide satisfactory temperatures within the limits of acceptability, the transport time may be too long for short shelf-life products to be transported over long distances. On the other hand, the speed of air transportation makes it a tempting alternative for transporting highly perishable and very short-life commodities. However, one should bear in mind that air transport typically involves a significant break in the cold chain of perishables handling. The major causes for this rupture are either the fluctuating or very high and low temperatures often encountered during flight and ground operations. Although the temperature throughout the trip by truck can be maintained within the limits of acceptability, the length of the transport significantly reduces the marketability time considering the relatively short shelf life of some produce, such as strawberries (5–7 days).
Healthy animals slaughtered hygienically after resting and fasting provide a practically aseptic meat. However, following slaughter, evisceration and dressing operations, microbial contamination occurs especially on the surface of meat, through contact with equipment, tools, hands, clothes, objects, etc. Due to the chemical composition of meat which is rich in proteins, lipids and water, it is a particularly favorable substrate for the growth of microorganisms. The lipid content of meat also makes it very sensitive to oxidation (the reaction of oxygen with fatty acids) and subsequent production of peroxides. The breakdown products of the peroxides produce the characteristic objectionable odor and flavor of rancid meat. In general, meat spoilage can be avoided by maintaining the required cold chain, starting from its production until it reaches consumers.
If cold chain control is violated at any point, meat safety, quality and hygiene will be compromised. The factors that control the cooling of a side of meat are the rates at which heat can be conducted from the innermost tissues to the surface and from the surface to the circulating air in the chill room. Air temperature, air velocity, and –to a limited extent– relative humidity, are the environmental factors that affect the cooling time of carcass sides. Relative humidity has a greater effect on weight loss than on cooling rate. Cooling rate is also a function of the weight and fat cover of a given side.
Meat should be loaded into refrigerated containers and transported to the port or airport under strict temperature controlled conditions. To maintain the optimal shelf life and quality of beef, sheep and goat meat during transport, the temperature should be maintained at 0°C (±1°C) for chilled and below -10°C for frozen products.Throughout transport to the country of destination, container temperatures should be regularly monitored.
Refrigerated transport is not designed to reduce the temperature of product but only to maintain the temperature during transport. Trucks generally don’t have the refrigeration capacity to reduce meat temperatures. Thus meat must be loaded and dispatched at 7°C for carcasses or 5°C for meat products. These temperatures relate to the preferred living conditions of bacteria. Different microorganisms prefer different conditions, but the main ones that cause food poisoning generally do not grow at or below these temperatures. So, keeping the meat at or below these temperatures and keeping it clean, will fulfill the required quality and hygiene. All meat processors are required to record the temperature when meat is received, processed as well as the temperature at load out. Temperature of product and the transportation environment should also be monitored and recorded during shipment. Meat and carcasses must be transported from the abattoir to the port of embarkation in sealed and specially designed vehicles. Vehicles for transporting meat and carcasses should be considered as an extension of the refrigerated storage.
Vehicles must be fitted with a refrigeration system and minimum and maximum thermometer or other temperature sensing or recording device to monitor cold chain inside the meat container. If the temperature is monitored, it should be documented. The temperature reader should be located in a place where the driver can monitor while driving. Refrigeration units should be serviced regularly. The cooling unit must be in good repair and operation. Both truck drivers and plant personnel should regularly check the status of the trailer refrigeration unit. Meat should hang on rails. If stockinet is put on carcasses, it must be clean. Meat trucks should not carry anything other than meat. Vehicles must be properly cleaned, disinfected out and air-dried before they are allowed to transport meat and carcasses. Vehicle body should be sufficiently insulated and be in good repair with no holes in the body that might allow heat, dust, or other adulterants to enter the cargo area.Vehicle doors and seals should be securely closed and that there will be no air leaks.Vehicles should be free from residues of previous cargoes, cleaning and sanitizing compounds. Vehicles should be pre-cooled for at least 1 hour before loading to remove residual heat from the insulation, inner lining and the air of the trailer and it should be capable of maintaining the required temperature of the meat during the journey. For pre-cooling, the doors should be closed and the temperature setting of the unit should be no higher than 26°F (-3°C). Meat handlers and drivers should apply personal hygiene before handling meat.Meat and carcasses must be loaded, transported, unloaded or stored hygienically. In case of flight schedule breakdowns, it must be unloaded, stored and reloaded maintaining the required cold chain.The meat inspecting officer at the ports of embarkation must check and confirm that the meat or carcass is certified, transported in sealed and specially designed vehicles and that the minimum and maximum thermometer or other temperature sensing or - recording device reading is maintained at or close to 0°C.
Although air-freighting of meat offers a rapid method of serving distant markets, there are many problems because the product is unprotected by refrigeration for much of its journey. Up to 80% of the total journey time is made up of waiting on the tarmac and transport to and from the airport. During flight, the temperature is normally maintained between 15 and 20°C. Perishable cargo is usually carried in standard containers, sometimes with an insulating lining and/or dry ice but is often unprotected on aircraft pallets. As a result, Insulated containers should always be used to reduce heat gain.Meat should always be pre-cooled and held at the required temperature until loading. Containers should be filled to capacity.A thermograph should accompany each consignment.
Historically, it was the need to preserve meat during sea transport that lead to the development of mechanical refrigeration and the modern international trade in foodstuffs.
Developments in temperature control, packaging and controlled atmospheres have substantially increased the range of foods that can be transported around the world in a chilled condition. Refrigerated containers should incorporate insulation and have refrigeration units built into their structure. The units should operate electrically, either from an external power supply on board the ship or in dock. When the containers are fully loaded and the cooled air is forced uniformly through the spaces between cartons, the maximum difference between delivery and return air should be less than 0.8 °C. The entire product in a container should be maintained to within ±1.0 °C of the set point. For bulk transportation of frozen meat, refrigerated cargo ships should be used.Frozen meat should generally be stored and transported at -18 °C or below.
Once a meat shipment is accepted by the Federal Meat Inspectors, it should be immediately transferred to the cargo or placed in the air/sea port storage facility. The Inspectors should inspect the storage freezer before storing to assure it is in good working order.No substances known to be toxic or harmful should be stored or maintained in the meat storage areas. A refrigerated room used for the storage of chilled carcasses, sides, quarters or portions shall be maintained within the range of 1° to 5° C and the mean air speed over the product shall be maintained above 0.5 meters per second. The relative humidity shall be maintained below 95%. If the product is stored for longer than 72 hours, the relative humidity should be maintained below 90%; A refrigerated room used for the storage of offal shall be maintained at a temperature below –2° C. If the offal is stored for longer than 72 hours the temperature should be maintained below -10° C. A refrigerated room used for slow freezing of a carcass or meat shall be operated at temperatures below –18° C to freeze such carcass or meat within a period not exceeding 48 hours; A blast freezer used to freeze a carcass or meat within a period not exceeding 24 hours shall be maintained at a temperature below –25° C and the mean air speed over the carcass or meat shall be maintained at a value exceeding 2.5 meters per second;A refrigerated room used for the storage of a frozen carcass, side, quarter or portion, shall be maintained at a temperature below –18°C provided that if the storage period is less than 3 months, the refrigeration room shall be maintained at a temperature below –10° C. Adequate and proper cold air circulation is required for maintaining the desired uniform temperature in all areas of the freezers and refrigerators where meat is stored.
Proper temperatures in refrigerated and freezer spaces should be Freezer: –30° to – 18° C (–22 to 0 F) or lower; Refrigerator: 4°to 6°C (40 to 43 F).Relative humidity should be maintained at 85 to 90 percent in refrigerated spaces. High humidity in the freezer helps to decrease dehydration of the frozen items.The rotation of stock throughout the cold chain should be organized according to the first in-first out (FIFO) rule: the first lots to be stored are the first to be dispatched.From MEAT COLD CHAIN GUIDELINE; full document here
Cold chain management is crucial in the seafood industry. Maintaining fish at the correct temperature from catching until it reaches the consumer will ensure optimum freshness and quality. Spoilage cannot be stopped in fresh fish, it can however, be controlled to a great extent. The two most important words to remember when dealing with fresh fish are time and temperature. It is a legal requirement for food business operators to ensure that all chilled and frozen foods are maintained at the correct temperature during transport, storage, delivery and display. In addition, there must be sufficient refrigerated space to allow cooked and ready-to-eat food to be segregated from raw food. Poor temperature control leads to increased waste and consequently decreased profit for your business.
Fish starts to spoil from the time it is caught and this spoilage continues throughout its shelf-life. The main reason for fish spoilage is enzyme activity and bacterial growth. In addition, oil-rich fish such as mackerel and herring will spoil due to oxidation. All of these activities occur more rapidly at higher temperatures.
Bacteria are the major cause of fish spoilage. Pathogenic bacteria can cause food poisoning. Millions of bacteria live on the skin, on the gills and in the intestines of live fish. After harvest these bacteria invade the flesh of the fish through the gills, skin and belly cavity lining. Other bacteria, not naturally present in the fish, can be introduced from humans and the environment through handling or contact with contaminated boxes, knives and other equipment.Histamine poisoning (scombroid poisoning) is caused by consuming fish containing high levels of histamine. Naturally occurring bacteria in fish produce an enzyme which converts histidine to histamine. Histamine poisoning occurs very quickly after eating the fish, usually within 30 minutes. Common signs of histamine poisoning may include a tingling or burning sensation in the mouth, a rash on the upper body, headaches, dizziness and itching of the skin. In some cases, nausea, vomiting and diarrhoea may occur. Species associated with histamine poisoning include mackerel, sardines, tuna and swordfish. Once histamine has formed in the product, subsequent cooking will not destroy it.
The best way to prevent histamine poisoning is to ensure that the fish is maintained at a temperature below 4°C.
Enzymes in live fish help to build tissue and digest food. After the fish dies, enzyme activity continues and starts to digest or breakdown the flesh. This causes the flesh to soften resulting in poor quality. Enzyme activity destroys the lining of the gut allowing bacteria to enter the flesh of the fish.
Oxygen in the air reacts with oils in fish and causes rancidity, off-odours and off-flavours. This occurs in oil-rich fish such as salmon and mackerel.
Small fish tend to spoil faster than larger fish. Certain species will spoil faster than others e.g. whiting will spoil faster than plaice. Fish that have recently spawned or have been feeding heavily will spoil more rapidly.
The control of spoilage by reducing the temperature is the most common and practical way of keeping fish fresh. The lower the temperature, the longer it will take for the fish to spoil. Remember, fish may already be several days old by the time it reaches you. “Use-by” dates placed on products by suppliers are only relevant if strict temperature control is adhered to at all stages from delivery, during storage and on display. While some fish may have a shelf-life of up to fifteen days from date of catch if maintained in optimum conditions, the intrinsic quality of the fish at the time of catching may also affect the shelf-life. High temperatures increase the rate of bacterial growth, enzyme activity and oxidation leading to rapid spoilage, decreased shelf-life and possible food safety risks. Consequently, poor temperature control leads to increased waste and decreased profit for your business.
It is generally recommended that chilled food products are maintained at a temperature between 0°C and 5°C. Because fish is highly perishable, the shelf-life is greatly increased if it is maintained at a temperature between 0°C and 2°C. The most effective way of maintaining product temperature between 0°C and 2°C is the liberal use of ice. This is an excellent way of chilling fish without freezing it. Correctly used, ice can rapidly reduce the temperature of fish. Ice should be made from potable water. Note: It takes approximately 10-15 minutes to chill a 0.5kg fillet of cod from 5°C to 2°C using ice. It will take up to 2 hours to chill the same fillet using refrigerated air. The retailer must take care to ensure that fish is maintained at the correct temperature and that the cold chain is not broken.
Fish should be transported and packed for delivery as per the specification agreed with the supplier.Fresh fish should be delivered, packed in ice, in clean, unbroken boxes or cartons.
Maintaining the temperature between 0°C and 2°C in storage is readily achieved through a combination of ice and refrigeration. Fish should be re-iced as necessary and not allowed to remain in melt-water. Whole, ungutted fish should be stored belly up and layered with ice while whole gutted fish should be stored belly down and layered with ice.Fish fillets should be stored flesh to flesh and layered with ice. Salmon cutlets, darnes, fillets, tuna and trout fillets should be protected with polythene film before adding ice.
On display, maintaining the temperature of fish between 0°C and 2°C can be more challenging. Therefore, temperatures up to 4°C are generally acceptable, provided the fish is not maintained at this higher temperature for long periods.Fish fillets should be displayed in thin layers, flesh to flesh and no more than two deep in order to maintain the correct temperature.Fish on display should be top-iced lightly at regular intervals.Avoid displaying large quantities of fish which have to be returned to chilled storage at the end of the day. If fish is returned to the chill at the end of the day, it should be clearly labelled to ensure correct stock rotation.Live molluscs should not be placed directly on ice as the low temperature will result in some mortalities. Ice should not come into direct contact with smoked fish, tuna, or with the flesh of salmon or trout as it tends to leach out the colour.Display fixtures should be placed in a suitable location to ensure that the fish temperature cannot be increased by heat from overhead lights, wall heaters or direct sunlight. Some retailers choose not to use ice and instead use specialised refrigerated display units. These units can be very effective at maintaining low and consistent temperatures. Care must be taken to ensure that fish does not become dried out. Suitable trays must be used and any melt-water removed regularly.
Reducing the amount of oxygen may increase the shelf life by reducing the growth of aerobic spoilage bacteria. However, there may be an increased risk of Clostridium botulinum toxin formation in these products if strict temperature control is not adhered to. This process step should be considered as part of the food safety management system and appropriate controls introduced. It is recommended that these products are maintained at less than 3°C throughout the shelf-life.
COLD CHAIN MANAGEMENT FOR SEAFOOD.Full document here
Immunization in the 1960s and 1970s
Only a few vaccines were available in the early 1960s, and few children around the world received them. Smallpox was among the infectious diseases that were rampant, and the World Health Assembly received numerous reports of the catastrophic consequences of smallpox among its Member States. But vaccine technology existed for smallpox, offering the potential for protection. In 1966, the World Health Organization (WHO) launched a global campaign to eradicate smallpox. This successful campaign demonstrated both the power and portability of vaccines. Within less than two decades, smallpox had been eradicated—a public health achievement that still stands as one of the greatest in history.
The Expanded Program on Immunization was designed 40 years ago for two types of vaccines: those that are heat stable but freeze sensitive and those that are stable to freezing but easily damaged by heat. A cold chain was developed for transport and storage of such vaccines and established in all countries, despite limited access to resources and electricity in the poorest areas. However, cold chain problems occur in all countries. Recent changes to vaccines and vaccine handling include development and introduction of new vaccines with a wide range of characteristics, improvement of heat stability of several basic vaccines, observation of vaccine freezing as a real threat, development of regulatory pathways for both vaccine development and the supply chain, and emergence of new temperature monitoring devices that can pinpoint and avoid problems. With such tools, public health groups have now encouraged development of vaccines labeled for use in flexible cold chains and these tools should be considered for future systems.
In order to ensure quality and integrity of the vaccine products, their storage and distribution conditions should be monitored continuously. The general practice in vaccine refrigerators is to use a thermometer (stem thermometer or bi-metal thermometer). A thermometer, however, only provides a snapshot of the temperature at the point in time when it is checked and cannot be considered as an ‘appropriate’ monitoring tool. If a temperature value of between +2°C and +8°C is found while checking, health workers may erroneously conclude that the vaccines are safe since this snapshot reading provides a value only when it is checked and does not cover the rest of the daytime/nighttime period. Unless a temperature excursion is seen at the time the temperature is checked with a regular thermometer, almost all temperature violations go unnoticed.