5. DESCRIPCIÓN DEL PROCESO DE FISCALIZACIÓN Y LIQUIDACIÓN
5.2. Descripción de los procedimientos
5.2.1. Gestión administrativa documental
The composition of the atmosphere surrounding foodborne microbes can be controlled by modifying the gas mixture in the food pack. This is known as modified atmosphere packing (MAP) and it comes in three forms:
136 Control
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vacuum packing (VP);•
gas flushing or modified atmosphere packing (MAP);•
controlled atmosphere (CA) storage.All three forms of MAP are used in combination with refrigeration. Vacuum packing has become very popular in the foodservice industry, as it extends the shelf life of many foods and saves preparation time in the kitchen. In the retail sector, the combination of MAP with refrigeration has made it possible to develop a vast new range of chilled ready meals and ready-to-eat products that are sold directly to the consumer. The technology offers not only convenience but also a ‘clean label’ as no chemical preservatives are retained by the food once the packs are opened. The label on MAP foods simply reads: ‘Packed in a protective atmosphere’. Like the food preservatives discussed above, MAP is useful in controlling low levels of contamination and is not a substitute for good hygiene.
At this point it would be timely to explain the meaning of shelf life. The shelf life of a food product is defined as:
the period of time during which the food maintains its microbiological safety and sensory properties (flavour, texture, aroma) at specified storage conditions.
The shelf life of all foods is indicated on the packaging in the form of ‘use by’ and ‘best before’ dates. The two designations have very different meanings but are often confused by consumers and food professionals alike.
The ‘use by’ date is about safety and often appears on foods with short shelf lives, such as fresh meat, chilled ready meals and prepared salads. Foods that have passed their ‘use by’ date should be discarded, as they could make someone ill. Storage instructions on such foods must be strictly followed as improper storage could make such foods hazardous before the expiry of the ‘use by’ date. For example, if chilled foods are stored in a faulty refrigerator, faster spoilage and food poisoning are more likely to occur. The shelf life of a chilled food can be extended beyond the ‘use by’ date by freezing it.
The ‘best before’ date is about quality and is often used for foods with long shelf lives, such as canned, dried and frozen foods. If a packet of biscuits has passed its ‘best before’ date, this does not mean that eating it will make you ill. It simply means that the quality (flavour, aroma, colour, texture) will gradually deteriorate after that date. The biscuits will eventually become softer and the fats within them may become rancid, leading to off-flavours. Confusing the ‘best before’ date with the ‘use by’ date can lead to unnecessary waste of food that is still perfectly edible.
Some retailers use ‘display until’ and ‘sell by’ dates on their food packaging. These are instructions for shop staff, not consumers, and are intended to help with stock control.
137 Othermethodsofcontrollingmicrobialgrowth:preservativesandmodifiedatmospheres
Vacuum packing (VP) is the simplest form of MAP. A food product is placed in a plastic bag, the air is extracted using a vacuum packing machine until the packaging film collapses around the product and the bag is heat sealed. The choice of plastic packaging is important, as it needs to exclude oxygen but retain moisture. A range of plastic laminates is available, depending on the food to be packed.
VP is often used in the foodservice sector for bulk-packing of fresh meat and fresh-cut, ready-to-cook vegetables. Good-quality meat packed in a vacuum and chilled keeps up to five times longer than the same meat packed aerobically. Vacuum-packed fresh meat can sometimes look slightly off-putting as the meat protein myoglobin is purple without oxygen. However, this reaction is reversible and the red colour returns rapidly once the pack is opened and the meat is exposed to air. In the retail sector, VP is used extensively for cooked meats, sliced deli meats and smoked fish.
VP works by preventing growth of aerobic microbes. Some spoilage bacteria can grow in the absence of oxygen but they do so more slowly than would be the case under aerobic conditions. The main concern in VP is the potential for growth of non-proteolytic strains of Clostridium botulinum, particularly if the cold chain is not carefully controlled and temperatures creep above 3°C. At 10°C, C. botulinum can grow and produce toxin within a typical shelf life of 10 days. Consequently, all manufacturers of VP machinery are advised to include instructions regarding the risks of C. botulinum growth in VP foods. In addition, the Food Standards Agency in the UK has published guidelines regarding both VP and MAP foods as shown in Box 8.2.
Cuisine sous-vide (French for ‘cooking under vacuum’) is a variant of VP developed in the 1970s in France. This involves heating vacuum-packed foods at low temperatures and for a longer period of time than traditional cooking. The temperatures used are usually between 50°C and 65°C but can be as low as 40°C for fillets of fish such as cod and halibut. Since temperature control is crucial in this process, specially designed water baths are available for purchase by restaurants wishing to use the technique.
Cuisine sous-vide has been adopted enthusiastically by many top chefs because of the supposedly superior gustative properties of dishes cooked in this way. Meats are said to be more juicy and tender while vegetables retain more of their original flavour, aroma, texture and shape than traditionally cooked foods. However, the practice has a high element of risk because the cooking is done within the temperature danger zone (5–63°C) under anaerobic conditions and so may trigger germination of C. botulinum spores (see Chapter 7 for more on this organism). In addition, there is some evidence in the scientific literature that exposing pathogens such as Salmonella to mild heat ‘stresses’ equivalent to some of those used in cuisine sous-vide may render the organism more virulent (i.e. able to cause more severe illness).
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Modified atmosphere packing (MAP) other than VP involves replacing the air normally surrounding a food with a gas mixture enriched with carbon dioxide. As shown in Table 8.5, carbon dioxide is used extensively in fizzy drinks to inhibit microbial growth. Not all microbes are equally sensitive to carbon dioxide. Moulds and many Gram-negative bacteria are very sensitive but some Gram-positive bacteria and several species of spoilage yeasts are more tolerant.
In MAP, food packs are flushed through with a gas mixture containing from 35 to 80 per cent carbon dioxide, depending on the product, with the remainder consisting of nitrogen and oxygen. During storage, the composition of the gas atmosphere changes due to respiration by microorganisms and foods, gas permeability of the plastic packaging and dissolution of carbon dioxide in the food to form carbonic acid. Large changes during storage can be reduced if the gas-to- product volume ratio is large. This is why meat joints are often sold in packs that seem excessively voluminous for the size of the product inside. Alternatively, oxygen scavengers may be used. These can be seen in packs of sliced deli meats where they often take the form of coin-sized sachets sealed to the inside of the lid and labelled ‘Do not eat’.
Controlled atmospheres (CA) are used mainly for bulk storage of fruit and vegetables. In this way, it is possible to make seasonal produce such as apples and