Shelf Life


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It is an offence to sell packaged food past its use-by date and this form of date marking is tied to food safety. The best-before date is the open date which most packaged foods carry and is defined in the FSC as 'the date which signifies the end of the period during which the intact package of food if stored in accordance with any stated storage conditions, will remain fully marketable and will retain any specific qualities for which express or implied claims have been made'.

An exemption from the open date marking still applies if the best-before date of the food is two years or more. However many manufacturers whose products fall into this category elect to date mark these foods. The most direct way of doing this is to conduct properly constructed storage trials under realistic, defined conditions. This may not be possible for smaller manufacturers, in particular those just entering the market. They frequently are looking for some rapid method to measure and estimate shelf life to allow them to put their product on the market as quickly as possible.

Established manufacturers also are reluctant to rely solely on conventional storage trials to determine shelf life. Commercial pressures usually mean that a product must be marketed as quickly as possible after its development. Retailers may also have their own demands about shelf life of particular product categories especially those with a relatively short shelf life. Indirect methods of shelf life determination are frequently used to yield results which otherwise would be time consuming to obtain. These may involve so-called accelerated shelf life tests usually based on storage of the product at higher than normal temperatures or computer-based models.

Storage of foods at higher than normal temperatures can induce changes in the food which would not occur at normal ambient temperatures. Also the rate at which normal changes are accelerated by higher temperatures must be known with acceptable accuracy. Models are useful only if they have been shown to mimic spoilage rates in like foods and not merely been developed under laboratory conditions. These models are not designed to be used beyond the range of data used to construct them.

No single factor may determine the shelf life of a food but the most important to be considered in shelf life studies are:.

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Unless a food has undergone a commercial sterilisation process e. Not only is water measured as water activity a critical factor which determines which, if any, microorganisms will grow in a food, many foods are sensitive to loss or gain of water. This in turn can be affected by the choice of packaging and in many instances will determine which packaging is used. Many biscuits and savoury snacks including nuts suffer in quality as a result of moisture gain.

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Some baked foods such as cakes may suffer from moisture loss. The most important are oxidation, non-enzymic browning, enzymic browning and, in some cases, food and packaging interaction. Oxidation of fats and oils leads to the development of rancidity marked by off odour and flavour. This may limit the shelf life of fats and oils but can also limit the shelf life of many other foods containing fats and oils. Examples of foods stored at ambient temperatures which can develop rancid off flavours are nuts, potato crisps and biscuits.

Storage of these foods in high oxygen atmospheres can sometimes be used to accelerate shelf life studies but atmospheric oxygen is not the only initiator of oxidative spoilage. While freezing arrests microbial activity, chemical reactions proceed at a much reduced rate even at recommended storage temperatures. Examples of frozen foods whose storage life is limited by oxidation include fish and meats.

A number of different vitamins are sensitive to oxygen including vitamin C ascorbic acid and vitamin B thiamine. When vitamins are added to fortified foods such as breakfast cereals or sports drinks and a label declaration made, then shelf life determinations will have to take account of any vitamin degradation which will occur with time in addition to any other changes in quality.

In some circumstances the desired shelf life can be a major factor in the selection of a packaging material.

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For example, if for a particular market segment, the manufacturer of a snack food packed under a modified atmosphere determines that a shelf life of only six weeks is necessary, it may be possible for the product to be successfully packed in a plastic with lesser barrier properties than if the manufacturer was seeking a six month shelf life. In either case, the expected shelf life will be dependant on the integrity of the package seal to maintain the atmosphere within the package beyond any expected gas transmission across the packaging film for the nominated shelf life.

A special case of food and packaging interaction is the use of tin plate cans with welded side seams in the canning industry. Most canned foods are now processed in lacquered cans which substantially reduces the possibility of tin dissolution in the food. However tin dissolution from the can is essential in some canned foods which would otherwise be subject to discolouration.

Asparagus is one example of such a food. Sufficient tin is therefore left exposed in such canned foods to ensure the expected quality of the food through its nominated storage life without it exceeding the regulatory limit. All shelf life studies includes an assessment of the safety of the product and this assessment will normally precede any assessment of shelf life.

It is widely recognised that the most effective way to ensure food safety is to meet the internationally recognised Hazard Analysis and Critical Control Point HACCP system as adopted by the Codex Alimentarius Commission and written into legislation in many countries including Australia.

Standard 3. Because of the wide range of foods in this category, which includes cook-chill foods, shelf life studies and safety evaluations are usually assessed via a challenge study rather than from accumulated knowledge as is the case with most frozen foods. Challenge testing is a laboratory investigation to determine what can happen to a food product during processing and storage following inoculation with one or more appropriate microorganisms.

A challenge study is most frequently used to determine if pathogens will be controlled or to estimate the time it takes for them to grow to potentially hazardous levels, but can also be used for shelf life studies using potential spoilage organisms. Challenge testing is a specialised procedure that is time consuming and expensive but it remains an important procedure in both safety studies and shelf life determination.

Non-vertebrates make up more than 90 percent of all living animal species, so it's not surprising that the largest Museum collection resides in the Division of Invertebrate Zoology.

Shelf Life

Among the more than 23 million specimens, the single largest component is Alfred Kinsey's—yes, sex researcher Alfred Kinsey's—collection of Cynipidae, or gall wasps. Numbering some 7. Dinosaurs are among the Museum's biggest attractions—but the T. Split among four departments— Ichthyology fishes , Ornithology birds , Mammalogy mammals , and Herpetology reptiles and amphibians —the vertebrate collections house more than 3. Among the species represented are such rare animals as coelacanths and extinct species including the dodo and Tasmanian wolf.

More than half a million objects amassed over more than years include significant archaeological collections from the Americas, including some of the oldest textile fragments found in the New World , as well as extensive ethnological collections from North America , Africa , Asia, and Oceania. There are shelves, there are jars, and then there are liquid nitrogen-cooled vats.

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