Image: iStock

Tom Ross, University of Tasmania

Most foods degrade and decay over time due to reactions with oxygen, decomposition of the food’s structure or flavour compounds, or microorganisms (or “microbes”) causing the

to spoil. The result can be food that is rancid, smelly, slimy, has lost its colour or flavour, or is growing things like

mould.

We apply our understanding of spoilage mechanisms to extend the shelf life of foods by slowing the rate of spoilage. We exclude oxygen by packaging, slow reaction rates by refrigerating, gently heat foods (blanching, pasteurisation) to stop enzymes and to kill microbes. Nonetheless, as consumers we want “fresher”, more natural foods but many fresh and lightly preserved foods will degrade quickly.

Food quality can deteriorate before we perceive obvious signs of spoilage. If allowed to grow to high levels, some microbes that may contaminate foods (collectively called “pathogens”) can cause foodborne illness, or “food poisoning”. Often these microbes don’t visibly spoil the food so we can’t tell if a food has become unsafe.

To protect consumers against poor quality or potentially hazardous foods, governments have introduced “date codes” to help consumers evaluate the “freshness” of foods. Food producers also embrace date codes to help them provide safe, high quality products to consumers.

In Australia and New Zealand, we specify “use-by” and “best-before” dates for perishable and semi-perishable foods that are ready-to-eat without cooking. Food expected to remain wholesome for more than two years, in unopened packages, doesn’t require these labels and there are other types of date codes for bread.

Watch: Here’s a delicious way to prepare Quinoa, as demonstrated by Paper Tiger. (Post continues after video.)

Similar regulations operate in European Union countries, but the United States and other nations have a plethora of food date codes that don’t readily correspond with our “use-by” and “best-before” dates. In general, there is little harmonisation internationally for food date codes which has been identified as a barrier to trade. Perhaps unsurprisingly, surveys in the United Kingdom and US showed that many consumers don’t understand the meaning of various date codes on foods.

Use-by

A “use-by” date is required for foods that might, over time, support the growth of certain pathogens under the specified storage conditions. A “use-by” date, then, relates to food safety and indicates the time when the food may become less safe to eat.

Foods cannot legally be sold, and should not be consumed, beyond their “use-by” dates and should be discarded. “Use-by” dates are also required on specially formulated foods for medical purposes given, for example, to people with inherited metabolic disorders whose dietary needs cannot be met by a normal diet.

For these foods, the “use-by” date indicates when essential nutrients in the food will have degraded to levels so low that the food no longer provides the intended therapeutic benefit. (Post continues after video.) 

10 foods you never knew were healthy

Bread

KATIE THOMSITT, Dieticians Australia spokesperson says: "Lots of people shy away from bread to achieve weight loss. But bread is such an important source of fibre, and plays such a helpful role in weight loss and preventing bowel cancer. A couple of slices of a dark, seedy bread per day is absolutely fine."

Cheese

KATIE SAYS: "Cheese is definitely a higher fat source of dairy, but still a good dairy fat. Choose low-fat options if you have it regularly, otherwise consume it in moderation. One serve of dairy is 30g, so a couple of slices is absolutely fine."

Chocolate

KARA LANDAU, The Travelling Dietician says: "Studies have been able to show that dark chocolate can improve insulin sensitivity, reduce blood pressure in healthy individuals, protect against heart disease, and improve HDL good cholesterol (not a bad start for such a tasty food!). Dark chocolate also contains polyphenols, whilst white chocolate does not. These polyphenolic compounds are able to relax blood vessels allowing for better blood circulation, and thereby assisting with the maintenance of healthy blood pressure levels."

Coffee

KATIE SAYS: "Coffee is a really good snack, in particular if its milk-based to get the dairy in - for example, a skim latte. As long as its in moderation - daily guidelines say a maximum of three per day! And you want lots of water on top of that."

Eggs

KARA SAYS: "Yes, even the yolks are good for you! Healthy fat soluble vitamins, as well as half the protein found in an egg, are all found in the yolk!"

Avocado

KATIE SAYS: "Avocado is a healthy fat. Lots of people think its high-fat and not good for you, but its rich in mono unsaturated fats, which give you protection against heart disease. It also helps with controlling lower cholesterol levels."

nuts

KATIE SAYS: "Nuts fall into the same category as avocado - they have lots of healthy oils and fibre."

dairy

KARA SAYS: "Often milk and yoghurts are fortified with Vitamin D (a fat soluble vitamin) which requires a small amount of fat to be present in order for the body to absorb it, therefore having the full fat variety can be of value to enhance the nutritional benefits from the products' consumption. The fat in the dairy also aids with satiety, which could prevent unhealthy snacking at a later point in the day."

Potato

KATIE SAYS: "Potato always gets a bad rap as a starchy vegetable, but it's an excellent source of fibre. Sweet potato in particular is great for weight management and sugar level control. Potatoes are also really rich in potassium."

Red meat

KARA SAYS: People tend to restrict red meat unnecessarily, thinking that its high in saturated fat. "But lean red meat is high in protein, CLA (which has been found to be associated with lower body fat percentages), B12, iron and zinc. These are all nutrients we want to get into our body!"

 Best before

A “best-before” date provides advice about the expected quality of the product and is the time beyond which, in the food manufacturer’s opinion, the product will no longer be in optimal condition. It will, however, probably still be edible and nutritious for some time after that date.

Food producers usually apply conservative “best-before” dates to ensure that consumers have enough time after purchase to use the food in good condition. Consumers can exercise judgement about foods beyond their “best-before” date: if it looks OK, and smells OK, it’s probably OK to eat, though not at its best.

This approach must not be used for foods beyond their “use-by” date, since pathogens can be present without affecting the sensory qualities of the food.

Foods cannot legally be sold beyond their “use-by” dates. (Image: iStock)

Waste not, want not

Accurately specifying “use-by” and “best-before” dates is challenging, requiring extensive scientific trials and/or knowledge because of the range of foods, spoilage processes and food preservation technologies.

Expert guidance is available to food producers from a number of sources. Sometimes, however, there’s uncertainty about whether a “use-by” or “shelf life” date should be applied if it's not known whether pathogens are realistically likely to be present, and able to grow, in the particular type of food or not.

Our capacity to produce enough food for Earth’s population is becoming a real concern, yet 20-30% of the world’s food is wasted. A consequence of confusion about the correct specification of “best-before” and “use-by” dates is that some foods are unnecessarily discarded even though they are safe to eat and nutritious.

Look closely (Image: iStock)

Developing appropriate “use-by” and “best-before” dates could help reduce this wastage. Helping consumers to minimise their wastage of food through understanding of “best-before” dates offers another small, but potentially useful, contribution to global food security.

As an additional tip to reduce wastage, if foods are unlikely to be consumed before the “use-by” or “best-before” date, they can be frozen (which essentially stops spoilage processes) and thawed for consumption later, provided they’re eaten soon after thawing.

Do you pay attention to use by and best before dates when you consume food? 

Dr. Wayne Anderson, Director Food Science and Standards Division, Food Safety Authority of Ireland, co-authored this article. Wayne is also a member of the International Commission on Microbiological Specifications for Foods.

Tom Ross , Associate Professor in Food Microbiology, Food Safety Centre, School of Land and Food, University of Tasmania

This article was originally published on The Conversation . Read the original article .