How modified atmosphere and vacuum packaging works
Some food is sold in vacuum packaging and modified atmosphere packaging (MAP).
Vacuum packaging removes all the air around the food in the package.
MAP replaces the air around the food with a mix of gases. The main gases used are oxygen, carbon dioxide, and nitrogen.
These preserve food quality and slow down food spoilage by:
- reducing the speed of chemical reactions in the food
- stopping or slowing the growth of bugs like bacteria, yeasts, and moulds.
Foods packaged in MAP and vacuum packaging can be kept longer than foods without such packaging.
Common MAP and vacuum packaged foods
- Vegetables and leafy salads
- Fruit
- Fresh pasta
- Raw meat, deli, and cured meats
- Seafood
- Cheeses
- Bakery products (like sandwiches)
Be careful with MAP and vacuum packaging
These packaging methods slow down the growth of bugs. But it doesn't mean they're not in the food. Some can even be encouraged to grow, such as C. botulinum in vacuum packaging.
Signs of spoilage and decay include mould, 'off' smells, or discolouration. But none of these may be present in MAP or vacuum packaging. Food can still be unsafe to eat if good practices were not followed when it was packaged or stored.
Follow the label to minimise risk
There is always some risk when eating foods in MAP or vacuum packaging. To help minimise this risk, follow storage instructions on the label.
Most fresh and minimally processed foods packaged in MAP and vacuum packaging still require refrigeration. There may be separate instructions to follow before and after the package is opened. Eat the food by the use-by date, and discard uneaten food after this date.
Meat in vacuum packaging can sometimes be discoloured
Fresh meat appears red because of the way its natural pigments (myoglobin) interact with oxygen. The absence of oxygen in vacuum packaging causes meat to turn a purple-red colour. This is not desirable but still safe to eat. The bright red colour returns when the package is opened and the meat is back in contact with air again.
This is less common with MAP. The food is in contact with different gases, including some oxygen. The gas compositions in the package are designed to keep the meat an attractive colour.
Who to contact
If you have questions about modified atmosphere and vacuum packaging, email info@mpi.govt.nz
