Types of plastic packaging

The type of Packaging can interfere in the growth of bacteria.

Gas permeable packaging

Aerobic bacteria can grow. Fresh meat packed in cellulose film so as used in tray packaging is threatened by Pseudomonads like Pseudomonas fluorescens and Pseudomonas fragi as dominant bacteria producing smell and slime.

Gas barrier, closed packaging

The atmosphere in the packaging can be modified according to the food which is being packed.
Enzymes, temperature and competitive growth can produce gas like CO2.
For some food gas packaging with modified atmosphere are used.

Vacuum packaging

Vacuum inhibits the growth of aerobic microbes such as Pseudomonas,Bacillus, moulds. In these packagings the growth of lactobacillus is dominant. Enterobacteriaceae can grow under anaerobic conditions.

Modified Atmosphere Packaging MAP

Nitrogen, CO2 and in some cases O2 are used.
Nitrogen has no activity against bacteria. It increases shelf life substuting oxygen.
CO2 acts bacteriostatic on gram negative aerobic bacteria and bactericide because of its undissociated part of H2CO3 which enables CO2 to trespass the cell membrane and act bactericide on the cells of the bacteria.
Lactobacillus is not affected by CO2.
CO2 can reduce growth of Listeria on meat.

Polymer used as Filling product
PVdC,EVOH,Acrylnitril Oxygen barrier  
PET/PVdc-PVC/PE multilayer foil red meat
HDPE, PVdC,PP water vapor barrier  
PA/PE-PVC/PE multilayer foil treated meat
HDPE,PP stability,suitable  
  for microwave oven  
PET/PVdC/PE multilayer foil poultry
Nylon high temperatures  
  resistant  
PET/PE/PVdC-PVC/PE multilayer foil fresh fish
CPET mechanical resistance,  
  high temperatures  
  resistant, oxygen barrier  
PET/PVdC/PE multilayer foil Pizza
APET mechanical resistance,  
  oxygen barrier  
PET/PE/PCdC multilayer foil Cheese
Polyester high temperatures  
  resistant, flexibility  
  and resistant to perforation  
Metallized PET/PE-metallized PA/PE multilayer foil dried products,coffee
PVC/PET mechanical stability,  
  some types  
Micropore foil-LDPE/OPP/PVCPA/PE multilayer foil fresh vegetables
LDPE, HDPE, EVA sealing layer  
EVA highly permeable to  
  oxygen and CO2  

Multilayer foils may have PE, PVdC and PET as typical components.

Packaging as short news:

  • Plastic bags are bad because they may contain PVC which develops toxic gases as it is burned. Use paper bags.
  • Aluminum cans are hostile to environment because they can hardly be recycled.
  • Greaseproof paper is better as plastic foodwrap because the later may contain harmful softener

Nonylphenol in food

Nonylphenol is an industrial chemical which interacts with human hormones and produces cancer. Its synonyms are p-nonylphenol,4-nonylphenol, C15H24O. Nonyphenoles were found in mineral waters due to migration from the plastic seal of the caps of bottles.
Another source of nonylphenol in food are the nonylphenolethoxylate which are used in the production of plastics for wrappings and packagings of food. Nonylphenolethoxylate act as emulsifier and stabilizer in plasticizers for Packagings. Nonyphenoles are breakdown products of norylphenolethoxylate detergents used in household and industrial cleaning products.which contaminate food. Their contact with foods leads to the contamination with nonyphenoles.
Very high amount of nonylphenoles were found in apples and in tomatoes by the Research Center in Julich.
The estimated human intake of nonylphenoles is 7.5 microgram a day. The content of nonylphenole in pesticides are now being analyzed.

Product Modified atmosphere Remarks
Red meat 80% O2 + 20% CO2 CO2 reduces growth of Pseudomonas
    aerobic bacteria which often
    spoils red meat.High concentration
    of oxygen is needed to keep red colour.
     
Porc 60% O2 + 40% CO2 CO2 reduces growth of aerobic bacteria
    less O2 is needed because of reduced red
    colour of porc compared with beef
     
Poultry 50 - 80%CO2 + 20 - 50% N2 A high headspace with gas is important
     
Sausages 20% CO2 + 80% N2  
     
Sliced heated meat 20% CO2 + 80% N2  
     
Fish, high-fat 60 - 70% CO2 + 30 - 40% N2 No oxygen should be used
    to reduce rancidity
     
Fish, low-fat 30 - 40% O2 + 30 - 70% CO2 Oxygen is used to keep red
  + 0 - 40% N2 colour of low-fat fish and seafood
    It also reduces growth of anaerobic
    bacteria such as Clostridium
    and its toxins
    in case of long shelf life
     
Sliced fish,cooked 20% CO2 + 80% N2  
Hard Cheese 80 - 100% CO2 + 0 - 20% N2  
Sliced hard cheese 80 - 90% CO2 + 10 - 20% N2  
Soft cheese 20 - 40% CO2 + 60 - 80% N2  
     
Gateau 50 - 70% CO2 + 30 - 50% N2 Storage at +4 - +7 C
Cake and bread 20 - 40% CO2 + 60 - 80% N2  
     
Pizza 30 - 60% CO2 + 40 - 70% N2  
Pommes frites 70 - 80% CO2 + 20 - 30% N2  
Salads with dressings 100% N2  

Some special remarks concerning CA packaging (Controlled Atmosphere packaging

Spoilage of food can be caused by:

  1. The nature of bacteria and their amount.
    Bacteria can be aerobic, growing in presence of oxygen such as Pseudomonas, Acinetobacter and moraxella.Or they are anaerobic, growing in absence of oxygen such as Clostridium producing toxins and Lactobacillus producing lactic acid.
  2. Water activity aw
  3. pH
  4. Cell breathing
  5. Composition of the food
  6. Storage temperature.
    Low temperatures reduces bacteria growth.
    Some bacteria grow even under low temperatures, the psycrophilic like Pseudomonas
  7. Hygiene during production
    Bacteria can be present in the raw material,additives and environment, such as our skin,used utensils and air.
  8. Gasatmosphere
    oxygen can cause rancidity, oxidizes vitamins, Nitrogen can replace oxygen.
    Oxygen is sometimes necessary to keep the red colour of fresh meat.
    The choice of the gas to be used during filling is therefore very important and varies from one food to another.
  9. Good Manufacturing Practice

CO2 reacts with water forming carbonic acid which increases acidity of the product reducing bacteria growth.Nitrogen can replace CO2 In Products such as cottage cheeseand dairy cream CA packaging with nitrogen instead of oxygen is being used. Hard cheese is packed under up to 100% CO2 to reduce bacterial activity and stabilizes consistency of the product. Soft cheese is packed under 20 - 40% CO2 because otherwise the packaging would shrink because the gas gets in solution with the product.In this case 30% of of CO2 should not be exceeded.