By admin on Sat, 11/03/2012 - 04:24

Vegetable canning

Vacuum is employed to retard oxidative aerobic (or air loving) microorganisms.

Dried Foods:

"Instant" beverages such as coffee, freeze dried and vacuum dried foods contain very low levels of moisture in the range 1-3%.

Dried foods which contain only 1-3% moisture have erh values which are below 20% and may even be below 10%. As the humidity of ambient air is rarely in this low range, such foods absorb water vapour freely from the air surrounding them. These foods often have a porous nature and a high surface to weight ratio, thereby increasing the hygroscopicity uptake of water vapour may be so rapid that packaging is done in an air-condiioned room in which low RH is maintained. Some very low moisture dried foods are highly susceptible to oxidative deterioration, so they must be packaged in container which are impermeable to water vapor and to oxygen. Hermetically sealed jars, lever lid cans and heat-sealable multiwall laminates witha foil layer are generally used. They are often packed initially under vacuum or in an inert gas. Many like "instant" coffee, must be packed in resealable containers. These products are relatively expensive and can toletae expensive packaging. If they are inadequately packaged, they cake and will not reconstitute, and can also lose much of their volatile flavouring components. In package desiccants, or oxygen scavangers are sometimes sealed in with dried foods which are susceptible to deterioriation caused by minor changes in moisture or oxygen level. The packages for these scavangers must transmit gases and vapours but be sift-proof to avoid contaminating the food.

Comments

Reasons for creating a vacuum in the container: a) To preserve flavour characterisctics and multiline components that are vulnerable to oxidation. b) To leave rooms for gases that may be liberated during heat processing that might otherwise cause the can to distort in a manner similar to a can containeing a product spoiled by microbilogical action. c) To avoid strains to internal pressures. d) To minimise or eliminate corrosion caused by oxygen.
Thu, 11/08/2012 - 05:09

Vacuum packaging provides some increase in shelf-life, but the possible advantages are outweighed by the risks. Vacuum packaging gives rise to anaerobic conditions and is therefore unsafe for fish products with pH over 4.5 or less than 4.5% salt content in the watery phase. Such products should be kept at a temperature below 4 degree c (39 degree F) during retailing and preferably distributed frozen. The tough vacuumized and shrunk bags protect the birds in the brine bath and prevent freezer burn during prolonged storage. Most duck packs are blast frozen and vacuumizing  is carried out by machine. Bacon is vacuum packed mainly to preserve its colour. However, the growth of spoilage on bacon is inhibited by vacuum packing and packaged in tis way has a long shelf life which may finally be limited by the growth of lactic acid bacteria which cause souring. lactic acid bacteria will usually grow on vacuum packed cooked meats and will limit their shelf life by souring.
Fri, 11/09/2012 - 23:22

Vacuum packaging where foods are susceptible to oxygen, as frequently occurs in the presence of light, it is helpful to prevent air from entering the package. Oxidation of certain foods can therefore be reduced by using a packaging material of low oxygen permeability, seals and closures for the package must, of course, be 100% efficient. Vacuum packaging is more a means of keeping food at a bettr level of quality during its natural lefe (which is dependent on the temperature) than a means of increasing its shelf-life. This is because it is virtually impossible to remove all the oxygen (small quantities will betrapped within the food), also, spoilage factors, such as some anaerobic organisms which are not affected by oxygen, are not reduced. Suitable materials for vaccum packaging must then combine a high resistance to gases adn water vapour with perfect seals and good mechanical strength. Typical materials used are: 1) PE/Copolymer coated Cellulose film laminates, PE/PET film laminates and PE/PA film laminates, usually used as heat sealed sachets with the PE inside to promote efficient heat seal. 2) laminates of plastics film with alumninium foil. 3) PVdC coplymer films, PET films and PA films, often applied in tubular form and usually shrunk tighter after enachating. Bacon slices and joints, ham, some cured fish, cheese and coffee are products which are vacuum packed at present.
Thu, 11/15/2012 - 23:46