Canning and Fish Packaging Technology

Unit 4 - Thermal process for canned foods

4.10.2.Sterilization of the packaging
Before packing the food in aseptic packaging, the packaging container must be sterilized separately. The principal requirements of any method of sterilization for the package or packaging material are that they should be continuous, rapid and economical as well as safe without any side effects or environmental risks to operators. The methods currently in use are

• Physical processes include sterilization by steam or hot air and heat or by utilizing energy applied in the process of making material or containers.
• Chemical process utilizes such chemicals as chlorine, per acetic acid and hydrogen peroxide.
• Combination technique: Hydrogen peroxide in conjunction with heat and at much lower concentration in conjunction with U.V. irradiation is the main combination techniques.
  

To reduce contamination, sterilization of packaging materials is not carried out until just before filling. The oldest method still in use is exposure to super heated steam or hot air. However, because of high temperature involved in this method, the choice of packaging is limited to glass container or cans. Treatment of plastics or tetra packs are mainly carried out using chemicals or combination systems.

A better way to use heat sterilization is to take advantage of the heat generated during the manufacture of packaging. The temperature reached during melting and extruding plastics are usually well above that needed for sterilization. Therefore immediately after forming plastic containers films or laminates are quite sterile. In some systems, the formed bottle is passed to the filling head under sterile condition immediately. In another system plastic bottle is sealed and hence interior is kept sterile, till it is filled. Such containers can be kept for a long time without becoming infected. A similar principle adopted even with extruded sheets, where a protective peelable layer is provided both on the material used for thermoformed containers and the lidding material. Just prior to processing, the protective layer is peeled off.

In continuous process, web sterilization is carried out using hydrogen peroxide and heat. The packaging materials passes into and through a both of chemicals, surplus liquid is removed by rollers. The container is then formed by heat sealing (in the form of a tube) the remaining peroxide is then removed by a radiant heat. The materials from which containers are to be made are sometimes sterilized by chemicals e.g. Ethylene oxide before it leaves the converter. The container is then formed at the packers plant and sterilized with a spray of peroxides by blowing with sterile hot air to remove excess.