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Freshly baked products such as bread, cake, chapatti, pickles, chutney and sauces are high moisture foods. Equilibrium relative humidity (ERH) is higher in these products, they breathe out moisture. So plastic films like low density polyethylene (LDPE) are permeable to water vapour and are used for packing for shorter shelf life.
For longer shelf life, microbial spoilage is the main consideration. The products are sterilized and packed in hermetically sealed containers such as cans, retort pouches or aseptic packs.
Oxygen/air permeability
Ready to cook foods contain fat and other ingredients that get oxidized if oxygen comes in contact. Hence packaging material should have low oxygen permeability.
Nitrogen permeability
To protect the food from oxygen/moisture, the food is packed in inert atmosphere of nitrogen. The nitrogen permeability of package should be low to prevent its escape into atmosphere.
Grease resistance property
- The packing material such as HDPE and LDPE are affected by fat and are not suitable for packing fatty products. Polyester films, cellophane, polypropylene and inomer films are suitable.
- If made in laminates, then film offering excellent grease resistance is used in inner most layer of the laminate.
Flavour and essential oils
Flavour and essential oils contribute to the organoleptic qualities of ready to cook foods. It is necessary to block the oxygen and entry of air that starts oxidation inside the pack.
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Light sensitivity:
Light accelerates oxidative changes associated with flavour and fats in foods. Opaque materials such as cans, aluminium foil offer best protection from light. Metallized polyester and pigmented plastics are found satisfactory.
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