Package Attributes -

Adequate shelf-life

	No refrigeration is required by the packer, retailer or consumer
	Product taste, quality, and flavour are excellent, due to minimal process time
	85% space reduction in empty goods inventory when compared to rigid containers
	Very low pack weight - Filled pouches require less space compared to rigid containers
	Foods can be quickly heated (3-5 min in boiling water)
	Ease of preparation, clean up, and disposability
	An approximate 30-50% reduction in process time can be achieved due to achieved due to narrow profile of filled pouch - Total energy costs for retort pouch foods are estimated to be 55-60& less than the total related energy cost for frozen foods. This includes energy consumed during distribution, processing, packaging, and consumer preparation.
	Due to thin cross-section of the filled pouch, the processing time required to contain commercial sterility much less than in the case of rigid containers. This reduction in process time means that there is no overcooking of foods near the surface of the container. The food quality is enhanced, and the addition of liquid or brine is not required as a heat transfer medium.
	When properly packed in an outer carton, the resistance to rough handling is improved. Foil retortable pouches have successfully held foods in excess of five years in the shelf.

PLASTICS PACKAGING IN MICROWAVE OVENS

One most exciting market for plastic food packaging is that of microwave ovens. The growing use of microwave ovens at home and the industry has created an expanding market for non-conductive packages for heating food.

Convenience Foods : Basically, convenience foods, today, fall into two categories; frozen and shelf-stable. The current trend in frozen foods is dual ovenability i.e. products that can be heated in a microwave oven and conventional oven. For a variety of reasons, shelf-life, retortable foods are better suited to microwave heating. Along with changes in the food itself, come drastic changes in packaging. Aluminium trays, which represented 85% of the market in the eighties, are quickly being overtaken by other materials, owing to the growing importance of microwave ovens.

Materials : Among the materials being looked at are paperboard, thermoset plastics and thermoplastics. Paper has an image as well as a functional problem. Consumers perceive it as a low quality material. In addition it softens in the presence of moisture and char under high temperature conditions.
Three critical properties emerge, when selecting thermoplastics for dual-ovenable packages: dimensional stability up to 200° to 250° C, good impact strength at freezer temperatures to reduce shipping and storage damage, and microwavability.
Other important properties include compliance with FDA regulations, the absence of taste or odour, good value in the consumer's eyes and good release characteristics, so that food does not stick. This last property is particularly important for baked foods.

OVENABLE FOOD TRAYS :

Ovenable plastic-based food trays commonly used by the retail segment of the prepared packaged food business as well as by the airline sand railways are typically manufactured by thermoforming sheets of polypropylene (PP), high impact polystyrene (HIPS) and crystalline polyethylene terephthalate (CPET), each material offering specific advantages in performance and economics. The trays are vacuum formed or thermoformed from a reel of sheet. The sheet is first preheated to about 150°C till it softens and is then drawn over a mould containing multiple tray cavities. When the softened sheet has traveled close to the mould surface, vacuum is applied so that the air between the sheet and the mould is evacuated and the sheet is snugly pulled over the mould to get formed into the desired shapes. In the next operations, the trays are trimmed by metal dies and the remaining portion of the sheet is sent for reprocessing. In some cases, the edges are turned on a special machine. When extended shelf-life is required, pp coextruded with barrier resins such as EVOH to improve barrier properties is used for forming. PP trays cannot withstand conventional oven temperatures and as such, are only microwave use. Foamed polystyrene trays with special blends of low density polystyrene can withstand much higher temperatures, however, they are used generally only for microwave with an advantage of good cost saving as compared to the CPET trays. CPET trays have a distinct advantage of dual openability. They also very remarkably withstand the abuse of retail distribution. Their other advantages include design flexibility, resistance to oil and grease and no appreciable effect on food taste. CPET trays are stable from -40°C to as high as 200°C and exhibit improved oxygen and water vapour barrier.
All plastics trays can be topped with heat-sealable lidding films or snap-on plastics domes.

OVENABLE BOARD :

Earlier developments were based on paperboard coated with TPX (trade name of ICI's polymethyl pentene). This was expensive and the preferred material now is solid bleached sulfate board, extrusion coated with polyethylene terephthalate (PET). This is resistant to exposure in hot-air ovens to temperatures of 200-250°C and is also been used for containers for food to be re-heated in microwave ovens only, but even here the end-use must be carefully controlled so that high temperature resistance is not required. The coated board is made into containers by two main methods. One technique produces containers by press forming to give trays or dishes similar in general form to give trays or dishes similar in general form to conventionally pressed foil trays. An alternative system is based on existing carton technology and erects trays from flat carton blanks. The main reasons for the current interest in ovenable board trays are:

	Growing popularity of convenience foods
	Developments of the microwave oven
	Development of polyester coated ovenable board that is suitable for use in both microwave and conventional hot-air ovens.

Ovenable board containers have to satisfy a number of performance requirements. First and foremost, the material must be permeable to microwave radiation. Metal surface reflect microwave radiation so that aluminium foil dishes are not rally suitable for microwave oven use. Containers intended for general use must also be heat resistant at temperature up to 200-250°C which will normally be encountered in hot air ovens. Resistance to heat includes a requirement that there should be no thermal degradation, browning or odour development. The material in contact with the food must be chemically inert and have food contact approval. It should also be grease resistant. The coating should be heat sealable and the material as a whole should be easily convertible at high speeds. Because the filled containers will normally be stored under deep-freeze conditions, the ovenable board must have good deep-freeze performance. Good printability is also a requirement.
Production of PET-coated board is carried out by extrusion coating. Pretreatment of the board is necessary to give good adhesion of the coating. The behaviour of the total coated structure of both flame and corona board is limited by the cohesion of the clay coating.

ASEPTIC PROCESSING AND PACKAGING :

Aseptic processing and packaging connotes the filling of a commercially sterilized and cooled product into presterilized containers under aseptic conditions and sealing with a presterilized closure in an atmosphere free of micro-organisms. The basic operations in aseptic packaging consist of:

	Heating the product to sterilization temperatures (140-170°C)
	Maintaining the sterility of the products till they are cooled
	Filling into sterile containers and sealing aseptically.

Aseptic Packaging Materials :

Many physico-chemical and optical properties are sought for in packaging materials and forms to be suitable for aseptic packaging from total packaging system and marketability criteria. The main characteristics, which are essential from the basic functional visew point, are the following:

	Low water-vapour transmission rate; very low or nil for long term storage
	Low gas transmission rates, especially to oxygen. This is important to preserve the colour, flavour and nutritional constituents in the products
	Good physical or mechanical strength, sufficient to resist any falls, shock and puncturing during manufacture and distribution.
	Good sealing characteristics to prevent ingress of external contaminants and other deteriorative factors
	Capability to perform well on machine; ability to being handled on automatic fabricating and filling equipment
	Resistance to withstand the temperatures encountered during filling of product as well as that during storage and distribution
	Chemically resistant to the product packed and ability to withstand sterilization conditions-gas, liquid or radiation's
	Resistance to microbes, insects and other types of biological hazards.
	Compatibility with the type of food product packed. The packaging material should not taint the product packed. Further, the material constituents and additives etc. should be inert with low migration levels in accordance with the appropriate codes of practice and standards
	Economical in cost in commensurate with the packaged products and its free availability in the market.