Food packaging has become the heart of modern food industry, which helps to store food and beverages in hygienic manner. Packaging is enclosure of products, items or packages in a wrapped pouch, bag, box, cup, tray, can, tube, bottle or other container contributing achieve functions such as containment, protection and /or preservation, communications and utility or performance. Packaging industry is one of the fastest growing industries in the world representing 11% growth in volume terms. Ready-to-eat food products have dominated packaged food Industry. Ready to eat foods (RTE) are convenience foods, enclosed in metal container or flexible pouches that only need to be cut open and heated before being served. RTE food includes wide range of ethnic food products viz. vegetarian / non-vegetarian, basic food / delectable desserts.
Changing lifestyle and nuclear families leads to exponential increase in the demand of ready to eat processed food. Retorting or In-bottle Sterilization is one of the major technique used for the thermal processing of convenient foods which are packed either in semi rigid flexible laminates or in metal or alloy cans. Packaging before heat treatment providing the advantage of both processing the food and packaging together, making filled product more commercially stable. This technique involves heating of food products prone to microbiological spoilage in hermetically sealed container to extend shelf life for commercialization of traditional or ethnic dishes, which are important due to their delicacy and are of high demand.
Processing techniques differ from product to product and from package to package, hence, retort designs and operating procedures vary. Traditionally, metal cans were used for retort processing however, over the years we have seen wide usage of pouches, plastic pots and trays, allowing more convenience, better product quality through reduced processing time, reduction in costs for food manufacturers and better surface to provide intended marketing information for consumers.
The materials of packaging must be inert, heat sealable, dimensionally stable and heat resistant (usually 115°C–125°C). They should have low oxygen and water-vapour permeability and be physically strong to resist penetration by the foodstuff contained and abuse during handling and storage.
Efficiency Determining Factor
A number of factors affects the Retort process, which includes
- Type of container – Glass is not a good conductor of heat. Therefore, product in a glass jar takes more time to heat compared to equivalent size/shape metal can.
- Size and shape of the container – A large container will take longer to heat than a small container, hence size of container matters.
- Retort temperature – A higher retort temperate will result in more rapid heating but also may lead to more over processing of product near the package surface.
- Agitation– Agitation of the containers will increase the heating rate by mixing the contents of the container, especially with viscous or semi-solid foods. End over end agitation is better than axial agitation.
- Type of product – Different products conduct heat more or less easily and have different heat capacities. Some products are more viscous than others are which can have a particularly significant effect in agitating retorts.
- Headspace – insufficient headspace can also affect the rate of heating, especially in an agitating retort.
- Traditional Retort Cans:
The market for canned food products continues to grow which is driven by its high mechanical strength, the need for convenience, appealing recyclable properties of the cans, thermal stability, resistance to pressure and excellent barrier properties, increase in shelf life and food safety. Generally, tinplate (Consists low-carbon, mild steel sheet or strip, 0.50–0.15 mm thick, coated on both sides with a layer of tin) and aluminium are used for metal container and closure construction for food and drink products. Both are relatively low-cost materials and nontoxic, having adequate strength and are capable of being work hardened. Cans are used for safe preservation of low acidic food such as meat, seafood, poultry, dairy products etc. They have high mechanical strength but major disadvantage associated with them is that they take more time to transfer heat as compared to retort pouch.
- Retort Cartons:
Retort cartons is a new entry on this segment with only Tetra Recart developing world’s first retortable carton packaging system designed for low acid, shelf-stable food products with particles of almost any size. Tetra Recart cartons differs from other Tetra Pak cartons as the paperboard material used for this process are moisture resistant. Though it resembles in having six layer construction consisting of primary polypropylene layer that comes in direct contact with the product, then a second layer of an aluminium foil, again a layer of polypropylene, then comes paperboard (approx. 65% of composition of packaging), again a layer of polypropylene and lastly a lacquer protected flexo-printed graphics that has an appealing effect and promotes marketing.
- Retort Pouch
Retort pouch is a flexible or semi-rigid package made from heat-resistant laminated metal – plastic, into which food products are placed, sealed and sterilized at temperatures up to 121°C. The resulting product is then sterile and shelf-stable. Retort pouches comes up in various styles such as three sided seal, four sided seal, stand up, stand up fitment and pre made form seal.
Retort pouches are used in several countries for a wide range of processed ready-to-serve shelf-stable products. Laminate films used for retort pouch manufacture vary depending upon their specific application.
Composition of Pouch
Mainly these flexible pouches are constructed with 4-ply laminate consisting of four layers:
- Polyester: It offers high temperature resistance, toughness and printability.
- Nylon: It acts as puncture and Abrasion resistance
- Aluminium: It acts as a complete barrier to light, Gases, Microbes, odours, extended shelf life, stiffness
- Food Grade Polypropylene: it can be used as bonding and sealing layer, which gives strength and flexibility to the pouch.
There are also disadvantages associated with retort pouches. One disadvantage is the lack of strength of the material compared to metal cans. Retort pouches are much more prone to abrasions and punctures that ruin package integrity and potentially the product. More care and expense is needed when packaging retort pouches. Another disadvantage of retort pouches in the mode of retort generally used. Many continuous agitating retorts currently in use in industry were designed for compatibility with metal cans, and retort pouches cannot be processed in the same equipment. Therefore, retort pouches are frequently processed in less efficient still batch retorts resulting in higher operating costs. Batch operations are less efficient than continuous operations because of time needed for loading and unloading between batches
Quality checks should be carried out on pouches:
- Visual assessment: to check there are no defects on the pouches both decorative and that may have an adverse effect on the process and shelf-life of the product.
- Seal strength: to measure the strength of the seal for processing and storage.
- Burst testing: to ensure the pack has adequate seal strength and integrity.
- Oxygen and water transmission rates: to measure the barrier properties of the pouch.
- Bond strength: to ensure the pouch has sufficient strength to prevent delamination of the layers.
- Dye Test: The dye test can be used to identify the location of very minute holes.
- Tensile Testing: Tensile tests are used as a quality assurance tool for assessing the inherent sealing qualities of flexible packaging films and are employed as an optional test.
Retort processing has evolved significantly since its incorporation into US Department of Defence and NASA food system. While the technology still relies on aggressive application and penetration of heat throughout foods, recent advancement in process engineering coupled with evolution of packaging technology have allowed for overall improvement of the technology. Retort processing presents the advantage of increased shelf life with less loss of nutrients due to which it can be applied to process ready to meal, marinades, vegetable curry, soups and rice.