Packaging materials used for ready to eat (RTE) and ready to cook (RTC) foods

Convenient food is an idea that developed and is prevalent for a long time. With the current COVID-19scenario most people can’t dine out and the number of online deliveries has increased drastically. Similarly, the concept of ready-to-eat (RTE) and ready-to-cook (RTC) are fast becoming popular even in the Indian market to save time and labour. One of the major selling points for RTE meal products is their presentation. Manufacturers use creative packaging design to emphasize freshness, taste and enhance products shelf life. 

Another major concern for manufacturers is that this packaging not only ensure the product’s safety and freshness but also needs to function as a dish to cook. Therefore the packaging materials are selected based on these factors. Moreover, consumers are demanding more eco-friendly options and are willing to pay extra for such packaged products. Businesses that keep up with ongoing trend will be able to reap the rewards. The desired shelf life for an RTE or RTC food dictates the type of processing and packaging to be used. 

Convenience food can be classified into the following categories:

• Shelf-stable convenience food

• Ready-to-Eat (RTE) and Ready-To-Serve (RTS) food 
• Ready-to-Cook (RTC)

• Frozen convenience food

Ready-to-Eat (RTE) foods are normally consumed within a short time, but with appropriate processing and packaging, the shelf life can be extended up to years. Ready-to-eat food product does not require any extensive processing or cooking procedures and the pack is opened in an appetizing form. RTE snacks such as idlis, dosa and pav bhaji have a short shelf life and hence they have packaged into injection moulded plastic containers with low water vapour, oxygen permeability and good barrier strength. 

RTE foods such as upma, curry rice and vegetable briyani are processed by retort for longer shelf life. In retort processing low acid foods with medium to large particle size are preferred and used because it is easier to remove the oxygen from the headspace by gas flushing. 

Retort pouches are a special flexible laminate that can withstand thermal processing up to 121°C as it combines the advantages of metal can and boil in bag functionality preserving food by physical and chemical means. Retort pouches provide good barrier strength, puncture resistance and toughness, which can withstand abuse in handling and distribution. Retort pouches are proven to be a good substitute for cans as it eliminates the additions of brine or sugar syrup. To sum, retort pouches’ demand is continuing to grow as they getting accepted equally to a glass or metal container. 

Retort pouches are made of a three-ply laminate consisting of PET/Al Foil/PP, ethylene vinyl alcohol (EVOH), polyvinylidene chloride (PVDC) and silica-coated nylon providing a shelf life of up to one year. 

Ready-to-Cook (RTC) Foods are classified as low moisture food, medium moisture food and high moisture foods. Low moisture food (1 to 5% moisture) tend to absorb moisture from the environment and become soggy. The moisture vapour transmission rate (MVTR) of the packaging materials is less than 1 gm / m2 per 24 hours. Barrier property (MVTR) requirement in medium moisture foods (6 to 20% moisture) is less stringent and useful for long shelf life. Typical examples of foods used in this method are Indian savoury snacks, sweetmeats. However, the use of preservatives is required for long shelf life. 

High moisture foods have a moisture content between 20 to 60%, in which freshly based products as cake, chapatis, pickles and chutneys are made in this segment. Medium and high moisture foods are very susceptible to biological spoilage and need additional preservation methods before packaging. 

Based on their ingredients used in ready to cook mixes, RTC foods can be divided into four groups. The first category is cereal-based consisting of batter mix for idli, dosa which are very sensitive to moisture. These ingredients become soft and unacceptable at about 8 to 13% moisture content. Polyolefin plastic pouches (37 to 75µ) thickness are used for packaging cereal-based ingredients with 3-4 months of shelf-life.

Secondly, Legume or pulses based mixes for vada, bonda, have requirement similar to cereal-based mix. However, they are less permissible to moisture. Therefore, this segment of goods needs materials with water vapour impermeability, such as LDPE and PP providing between 3 to 6 months of shelf life based on temperature/RH storage conditions. 

Thirdly, mixes of Jamun, doughnut and cake have high-fat content and milk solids which are prone to rancidity and exchanges with oxygen and water vapour. CPP pouches, printed polyester with LDPE or HD-LDPE co-extruded films are used for products in this category for a different point of protection and attractive appearance. 

Finally, Spice mixes, rasam, sambar, and soup are highly susceptible to aroma loss, and oxidative changes which will deteriorate the final product. Functional packaging based on metallised PET/PE and films with polyamide core layer provides a longer shelf-life for products in this category. HD-LDPE coextruded film provides good heat sealability. 

 

Frozen Convenience Food

Food packaging for frozen foods requires oven-ability, which can either be microwave or conventional oven. Retort-able food packages are made suitable for microwave heating. Aluminium trays are being replaced by paperboard, thermoset plastics and thermoplastics. 

Consumers perceive paperboard as a low-quality material which softens with water and chars at high temperature. Thermoset plastics are brittle, stains easily, expensive and heavy, and adds costs to shipping. Therefore manufacturers are looking at thermoplastics for dual-ovenable packages with stability up to 200°C to 250°C, and also at freezer temperatures to reduce costs and enhance microwave ability. The thermoplastics also need to be absent of any trace taste, odour and non-sticky as per FDA regulations, which is crucial for baked foods. 

Thermoforming sheets of polypropylene (PP), crystalline polyethene terephthalate (CPET) and high impact polystyrene (HIPS) have shown advantages in performance and functionality. Developments of these polyester coated boards are suitable for both conventional and microwave ovens. 

Firstly, the material has to be permeable to microwave radiation, unlike metal surfaces which reflects the radiation. Secondly, heat resistance indicates that the material should not be degradable or develop odour and browning. Moreover, the material should be chemically inert and should have good deep freeze functionality.