Ready to eat (RTE) food products have gained immense popularity due to drastic lifestyle changes in the present-day context. With the women-folk working outdoors, the rise in the number of nuclear families, the younger generation being in a rush, the kitchen space is shrinking, paving the way for a rise in demand for convenience food products. RTE products correctly reflect this changed lifestyle.
RTE food products fall into the broad category of convenience foods. Convenience food is defined as commercially prepared foods designed for ease of consumption. Products marked as convenience foods are often prepared foodstuffs that can be sold as ready-to-eat meals at room temperature, shelf-stable products, or refrigerated or frozen products requiring minimal preparation, typically by just heating.
RTE food products can be directly consumed from the package with or without warming, thawing, and without prior preparation. So, these could be precooked, partially cooked, frozen, or preserved to be eaten instantly. It encompasses a wide range of fried snacks, cereal, or pulsed based extruded snacks, dairy snacks like processed cheese, retort processed foods, frozen foods, relish, and bakery products.
Global food products are divided based on product types like meat-based, cereal-based and vegetable-based. And based on packaging criteria, it can be classified as canned products, frozen and retort.
In an industrial setup for manufacturing RTE meals, there are four essential steps, namely (1) filling of tray or container with ingredients manually or with robotic assistance, (2) sealing of the tray, cooking/pasteurisation process to ensure that all the viable microorganisms are eliminated, and (3) cooling so that the cooking process is stopped, (4) the entire processing line should be equipped with suitable processing and packaging machinery.
Raw materials such as meat-based, vegetable-based or lentil-based, or even dairy-based products such as paneer must be cooked and allow the lowest internal temperature to reach a minimum temperature for a minimum holding time to destroy microorganisms.
Effective pasteurisation technologies such as steam pasteurisation and microwave pasteurisation are employed for commercial production of RTE meals or frozen products. The primary concern raised by the consumers is that whether RTE food products are safe for consumption or not, to ensure safety RTE products should be free from foodborne pathogenic microorganisms such as Listeria monocytogenes, pathogenic Escherichia coli, and Salmonella spp., To ensure microbial-free RTE products without compromise in consumer preferences, in-package pasteurisation method is employed.
Canning technology for RTE
Canning leads to the drastic development of the RTE product market. Canning of fish, pickling of vegetables, preserving fruits that were offseason were made available throughout the year with the adaption of canning technology.
The canning process flow includes filling, lacquering, brining, exhausting, thermal processing of canned products and cooling. Canning is a preservation technique that involves placing food products in a container followed by the addition of required preservatives or bringing solutions and heating them to a designated time-temperature combination that destroys microorganisms responsible for food spoilage. During this heating process, the air is driven out of the jar, and as it cools vacuum seal is formed. Immediately after processing, cans are cooled to room temperature in a cold-water bath.
Retort technology for RTE
Retort technology has turned tables in the RTE sector. This technology has paved the way for the launching of a wide range of food products. The retorting or sterilisation process ensures the stability of the RTE foods in retort pouches at room temperature. This technology eliminates all foodborne pathogenic microorganisms, thereby increasing the shelf life of food.
The retort pouches are multi-layered that can withstand high temperatures during the sterilisation process. Retort pouch processing technology can be considered as an alternative for canning to produce thermally processed shelf-stable foods.
Retort technology holds an upper hand when shelf-life stability because retort pouch laminates permit less chance to overcook during the retorting. Thus, products having better colour, texture & fewer nutrients loss require less energy for sterilisation. It requires storage space; it has low oxygen & moisture permeability and requires no refrigeration.
Microwave pasteurisation technology of RTE
Microwave heating offers shorter processing time and better heating uniformity than conventional thermal processing using steam or hot water. Microwave pasteurisation offers opportunities for the food industry to produce high quality frozen RTE meals. It is particularly suitable for pasteurisation of pre-packaged heat-sensitive, high-viscous, semisolid, solid, and multi-component meals.
Microwave heating generates steam inside the packaging containers, causing expansion of the headspace in each tray. The internal pressure increases with microwave heating until it opens the valve and vents the steam and air. After exiting the heating zone, the product cools, the valve closes, and the remaining steam condenses, thereby creating a vacuum in the package.
A microwave-assisted pasteurising system consists of four sections: (1) preheating, (2) microwave heating, (3) holding, and (4) cooling, each having a water circulation system for cooling along with temperature control. Food trays or pouches are moved through the four sections in stainless steel carriers.
Frozen RTE foods
Freezing is a post-pasteurisation process. Frozen foods have improved texture, colour and better retention of taste when compared to canned products. In this process, the food products are exposed to lower temperatures (-18 °C) during freezing.
Quick freezing ensures the development of smaller ice crystals within the products ensuring less damage to the products. Nowadays, freeze-drying technology is implemented for developing frozen RTE.
In the freeze-drying method, the food is quickly frozen to lower temperatures up to -40 °C and then placed in a vacuum. The ice crystals formed while the freezing process gets transformed directly into the gaseous state, and the product gets completely dehydrated. The product can be preserved for a long time. Frozen foods are thawed or microwaved before consumption.
Extruded RTE snacks
Extrusion cooking is one of the most reliable food processing technologies applied to prepare various RTE snacks. The extruded snack category has immense potential for growth among snack foods. Extrusion technology provides the opportunity to process a variety of food products by incorporating dry ingredients.
Pulses or cereal grains or grits are subjected to a cooking process that gelatinises the starch and then expands the product. Extrusion cooking involves a screw turning in a barrel that has a die at the end. The screw transports meal through the barrel and subjects it to pressure, shear, and heat.
Pulses and cereal grains or grits are subjected to a cooking process where the product expands because starch's gelatinisation takes place. As this material emerges through the die, the superheated water within it vapourises, expanding the product. The expansion process resulting from the vaporisation of superheated water within the products gives RTE foods their characteristic crunchy texture. After processing, flavourings are added to snacks and breakfast cereal.
Puffing is a thermal process in which rapid heat transfer occurs to phase shift the water to a vapour. Rice and wheat are the most widely used cereals for puffing. They are puffed as whole kernel grains. In gun puffing, high temperatures are attained 600-800 F, followed by a pressure drop of 100 - 200 psi. The moisture in the grain is converted into steam when the rotating gun is heated. The internal pressure is released when the lid is opened, and the puffed grain is collected in a vented bin.
Packaging technology
With various technological interventions in food processing methods and packaging technology, we are now able to produce RTE food products that have a longer shelf life and products that are less prone to microbial attack .with the advancement in packaging technology. It is possible to produce RTE food commercially with the extended shelf-life period up to a few years.
The packaging materials generally used are injection moulded plastic containers, plastic pouches or paperboard cartons. For retort packaging, 3-ply laminate, consisting of Polythene Aluminium Foil and polypropylene, is commonly used. The product packed in such retort pouches has a shelf-life of one year.
Conclusion
The driving force for RTE growth would be drastic changes in lifestyles. There is a huge growing demand for instant food products that are readily available, convenient, and safe, without compromising on sensory parameters. Improved processing and packaging technology paved the way for developing safer food with more extended shelf-life stability.
(Dr Venkatachalapathy is Professor and Head, Department of Food Engineering, Yashaswini and Kulbushan are research scholars of the same department at Indian Institute of Food Processing Technology (IIFPT), Thanjavur. They can be contacted at venkat@iifpt.edu.in)