Current lifestyle has directly influenced the way food is consumed, evolving towards more convenient options such as ready-to-eat products or products that can be cooked in the package itself

Carmen Toledo and José M. Bermúdez - ITENE

 

At the same time, consumers show a greater interest in healthy and fresh products with fewer food additives, such as colourings and preservatives, but adaptable to their lifestyle, offering them enough durability so that their visits to the supermarket are not increased and to reduce food waste. All this presents a challenge for the packaging industry, which has had to adapt to meet these demands without neglecting the fulfilment of its basic functions: contain, protect, handle, distribute and present. For this reason, nowadays, food packaging is designed practically to measure for each type of product, considering its specific requirements. Therefore, the packaging technology used, as well as the type of material chosen, its permeability, shape and appearance, will depend on the product and its future use.

 

Image: Alimentaria 2018 (Infopack)

 

The packaging industry has been forced to develop different packaging technologies over time to meet these challenges, leading to the development of compatible new materials and equipment.

In the late 1960s, Tetrapack launched its first aseptic packaging equipment. This type of packaging consists of cold packaging a commercially sterile product (such as milk, juices, broths) in a hermetic and pre-sterilised container, under sterile conditions that prevent recontamination of the product until it is closed and afterwards. For this purpose, the containers must be hermetic and have a high barrier (impermeable to gases, vapours and occasionally radiation). There are no format limitations or limitations due to the thermal resistance of the materials, as no heat is applied to the packaged product. Although the most recognized conventional containers in this technology are made with complexes of cardboard, plastic and aluminium foil, it is also used for PET bottles, bag in box and large containers and deposits.

 

Image: Alimentaria 2018 (Infopack)

 

Revolutionary packaging technology

Another revolutionary packaging technology was packaging under modified atmospheres. Vacuum packaging removes air from the inside of the container, creating an absence of oxygen that slows the microbial deterioration of the product and prolongs its durability. It is conventionally carried out in chamber packaging machines using high gas barrier bags, but the technology has evolved in such a way that thermoforming and thermo-sealing machines can also be used nowadays. In this way, skin packs are obtained, where the product is deposited on a flexible or rigid sheet, thermoformed or preformed, which is sealed to a top sheet after evacuating the gases. This packaging is used for high quality products in meat, poultry, fish and seafood sectors, ready-to-eat meals, cheeses, etc. They can also be vacuum-packed in thermoforming machines with shrink films that wrap the product tightly, fitting its shape and size.

 

Modified atmosphere packaging consists of replacing the atmosphere inside the package with a mixture of gases different from air, suited to the type of product, in order to maintain its shape, colour and freshness. Combined with refrigeration temperatures, it extends the useful life of minimally processed fruit and vegetables, as well as other fresh foods with a high protein content (meats, fish, cheeses), bakery and pastry products, nuts and ready-to-eat dishes. It is necessary to use materials with high gas and/or moisture barrier capacity and they can be produced in thermoformers and thermo-sealers, where the chosen gas mixture is injected after extracting the air from the inside of the container and before sealing it. There are also vertical and horizontal packaging machines that form flexible packages in situ from a film reel that wraps the product, injecting the gases of interest by means of continuous flow or by sweeping. 

 

Image: Alimentaria 2018 (Infopack)

 

For some products, the packaging needs to release moisture, gases or even heat. This occurs in fruit and vegetable products with high respiration rates that generate water vapor and residual heat, or climacteric products that generate ethylene, the accumulation of which accelerates the ripening processes of packaged fresh fruit and vegetables. In these cases, microperforated or macroperforated containers are used, which allow an exchange of atmosphere between the product and the environment, producing a balanced atmosphere in the container. These containers can be produced both in thermoforming and thermo-sealing machines, as well as in horizontal packaging machines.

 

In the 90s, high hydrostatic pressure technology appeared, based on the application of pressures between 100-900 MPa for short periods of time to packaged foods that are to be kept refrigerated. The most frequent commercial application is cold pasteurization, using pressures higher than 300MPa. The most interesting thing is that it eliminates vegetative pathogenic microorganisms (such as L. monocytogenes and Salmonella), reduces altering microorganisms and inactivates certain enzymes, causing a minimum effect on the nutritional and organoleptic properties of food and maintaining the product's freshness. Currently, one of its main uses is in fruit juice treatment, avoiding nutrient losses and flavour and smell changes caused by the temperature applied in conventional pasteurization processes. It is also used in cooked and cured ham, fish and seafood, guacamole, sauces and dressings.

 

Image: Alimentaria 2018 (Infopack)

 

Active packaging is one of the most recent developments in packaging technologies and in terms of improving product preservation. Active packaging fulfils the basic functions of a package while at the same time acts as a coordinated system within food and environment to improve the safety and quality of the product and prolong its useful life. In order to fulfil this function, they are designed in such a way that they intentionally incorporate components that: release substances into the food or its environment (antioxidants, flavours, antimicrobial agents, CO₂); or absorb substances from the food or its environment (O₂, CO₂, humidity, ethylene, flavours, undesirable substances). The active components may be incorporated inside the packaging together with the packaged product, but separate from it, in the form of small bags or labels made of permeable material. Although the presence of foreign elements inside the package could cause rejection on the part of the consumer, in addition to complicating the packaging technology, and the possibility of causing toxicity by circumstantial contamination. For these reasons, active packaging has been developed by introducing the active components into the packaging material itself or retained on its surface.

Given the benefits of this technology, it can be used as a substitute for conventional food processing techniques such as high temperature heat treatment, brine, acidification and dehydration. Among the most developed active containers are those that use oxygen sensors, antimicrobial agents, fruit and vegetable respiration controllers and absorbers of unpleasant aromas and odours.

Oxygen capture materials are used when a reduction in the proportion of oxygen inside the container is desired, achieving concentrations of less than 0.01%, which is very difficult to achieve using modified atmosphere technology. Most of these systems consist of small bags or labels of ferrous salts, although integrated solutions in the packaging material can also be found. Reducing the presence of oxygen limits the growth of microorganisms, respiration in vegetables, oxidation reactions, browning processes and the degradation of dyes and pigments.

 

Image: Alimentaria 2018 (Infopack)

 

For materials with antimicrobial activity, there have been developed containers capable of releasing antimicrobial substances incorporated in their structure, such as fungicides (ethanol, 2-nonanone, imazalil) or bacteriocines (nisin, lacticin, pediocine). But antimicrobial materials have also been developed from chitosan or alginates and materials with substances immobilized on the surface (silver salts in zeolites) that act by contact.

There are also CO₂ absorbing and releasing materials. In one hand, absorbers are used to retain CO₂ produced by the food itself slowing down deterioration after packaging. CO₂ can be generated by fresh fruit and vegetables due to their post-harvest physiological activity or released from roasted products such as coffee. The most commonly used in industry are sachets of calcium hydroxide. On the other hand, CO₂ releasing materials are used to keep the product in good condition, as a high level of this gas inhibits the growth of microorganisms such as fungi. The substances most used to generate or emit CO₂ are calcium bicarbonate and ascorbic acid, applied in the packaging of meats and vegetables.

 

Another way to stop the deterioration of fresh fruit and vegetables is to control the level of ethylene inside the package. Ethylene is a vegetable hormone that produces the ripening of climateric fruit and vegetables such as bananas, apples or tomatoes. But excessive production causes rapid deterioration of the product. Therefore, active materials capable of absorbing ethylene have been developed in such a way that the maturation of the product and its senescence are delayed. Most active systems are based on the use of permanganate salts in sachets or blankets. 

 

Intelligent packaging

Unlike active packaging, intelligent packaging does not produce changes in the product or its environment; it simply informs of its state and allows it to be controlled to ensure its quality and safety. There are many devices applicable to food packaging.  

Time-temperature indicators are simple and relatively inexpensive labels that provide information on the cumulative effect of time and temperature on the product, due to exposure to temperatures higher than recommended or that are critical for a given product. The response is visual, expressed by an irreversible colour change in the label, dependent on the temperature to which the product is exposed and the time of exposure, and correlates with the deterioration of the product.

 

Image: Alimentaria 2018 (Infopack)

 

Freshness indicators control the quality of the packaged product by responding to any changes in the food as a result of its metabolism or microbial growth. Many are based on the detection of metabolites generated by the microorganisms present in the product, such as: volatile compounds derived from nitrogen, amines, hydrogen sulphide, organic acids, etc. They are presented in the form of labels that change its colour irreversibly and must be adapted to each type of product and its metabolism.

In addition, there are humidity indicators with copper or cobalt chloride that change colour when the humidity increases, as well as impact indicators and anti-fraud devices that show when a container has suffered a blow or has been opened, respectively. 

Pressurizing containers using liquid nitrogen is another outstanding packaging technology. Nitrogen is one of the most widely used gases in the food industry due to its properties as an inert, colourless and odourless gas, and its low solubility in water and fats, as well as its use to inhibit oxidation due to oxygen displacement. This technology uses liquid nitrogen to pressurize PET containers for non-carbonated beverages and soft drinks and liquid food products (sauces, gazpacho, liquid yogurt) and solids (granulated coffee). By dosing a few small drops of liquid nitrogen into the bottle or container after filling and before closing, its gasification is enough to pressurize slightly the inside of the container. This makes it possible to reduce the weight of the containers, saving costs and obtaining environmental benefits, as well as providing enough rigidity to the container to facilitate labelling, palletising, storage and transport processes.

 

Finally, today's lifestyle has resulted in more eating out and less time for cooking for most consumers. For this reason, numerous alternatives have been developed in the food industry over the last few decades. From culinary preparations that can be consumed in their own packaging after microwave heating, to preparations or products that can be cooked in the package itself using an oven or a microwave. For this purpose, high temperature resistant materials have had to be developed to allow food to be cooked in them. These containers can be made in thermoforming machines and are used for high-protein foods (meat and fish), as well as for vegetables and ready-to-eat meals. It also allows the incorporation of dressings, spices and sauces to the products. They are usually packaged with skin packaging or modified atmosphere technology.

 

https://www.itene.com/en/