What is Aseptic Processing?
Aseptic Processing is sterilizing a product and filling it in and sealing the sterile container in a sterile environment so that microbes do not enter the product. When the product is commercially sterile, the microbes remaining cannot grow, thus making sure the product doesn’t spoil while in storage.
This ensures that the product can remain in ambient conditions for a very long time. Like canning, this is also a thermal process but the difference is that the product is filled in the container after processing. This allows the product to maintain its nutritional and sensory qualities.
Aseptic Process vs. Canning
The process of canning takes a considerable amount of time as the heat needs to travel from the sides of the can to it’s centre while passing through food. In aseptic processing, the processing is done at temperatures around 135 to 155°C for a few seconds. This is called the UHT (Ultra High Temperature) process. Since the temperature is very high, the duration needed for sterilization is very short. While it is very effective in killing microbes, it does not cause extensive damage to the nutrients, colour or flavour of the food. So the quality of these products is superior in comparison to canned foods.
After the UHT process, the food is filled in packages. The most commonly used is a 6 layer composite, having paper, plastic and aluminium, but can also be packed in bags, pouches, jars or metal cans. The filling must also be done aseptically without allowing the entry of microbes into the sterile product.
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The Heating Process
The food product is sterilized by passing it through a plate, tubular or scraped-surface heat exchangers or injecting steam into the product. One can also use a microwave or other methods of rapid heating. While extremely rapid heating and cooling can be achieved only with liquids, processes with some particulates in liquids have been developed. After being heated, it is cooled for some time and then passed on to the aseptic filler, a highly specialized piece of equipment that sterilizes the packaging material, fills the sterile product in the container and then seals the package.
The UHT method results in a higher retention of quality characteristics, such as vitamins, odour, flavour, and texture, while achieving the same level of sterility as the traditional canning process in which food is heated at a lower temperature for a longer period of time.
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Some examples of food products processed with UHT are:
- Liquid products- milk, juices, cream, yogurt, wine, salad dressings
- Foods with discrete particles- baby foods, tomato products, fruits & vegetable juices soups
- Larger particles– stews
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An aseptic packaging material not only has to assure sterile conditions within the package and protect the product from physical damage, but also to maintain the quality of the product inside the packaging. To achieve this, a laminate material is formed using semi-rigid paper, aluminium, and plastic. Paper provides the stiffness, strength, and the efficient brick shape to the package. Plastic placed on the innermost layer forms the seal that makes the package liquid-tight. Aluminium forms a barrier against light and oxygen, thereby eliminating the need for refrigeration and preventing spoilage without using preservatives.
Some of the advantages of Aseptic Processing:
- Longer shelf life: Properly processed and packaged product may last for a couple of years or more
- Wider packaging sizes: From a couple of hundred ml to a few litres. Bulk packages of 50 kg and more are also prevalent
- Convenience- Portable & Light consumer packs
- Optimizing product quality: Very little loss of nutrients and colour & flavour
The market for aseptic food is expected to be over 10 billion US dollars and rising rapidly. The most rapid rise is in Asia-Pacific where it is most useful as the food may be kept at room temperature without chilling. This is most convenient. The downside is the cost of aseptic process and package. Also the problem of recycling of used packaging material needs to be solved.
(Co-Author: Ms Swechha Soni, Nutritionist, PFNDAI)