Aseptic processing


Aseptic processing is a processing technique wherein commercially thermally sterilized liquid products are packaged into previously sterilized containers under sterile conditions to produce shelf-stable products that do not need refrigeration. Aseptic processing has almost completely replaced in-container sterilization of liquid foods, including milk, fruit juices and concentrates, cream, yogurt, salad dressing, liquid egg, and ice cream mix. There has been an increasing popularity for foods that contain small discrete particles, such as cottage cheese, baby foods, tomato products, fruit and vegetables, soups, and rice desserts.
Aseptic processing involves three primary steps: thermal sterilization of the product, sterilization of the packaging material, and conservation of sterility during packaging. To ensure commercial sterility, aseptic processing facilities are required to maintain proper documentation of production operations, showing that commercially sterile conditions were achieved and maintained in all areas of the facility. Any breach of a scheduled process for the processing or packaging system means that the affected product must be destroyed, reprocessed or segregated and held for further evaluation. In addition, the processing and packaging system must be cleaned and re-sterilized before processing and/or packaging operations can resume. Packaging equipment and packaging materials are sterilized with various media or combinations thereof.

Historical development in foods

Aseptic processing was derived from C. Olin Ball's heat-cool-fill machine, which was developed in 1927. While HCF was successful in improving the sensory quality of the processed chocolate milk as compared to canned product, the use of the equipment was hindered by its cost, maintenance, and inflexibility to process various container sizes, rendering the machine a failure.
In the 1940s, the Avoset process was developed by George Grindrod. Food products processed using the Avoset process were packaged under ultraviolet lamps and sterilized air inside a positive-pressurized room to keep the contaminants out of the processing room. Sterilization was achieved through the use of direct steam injection of and then cooled. The food treated using this technique was described as an "excellent cream product", and 75–100 containers were produced each minute.
Later in the 1940s, the Dole Aseptic Process was developed by McKinley Martin. The foods processed ranged from soups to specialty sauces, fruits, and dairy products. This process involved four steps:
  1. Sterilization of product by heating and immediate cooling
  2. Sterilization of containers and lids using steam
  3. Filling of cooled products aseptically into previously sterilized containers
  4. Sealing of lids at an atmosphere of saturated or superheated steam
The Dole aseptic machine overcame the hindrances that caused HCF's failure, since it was able to process various container sizes, needed less maintenance time, and cost less. The quality of products processed was consistent regardless of container size, an important characteristic for heat-sensitive foods, due to its short processing time. Split pea soup was treated using the Dole aseptic machine at the following dosage: heat time of for 3.53 seconds, hold time of 8.8 seconds, and cooling to in 14.0 – 17.0 seconds, compared to the normal processing time of 40–70 minutes at. The lack of consumer interest drove the foods that were processed in the Dole aseptic machine to be discontinued. File:Erik_Wallenberg_inventor_of_Tetra_Pak_first_package.jpg|thumb|Erik Wallenberg, the inventor of the Tetra Classic packaging at Tetra PakRoy Graves began sterilizing milk in the 1940s. The milk that was drawn from the cow went through a pipeline, into a vacuum tank, which was then heated to 285 °F, then cooled to room temperature. The product, packaged in metal cans, was widely accepted by consumers lacking access to fresh milk, including the U.S. military.
In 1959, the food industry saw the advent of the use of paper-foil-plastic laminated containers called tetrahedron. In 1962, the Swedish company Tetra Pak, introduced this container to the United States market. They sold pasteurized milk and beverages in the containers. Roy Graves' company started sterilizing this container with chlorine and was able to aseptically fill and hermetically seal the container. The use of these containers was not accepted by American consumers due to their difficulty in opening. It was widely used by the U.S. Navy.
In 1981, hydrogen peroxide was approved by the FDA to be used to sterilize containers.
Today, ships used for continental food transport are equipped with aseptic tanks to transport fruit juices. Another means of transporting aseptically processed food is the use of aseptic bags.

Processing

Aseptic processing allows for the food to be properly sterilized outside the container and then placed into a previously sterilized container, which is then sealed in a sterile environment. Most systems use ultra-high temperature sterilization to sterilize the food product before it is packaged. UHT sterilizes food at high temperatures, usually above 135 C for 1–2 seconds. This is advantageous because it allows for faster processing, usually a few seconds at high temperatures and better retention of sensory and nutritional characteristics. Aseptic products have a non-refrigerated shelf-life of a few months to several years.
Sterilization of aseptic packaging material is a crucial step in aseptic food processing. These containers are sterilized to kill microorganisms present on the containers during forming, transport, and before filling. There are numerous methods used to sterilize the containers, the most commonly used methods include: heat, hot water, chemical sterilants, and radiation or a combination of methods.
UHT food products can be sterilized using either direct or indirect methods of heat transfer. Direct heat transfer can be achieved through steam injection and steam infusion. Food products processed with a steam injector go through an injection chamber, where steam is injected into the product, then the product is flash cooled to 70 °C. Direct heat transfer is suitable for heat-sensitive foods such as milk. However, only low viscosity liquids can be processed using steam injection, and high-quality steam is required to ensure sterilization. Steam-infused food products involve food free-falling into highly pressurized steam, which heats the food to approximately 145 °C, and then it is flash cooled to 65–70 °C. Steam infusion provides processors with great control compared to steam injection, and the risk of burn-on and overheating is reduced. It can process higher viscosity foods compared to steam injection, but risks the blockage of nozzles in machinery. Indirect forms of heat transfer include: plate heat exchangers, tubular heat exchangers, or scraped-surface heat exchangers. Plate heat exchangers are mostly used because they are inexpensive and allow for easy changes during production. Tubular and scraped-surface can heat viscous food with particulates or high pulp content with minimal damage.

Equipment and systems

Equipment used in aseptic processing of food and beverages must be sterilized before processing and remain sterile during processing. When designing aseptic processing equipment there are six basic requirements to consider: the equipment must have the capability of being cleaned thoroughly, it must be able to be sterilized with steam, chemicals, or high-temperature water, sterilization media should be able to contact all surfaces of the equipment, meaning the equipment does not contain any cracks, crevices or dead spots, the equipment must be able to be kept in a sterile state, it must have the ability to be used continuously, and lastly, the equipment must comply with regulations.
Aseptic packaging are generally placed in the following categories: fill, erect, form, thermoform, blow mold, and bulk packaging and storage systems.
  1. Fill and seal. The containers are filled and sealed in a sterile environment to avoid contamination.
  2. . A plastic container is erected then sterilized, filled and sealed.
  3. Form, fill and seal. In this system, a roll of film is first sterilized. After sterilization it is formed into the desired shape, filled and sealed.
  4. Thermoform, fill and seal. A roll of film is heated and thermoform on a sterile surface or environment. It is then filled and seal, also in a sterile environment.
  5. Blow mold, fill and seal. The process requires an extrudable material to be first blow-molded into a sterile package before filling and sealing. This process is usually used to produce bottle products like juices and sodas.
  6. Bulk packaging and storage systems. Packaging used for bulk storage are sterilized using either heat or disinfectants. After sterilization they are able to be filled and sealed.

    Packaging material

Aseptic packaging consists of filling and sealing a sterilized packaging material with a sterilized product. Aseptic packaging material not only has to assure sterile conditions within the package and protect the product from physical damage, but also maintain the quality of the product inside the packaging. To achieve this, a laminate material is formed from the following components: semi-rigid paper, aluminum, and plastic. Paper provides the stiffness, strength, and the efficient brick shape to the package; potential for bacteria needs to be addressed. Low-density polyethylene, the most common plastic used for aseptic packaging, located on the innermost layer forms the seals that make the package liquid-tight. Aluminum is located on the inside of the aseptic package, forming a barrier against light and oxygen, thereby eliminating the need for refrigeration and preventing spoilage without using preservatives. Most packaging material used in aseptic packaging is made from plastics instead of metal or glass containers due to the relatively low cost of producing plastic material when compared to metal and glass. Plastics are lighter than metal or glass making them cheaper and easier to transport. Plastics also required much less energy to produce than metal and glass. These factors have made plastic the packaging material of choice for use in aseptic processing.