Nonthermal Processing

The major disadvantage of an aseptic processing (and any thermal processing system) is that heat treatment results in destruction of nutrients and organoleptic properties of foods. An alternative to aseptic processing is nonthermal preservation of food. Methods of nonthermal preservation include Pulsed Electric Field (PEF), High-Pressure Processing (HPP), and Ultraviolet Processing (UV). PEF treatment and UV are inherently adaptable to a continuous processing system, whereas HPP was developed as a batch system, although there is one continuous HPP system.

PEF is a process that uses very short duration (~2/is) of high electric field pulses (—30—50 kV) to destroy microorganisms in liquid and other pumpable foods. Research has shown that PEF is very effective against vegetative microorganisms; however, its effect against spore-forming microorganisms is still under study. PEF causes an elec-troporation of the semipermeable microbial cell envelope causing cell injury and eventual death.

HPP involves the application of high pressures (up to 140,000 psi) to food. The high pressure disrupts microbial cells and deactivates certain enzymes. Up until recently HPP has been a batch operation. However, one company, Flow International, has developed a semicontinuous high-pressure system that is currently undergoing testing. HPP has also been shown to be quite effective on vegetative microorganisms; however, for HPP to be effective against spore formers, moderate heat (60-70°C) is necessary in combination with the high pressure.

UV processing, as the name implies, uses ultraviolet electromagnetic rays to affect microbial destruction. Currently, UV has been shown to be effective only against vegetative microorganisms. UV has also been used effectively for water treatment.

ASEPTIC PACKAGING SYSTEMS Basic Requirements

Aseptic packaging units are designed to combine sterile product with a sterile package, resulting in a hermetically sealed shelf-stable product. As with aseptic processing systems, certain features are common to all aseptic packaging systems. The packaging units must do the following:

1. Create and maintain a sterile environment in which the package and product can be brought together

2. Sterilize the product contact surface of the package

3. Aseptically fill the sterile product into the sterilized package

4. Produce hermetically sealed containers

5. Monitor and control critical factors

Sterilization Agents

Sterilization agents are used in aseptic packaging units to sterilize the packaging material and the internal equipment surfaces to create a sterile packaging environment. In general, these agents involve heat, chemicals, high-energy radiation, or a combination of these. For aseptic packaging equipment the sterilization agents used must effectively provide the same degree of protection in terms of microbiological safety that traditional sterilization systems provide for canned foods. This requirement applies to both the food contact surface of the packaging material and the internal machine surfaces that constitute the aseptic or sterile zone within the machine. The safety and effectiveness of these agents must be proven and accepted or approved by regulatory agencies for packaging commercially sterile low-acid or acidified foods in hermetically sealed containers. Food processors considering use of an aseptic packaging unit should request written assurances that the equipment has passed such testing and that the equipment and sterilizing agents are acceptable to the regulatory agencies for their intended use.

Heat is the most widely used method of sterilization. Steam or hot water is commonly used and referred to as moist heat. Superheated steam or hot air may also be used in certain situations and is referred to as dry heat. Dry heat is a much less effective sterilization agent than moist heat at the same temperature. Systems that use moist heat operate at elevated pressures compared with dry heat systems, which operate at atmospheric pressures. Other methods may be used to generate heat, such as microwave radiation or infrared light. As new methods are developed, they will have to be evaluated by aseptic processing authorities.

Chemical agents, primarily hydrogen peroxide, are often used in combination with heat as sterilization agents. The Food and Drug Administration (FDA) regulations specify that a maximum concentration of 35% hydrogen peroxide may be used for food contact surfaces. If hydrogen peroxide is used as a sterilant, the packaging equipment must be capable of producing finished packages that also meet FDA requirements for residuals. Not more than 0.5 ppm hydrogen peroxide may be present in tests done with distilled water packaged under production conditions. These regulations apply also to products regulated by the U.S. Department of Agriculture (USDA).

Other sterilants, such as high-energy radiation (UV-light, y radiation, or electron-beam radiation), could be used alone or in combination with existing methods. Com pletely new alternative sterilants may be developed in the future. Whatever methods are developed, they will have to be proven effective in order to protect the public health and will be compared with existing methods.

Aseptic Zones

The aseptic zone is the area within the aseptic packaging machine that is sterilized and maintained sterile during production. This is the area in which the sterile product is filled and sealed in the sterile container. The aseptic zone begins at the point where the package material is sterilized or where presterilized package material is introduced into the machine. The area ends after the seal is placed on the package and the finished package leaves the sterile area. All areas between these two points are considered as part of the aseptic zone.

Before production, the aseptic zone must be brought to a condition of commercial sterility analogous to that achieved on the packaging material or other sterile product contact surfaces. This area may contain a variety of surfaces, including moving parts composed of different materials. The sterilant(s) must be uniformly effective and their application controllable throughout the entire aseptic zone.

Once the aseptic zone has been sterilized, sterility must be maintained during production. The area should be constructed in a manner that provides sterilizable physical barriers between sterile and nonsterile areas. Mechanisms must be provided to allow sterile packaging materials and hermetically sealed finished packages to enter and leave the aseptic zone without compromising the sterility of the zone.

The sterility of the aseptic zone can be protected from contamination by maintaining the aseptic zone under positive pressure of sterile air or other gas. As finished containers leave the sterile area, sterile air flows outward, preventing contaminants from entering the aseptic area. The sterile air pressure within the aseptic zone must be kept at a level proven to maintain sterility of the zone. Air or gases can be sterilized using various sterilization agents, but the most common methods are incineration (dry heat) and/or ultrafiltration.

Production of Aseptic Packages

A wide variety of aseptic packaging systems are in use today. These are easily categorized by package type:

1. Preformed rigid and semirigid containers, including

а. Metal cans b. Composite cans c. Plastic cups d. Glass containers e. Drums

2. Web-fed paperboard laminates and plastic containers

3. Partially formed laminated paper containers

4. Thermoform-fill-seal containers

5. Preformed bags or pouches

б. Blow-molded containers

A number of different packaging systems are represented in these categories. Not all of these systems, however, are being used in the United States for aseptic applications.

Containers in these categories may be sterilized by a variety of means. For example, one system utilizing metal cans uses superheated steam to sterilize the containers. In other systems, preformed plastic cups may be sterilized by hydrogen peroxide and heat or by saturated steam. Systems using containers formed from paperboard laminates also utilize hydrogen peroxide and heat or hydrogen peroxide and ultraviolet irradiation to sterilize packages. Thermoform-fill-seal containers may be sterilized by the heat of extrusion (dry heat) or by hydrogen peroxide and heat. Plastic pouches or bags may be sterilized by gamma irradiation, by the heat of extrusion, or by chemical means such as hydrogen peroxide.

Research is now being conducted to explore alternative sterilization methods for most categories of packaging. Thus, it can be said with some certainty that currently familiar equipment may not be state of the art tomorrow. Nevertheless, whatever equipment or sterilant or packaging material is used, the monitoring and control of critical factors will be vital to successful operation.

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