High-energy electron beam technology has been used to sterilise medical devices and food materials for some years. Now compact, low-energy emitters are opening the door to in-line aseptic packaging and equipment sterilisation. Susan Birks reports.
Electron beam (EB) technology employs a beam of accelerated electrons to achieve effects such as the sterilisation of medical devices, insect de-infestation of foodstuffs, crosslinking of polymers, doping of semiconductors and the degradation of polymers or pollutants in stack gas or water. Traditionally such sterilisation methods have required large, specialised plants built to produce and contain the high-energy electron beams. As a result, goods for sterilisation need to be transported to and from the specialised facility, making it expensive and cost-effective only for large product volumes. However, over the past couple of years new, smaller lower-energy electron beam systems have been developed. These offer the potential to exploit the technology for food packaging applications and there is an expectation that the US FDA will approve the use of several systems in the near future.
One of the applications being looked at is EB sterilisation for aseptic packaging lines, where the key benefits are no chemical residuals and low operating costs. For example, the US company Advanced Electron Beams (AEB), headquartered in Wilmington, MA, has recently unveiled a compact, low-energy (≥150keV) electron beam emitter system for a wide range of industrial applications. The small, modular nature of the emitter makes it an ideal technology for the in-line sterilisation of medical devices and packaging components, primarily for the pharmaceutical, food and beverage industries.
AEB believes this technology has the potential to replace bulk sterilisation methods that use traditional high-energy electron beam (≥5MeV), gamma radiation, chemical treatment or thermal methods.
Although the use of low-energy electron beams of 200keV and 225keV has been proven to be successful in sterilising the interior surface of open bottles, until recently no work had been done at the energy regime below 200keV. AEB therefore conducted a study to demonstrate the capability of using such low-energy electron beam emitters to sterilise the plastic films typically used in pouch, blister and form-fill-seal (FFS) packaging (see box opposite for details).
AEB has since launched the e25ITB electron beam emitter designed for sterilising the interior surfaces of bottle-shaped packaging. Its launch marks the arrival of a new class of aseptic and extended shelf life filling approaches for beverage bottles. The big advantage of a system that sterilises the surfaces of the packaging material at high speeds with a stream of energetic electrons is that no chemicals are used in the sterilisation process. This means there is no need to rinse or dry the material and no risk of residual chemical sterilants contaminating the packaged product.
In addition, the electron beam treatment is a room temperature process, allowing manufacturers to use lighter packaging material, says AEB. Furthermore, by eliminating non-value added steps, filling systems based on AEB’s technology will be smaller, saving valuable production floor space. The company claims the technique offers the lowest operating cost of any bottle sterilisation technology.
“AEB’s bottle sterilisation technology for aseptic packaging will let the beverage industry continue to innovate with new products and new package concepts, while reducing the environmental footprint of the packaging process,” says Mitch Tyson, ceo of AEB.
It is a technique likely to be adopted widely in the next five years, since the company is involved in many development partnerships with equipment manufacturers and major beverage, dairy and liquid food producers. For example, GEA Procomac’s Sterilbeam cap sterilisation system already uses AEB emitter technology; the EU agriculture group Farmright has produced an aseptic stick packaging system designed in collaboration with AEB; and Aseptic Innovation, of Missouri, US, is working with the company on a cap sterilisation system for a linear aseptic bottle filler.
AEB also sees a significant opportunity to address the challenges of critical surface sterilisation of food equipment and plant using its new technology. The challenge arises from the difficult nature of controlling and ensuring sterility on all pieces of equipment that come into contact with the products. While some surfaces are easily accessible for sterilisation, others may be out of reach or difficult to access, says AEB, and this can lead to catastrophic results. For instance, last year an outbreak of listeria in Massachusetts was traced to a key piece of equipment used in the filling process.
The conditions in processing facilities, especially those carrying out wet processes, are favourable environments for bacteria growth and attachment. The complexity of processing equipment creates difficult-to-clean nooks and crannies that are perfect spots for bacteria growth that can escape sanitising treatments. Once bacteria attach to surfaces, it is often very difficult to remove them completely using normal cleaning and sanitation procedures. Currently, high temperature chlorinated water or various chemical sterilants are used to sanitise processing and aseptic packaging equipment.
Although effective, the chemical cleaning practice has some significant disadvantages, including: the potential for the formation of toxic or carcinogenic compounds; the energy intensive nature of the process due to heat requirements; the persistence of chlorine in the environment after usage; and the requirement for special containers for transportation and storage of chlorine compounds.
“Electron beam technology has proven to be a safe and effective method for sterilisation. Novel configurations of electron beams can be leveraged to ensure sterility of problem areas of equipment,” says Tyson.
As microbial contamination proves to be a constant and critical issue for manu-facturers in the food and health industries, there are sure to be more interesting developments of electron beam technology in the near future.
Proof of effectiveness study for low-energy electron beam emitter In this study AEB used the eBeam 250, an electron beam emitter with beam dimensions of 75 x 250mm, to irradiate the plastic pouch material used in beverage pouch packaging. The electrons were directed perpendicular to the pouch surface, in order to penetrate through the material and sterilise the interior pounch surfaces.
The pouches were made of three sandwiched layers of polyethylene-aluminum-polyethylene (PAP) with a total thickness of approximately 120µm. The samples were irradiated using a vacuum acceleration voltage of 150kV, yielding electrons into ambient air with one of the six different doses: 3, 6, 12, 15, 20 and 25kGy. The pouches, placed directly on the conveyor system tray of an AEB Applications Development Unit, moved across the 75mm width of the emitter during the irradiation process. The electron beam exposure times ranged from 0.3 to 0.5 seconds.
Micro-organism inoculation, spore recovery and microbiological testing of the pouches were performed by the qualified laboratory, Apex Laboratories. The samples were express-shipped to AEB for electron beam treatment and returned immediately to Apex Laboratories for the subsequent microbiological tests. Direct count of survivors and fractional outgrowth methods were used in this test. A suspension of Bacillus pumilus ATCC 27142 spores was chosen as the test organism due to its high resistance to ionising radiation. A bacteriostasis study showed no inhibition of outgrowth when 2ml of Tryptic Soy Broth (TSB) containing ~21 Colony Forming Units (CFU) was incubated at 30–35°C.
The direct counting method was implemented for low-dose irradiation (3kGy and 6kGy) and control samples (0kGy). The surviving colonies from each exposure dose were counted and the values used to construct a survivor curve and determine the D-value.
For the irradiation doses greater than 6kGy, the fractional outgrowth method was used. The pouches were cut open and their interior surfaces were spot inoculated with 1x106 CFUs of B. pumilus spores. The spore suspension was then dried at ambient temperatures under a laminar flow hood and the open end of the pouch was impulse sealed to create a hermetic package. After electron beam irradiation, an approximate 2ml of TSB was injected into the exposed pouch using a sterile syringe. After the syringe was removed, the needle entry point was sealed with the silicone sealant. The pouches were visually examined for growth over a seven-day period of incubation at 30–35°C.
Since growth was not readily apparent inside the pouches, a small sample of the broth was then aseptically removed and plated onto TSA. The plated samples were incubated at 30–35°C for two days and examined for the presence of viable organisms. The method was designed to demonstrate that pouch contents were devoid of surviving B. pumilus.
The results of the study verified that: 1. The achieved kill rate is comparable to those previously obtained by other researchers who used ionising radiation techniques of either electron beam or gamma radiation 2. The electron energy of 150keV is sufficient for transmission through the plastic material in order to sterilise the interior surface of the material.
A white paper outlining this study is available at http://www.aeb.com/resources/white_paper_beverage_pouch_sterilization/
CONTACT Advanced Electron Beams T +1 978 658 8600 www.aeb.com GEA Procomac T +39 0521 839411 www.procomac.it Aseptic Innovation T +1 636 281 1500 http://asepticinnovation.com