PACKAGING TECHNOLOGY AND SCIENCE VOL 8 299-301 (1995)

Conference Report-International Symposium on Advances in Aseptic Processing and Packaging Technologies

Yngve Dagel Regional Editor, Europe Seglarvagen 5, 181 62 Lidingo, Sweden

An international symposium on Advances in Aseptic Processing and Packaging Technologies took place in Copenhagen, September 1 1-12 1995. The symposium was organized by five leading centers for research in aseptic processing and packaging technologies from three different continents. The symposium was also the final activity of the Nordfood Project ‘Safety in Aseptic Products’, that has been performed as an industrial cooperation project with 12 industries and six laboratories in the Nordic countries during 1993-1995.

The symposium organizers were as follows: Campden and Chorleywood Food Research Association, UK, Food Science Institute, Purdue University, USA, North Carolina State University, USA, Food Industry Research and Development Institute, Taiwan, and SIK, the Swedish Institute for Food Research, Sweden.

The symposium attracted 160 participants from 20 countries representing the Food Industry and the Packaging Supply & User Industries as well as research organizations. 16 lectures were presented and documented. The presentations were completed by 30 posters. The symposium was very well organized and offered good possibilities for questions and discussions.

Aseptic processing and packaging is used throughout the world for drinks and liquid food products. International trade in aseptic shelf-stable products is increasing. Recent research activities in aseptic technologies have led to the development of new processing methods that extend the application area for aseptic technologies to more complex and value-added food products. Other research activities have aimed at ensuring product safety, including hygiene, automated process control methods and individual package seal integrity. The symposium mirrored all these activities but considering the main interests of the readers of Packaging Technology and Science only the typical packaging lectures will be reported here.

Wayne Clark from Pure Pulse Technologies Inc., San Diego, CA, USA, gave a lecture with the title Light Flashes for Sterilization of Package Surfaces.

By storing electrical energy in a capacitor and releasing it in short pulses, high peak power levels can be generated. Such pulses of electrical energy can be used to create

CCCOS94-3214/95/060299-03 0 1995 by John Wiley & Sons, Ltd.

Received 15 September 199.5 Accepted 20 September 1995

300 YNGVE DAGEL

intense pulses of light or electric field. The high intensity of these pulses results in unique bactericidal effects that are not observed when the same energy is provided at low intensity.

Short duration flashes of broad spectrum ‘white’ light are used to kill a wide range of microorganisms, including microbial and fungal spores. Each pulse or flash of light lasts only a few hundred millionths of a second (i.e. a few hundred microseconds). During each flash the intensity of the light is about 20000 times the intensity of sunlight at the Earth’s surface. The flashes are typically applied at a rate of about 1-20 flashes/s. The flashes can be used to sterilize packaging material surfaces for the food, medical and pharmaceutical industries.

The flashes can be used to effectively sterilize packaging materials for aseptic packaging applications. Greater than lo6 per cm B. pumilus spores, a relatively resistant spore, are killed with 2-3J/cmP2 flashes. No adverse chemical or functionality effects on packaging materials have been found at treatment levels needed to achieve commercial sterility. Smooth, accessible package surfaces are excellent candidates for light flash treatment.

The benefits of the light flash process over other packaging sterilization systems include extremely rapid (fractions of a second) on-line treatment, easy monitoring, control and verification of the treatment, and the elimination of bactericidal chemicals and their residues.

The light flash method also delivers more than enough microbial kill for effective use in ‘super clean’ non-aseptic package applications for perishable, refrigerated products with extended shelf-life requirements.

Determination of Critical Leak Size by Analyses of Gas and Aerosol Flow was the title of a paper presented by John D. Floros, representing research work done together with Vivek Gnanasekharan at Purdue University, West Lafayette, IN, USA.

Leaks, such as seal channels and pinholes, are the major reason for post-process contamination of packaged food. Aseptic packages, including metal cans, are particularly susceptible to package integrity problems. Several destructive and nondestructive methods of evaluating package testing exist, but the only requirement by the FDA is biotesting. Biotests are destructive, time consuming and expensive, and require that the package be immersed in or sprayed with highly concentrated bacterial suspensions. Contrary to such an unrealistic testing protocol, non- destructive tests are fast, relatively inexpensive and can be used for 100% on-line inspection.

The majority of commercial non-destructive test equipments are based on the pressure difference principle. As the name suggests, pressure difference tests create a pressure differential across the package wall. If leaks are present, headspace gases may flow out, or surrounding gases may flow into the package. Both of these are mass transfer phenomena (gas flow) that result in changes in the package or the surrounding environment, which are detected by the equipment.

Floros and Gnanasekharan have studied the minimum leak size that can be reliably detected by current non-destructive package integrity equipment and found that 50ym seal leaks and 20ym pinhole leaks can be detected by pressure and vacuum

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lid deflection tests. Methods that measure chamber pressure may detect seal leaks of 30 pm and pinhole leaks as small as 5 pm.

The authors have also tried to define a minimum leak size that permits microbial ingress into and contamination of packaged foods and conclude that information on microbial ingress through leaks is contradictory, but aerosol theory can be used to find a ‘critical’ leak size.

E. Hurme, G. Wirtanen and R. Ahvenainen, of VTT Biotechnology and Food Research, Finland, together with L. Axelson-Larsson, Packforsk, Sweden, have also studied the integrity problem and reported their findings in a paper with the title Evaluation of Non-Destructive Pressure Difeerential Package Leakage Testers.

Although many types of commercial equipment for testing integrity have been on the market for years, little data is as yet available concerning the reliability and suitability of methods to identify all leakages which can cause microbial contamination of an aseptic product. The aim of the reported research work was to evaluate the requirement for the sensitivity, reliability and other factors of non- destructive integrity testing.

The critical microhole size for microbial penetration is the basis for the selection of leak testing methods for aseptic packages. Microbes may be as small as 0.5pm in diameter, but detecting holes of this size is difficult, and the tester need not necessarily find smaller leaks than those that cause microbial contamination.

In food packages, the determined minimum microhole size for penetration by different test bacteria varies between 5 and 25pm in diameter. However, critical hole sizes of even 1-5 pm in diameter have been determined in model capillary tubes or orifices. The main reason for the variation between different studies have been differences in biotest procedures, packaging materials, hole structure and testing foodstuffs. For example, low viscosity rather than high viscosity model foods have been observed to promote the penetration of test bacteria through the holes.

An interesting observation is that a study of commercially produced and distributed retail aseptic packages revealed that although 40% of the packages had leaks of about 10pm diameter, none of them showed any signs of microbial contamination (Axelson et al., 1990, Packaging Technology and Science, 3, 141-162).