CSIRO’s Role in Food Packaging

Robert J Steele

CSIRO’s role in packaging research has enabled consumers to enjoy the benefits of safer, fresher and tastier food. From the earliest days of CSIR¹ the need to fund research into food preservation was recognised. "Food preservation in store and transport will always be to the fore amongst questions confronting people in a country of huge internal distances and separated by thousands of miles from the main markets in the world" (Rivett 1928).

Initial packaging research centred around the packaging of frozen and chilled beef as well as on canned food. Thermal processing, a foundation stone of canning technology, was not put on a solid foundation until the 1920s and later studies enabled the safe export of Australian canned low-acid foods. An important aspect of this research was the development of the 'Approved persons’ course', established and initially run by CSIRO to ensure canners are fully able to safely process and export low-acid canned foods.

Active Packaging

The studies on active and intelligent packaging started when E Davis built a cell for measuring the permeability of film materials (Davis and Huntington 1977). While the cell offered flexibility in measuring the permeability of a wide range of films its use was limited by its lack of sensitivity. A spectrophotometric technique (Holland et al. 1980) was devised for oxygen which enabled the simultaneous measurement of permeability on many samples. This technique took advantage of some in-film chemistry (Rooney and Holland 1979), namely a light-generated singlet oxygen, that was to have much wider ramifications for further packaging studies.

Research into active packaging followed from the successful application of in-film chemistry to permeability measurements. This research was facilitated by the collaboration of materials scientists and horticulture scientists from the CSIRO Divisions of Materials Science and Horticulture respectively. Although the research continued for more than ten years the technologies developed below did not achieve widespread commercial success. The many factors for this lack of commercial success include cost of developing the new technology, clearing the regulatory and environmental hurdles, difficulties in finding the most appropriate commercial partner, and a cost sensitive industry.

Oxygen scavenging

Oxygen scavengers had been successfully applied as pouch inserts into a range of foods for many years. Rooney and Holland (1979) saw an opportunity to eliminate the cost and risks associated with such inserts by making oxygen scavenging an integral part of the package. Because oxygen is responsible for a wide variety of deteriorative reactions in food, a substantial research team was assembled and several patents resulted (Rooney 1993). The in-film chemistry involved in permeability measurements allowed Rooney and Holland (1979) to choose relatively freely from a wide range of photoactive dyes. However the requirements for an oxygen scavenging film constrained the choice considerably. The chemicals needed to have high capacity, be fast reacting, non-toxic (or at least not migrate to the food), recyclable, preferably colourless, able to be triggered at time of manufacture and most important, affordable. Initial compositions of natural rubbers demonstrated the principle of using a single polymer as both reagent and reaction medium.

The wine and beer market was recognised as vital for the success of oxygen scavengers and the Oxbar™ transition-metal catalysed scavengers had demonstrated the application of MXD-6 nylon to yield an excellent barrier. Rooney (1993) developed a triggered in-film oxygen-scavenger based on photoreducible quinones and related compounds which met many of the constraints outlined above. Many skills were required to develop this form of active packaging to a demonstrable technology. The enhanced retention of vitamin C in an oxygen scavenging laminate was demonstrated in orange juice (Zerdin, Rooney and Vermüe 2003). The oxygen-scavenging technology was shown to reduce dissolved oxygen content of UHT milk by 23-28% during storage. Reduced levels of some stale flavor volatiles, including three methyl ketones and two aldehydes, were also observed.

Ethylene scavenging

The shelf life of some fruits, flowers and vegetables is considerably shortened when the produce is exposed to ethylene, a known endogenous plant hormone. Ethylene generated by bruised or over-ripe produce or from exogenous sources such as vehicle exhausts can trigger senescence in otherwise good produce. These deleterious effects have been the subject of many studies and interventions aimed to prevent premature ripening of produce. Holland (1991) found that electron deficient dienes or trienes such as the dicarboxyoctyl ester of tetrazine reacted rapidly with ethylene. Holland (1991) stated that the scavenger would be preferable to the use of potassium permanganate as the compounds could be safely incorporated in hydrophobic polymers such as polyethylene or preferably silicone polycarbonate. Since the quantities of ethylene needed to be removed are small this invention did not have the demands that an oxygen scavenging film has. Furthermore when the red tetrazine dicarboxyoctyl ester reacted with ethylene the color disappears which allowed the use of the film as an indicator of ethylene as well as a scavenger.

Anti-microbial packaging

The successful marketing of table grapes, dried tree fruits and wine has for many years relied on the preservative action of sulfur dioxide. Table grapes are sent to the retailer with inserts containing sodium bisulfite which release gaseous sulfur dioxide when the sheets are exposed to high humidity. Catastrophic release of sulfur dioxide occurs too frequently and is triggered when the sheets were exposed to condensation. Steele and Jiang (1994) patented a sulfur dioxide release technology which successfully demonstrated the controlled release of sulfur dioxide by laminating a sulfite-containing film to a film containing a food grade organic acid such as citric or succinic acid. These laminates could be tailored to the various varieties of grapes according to their sensitivity of the bleaching action of sulfur dioxide and their susceptibility to infection. It was also noted that the acid laminate could be used as an anti-microbial film in its own right.

Condensation control

Although the sulfite film was successful in trials the same trials also showed that a condensation control technology (Patterson and Cameron 1992, Patterson 1993) was equally successful in preventing catastrophic release of sulfur dioxide when table grapes were subject to temperature fluctuations that would normally produce condensation. The packaging material maintained a controlled high humidity while at the same time avoiding condensation of water. The package included an absorbent material (non-woven cloths, woven textiles, porous plastics) arranged to draw the liquid form of the substance away from the grapes.

Intelligent packaging

Another outcome of the development of in-film chemistry for permeability measurements was the co-development of intelligent packaging. Red tetrazine-containing films became clear when exposed to ethylene and some of the oxygen-based indicators such as rubrene were investigated as potential tamper evident intelligent packaging.

Conclusion

Despite the intensive research into active and intelligent packaging at CSIRO little commercial success has resulted. As discussed by Robertson (2006) the considerable technical, legislative, environmental, economic and consumer hurdles have severely limited the commercial application of these technologies. However as Robertson (2006) explains the lack of rigorous peer-reviewed assessment of the innovations hinders acceptance of technologies to pass the first test for approval – namely they must demonstrate a consumer benefit. There remains a pressing need for these technologies to be evaluated in independent laboratories and the results to be published in quality peer-reviewed journals.

References

Davis, EG and Huntington, JN (1977) New cell for measuring the permeability of film materials. CSIRO Food Res. Q.. 37: 55-59.

Holland, RV (1991) Absorbent material and uses thereof. International Patent WO91/04292 PCT/AU90/00413.

Holland, RV, Rooney, ML and Santangelo, RA (1980) Measuring oxygen permeabilities of polymer films by a new singlet oxygen technique. Die Angew. Makromol. Chemiel 88:, 209-221.

Patterson, BD (1993) Packaging material for control of condensation within package has water impermeable sheet with one hydrophilic side provided with fibres conducting water by capillary action. PCT International Patent Application. WO9301101-A; EP592516-A; WO9301101

Patterson, BD and Cameron, A (1992) Modified atmosphere packaging. PCT International Patent Application. WO 92/21588 A1.

Rivett, ACD (1928) The policy and aims of the Council for Scientific and Industrial Research. J. CSIR 1(3): 138.

Robertson, GL (2006) Food Packaging Principles and Practice, 2nd Edn. ISBN: 9780849337758. Boca Raton, FL: CRC Press; p 308.

Rooney, ML (1993) Oxygen scavengers independent of transition metal catalysts. International Patent Application PCT /AU93/00598.

Rooney, ML and Holland, RV (1979) Singlet oxygen: an intermediate in the inhibition of oxygen permeation through polymer films. Chem. Ind. 24: 900-901.

Steele, RJ and Jiang, XZ (1994) Sulphur dioxide film. PCT International Patent Application. WO 94/10233 A1.

Zerdin, K, Rooney, ML and Vermüe, J (2003) The vitamin C content of orange juice packed in an oxygen scavenger material. Food Chem. 82: 387-395.

Dr Robert Steele is a Post Retirement Fellow at CSIRO Food and Nutritional Sciences, North Ryde, NSW 2113, Australia; E-mail: bob.steele@csiro.au

¹Previously Council for Scientific and Industrial Research, later became the Commonwealth Scientific and Industrial Research Organization (CSIRO)