INTELLIGENT PACKAGING- PART II

TIME-TEMPERATURE INTEGRATOR (TTI’S)

      

       TTI’s are devices that show an irreversible change in a physical characteristic, usually color or shape, in response to temperature history. Time-temperature indicators (TTI) attached to the package surface designed for integrate the cumulative time-temperature history of the package throughout the whole distribution chain, and therefore, gives indirect information on the product quality.        Time temperature indicators which are commercially available are based on various reaction mechanisms diffusion, polymerization or enzyme reaction. The temperature dependent reaction kinetics of the indicator and activation of the indicator at the moment of packaging is a common feature for all concepts.

TTIs may be classified into three categories (Taoukis, Labuza, 2003)

       Critical temperature indicators (CTI) show exposure above (or below) a reference temperature. Denaturation of an important protein above the critical temperature or growth of a pathogenic microorganism is other important cases where a CTI would be useful.

       Critical temperature/time integrators (CTTI) are useful in indicating breakdowns in the distribution chain and for products in which reactions, important to quality or safety, are initiated or occur at measurable rates above a critical temperature. Examples of such reactions are microbial growth or enzymatic activity that is inhibited below the critical temperature.

       Time temperature integrators or indicators (TTI) give a continuous, temperature dependent response throughout the products history.

       TTIs may be classified as either partial history or full history indicators, depending on their response mechanism. Partial history indicators do not respond unless a temperature threshold has been exceeded and indicate that a product has been exposed to a temperature sufficient to Cause a change in product quality or safety. Full history TTIs give a continuous temperature-dependent response throughout a products history.

       Ideally, TTIs should also be low cost, small, reliable, easily integrated into food packaging, have a long pre and post-activation shelf life and be unaffected by ambient conditions other than temperature. TTIs should also be flexible to a range of temperatures, no toxicological or safety hazard and convey information in a clear manner.

      

A large number of TTI types have been developed and patented

Diffusion-based TTIs: An indicator dependent on the diffusion of a coloured fatty acid ester along a porous wick made of high quality blotting paper. The useful range of temperatures and the response life of the TTI are determined by the type and concentration of ester.

Enzymatic TTIs: Based on a colour change induced by a drop in pH resulting from the controlled enzymatic hydrolysis of a lipid substrate. The indicator consists of two separate compartments containing an aqueous solution of lipolytic enzymes and another containing the lipid substrate suspended in an aqueous medium and a pH indicator mix. Different enzyme substrate combinations are available to give a variety of response and temperature dependencies. Activation of the TTI is brought about by mechanical breakage of a seal separating the two compartments and may be done manually or by on-line automation. Hydrolysis of the substrate causes a drop in pH and a subsequent colour change in the pH indicator from dark green to bright yellow. Visual evaluation of the colour change is made by reference to a five-point colour scale.

Polymer-based TTIs: Based on temperature dependent polymerization reactions in which diacetylene crystals polymerise via 1,4 addition polymerisation to a highly coloured polymer. Resulting changes in reflectance can be measured by scanning with a laser optic wand.

Commercially available TTIs

§  3M MonitorMark® (3M Co., St Paul, Minnesota) is diffusion-based indicator label and is on the color change of an oxidable chemical system controlled by temperature-dependent permeation through a film.

§  The Timestrips® (Timestrip UK Limited, UK) are smart labels for monitor how long a product has been open or how long it has been in use.

§  The Fresh-Check®TTI (Temptime Corp., Morris Plains, NJ, USA) is based on a solid state polymerization reaction, resulting in a highly coloured polymer. This indicator may be applied to packages of perishable products to ensure consumers at point-of-purchase and at home that the product is still fresh. These indicators have been used on fruit cake, lettuce, milk, chilled food.

REFERENCES

·      AHVENAINEN, R., 2003: Novel Food Packaging Techniques. Cambridge UK: Wood head Publishing, 400 p. ISBN 978-1-85573-675-7.

·      COLES, R., MCDOWELL, D. and KIRWAN, M. J., 2003: Food Packaging Technology. Oxford, UK: Blackwell Publishing, 346 p. ISBN 978- 0849397882.

·      C. Suzuki, J. Chem. Ed. 68, 588–589 (1991).

·      FQSI International, FreshQt smart sensor label web information. Available at http://www.fqsinternational.com/products.htm. Accessed March 2008.

·      International published Patent WO 2006/032025 A1, J. R. Williams, K. E. Myers, M. M. Owens, and M. A. Bonne (to Food Quality Sensor International, Inc.).

·      R. Want, ‘‘Enabling Ubiquitous Sensing with RFID,’’ Computer 37, 84–86 (2004).

·      S. Nambi, S. Nyalamadugu, S. M.Wentworth, and B. A. Chin, ‘‘Radio Frequency Identification Sensors,’’ 7th World Multiconference on Systemics, Cybernetics and Informatics, Dubna, Russia, July 30–August 2, 2003.

·      SUMMERS, L., 1992: Intelligent packaging for quality. So_ Drinks Management International, Vol. 36, p. 32–33. ISSN 0953–4776.

·      RODRIGUES, E. T. and HAN, J. H., 2003: Intelligent packaging. In: Heldman, D. R. and Moraru, C. I. (ed.). Encyclopaedia of Agricultural, Food and Biological  Engineering. 2nd edition, New York: Marcel Dekker, pp. 528–535. ISBN 978-1439811115.

·      HAN, J. H., HO, C. H. L. and RODRIGUE, E. T., 2005: Intelligent packaging. In: Han, J. H. Innovation in food packaging. UK, London: Elsevier Academic  Press, p. 138–155. ISBN 978-0123116321.

·      Gontard, N. Active packaging for food processing and preservation. In: International Congress on Engineering and Food: ICEF 9, 7e11 March 2004, Montpellier, France.

 To be continued.................