NEW RESEARCH RESULTS: Surface treatment for food packaging materials

Tuesday, 30 September 2008 14:26

Jari Vartiainen, Marjaana Rättö, Raija Lantto, Kalle Nättinen and Eero Hurme developed a new surface treatment for food packaging materials: tyrosinase-catalysed grafting of food-grade gallates to biodegradable polysaccharide.

Plasma-activated polypropylene films and paper substrate have been coated with functional polysaccharide (chitosan) solutions. Plasma treatment increased the amount of surface peroxide groups and carboxyl groups on the films. As a result of plasma activation, the surface energy increased from 30 to 50 dynes/cm. The enzyme tyrosinase was used to graft octyl gallate and dodecyl gallate to amino groups of chitosan polysaccharide. Resulting coatings exhibited strong antimicrobial activity against Gram-positive Staphylococcus aureus and Gram-negative Listeria innocua. After 24 h of incubation, a total reduction in both bacteria cell numbers varied between > 4.9 and 1.4 logarithmic units. Grafted dodecyl gallate and octyl gallate at pH 6 were found to have the lowest reduction values of <3 logarithmic units for S. aureus, while 1.4 logarithmic reduction value was obtained for grafted dodecyl gallate at pH 6 against L. innocua.

Chitosan coatings were also effective barrier layers against oxygen transmission although the transmission rates clearly increased in high-humidity conditions. In dry conditions, however, the transmission rate of 2 cm3/(m2 • 24 h) was obtained with chitosan-coated films. Coatings did not have any effects on water vapour transmission. Both gallates were successfully grafted at pH 6. As increased flocculation and colour formation indicated, the tyrosinase-catalysed grafting was more powerful with octyl gallate. Dodecyl gallate containing chitosan coatings was more hydrophobic as compared to octyl gallate. Total migration of substances into 95% ethanol was ≤ 5 mg/dm2, thus materials may be exploitable in packaging purposes in direct contact with certain foodstuffs.


Reference:

Vartiainen, J., Rättö, M., Lantto, R., Nättinen, K., Hurme, E. Tyrosinase-catalysed grafting of food-grade gallates to chitosan: surface properties of novel functional coatings. Packaging Technology and Science. Vol. 21 (2008) No: 6, 317 - 328.

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