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.