Tyrosinase‐catalysed grafting of food‐grade gallates to chitosan: surface properties of novel functional coatings

Abstract

Plasma-activated biaxially oriented polypropylene (BOPP) fi lms and paper substrate have been coated with functional chitosan solutions. Plasma treatment increased the amount of surface peroxide groups and carboxyl groups on the BOPP fi lms. As a result of plasma activation, the surface energy increased from 30 to 50 dynes/cm. The enzyme tyrosinase catalysed the grafting of 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 cm 3 /(m 2 · 24 h) was obtained with chitosan-coated BOPP. Coatings did not have any effects on water vapour transmission.Both gallates were successfully grafted at pH 6. As increased fl occulation 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/dm 2 , thus materials may be exploitable in packaging purposes in direct contact with certain foodstuffs.

Antimicrobial activity of chitosan attached to ethylene copolymer films

“…As observed by others, 8,18 chitosan did not migrate from the plastic in appreciable amounts, since buffer exposed to chitosan-coated fi lm either did not exhibit antimicrobial activity or reduced E. coli 29522 by only 1 log 10 over a 24 h incubation period after removal of the fi lm. Silver-containing chitosan-coated fi lm was considerably more bacteriocidal than the fi lm coated with chitosan alone (Figure 3), and its antimicrobial activity was released into the medium, since phosphate buffer exposed to silver/chitosan fi lm was bacteriocidal.…”

“…Examples of this type of fi lm are nylon irradiated to generate surface amine groups, 2,3 fi lms with immobilized enzymes such as lysozyme [4][5][6] and plasma-activated biaxially oriented polypropylene to which chitosan is cross-linked via glutaraldehyde 7 or is simply added as coating. 8 The utility of such fi lms is likely limited to applications where fi lms directly contact food surfaces or liquid suspensions within the food package, but such fi lms offer the advantage of not altering the content of the food and of potentially facing fewer regulatory concerns than fi lms in the fi rst category.…”

Enzyme Initiated Radical Polymerizations

“…When using gallic acid esters, increased water repellence was achieved. Chitosan-composites with gallic acid (derivates) [136][137][138][139], ferulic acid [140], flavonoids [141] exhibit increased antioxidant activity. An interesting extension of this concept is to use amine-functionalized inorganic supports [142].…”

“…A practical application of this grafting technology may be in the textile and food industry yielding products with antimicrobial activity and modified rheological properties [130,138,139,[143][144][145][146].…”

Electrochemical Insights on the Hydrophobicity of Cellulose Substrates Imparted by Enzymatically Oxidized Gallates with Increasing Alkyl Chain Length

“…In addition, they have been shown to possess amphiphilic and anticancer properties [11][12][13] . Several studies have employed gallates of variable alkyl chain length to modify the properties of materials such as wool 14 , cellulose 15 , chitosan 16 , titanium dioxide 17 , and ceramics 18 , conferring improved thermal and thermo-oxidative stability (polymers, foams) or dispersibility.…”