Evaluation of the potential of fungal and plant laccases for active-packaging applications

Laccases from Trametes versicolor (TvL), Myceliophthora thermophila (MtL), and Rhus vernicifera (RvL) were investigated with regard to their potential utilization as oxygen scavengers in active packages containing food susceptible to oxidation reactions. The substrate selectivity of the laccases was investigated with a set of 17 reducing substrates, mainly phenolic compounds. The temperature dependence of reactions performed at low temperatures (4-31 °C) was studied. Furthermore, the laccases were subjected to immobilization in a latex/clay matrix and drying procedures performed at temperatures up to 105 °C. The results show that it is possible to immobilize the laccases with retained activity after dispersion coating, drying at 75-105 °C, and subsequent storage of the enzyme-containing films at 4 °C. TvL and, to some extent, MtL were promiscuous with regard to their reducing substrate, in the sense that the difference in activity with the 17 substrates tested was relatively small. RvL, on the other hand, showed high selectivity, primarily toward substrates resembling its natural substrate urushiol. When tested at 7 °C, all three laccases retained >20% of the activity they had at 25 °C, which suggests that it would be possible to utilize the laccases also in refrigerated food packages. Coating and drying resulted in a remaining enzymatic activity ranging from 18 to 53%, depending on the drying conditions used. The results indicate that laccases are useful for active-packaging applications and that the selectivity for reducing substrates is an important characteristic of laccases from different sources.