关键词: 毛竹, 漆酶, 碘, 防霉性能, 抗流失性能

Abstract:

Objective: Bamboo is widely used in traditional fields such as making of cutting boards, chopsticks and toys for children, however mildew negatively affects its various enterprises and consumers. The existing anti-mildew agents are mainly poisonous and easily leach out of the treated material. Enzymatic bio-catalytic oxidation can form a stable chemical bond between non-toxic iodine and bamboo to improve leaching resistance of iodine and enhance the anti-mold efficacy of bamboo at the same time. It also provides a new idea for the development of natural and non-toxic fungicides. Method: Using ABTS as mediator, potassium iodide was catalyzed by laccase and the liberated iodine was fixed on bamboo, and these led to improved leaching and mildew resistances. Fourier transform infrared(FTIR)and X-ray photoelectron spectroscopy(XPS)were used to study the changes effected by the treatments on the chemical constituents of bamboo. The effects of different concentrations of laccase on the antifungal properties of bamboo were studied by using 4-year-old bamboo samples as the experimental materials, and Trichoderma viride, Aspergillus niger and Penicillium citrinum strains as the test fungi. In order to know the fixation of the active ingredient in the bamboo, the content of iodine was determined by inductively coupled plasma mass spectrometry(ICP-MS), and the fixation rate of iodine in the bamboo was calculated. The anti-mold efficacy of the blocks before and after leaching was tested for the three mold fungi. Result: Laccase catalyzed iodine treatment of bamboo can effectively improve the anti-mildew effects of bamboo, and the participation of laccase in various weight percent (wt.%) showed better performances than the block treated with potassium iodide alone. The laccase treatment KI with a concentration of 4.8×10^-3 wt.‰ had the best resistance to Trichoderma viride, followed by Aspergillus niger and Penicillium citrinum that almost completely covered the samples after 21 days' treatment. The leaching experiment showed that the iodine fixation rate could be increased to 86.13% after the treatment of samples with laccase at the concentration of 4.8×10^-3wt.‰, while iodine fixation rate was only 37.47% after the block treated with potassium iodide alone. Potassium iodide had a limited anti-mildew efficiency in the environment of a mixture of the three fungi, but adding laccase could significantly improve the anti-mildew efficiency. FTIR and XPS analyses showed that laccase catalyzed iodine treatment could modify bamboo lignin forming C-I bond, but with less influences on cellulose and hemicellulose. Conclusion: Laccase catalyzed iodine could improve the mildew and leach resistances of bamboo which increase with laccase concentration. The immobilization rate of iodine in the blocks could be effectively improved by adding laccase to catalyze iodine. The results of comprehensive anti-mildew test showed that laccase catalyzed iodine treatment was significantly higher than for potassium iodide. This study not only broadened the application of laccase and other biological enzymes, but also provided a safe and reliable fungicide for bamboo products that directly get in contact with food or humans.

Key words: bamboo, laccase, iodide, mold resistance, leaching resistance