ANTIFUNGAL PROTECTION AND SIZING OF PAPER WITH CHITOSAN SALTS AND CELLULOSE ETHERS. PART 2, ANTIFUNGAL EFFECTS
MARIA DEL PILAR PONCE-JIMÉNEZ, FERNANDO A. LÓPEZ-DELLAMARY TORAL, & HUMBERTO GUTIERREZ-PULIDO
Part 1 of this article showed the physical and mechanical changes in samples of Whatman no. 1 filter paper consolidated with cellulose ethers and chitosan salts (Ponce-Jiménez et al. 2002). In this article, we compare the antifungal protection of these consolidants against six selected fungal strains.
When a paper object has been attacked by fungi, the deterioration is shown by color spots, weakening of the fibers due to depolymerization of cellulose, and shifts in pH to acidic. Development of filaments or hyphae and proliferation of spores may also occur. This situation is deleterious because even after fumigation, latent spores can remain in the paper and germinate anew. Further, deterioration already present in the paper could facilitate new fungal attacks when conditions become favorable; some products of enzymatic hydrolysis of the cellulose are inductors of cellulolytic enzymes in many species of fungi (Mandels and Reese 1960).
The paper conservator must use the most effective substances for the protection of documents and works of art damaged by fungi. Conserving the paper object while minimizing collateral risks to people and to other objects is the most critical goal. It is urgent to exterminate fungi immediately and achieve the best possible protection (Dersarkissian and Goodberry 1980; Santucci 1983).
The cellulose ethers—for example, carboxymethyl-cellulose and methylcellulose—are the substances used most frequently in restoration and conservation of paper, mainly as sizing and reinforcing agents, but cellulose ethers are susceptible to enzymatic degradation. This effect is manifested in the reduction of the molecular mass. Only cellulose ethers with a high substitution degree and uniform substitution pattern along the chain can be more resistant against microbial degradation (Strnadová and Durôvic 1994).
1.1 ANTIFUNGAL PROPERTIES OF CHITOSAN
Leuba and Stossel (1986) and Hardwiger et al. (1986) demonstrated the antifungal effect of chitosan on some plant root diseases.
While chitin and chitosan both have antifungal properties, chitosan is more effective. Chitin suppresses fungi indirectly via antagonistic soil micro-organisms, while chitosan has both direct and indirect effects (Leuba and Stossel 1986). It can activate specific genes in plants and, at similar concentrations, can completely inhibit RNA synthesis in some fungal organisms (Hardwiger et al. 1986).
Chitosan can inhibit both Epidermophyton floccosum, an athlete's foot–inciting fungus, and Ceratocystis ulmi, the causal agent of Dutch elm disease, which attacks certain kinds of trees (Hardwiger et al. 1986). Chitosan treatments of wheat seeds prior to planting can afford the wheat plant protection from some of the detrimental effects of root pathogens that cause lodging (fallen wheat) and yield loss (Hardwiger et al. 1986).
Hardwiger et al. (1986) attribute the biological activity of chitosan to interaction among positively charged amino groups of chitosan and negatively charged phosphate groups of nucleic acids. The chitosan polymer must be seven or more sugar units in length to optimally induce plant genes and inhibit fungal growth. This length requirement suggests that a series of positive charges match up with phosphate negative charges in the grooves of the DNA helix in the B form, possibly converting it to the Z form (Hardwiger et al. 1986). Chitosan agglutinates a variety of bacteria and yeasts as well as cells of mammalian origin (Leuba and Stossel 1986).
Chitosan is also a component in the wall of some fungi, species that are less sensitive to its antifungal effects (Leuba and Stossel 1986). These fungi presumably alleviate the potential destruction of chitosan through exclusion, rapid degradation, and so on. (Some species of fungi [e.g., Fusarium] have some potential to regulate chitosan levels, preventing fungal or germination growth for defined periods [Hardwiger et al. 1986].)
Chitosan also accumulates in dormant chlamydospores, but the level is much lower in mycelia following germination of these spores. Thus, chitosan may be utilized by the fungus as a natural regulator molecule to manipulate the dormant state (Hardwiger et al. 1986).
In this article, we evaluate the effect of three chitosan salts as antifungal consolidants for potential applications in conservation treatments of documents previously attacked by fungi and as a preventive against deterioration. In tests, six celluloytic fungal strains were employed with previous evaluation of their effects on Whatman no. 1 filter paper.