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Antifungal effect of different methyl and propyl paraben mixtures on the treatment of paper biodeterioration
International Biodeterioration & Biodegradation 63 (2009) 267–272
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Antifungal effect of different methyl and propyl paraben mixtures on the treatment of paper biodeterioration Eva Raquel Neves a, Stephan Scha¨fer a, Alan Phillips b, Joa˜o Canejo c, Maria Filomena Macedo a, * a
˜o e Restauro, Faculdade de Cieˆncias e Tecnologia, Universidade Nova de Lisboa, Monte da Caparica, 2829-516 Caparica, Portugal Departamento de Conservaça ˜o Auto ´noma de Biotecnologia, Faculdade de Cieˆncias e Tecnologia, Universidade Nova de Lisboa, Monte da Caparica, 2829-516 Caparica, Portugal Secça c Departamento de Cieˆncias dos Materiais, Faculdade de Cieˆncias e Tecnologia, Universidade Nova de Lisboa, Monte da Caparica, 2829-516 Caparica, Portugal b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 April 2008 Accepted 7 July 2008 Available online 25 November 2008
With many important artistic works and documents made of paper, and thus susceptible to biodeterioration by fungi, research is required in an effort to replace toxic chemical products with other more benign ones. In this work the antifungal effect of methyl and propyl paraben mixtures at different concentrations was evaluated. The fungi used in the experiments were a Cladosporium species and Penicillium corylophilum, both of which are well known as paper-biodeteriorating fungi. The results demonstrate that a mixture of 0.5% methyl paraben and 1% propyl paraben, in 85% ethanolic solution, is the lowest concentration necessary to provide an efficient antifungal action. A deacidification agent, 5% calcium propionate, was added to this mixture to produce a multi-purpose formulation to treat acidification and fungal contamination of paper documents. Tests carried out on paper samples before and after application of this mixture showed only a minor increase in yellowing and a slight decrease in tensile strength, while substantially raising the pH, and thus the alkaline reserve, and also a slight increase in the percentage of deformation. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Paper Antifungal Parabens Cladosporium Penicillium corylophilum
1. Introduction Paper is the main material of large artistic and document collections. It is also the most significant carrier of information for many centuries. However, given its organic nature, paper suffers from biodeterioration. Fungi are an almost daily contaminant on paper collections. Infestation is fostered by inadequate storage and display conditions, which allow conidia dispersed in the air to fall on damp and dirty papers (Florian, 1997; Maggi et al., 2000; Lugauskas and Krikstaponis, 2004); mould growth starts when relative humidity and temperature are favourable for spore germination (Caneva et al., 1991). Microfungi are the main microorganisms responsible for paper biodeterioration (Zyska, 1997, 2002; Adelantado et al., 2005). The activity of fungi on paper can produce several types of damage, such as different coloured stains (Szczepanowska and Lovett, 1992; Aranyanak, 1995; Arai, 2000), discolouration of pigments and inks, and changes in the chemical and physical properties of the paper (Caneva et al., 1991; Nitte´rus, 2000). Traditionally, conservators used fungicidal treatments that involved toxic and potentially damaging chemicals to inhibit fungus growth on paper. Some studies propose replacing these
* Corresponding author. Tel./fax: þ351 21 294 83 22. E-mail address: [email protected] (M.F. Macedo). 0964-8305/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibiod.2008.07.011
traditional antifungal agents with others that are less toxic (Dersarkissian and Goodberry, 1980; Fabbri et al., 1997; Bubiniene`, 1999; Rakotonirainy et al., 1999; Ricelli et al., 1999; Silva et al., 2006). Nowadays, antifungal agents with low toxicity and high efficacy are already used in the cosmetic, food, and pharmaceutical industries. Parabens (p-hydroxybenzoates) are one of the most common antifungal and preservative agents used in these industries (Rastogi, 2000; Perlovich et al., 2005; Zhang et al., 2005). Parabens are already largely studied, possess minimal side effects, and have low costs associated with them (Reynolds, 1996; Doron et al., 2001). They are generally used in combination, the most common combination being methyl and propyl parabens (Soni et al., 2005). Paper documents and artistic works containing cellulose also suffer from the acidification process. This is due to the degradation of cellulose that generates aliphatic acids such as acetic, formic, oxalic, and lactic acids, when aging. Nowadays, deacidification treatment is a usual procedure in paper conservation. Manual treatments are normally by baths with aqueous solutions of alkaline salts (calcium or magnesium carbonate or calcium hydroxide) (Dupont et al., 2002; Cheradame et al., 2003; Sundholm and Tahvanainen, 2003; Zappala` and Stefani, 2005). However, there are paper documents and artistic works with water susceptible media and inks that make these procedures useless. Therefore it is necessary to improve non-aqueous deacidification treatments. There are some studies that show the possibility of using new
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Fig. 1. Diagram of the experimental procedure used for the evaluation of fungal resistance of paper previously treated with paraben mixtures.
deacidification products, soluble in ethanol, such as calcium propionate (Zappala`, 1990) or aminosilanes (Cheradame et al., 2003). The combination of a paraben mixture with a deacidificant would result in a multi-purpose formulation for the treatment of acidified and biocontaminated paper documents. The present work focused on the study of the antifungal action of methyl and propyl parabens and the subsequent addition of a deacidification agent. The antifungal effect of different concentrations of methyl and propyl paraben mixtures was evaluated with the goal to select the lowest inhibitory concentration mixture with the highest antifungal efficiency, and to evaluate the changes in paper properties due to the use of the selected mixture together with a deacidification agent.
2. Materials and methods The experimental work started with the evaluation of fungal resistance of paper previously treated with different mixtures of methyl and propyl parabens. The most efficient mixture was selected and a deacidificant was added. Then a study was performed in order to check if this mixture was efficient in the treatment of paper previously contaminated with fungi. Finally, changes in paper properties due to the treatment with the selected mixture were evaluated.
2.1. Paper Whatman filter paper #1 was used for its high pure cellulose content (98% w/w) and also because its chemical, physical, and structural characteristics are well known. Moreover, it is additivefree and serves as a point of reference with respect to other experimental works since it is widely used for laboratory testing (Adamo et al., 1998, 2003; Canhoto et al., 2004; Vives et al., 2004). 2.2. Fungal strains and culture media After an exhaustive search of the literature on the occurrence of fungi on paper documents, it was found that the most frequent genera were Aspergillus, Chaetominum, Cladosporium, Penicillium, and Trichoderma (Caneva et al., 1991; Rebrikova and Manturovskaya, 1993; Aranyanak, 1995; Florian, 1997; Zyska, 1997; Florian and Manning, 2000; Maggi et al., 2000; Szczepanowska and Cavaliere, 2000; Bonaventura et al., 2003; Corte et al., 2003; Lugauskas and Krikstaponis, 2004; Silva et al., 2006). Penicillium corylophilum Dierckx and a Cladosporium sp., isolated from contaminated paper documents found in the Direcça˜o Geral de Edifı´cios e Monumentos Nacionais Archive collection (Lourenço et al., 2005) were selected for this study. The isolated strains were maintained on potato dextrose agar (PDA) at 20 C. To inoculate paper samples a suspension was prepared of semi-solid detergent agar (SDA) with fungal conidia of each strain.
Fig. 2. Schematic representation of the experiment conducted to test the efficacy of two mixtures in the treatment of contaminated paper.
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269
Table 1 Development of the fungi Cladosporium and P. corylophilum on paper previously treated with different mixtures of MP and PP Paper
Paper and solvent
Cladosporium
P. corylophilum
Cladosporium
Treated paper P. corylophilum
Cladosporium
P. corylophilum
Treatments
Days
D
G
D
G
D
G
D
G
D
G
D
G
0.5% MP and 0.25% PP
2 8 15 2 8 15 2 8 15 2 8 15 2 8 15
2.33 5.50 5.5 3.20 4.27 5.5 2.33 5.23 5.5 3.20 3.60 5.5 3.20 3.60 5.5
þþ þþ þþ þþ þþ þþ þ/ þþ þþ þþ þþ þþ þþ þþ þþ
2.03 5.17 5.5 4.40 5.17 5.5 2.03 5.5 5.5 4.43 4.53 5.5 4.43 4.53 5.5
þþ þþ þþ þþ þþ þþ þ/ þþ þþ þþ þþ þþ þþ þþ þþ
2.00 4.90 5.5 3.50 4.33 5.5 0 4.97 5.5 3.50 3.87 5.5 3.50 3.87 5.5
þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ
1.93 5.5 5.5 4.47 4.30 5.5 0 5.5 5.5 3.47 4.87 5.5 3.47 4.87 5.5
þ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ
0 3.73 5.5 0.67 1.57 3.00 0 0 2.47 0 0 0 0 0 0
þþ þþ þ/ þ þþ þ/ þþ
0 3.40 5.5 0.33 1.47 3.22 0 2.2 4.8 0 0 0 0 0 0
þþ þþ þ/ þ þþ þþ þþ
0.25% MP and 0.5% PP
0.375% MP and 0.75% PP
0.5% MP and 1% PP
1% PP and 0.5% MP and 5% Ca propionate
D: average of colony diametral growth (cm) development on three Whatman paper replicates (0 ¼ without development and 5.5 ¼ diameter equal or superior than paper discs). G: growth of fungi (, without any development; þ/, hyphae development; þ, hyphae and conidial development; þþ, colony 2 cm).
2.3. Deacidificant The paper deacidificant selected for this study was a 5% (w/v) solution of calcium propionate, as recommended by Zappala` (1990). 2.4. Methyl and propyl parabens mixtures In order to treat paper samples four different mixtures of methyl paraben (MP) and propyl paraben (PP), in 85% (w/w) ethanol– water, were tested: 0.5% MP and 0.25% PP, 0.25% MP and 0.5% PP, 0.375% MP and 0.75% PP, and 0.5% MP and 1% PP. A fifth solution with 5% of calcium propionate (the deacidificant) and 0.5% MP and 1% PP was also tested. 2.5. Evaluation of fungal growth on paper previously treated with different mixtures of parabens The experimental procedure for testing fungal resistance of treated paper was based on the ASTM D 2020-92 standard. Each experiment consisted of nine glass petri dishes (B ¼ 15 cm) with PDA at the bottom and three Whatman paper discs (B ¼ 55 mm) on top, as shown in Fig. 1. These petri dishes were divided into three groups of three dishes each. One group had untreated paper samples, the second group had paper samples previously immersed in the solvent (85% [w/w] ethanol–water), and the third group had paper immersed in parabens mixtures. For each of these groups, the paper samples inside one petri dish were inoculated with a 0.5-ml conidial suspension of Cladosporium sp. and the paper samples of another petri dish were inoculated with a 0.5-ml conidial suspension of P. corylophilum. The remaining paper samples were not inoculated with fungi, to serve as a control. A total of five experiments were conducted using the different treatments (mixtures of parabens) as indicated in Section 2.3. All experiments were conducted over 15 days at 24 C. Fungal development was determined daily by visual examination, following the ASTM D 2020-92 standard recommendations, and the diameter of growth of each colony was measured. The percentage of growth inhibition (% inhibition) was calculated from the following formula adapted from Ansari et al., 1990
% inhibition ¼
Dc Dt 100 Dc
where Dc ¼ average results of diametrical growth of the fungus in control (cm). Dt ¼ average results of diametrical growth of the fungus in treatment (cm). 2.6. Evaluation of efficacy of the mixtures in the treatment of contaminated paper The mixture of 0.5% MP and 1% PP and the same mixture with 5% calcium propionate were tested in order to evaluate their efficacy in treating contaminated paper documents. For this experiment the first step was the development of fungi on Whatman paper. Paper discs were sterilized and then inoculated with 300 ml of spore mycelial suspension of Cladosporium sp. and P. corylophilum, at 20 C 5 C and 97 2% relative humidity. Half of the contaminated paper discs were immersed in the 0.5% MP and 1% PP mixture and the other half were immersed in the same mixture with 5% calcium propionate. Afterwards all the samples were placed on petri dishes of PDA according to the scheme of Fig. 2. Contaminated paper samples without any treatment were also considered in this experiment as control samples. All six dishes were incubated at 24 C in the dark for 15 days, after which the fungi development was observed. 2.7. Paper properties Changes in paper properties after the treatment with 0.5% MP and 1% PP and the same mixture with 5% calcium propionate were evaluated in terms of chromatic measurements, pH, and tensile strength. 2.7.1. Chromaticity measurements Colour changes were evaluated by measuring the chromatic coordinates according to the CIE L* a* b* Colour System with Data Color International – Microflash, using D65 illuminant.
Table 2 Percentage of inhibition of fungal growth, after 15 days of incubation, calculated for the different treatments Fungus treatments
Cladosporium sp.
P. corylophilum
0.5% MP and 0.25% PP 0.25% MP and 0.5% PP 0.375% MP and 0.75% PP 0.5% MP and 1% PP 0.5% MP and 1% PP and 5% calcium propionate
32% 59% 55% 100% 100%
34% 41% 13% 100% 100%
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2.7.2. Hydrogen ion concentration (pH) of paper extracts (cold extraction method) This measurement was carried out using TAPPI standard T509 om-02, with a pH MeterLab PHM 240 pH/ion METER. 2.7.3. Tensile strength Tensile strength resistance was measured following TAPPI standard T 494 om-01 using a SHIMADZN AG-50 KNG elongation apparatus.
Table 3 Colorimetric alteration measured in Whatman paper due to the treatment with the solution of 0.5% MP and 1% PP and the same solution with 5% calcium propionate
DL* Whatman #1 treated with 0.5% MP and 1% PP Whatman #1 treated with 0.5% MP and 1% PP and 5% calcium propionate
Db*
DE*
0.21
Da* 0.36
3.90
3.92
0.28
0.02
0.78
0.83
4. Results and discussion All treatments showed some capability of fungal growth inhibition (Tables 1 and 2). In the first three treatments (0.5% MP and 0.25% PP, 0.25% MP and 0.5% PP, 0.375% MP and 0.75% PP) a tendency toward an irregular colony development was observed. However, 100% of fungal growth inhibition for the two species was found for the mixture of 0.5% MP and 1% PP (Table 2). The same result was obtained when the deacidificant was added to this mixture. This treatment was efficient for fungal growth inhibition during more than 15 days of incubation. All control tests (untreated paper and paper with solvent) showed a normal fungal development. These results demonstrate that parabens mixtures with the best inhibition percentage were efficient for preventive paper treatment. Fig. 3 presents the results of the experiment carried out with a mixture of 0.5% MP and 1% PP and the same mixture with 5% calcium propionate to evaluate the efficacy of these treatments on contaminated paper documents, after 15 days of incubation. It can be seen that in the treated paper there was no fungal growth. This shows that these treatments are very efficient in inhibiting fungal growth. Table 3 shows the Whatman paper change in colour due to the treatment with the solution of 0.5% MP and 1% PP and the same
solution with 5% calcium propionate. It can be seen that there is a small yellowing of the paper treated with 0.5% MP and 1% PP (DE* ¼ 3.92). However, when the deacidificant was added to the mixture an insignificant colour change was observed (DE* ¼ 0.83) (Johnston-Feller, 2001). Table 4 shows the pH values found for the paper samples with and without treatments with parabens mixtures. The results indicate a small increase in the paper pH due to the treatments. These treatments did not acidify the paper; in fact the pH values obtained are above the recommendation of 7.5 proposed by ISO 9706 E (1994). Fig. 4 presents the tensile strength resistance (N/m) of the paper samples with and without treatments. From the examination of these results we can observe that treated papers allowed a higher deformation (Whatman paper ¼ 2.48%; Whatman paper with 0.5% MP and 1% PP ¼ 2.79%; Whatman paper with 0.5% MP and 1% PP and 5% calcium propionate ¼ 2.95%). Paper treated with parabens but without the calcium propionate support a lower tension (Whatman paper ¼ 2523 184.4 N/m; Whatman paper with 0.5% MP and 1% PP ¼ 1846.5 87.85 N/m). Therefore, the addition of the deacidificant is important in order to maintain the paper strength (Whatman paper with 0.5% MP and 1% PP and 5% calcium propionate ¼ 2484 113.03 N/m).
Fig. 3. Photographic results of the experiment conducted to test the efficacy of two mixtures in the treatment of contaminated paper.
E.R. Neves et al. / International Biodeterioration & Biodegradation 63 (2009) 267–272 Table 4 Values of pH obtained in paper samples with and without treatments with parabens pH Whatman #1 Whatman #1 treated with 0.5% MP and 1% PP Whatman #1 treated with 0.5% MP and 1% PP and 5% calcium propionate
6.61 0.23 7.99 0.11 7.89 0.12
Fig. 4. Tensile strength resistance curves of the paper samples with and without treatments with paraben mixtures.
The addition of parabens to cellulose polymers is not well studied. However, the addition of these compounds to polymeric films, specifically polyethylene films, showed a diminution of tensile strength until rupture (Dobia´sˇ et al., 2000). The plasticizing effect of methyl paraben in a polymer was also evaluated by Wu and McGinity (1999), who verified some fragility in the polymer, but greater flexibility. In conclusion, the mixture of 0.5% MP and 1% PP with 5% calcium propionate is very efficient for inhibition of fungal growth on previously treated paper and also in the treatment of contaminated paper. The results also showed no significant changes in the paper properties due to the use of this treatment. This indicates that the mixture of 0.5% MP and 1% PP with 5% calcium propionate can be used both as a preventive method to avoid fungal growth on paper and as a treatment for paper already infected by fungi. This mixture has the advantage of being a multi-purpose solution for the treatment of acidified and biocontaminated paper documents. Nevertheless, further studies are needed to consider the influence of these treatments on paper after accelerated aging.
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Antifungal effect of different methyl and propyl paraben mixtures on the treatment of paper biodeterioration Eva Raquel Neves a, Stephan Scha¨fer a, Alan Phillips b, Joa˜o Canejo c, Maria Filomena Macedo a, * a
˜o e Restauro, Faculdade de Cieˆncias e Tecnologia, Universidade Nova de Lisboa, Monte da Caparica, 2829-516 Caparica, Portugal Departamento de Conservaça ˜o Auto ´noma de Biotecnologia, Faculdade de Cieˆncias e Tecnologia, Universidade Nova de Lisboa, Monte da Caparica, 2829-516 Caparica, Portugal Secça c Departamento de Cieˆncias dos Materiais, Faculdade de Cieˆncias e Tecnologia, Universidade Nova de Lisboa, Monte da Caparica, 2829-516 Caparica, Portugal b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 April 2008 Accepted 7 July 2008 Available online 25 November 2008
With many important artistic works and documents made of paper, and thus susceptible to biodeterioration by fungi, research is required in an effort to replace toxic chemical products with other more benign ones. In this work the antifungal effect of methyl and propyl paraben mixtures at different concentrations was evaluated. The fungi used in the experiments were a Cladosporium species and Penicillium corylophilum, both of which are well known as paper-biodeteriorating fungi. The results demonstrate that a mixture of 0.5% methyl paraben and 1% propyl paraben, in 85% ethanolic solution, is the lowest concentration necessary to provide an efficient antifungal action. A deacidification agent, 5% calcium propionate, was added to this mixture to produce a multi-purpose formulation to treat acidification and fungal contamination of paper documents. Tests carried out on paper samples before and after application of this mixture showed only a minor increase in yellowing and a slight decrease in tensile strength, while substantially raising the pH, and thus the alkaline reserve, and also a slight increase in the percentage of deformation. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Paper Antifungal Parabens Cladosporium Penicillium corylophilum
1. Introduction Paper is the main material of large artistic and document collections. It is also the most significant carrier of information for many centuries. However, given its organic nature, paper suffers from biodeterioration. Fungi are an almost daily contaminant on paper collections. Infestation is fostered by inadequate storage and display conditions, which allow conidia dispersed in the air to fall on damp and dirty papers (Florian, 1997; Maggi et al., 2000; Lugauskas and Krikstaponis, 2004); mould growth starts when relative humidity and temperature are favourable for spore germination (Caneva et al., 1991). Microfungi are the main microorganisms responsible for paper biodeterioration (Zyska, 1997, 2002; Adelantado et al., 2005). The activity of fungi on paper can produce several types of damage, such as different coloured stains (Szczepanowska and Lovett, 1992; Aranyanak, 1995; Arai, 2000), discolouration of pigments and inks, and changes in the chemical and physical properties of the paper (Caneva et al., 1991; Nitte´rus, 2000). Traditionally, conservators used fungicidal treatments that involved toxic and potentially damaging chemicals to inhibit fungus growth on paper. Some studies propose replacing these
* Corresponding author. Tel./fax: þ351 21 294 83 22. E-mail address: [email protected] (M.F. Macedo). 0964-8305/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibiod.2008.07.011
traditional antifungal agents with others that are less toxic (Dersarkissian and Goodberry, 1980; Fabbri et al., 1997; Bubiniene`, 1999; Rakotonirainy et al., 1999; Ricelli et al., 1999; Silva et al., 2006). Nowadays, antifungal agents with low toxicity and high efficacy are already used in the cosmetic, food, and pharmaceutical industries. Parabens (p-hydroxybenzoates) are one of the most common antifungal and preservative agents used in these industries (Rastogi, 2000; Perlovich et al., 2005; Zhang et al., 2005). Parabens are already largely studied, possess minimal side effects, and have low costs associated with them (Reynolds, 1996; Doron et al., 2001). They are generally used in combination, the most common combination being methyl and propyl parabens (Soni et al., 2005). Paper documents and artistic works containing cellulose also suffer from the acidification process. This is due to the degradation of cellulose that generates aliphatic acids such as acetic, formic, oxalic, and lactic acids, when aging. Nowadays, deacidification treatment is a usual procedure in paper conservation. Manual treatments are normally by baths with aqueous solutions of alkaline salts (calcium or magnesium carbonate or calcium hydroxide) (Dupont et al., 2002; Cheradame et al., 2003; Sundholm and Tahvanainen, 2003; Zappala` and Stefani, 2005). However, there are paper documents and artistic works with water susceptible media and inks that make these procedures useless. Therefore it is necessary to improve non-aqueous deacidification treatments. There are some studies that show the possibility of using new
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Fig. 1. Diagram of the experimental procedure used for the evaluation of fungal resistance of paper previously treated with paraben mixtures.
deacidification products, soluble in ethanol, such as calcium propionate (Zappala`, 1990) or aminosilanes (Cheradame et al., 2003). The combination of a paraben mixture with a deacidificant would result in a multi-purpose formulation for the treatment of acidified and biocontaminated paper documents. The present work focused on the study of the antifungal action of methyl and propyl parabens and the subsequent addition of a deacidification agent. The antifungal effect of different concentrations of methyl and propyl paraben mixtures was evaluated with the goal to select the lowest inhibitory concentration mixture with the highest antifungal efficiency, and to evaluate the changes in paper properties due to the use of the selected mixture together with a deacidification agent.
2. Materials and methods The experimental work started with the evaluation of fungal resistance of paper previously treated with different mixtures of methyl and propyl parabens. The most efficient mixture was selected and a deacidificant was added. Then a study was performed in order to check if this mixture was efficient in the treatment of paper previously contaminated with fungi. Finally, changes in paper properties due to the treatment with the selected mixture were evaluated.
2.1. Paper Whatman filter paper #1 was used for its high pure cellulose content (98% w/w) and also because its chemical, physical, and structural characteristics are well known. Moreover, it is additivefree and serves as a point of reference with respect to other experimental works since it is widely used for laboratory testing (Adamo et al., 1998, 2003; Canhoto et al., 2004; Vives et al., 2004). 2.2. Fungal strains and culture media After an exhaustive search of the literature on the occurrence of fungi on paper documents, it was found that the most frequent genera were Aspergillus, Chaetominum, Cladosporium, Penicillium, and Trichoderma (Caneva et al., 1991; Rebrikova and Manturovskaya, 1993; Aranyanak, 1995; Florian, 1997; Zyska, 1997; Florian and Manning, 2000; Maggi et al., 2000; Szczepanowska and Cavaliere, 2000; Bonaventura et al., 2003; Corte et al., 2003; Lugauskas and Krikstaponis, 2004; Silva et al., 2006). Penicillium corylophilum Dierckx and a Cladosporium sp., isolated from contaminated paper documents found in the Direcça˜o Geral de Edifı´cios e Monumentos Nacionais Archive collection (Lourenço et al., 2005) were selected for this study. The isolated strains were maintained on potato dextrose agar (PDA) at 20 C. To inoculate paper samples a suspension was prepared of semi-solid detergent agar (SDA) with fungal conidia of each strain.
Fig. 2. Schematic representation of the experiment conducted to test the efficacy of two mixtures in the treatment of contaminated paper.
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Table 1 Development of the fungi Cladosporium and P. corylophilum on paper previously treated with different mixtures of MP and PP Paper
Paper and solvent
Cladosporium
P. corylophilum
Cladosporium
Treated paper P. corylophilum
Cladosporium
P. corylophilum
Treatments
Days
D
G
D
G
D
G
D
G
D
G
D
G
0.5% MP and 0.25% PP
2 8 15 2 8 15 2 8 15 2 8 15 2 8 15
2.33 5.50 5.5 3.20 4.27 5.5 2.33 5.23 5.5 3.20 3.60 5.5 3.20 3.60 5.5
þþ þþ þþ þþ þþ þþ þ/ þþ þþ þþ þþ þþ þþ þþ þþ
2.03 5.17 5.5 4.40 5.17 5.5 2.03 5.5 5.5 4.43 4.53 5.5 4.43 4.53 5.5
þþ þþ þþ þþ þþ þþ þ/ þþ þþ þþ þþ þþ þþ þþ þþ
2.00 4.90 5.5 3.50 4.33 5.5 0 4.97 5.5 3.50 3.87 5.5 3.50 3.87 5.5
þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ
1.93 5.5 5.5 4.47 4.30 5.5 0 5.5 5.5 3.47 4.87 5.5 3.47 4.87 5.5
þ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ þþ
0 3.73 5.5 0.67 1.57 3.00 0 0 2.47 0 0 0 0 0 0
þþ þþ þ/ þ þþ þ/ þþ
0 3.40 5.5 0.33 1.47 3.22 0 2.2 4.8 0 0 0 0 0 0
þþ þþ þ/ þ þþ þþ þþ
0.25% MP and 0.5% PP
0.375% MP and 0.75% PP
0.5% MP and 1% PP
1% PP and 0.5% MP and 5% Ca propionate
D: average of colony diametral growth (cm) development on three Whatman paper replicates (0 ¼ without development and 5.5 ¼ diameter equal or superior than paper discs). G: growth of fungi (, without any development; þ/, hyphae development; þ, hyphae and conidial development; þþ, colony 2 cm).
2.3. Deacidificant The paper deacidificant selected for this study was a 5% (w/v) solution of calcium propionate, as recommended by Zappala` (1990). 2.4. Methyl and propyl parabens mixtures In order to treat paper samples four different mixtures of methyl paraben (MP) and propyl paraben (PP), in 85% (w/w) ethanol– water, were tested: 0.5% MP and 0.25% PP, 0.25% MP and 0.5% PP, 0.375% MP and 0.75% PP, and 0.5% MP and 1% PP. A fifth solution with 5% of calcium propionate (the deacidificant) and 0.5% MP and 1% PP was also tested. 2.5. Evaluation of fungal growth on paper previously treated with different mixtures of parabens The experimental procedure for testing fungal resistance of treated paper was based on the ASTM D 2020-92 standard. Each experiment consisted of nine glass petri dishes (B ¼ 15 cm) with PDA at the bottom and three Whatman paper discs (B ¼ 55 mm) on top, as shown in Fig. 1. These petri dishes were divided into three groups of three dishes each. One group had untreated paper samples, the second group had paper samples previously immersed in the solvent (85% [w/w] ethanol–water), and the third group had paper immersed in parabens mixtures. For each of these groups, the paper samples inside one petri dish were inoculated with a 0.5-ml conidial suspension of Cladosporium sp. and the paper samples of another petri dish were inoculated with a 0.5-ml conidial suspension of P. corylophilum. The remaining paper samples were not inoculated with fungi, to serve as a control. A total of five experiments were conducted using the different treatments (mixtures of parabens) as indicated in Section 2.3. All experiments were conducted over 15 days at 24 C. Fungal development was determined daily by visual examination, following the ASTM D 2020-92 standard recommendations, and the diameter of growth of each colony was measured. The percentage of growth inhibition (% inhibition) was calculated from the following formula adapted from Ansari et al., 1990
% inhibition ¼
Dc Dt 100 Dc
where Dc ¼ average results of diametrical growth of the fungus in control (cm). Dt ¼ average results of diametrical growth of the fungus in treatment (cm). 2.6. Evaluation of efficacy of the mixtures in the treatment of contaminated paper The mixture of 0.5% MP and 1% PP and the same mixture with 5% calcium propionate were tested in order to evaluate their efficacy in treating contaminated paper documents. For this experiment the first step was the development of fungi on Whatman paper. Paper discs were sterilized and then inoculated with 300 ml of spore mycelial suspension of Cladosporium sp. and P. corylophilum, at 20 C 5 C and 97 2% relative humidity. Half of the contaminated paper discs were immersed in the 0.5% MP and 1% PP mixture and the other half were immersed in the same mixture with 5% calcium propionate. Afterwards all the samples were placed on petri dishes of PDA according to the scheme of Fig. 2. Contaminated paper samples without any treatment were also considered in this experiment as control samples. All six dishes were incubated at 24 C in the dark for 15 days, after which the fungi development was observed. 2.7. Paper properties Changes in paper properties after the treatment with 0.5% MP and 1% PP and the same mixture with 5% calcium propionate were evaluated in terms of chromatic measurements, pH, and tensile strength. 2.7.1. Chromaticity measurements Colour changes were evaluated by measuring the chromatic coordinates according to the CIE L* a* b* Colour System with Data Color International – Microflash, using D65 illuminant.
Table 2 Percentage of inhibition of fungal growth, after 15 days of incubation, calculated for the different treatments Fungus treatments
Cladosporium sp.
P. corylophilum
0.5% MP and 0.25% PP 0.25% MP and 0.5% PP 0.375% MP and 0.75% PP 0.5% MP and 1% PP 0.5% MP and 1% PP and 5% calcium propionate
32% 59% 55% 100% 100%
34% 41% 13% 100% 100%
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2.7.2. Hydrogen ion concentration (pH) of paper extracts (cold extraction method) This measurement was carried out using TAPPI standard T509 om-02, with a pH MeterLab PHM 240 pH/ion METER. 2.7.3. Tensile strength Tensile strength resistance was measured following TAPPI standard T 494 om-01 using a SHIMADZN AG-50 KNG elongation apparatus.
Table 3 Colorimetric alteration measured in Whatman paper due to the treatment with the solution of 0.5% MP and 1% PP and the same solution with 5% calcium propionate
DL* Whatman #1 treated with 0.5% MP and 1% PP Whatman #1 treated with 0.5% MP and 1% PP and 5% calcium propionate
Db*
DE*
0.21
Da* 0.36
3.90
3.92
0.28
0.02
0.78
0.83
4. Results and discussion All treatments showed some capability of fungal growth inhibition (Tables 1 and 2). In the first three treatments (0.5% MP and 0.25% PP, 0.25% MP and 0.5% PP, 0.375% MP and 0.75% PP) a tendency toward an irregular colony development was observed. However, 100% of fungal growth inhibition for the two species was found for the mixture of 0.5% MP and 1% PP (Table 2). The same result was obtained when the deacidificant was added to this mixture. This treatment was efficient for fungal growth inhibition during more than 15 days of incubation. All control tests (untreated paper and paper with solvent) showed a normal fungal development. These results demonstrate that parabens mixtures with the best inhibition percentage were efficient for preventive paper treatment. Fig. 3 presents the results of the experiment carried out with a mixture of 0.5% MP and 1% PP and the same mixture with 5% calcium propionate to evaluate the efficacy of these treatments on contaminated paper documents, after 15 days of incubation. It can be seen that in the treated paper there was no fungal growth. This shows that these treatments are very efficient in inhibiting fungal growth. Table 3 shows the Whatman paper change in colour due to the treatment with the solution of 0.5% MP and 1% PP and the same
solution with 5% calcium propionate. It can be seen that there is a small yellowing of the paper treated with 0.5% MP and 1% PP (DE* ¼ 3.92). However, when the deacidificant was added to the mixture an insignificant colour change was observed (DE* ¼ 0.83) (Johnston-Feller, 2001). Table 4 shows the pH values found for the paper samples with and without treatments with parabens mixtures. The results indicate a small increase in the paper pH due to the treatments. These treatments did not acidify the paper; in fact the pH values obtained are above the recommendation of 7.5 proposed by ISO 9706 E (1994). Fig. 4 presents the tensile strength resistance (N/m) of the paper samples with and without treatments. From the examination of these results we can observe that treated papers allowed a higher deformation (Whatman paper ¼ 2.48%; Whatman paper with 0.5% MP and 1% PP ¼ 2.79%; Whatman paper with 0.5% MP and 1% PP and 5% calcium propionate ¼ 2.95%). Paper treated with parabens but without the calcium propionate support a lower tension (Whatman paper ¼ 2523 184.4 N/m; Whatman paper with 0.5% MP and 1% PP ¼ 1846.5 87.85 N/m). Therefore, the addition of the deacidificant is important in order to maintain the paper strength (Whatman paper with 0.5% MP and 1% PP and 5% calcium propionate ¼ 2484 113.03 N/m).
Fig. 3. Photographic results of the experiment conducted to test the efficacy of two mixtures in the treatment of contaminated paper.
E.R. Neves et al. / International Biodeterioration & Biodegradation 63 (2009) 267–272 Table 4 Values of pH obtained in paper samples with and without treatments with parabens pH Whatman #1 Whatman #1 treated with 0.5% MP and 1% PP Whatman #1 treated with 0.5% MP and 1% PP and 5% calcium propionate
6.61 0.23 7.99 0.11 7.89 0.12
Fig. 4. Tensile strength resistance curves of the paper samples with and without treatments with paraben mixtures.
The addition of parabens to cellulose polymers is not well studied. However, the addition of these compounds to polymeric films, specifically polyethylene films, showed a diminution of tensile strength until rupture (Dobia´sˇ et al., 2000). The plasticizing effect of methyl paraben in a polymer was also evaluated by Wu and McGinity (1999), who verified some fragility in the polymer, but greater flexibility. In conclusion, the mixture of 0.5% MP and 1% PP with 5% calcium propionate is very efficient for inhibition of fungal growth on previously treated paper and also in the treatment of contaminated paper. The results also showed no significant changes in the paper properties due to the use of this treatment. This indicates that the mixture of 0.5% MP and 1% PP with 5% calcium propionate can be used both as a preventive method to avoid fungal growth on paper and as a treatment for paper already infected by fungi. This mixture has the advantage of being a multi-purpose solution for the treatment of acidified and biocontaminated paper documents. Nevertheless, further studies are needed to consider the influence of these treatments on paper after accelerated aging.
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