A.F. Mohd-Adnan and R.M. Taha Institute of Biological Sciences, University of Malaya, Kuala Lumpur, Malaysia, and

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1 Effects of UV-B irradiation on poly (vinyl alcohol) and Ixora siamensis anthocyanins-coated glass N.A. Mat Nor and N. Aziz Centre for Ionics, Department of Physics, University of Malaya, Kuala Lumpur, Malaysia A.F. Mohd-Adnan and R.M. Taha Institute of Biological Sciences, University of Malaya, Kuala Lumpur, Malaysia, and A.K. Arof Centre for Ionics, Department of Physics, University of Malaya, Kuala Lumpur, Malaysia Abstract Purpose The purpose of this paper is to evaluate the potential of natural colourants from fruits of Ixora siamensis for coating applications, to study its glossiness and effectiveness against UV-B irradiation. Design/methodology/approach In this study, natural colourants from the fruits of Ixora siamensis were extracted using trifluoroacetic acid-methanol solution. Anthocyanins and organic acid variants were mixed together to form co-pigments. Different concentrations of ferulic and gallic acid co-pigments were added to a blended solution of poly (vinyl alcohol), PVA and anthocyanin (from Ixora siamensis) to form a coating system. The coatings were exposed to UV-B irradiation at room temperature in air using a UV-lamp which emitted radiation at 312 nm. The effects of UV-B irradiation on the coating system were evaluated using glossiness test and UV-visible spectroscopy. Findings Anthocyanins are unstable and can quickly lose their colour. One of the methods of preserving the stability of these pigments is by co-pigmentation. Co-pigmentation of anthocyanin with organic acid variants resulted in an increase in both hyperchromic effects (DA) and bathochromic shifts (Dl). In this study, ferulic acids yielded better results compared to gallic acids. Research limitations/implications Samples with co-pigmentation give better result compared to the untreated samples. The addition of.5 and 1. per cent ferulic acid improves the gloss properties and resistivity of the samples towards the UV irradiation. Thus, in order to study the effectiveness of ferulic acid as additive and improving the properties of the samples, the percentage of ferulic acid added and exposure time could be increased. Practical implications The method developed provided a simple and efficient solution for improving the UV resistance of anthocyanin blend with poly (vinyl alcohol), PVA UV absorber. Effect of ferulic acid as UV absorber, if added in more concentration, can be further studied for optimization. Social implications The social implication is the use of local plant species as a low cost source of natural pigments in coating system. Originality/value The method for improving the resistance towards UV irradiation of anthocyanin blend with poly (vinyl alcohol), PVA was novel and could find numerous applications for natural product based on plant pigment. Keywords Anthocyanins, Ixora siamensis, Co-pigment, UV-B, Glossiness, UV-visible spectroscopy, Ultraviolet radiation, Coatings technology, Coating processes Paper type Research paper Introduction There has been a great increase in the utilisation of natural plant pigments to replace synthetic colorants because of health and safety reasons. However, natural colorants have lower resistance against degradation and is less stable to oxidation, temperature changes and UV irradiation compared to synthetic colorants (Fabre et al., 1993; Navidra, 22; Bakhshayeshi et al., 26). This continual increase in the utilisation of natural colorants makes the search and development of new and alternative The current issue and full text archive of this journal is available at 42/3 (213) q Emerald Group Publishing Limited [ISSN ] [DOI 1.118/ ] sources of natural colorants worthwhile (Zhong et al., 25; Laleh et al., 26). Anthocyanins (glycosylated polyhydroxy derivatives of 2-phenylbenzopyrylium salts) are natural, watersoluble, non-toxic pigments responsible for some of the colours of fruits, vegetables, flowers, and other plant tissues (Mazza and Brouillard, 199). The basic structure of anthocyanin is shown in Figure 1. Anthocyanin has been regarded as a safe colorant for use since ancient times. The variety of their colours, such as orange, red, maroon and blue, makes them an attractive alternative to synthetic colouring agents in food industries (Francis, 1989). A solution of anthocyanin may exhibit different colours, depending on its ph. Below ph 2, anthocyanins appear red due to the presence of flavylium cations. At ph 6, the flavylium cation is converted into purple quinonoidal bases. These compounds are labile and can transform to the colourless The authors would like to thank the University of Malaya for financial assistance: postgraduate grant research (PPP) PS314/29C. 163

2 Figure 1 Basic structures of anthocyanin A + O1 Source: Konczak and Zhang (24) C 5 4 carbinol pseudobases and chalcone pseudobases (Abyari et al., 26; Setareh et al., 27). Isolated anthocyanins in neutral aqueous solutions are unstable and quickly lose their colour. Therefore, other agents must be added to anthocyanin solutions so that they maintain their colour (Yoshida et al., 23). Reports (Mazza and Brouillard, 199; Davies and Mazza, 1993) suggested co-pigmentation as a means of preserving the colour of anthocyanin solutions. A co-pigment is usually colourless, but when added to an anthocyanin solution can greatly enhance the colour. The co-pigment may be a secondary metabolite, amino acid, organic acid, nucleotide, polysaccharide, metal, or another of the anthocyanins (Mazza and Brouillard, 199). The exact mechanism of co-pigmentation is poorly known. Water often leads to colour loss. Hence, co-pigmentation was thought to protect the C-2 chromophore in the pyran ring of the colorant against nucleophilic attack by water (Awika, 28). Co-pigments are electron-rich p systems and are able to associate with the comparatively electron-poor flavylium ion. The complexation protects the flavylium ion from nucleophilic attack by water (Yoshida et al., 23). The water attack converts the flavylium ion into a colourless pseudobase, which consequently results in colour loss. The complexation of anthocyanin with a co-pigment results in hyperchromic effect (DA) and a bathochromic shift (Dl) (Chen and Hrazdina, 1981; Mazza and Miniati, 1993). The hyperchromic effect increases colour intensity while the bathochromic shift alters the wavelength of maximum absorbance (Bakowska et al., 23). In this study, fruits from Ixora siamensis were chosen as the anthocyanin source. Ixora siamensis is locally known as pokok jenjarum and it is a genus of the Rubiaceae family. This family comprises about 3-4 species (Fosberg and Sachet, 1989). The greatest diversity in Asia is Malaysia (Walter and Gillett, 1998) in particular. The plant species in the Rubiaceae genus is well known for their beautiful clusters of flowers in different shades of red, pink and yellow (De Block, 1998). Ixora siamensis are short bushy plants and are sometimes trimmed into hedges. The fruits are eaten and the flowers are used as a flavouring agent. However, due to the commercialisation of this species as ornamental plants, the utilisation of its fruit has been overlooked. The potential of the fruit as a source of natural colorants has yet to be explored ' 1' R 1 B 6' 3' 4' 5' R 2 The anthocyanin natural colorant from Ixora siamensis was used to colour poly (vinyl alcohol), PVA. PVA is water-soluble, has high water absorption capability (Shafee and Naguib, 23; Li et al., 25) and can easily form films. The hydroxyl groups in PVA make it strongly hydrophilic. It can form a hydrogel with wide applications in medicine and pharmaceuticals (Paradossi et al., 23; Oh et al., 24). Coloured polymeric materials are degraded when exposed to solar UV radiation, heat, moisture and other stress factors. The thinning of the stratospheric ozone layer has led to an increase in the level of ultraviolet-b (UV-B nm) radiation reaching the earth s surface. Ultraviolet-B irradiation stimulates the production of reactive oxygen species (ROS) (Casati and Walbot, 23) and antioxidant defences (Rozema et al., 1997; Jansen et al., 1998). It has been proposed that ROS function as destructive radicals during UV-B responses (Li et al., 25). The UV-B photons cause cellular damage by generating photoproducts in DNA (Sinha and Hader, 22) and directly damaging proteins (Gerhardt et al., 1999). Photochemical degradation of the coloured polymeric material leads to physical changes in the films, such as a decrease in thickness, loss of gloss, and cracking. Due to its promising antioxidant activity, gallic acid is added to various skin care products in the form of natural herbal extracts. It is also used as a standard substance in many antioxidant assays. Gallic acid has been shown to possess scavenging activities against several radicals: for example, superoxide anions, hydroxyl radicals, and singlet oxygen or peroxyl radicals. It is also able to protect cells from damage induced by UV-B or ionizing irradiation (Sawa et al., 1999). However, the main limitation of gallic acid is its poor water solubility (Phiriyawirut and Phaechamud, 212). Application of FA also could be in cosmetic formulations, in which to avoid the oxidation of their components, but it can also be used as a preservative agent in food packaging. Puoci et al. (21) in his work, reports that the direct polymerization of an antioxidant molecule and a suitable monomer in the presence of water-soluble redox initiators. In particular, methacrylic acid was copolymerized with ferulic acid, one of the most ubiquitous phenolic compounds in nature to form methacrylic-ferulic acid copolymer (PMAA-FA). Because of its ability to inhibit the autoxidation of oils, this molecule has been largely used as a food preservative. It also constitutes the active ingredient in many skin lotions and sunscreens designed for photoprotection (Trombino et al., 29). Puoci et al. (21) reported that, the applicability of a polymeric derivative of ferulic acid as photo-protecting agent to be used in cosmetic formulations was demonstrated. The presence of a broad absorption band in the spectral region between 375 and 25 nm makes the copolymer a good protecting agent against the damages caused by UVA and UVB radiation. According to previous study (Ou et al., 25), FA acid has been used to cross-link starch-chitosan blend films and its mechanical, thermal, physico-chemical properties and morphological features have been characterised for their application as edible films and coatings. Ferulic acid and its oxide, quinoid ferulic acid can cross-link polysaccharide molecules and thereby help to improve the properties of carbohydrate-based edible films. Ferulic acid can enhance the cross-linking between polysaccharides through several mechanisms; through free radical mediated cross-linking, by esterification with the hydroxyl groups of chitosan and starch or by quinone-mediated reactions. There were shift in absorbance 164

3 reading indicates the formation a ferulic acid-protein cross-link that may enhance the shelf life of foods by decreasing oxygen permeability. The aim of this work was to evaluate the potential of anthocyanins from the fruit of Ixora siamensis as a natural colorant coating. This study also examines the enhancement and stabilisation of UV-absorbing co-pigmented anthocyanins blended with PVA against UV-B irradiation since there are only limited reports on the effect of UV-B irradiation on the polymeric colour-co-pigment complex. In this study, two UV absorbers were used as co-pigments: ferulic and gallic acids which are rarely used in a coating system. The glossiness and spectroscopic properties of the prepared samples were investigated before and after exposure to UV-B irradiation in the presence and absence of co-pigments. The flower and fruit of Ixora siamensis are shown in Figures 2 and 3, respectively. Figure 2 Flower of Ixora siamensis Materials and methods Plant material Fruits of Ixora siamensis were chosen as the source of natural colorant. These fruits were collected in Banting, Selangor. The fruits were sealed in polyethylene bags, covered with aluminium foil and kept in a freezer (2188C) before analysis to maintain their freshness. Pigment extraction The fruits of Ixora siamensis were taken out of freezer and left at room temperature for 3 min to defrost. 1 g of fruits were ground using a pestle and mortar and.5 per cent trifluoroacetic acid (TFA) in methanol solution was used to extract the natural colorant. The extraction was performed at low temperatures to avoid hydrolysis of the acyl groups in the anthocyanin structure and degradation. After extraction, the solution was centrifuged at 1, rpm for 3 min. The supernatant liquid was filtered using Whatman No. 1 paper to remove any traces of residues and the methanol content was removed by evaporation under reduced pressure at relatively low temperatures (, 38C). After evaporation, the combined aqueous concentrates were washed several times with ethyl acetate to remove chlorophyll, stilbenoids, less polar flavonoids and other non-polar compounds from the mixture. The solution was evaporated again in a vacuum chamber for two days until 5 per cent of the initial methanol volume was reached. The concentrate was then diluted. Figure 3 Fruits of Ixora siamensis Preparation of samples The diluted samples were then blended with 3 per cent PVA, and 1 ml of.5 and 1 per cent of ferulic and gallic acids were added, respectively, as the UV absorbers. The chemical structures of these compounds are shown in Figure 4. The solutions containing the mixture of anthocyanin blended with PVA and the UVabsorbers were applied onto the surface of glass slides (each 2.54 cm 7.62 cm.1 cm) using the same coaters to avoid variations in thickness. All samples were prepared in triplicate. UV-irradiation The prepared samples were subjected to glossiness test and spectrophotometric measurements. These samples were exposed to UV-B irradiation first by placing them under a UV lamp which emitted radiation at 312 nm. The distance between the sample and the light source was fixed at 5 cm where the irradiation intensity was lux. Figure 4 Structures of (a) ferulic and (b) gallic acids O CH 3 O O (a) Source: Rein (25) (b) 165

4 Measurement of gloss Gloss is associated with the capacity of a surface to reflect more light in some directions than others. The 68 geometry was used for all samples. The gloss reading for each sample was taken before and after exposure to UV-B irradiation using the gloss meter MG series (MG 6-F1). The glossiness measurements were taken every 1 h for 24 h. Spectrophotometric measurements The film coated on glass slides were exposed to UV irradiation for 3, 6, 9, 12 and 15 min. The absorption spectrum of the UV-exposed films was recorded using UV-Vis spectroscopy in the range of 2-8 nm. The Shimadzu UV-311PC spectrophotometer was used for this analysis. The absorbance was measured before and after UV irradiation for each sample. Results and discussion Glossiness is an optical property that is due to the interaction of light with the surface of a material. Figure 5 shows the effect of the.5 per cent UV absorbers. The glossiness of the PVA-pigment complex was initially higher than the co-pigmented complex. However, after 15 h of prolonged exposure to UV-B irradiation, the co-pigmented films exhibited higher glossiness. This indicates that the ferulic and gallic acids had absorbed the UV-B irradiation and that fewer ROS were produced to reduce the glossiness. This study showed that the type and concentration of the co-pigment are important factors in colour intensity and glossiness. It was found that the cinnamic acid-type (ferulic acid) UV absorber performed better as a co-pigment for providing stability to the anthocyanin pigment compared to the benzoic acid-type UV absorber (gallic acid). After 24 h of UV-B irradiation, the glossiness of the ferulic acid co-pigmented complex was 25 per cent higher than the pigmented polymer. Figure 6 shows the pigmented polymer with the addition of 1. per cent co-pigments. It can be observed that with the addition of a higher concentration of co-pigment, the glossiness after 24 h of irradiation was higher. The results obtained in this work are supported by the results of other works (Davies and Mazza, 1993; Asen et al., 1972), which showed that the co-pigmentation reaction is definitely dependent on the molar ratio added. Apart from a hyperchromic effect, bathochromic shifts were also observed on UV-B irradiation. Even without co-pigmentation, bathochromic shifts were observed and the shift increased with irradiation time as shown in Figure 7. Figure 5 Glossiness of the 3 per cent PVA-anthocyanin pigment with and without co-pigments after 24 h of UV irradiation Glossiness PVA + Pigment PVA + Pigment +.5% PVA + Pigment +.5% ferulic acid gallic acid Time (h) Figure 6 Gloss of the 3 per cent PVA-anthocyanin pigment with and without co-pigments after 24 h of UV irradiation Glossiness PVA + Pigment PVA + Pigment + 1.% PVA + Pigment + 1.% ferulic acid gallic acid Time (h) Figure 7 UV-Vis spectra of the 3 per cent PVA þ pigment without co-pigments after 12 min of UV irradiation at l max ¼ nm min 6 min 12 min 592.5, , , It may be inferred that the addition of co-pigment reduces the bathochromic shifts for this study (Figures 8-11). From the figures, it can be seen that after 2 h of UV-B irradiation the ferulic acid co-pigmented samples exhibited lower shifts than the gallic acid co-pigmented samples. This also supports the results for the hyperchromic effect and supports the inference that ferulic acid plays a better role than gallic acid as a UV absorber. These results are correlated with previous study by Gauche et al. (21), which also found that ferulic acid act Figure 8 UV-Vis spectra of the 3 per cent PVA þ pigment with.5 per cent ferulic acid after 12 min of UV irradiation at l max ¼ nm min 6 min 12 min 584, , ,

5 Figure 9 UV-Vis spectra of the 3 per cent PVA þ pigment with.5 per cent gallic acid after 12 min of UV irradiation at l max ¼ nm Figure 1 UV-Vis spectra of the 3 per cent PVA þ pigment with 1. per cent ferulic acid after 12 min of UV irradiation at l max ¼ nm Effects of UV-B irradiation on anthocyanins-coated glass min 6 min 12 min 576, , ,.2333 min 6 min 12 min 589, , , as a good UV absorber compared to gallic acid. Moreover, the outcome results of co-pigmentation also dependent on co-pigment concentration (Setareh et al., 27). The hyperchromic and bathochromic shifts result from the formation of a longer chromophore due to the intermolecular interactions between the co-pigment and anthocyanin. As the concentration of anthocyanin was constant for each solution, it was the co-pigment that determined the bathochromic and hyperchromic effects. In this co-pigmentation mechanism, ferulic and gallic acids prevented the degradation of anthocyanin-pva blends by absorbing and dissipating the absorbed energy. UV-B irradiation does not result in the production of singlet oxygen, instead it increase the formation of ROS which are extremely reactive (Eva and Imre, 1996). It was shown that ferulic acid has a stronger capability as a UV absorber and colour enhancer than gallic acid. This was due to its phenolic nucleus and an extended side chain conjugation, which readily forms a resonancestabilised phenoxy radical. Furthermore, the UV absorption by ferulic acid catalyses stable phenoxy radical formation and thereby increases its ability to terminate free radical chain reactions. Application in coating technology Figure 12 shows the picture of anthocyanin from fruits of Ixora siamensis blended with 3 per cent poly (vinyl alcohol), PVA on coated glass. Conclusions In order to stabilise the polymer-anthocyanin compound and reduce the rate of photodegradation, ferulic and gallic acids were used as UV absorbers. Ferulic acid is a better UV absorbpigment with polymer-anthocyanin complex increased the hyperchromic effects, indicating that ferulic acid gives Figure 12 Pictures of (a) sample without co-pigmentation and (b) samples with addition of 1 per cent ferulic acid on coated glass Figure 11 UV-Vis spectra of the 3 per cent PVA þ pigment with 1. per cent gallic acid after 12 min of UV irradiation at l max ¼ nm min 6 min 12 min 584.5, , , (a) (b) 167

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7 Trombino, S., Cassano, R., Bloise, E., Muzzalupo, R., Tavano, L. and Picci, N. (29), Synthesis and antioxidant activity evaluation of a novel cellulose hydrogel containing transferulic acid, Carbohydr. Polym., Vol. 75 No. 1, pp Walter, K.S. and Gillett, H.J. (Eds) (1998), The Plant Book, 2nd ed., Cambridge University Press, Cambridge. Yoshida, K., Okuno, R., Kameda, K., Mori, M. and Kondo, T. (23), Influence of E, Z-isomerization and stability of acylated anthocyanins under the UV irradiation, Biochem. Eng. J., Vol. 14 No. 3, pp Zhong, Y.C., Sun, M. and Corke, H. (25), Characterization and application of betalain pigments from plants of the Amaranthaceae, Trends Food Sci. Technol., Vol. 16 No. 9, pp About the authors N.A. Mat Nor obtained her Bachelor of Science at University Technology Mara (UiTM) and Master of Science degree from University of Malaya. Her research interest covers pigments from plants, plant tissue culture and natural coating. N. Aziz obtained her Bachelor of Science at University Technology Mara (UiTM) and Master of Science degree from University of Malaya. Her research interest covers pigments from plants, plant tissue culture and natural coating. A.F. Mohd-Adnan gained his first degree in Biotechnology from Liverpool John Moores University in 1995 and obtained his Master of Biotechnology degree from University of Malaya in 22. He subsequently obtained his Doctor of Engineering, specializing in degradation and recycling of polylactic acid from Kyushu Institute of Technology in 28. He is currently a senior lecturer at Institute of Biological Sciences, Faculty of Science, University of Malaya. R.M. Taha obtained her Phd degree from the University of Wales, Cardiff, in UK. She is currently Professor at the Institute of Biological Sciences, Faculty of Science in University of Malaya. Her research interest covers pigments from plants, plant biotechnology, plant morphogenesis, plant tissue culture and cellular behavior of plants in vivo and in vitro. A.K. Arof obtained his Master s degree in Science at University College of Swansea, Singleton Park and PhD at University of Malaya (UM). He is currently Professor and was Head of Physics, Faculty of Science at the University of Malaya from September 27 till June 211. His research interest covers solid state ionics (ionic conductors, polymer electrolytes, batteries, solar cells, fuel cells, supercapacitors) and coating technology. A.K. Arof is the corresponding author and can be contacted at: akarof@um.edu.my To purchase reprints of this article please reprints@emeraldinsight.com Or visit our web site for further details: 169