3. Results and discussion
3.1. Testing principles
The general approach of the suggested test is selective adsorption of synthetic dyes in a test system resulting in color changes in a drink sample.In particular, the main component of the test system was suggested to be a specifically developed adsorbent that provides an adsorption of synthetic food dyes and substantially does not interact with natural dyes of drinks.Different polymeric adsorbents meeting this criterion were tested. The test samples were divided into two groups: N - natural red wines and juices; S - model drinks made by addition to white wine or apple juice the predetermined amount of synthetic dyes to give the same color characteristics, i.e. intensity (I) and tint (T) as measured for the drinks of the first group. The exemplified compositions of natural drinks (N1eN3) and drinks containing synthetic dyes (S1eS3), the total amounts of dyes as well as the color intensity and tint of such drinks are presented in
Table 1. The said drinks samples were treated with different adsorbentfor 15 min in order to evaluate intensity and tint changes after treatment. The adsorbents used were different modifications of activated carbon, microcrystalline cellulose, DEAE-cellulose, polyamide,chitosan, chitin and Riosorb. The chitosan containing adsorbent Riosorb was specially developed in our previous study (Komissarchik & Nyanikova, 2010) and provides high adsorption activity towards synthetic food dyes and almost does not adsorb dyes from natural drinks. The structure of chitosan is shown schematically in Fig. 1.
Fig. 2 illustrates the IR-spectrum of chitosan containing adsorbent Riosorb. Riosorb has free amino groups providing interactions with negatively charged groups of the synthetic food dyes, e.g., sulfo groups contained in all of the synthetic dyes studied. Nevertheless the adsorbent structure does not provide adsorption of natural dyes contained in the natural drinks.In order to evaluate the described selectivity, we used color intensity and tint changes. To combine the color intensity and tint changes we developed the Synthetic Dyes Index (SDI) expressed as a product of the relative intensity change with the relative tint change multiplied by 100. According to the general approach, the more synthetic dyes are
contained in a drink, the more relative intensity and tint changes are, and the higher is the SDI value. Hence, the values of SDI are higher for the drinks containing synthetic dyes when compared to SDI values obtained for natural drinks.
Based on this logic, we suggest the measure of selectivity to be the difference in SDI obtained for two drinks having the same initial color intensity and tint but one containing synthetic dyes and another made of natural ingredients.
The test results have shown that the most adsorbents either adsorbed both synthetic and natural dyes (like activated carbon), or showed low adsorption activity towards synthetic dyes. The best selectivity was shown for chitosan containing adsorbents. In particularly, chitosan containing adsorbent Riosorb showed the outstanding adsorption of synthetic dyes represented by the SDI values, whereas SDI for natural drinks was the lowest of all the SDI sobtained for other adsorbents.The SDI values for the samples of drinks illustrated in Table 1 treated with Riosorb are shown in Table 2.
The results shown in Table 2 indicated that the natural and synthetic drinks initially having similar color intensity and tint demonstrated the significantly different SDI values. The color changes during the treatment were also visually recognizable.
3. Results and discussion3.1. Testing principlesThe general approach of the suggested test is selective adsorption of synthetic dyes in a test system resulting in color changes in a drink sample.In particular, the main component of the test system was suggested to be a specifically developed adsorbent that provides an adsorption of synthetic food dyes and substantially does not interact with natural dyes of drinks.Different polymeric adsorbents meeting this criterion were tested. The test samples were divided into two groups: N - natural red wines and juices; S - model drinks made by addition to white wine or apple juice the predetermined amount of synthetic dyes to give the same color characteristics, i.e. intensity (I) and tint (T) as measured for the drinks of the first group. The exemplified compositions of natural drinks (N1eN3) and drinks containing synthetic dyes (S1eS3), the total amounts of dyes as well as the color intensity and tint of such drinks are presented inTable 1. The said drinks samples were treated with different adsorbentfor 15 min in order to evaluate intensity and tint changes after treatment. The adsorbents used were different modifications of activated carbon, microcrystalline cellulose, DEAE-cellulose, polyamide,chitosan, chitin and Riosorb. The chitosan containing adsorbent Riosorb was specially developed in our previous study (Komissarchik & Nyanikova, 2010) and provides high adsorption activity towards synthetic food dyes and almost does not adsorb dyes from natural drinks. The structure of chitosan is shown schematically in Fig. 1.Fig. 2 illustrates the IR-spectrum of chitosan containing adsorbent Riosorb. Riosorb has free amino groups providing interactions with negatively charged groups of the synthetic food dyes, e.g., sulfo groups contained in all of the synthetic dyes studied. Nevertheless the adsorbent structure does not provide adsorption of natural dyes contained in the natural drinks.In order to evaluate the described selectivity, we used color intensity and tint changes. To combine the color intensity and tint changes we developed the Synthetic Dyes Index (SDI) expressed as a product of the relative intensity change with the relative tint change multiplied by 100. According to the general approach, the more synthetic dyes arecontained in a drink, the more relative intensity and tint changes are, and the higher is the SDI value. Hence, the values of SDI are higher for the drinks containing synthetic dyes when compared to SDI values obtained for natural drinks.Based on this logic, we suggest the measure of selectivity to be the difference in SDI obtained for two drinks having the same initial color intensity and tint but one containing synthetic dyes and another made of natural ingredients.The test results have shown that the most adsorbents either adsorbed both synthetic and natural dyes (like activated carbon), or showed low adsorption activity towards synthetic dyes. The best selectivity was shown for chitosan containing adsorbents. In particularly, chitosan containing adsorbent Riosorb showed the outstanding adsorption of synthetic dyes represented by the SDI values, whereas SDI for natural drinks was the lowest of all the SDI sobtained for other adsorbents.The SDI values for the samples of drinks illustrated in Table 1 treated with Riosorb are shown in Table 2.The results shown in Table 2 indicated that the natural and synthetic drinks initially having similar color intensity and tint demonstrated the significantly different SDI values. The color changes during the treatment were also visually recognizable.
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