Extraction of dye from dry fruit of Rothmannia whitfieldii was carried out using four different extraction methods. Solvent and acid extraction methods gave a colourless supernatant solution after extraction time of 45 minutes at 60 °C. The alkali method gave a deep brown coloured supernatant solution while the aqueous method gave a dark coloured supernatant solution after extraction under the same conditions. From the result of the FTIR spectroscopy characterization of the coloured solutions and the dry powder of Rothmannia whitfieldii fruit, it was observed that only the alkali method extracted what can be called a dye with likely presence of tannins. The result also showed that the possible functional groups present in the supernatant solution after aqueous extraction are same with the functional groups present in the dry pulverized Rothmannia whitfieldii fruit. Hence, aqueous method did not extract any dye. Similarly, a mixture of the solution after aqueous extraction with drops of alkali solution produced a deep brown coloured solution indicating solubility of the dye component in alkali media.
Interest in the study and use of natural dyes especially from plant materials in recent times is on the increase mostly due to environmental hazard and toxic effect of most synthetic dyes on the human skin [
There are several dye yielding plants in Nigeria, however, for this research work, Rothmannia whitfieldii plant was investigated. Rothmannia whitfieldii (synonym: Randiamalleifera) is a plant of the Rubiaceae family found within tropical Africa from Senegal to Sudan and in the southern part of Africa: Angola and Zimbabwe to be precise [
Fresh Rothmannia whitfieldii fruit as earlier stated has been used mostly in Nigeria for body decoration and medicinal purpose with little or no interest in its cloth dyeing ability. It is important to note that the dry fruit of Rothmannia whitfieldii (shown in
Such work on determining the optimum condition to extract dye using different extraction methods from leaves of Indigofera tinctoria linn and from the floral part of Woodfordia fruticosa have also been done [
The fresh fruits of Rothmannia whitfieldii were sourced from a local market in Owerri, Imo State in the eastern part of Nigeria. Chemicals used for this work were of analytical value, they are sodium hydroxide (NaOH), citric acid (C6H8O7) and isopropanol ((CH3)2CHOH).
MethodsThe fresh Rothmannia whitfieldii fruits were dried under sun before opening up the fruit. The pulp and seed were removed and pulverized. The powder used was sieved to average particle size of 100 µm using a sieve with aperture size of 100 µm. Four extraction methods used include aqueous, alkali, acid and organic solvent.
1) Extraction
Extraction was done using 100 ml beakers for 45 minutes at 60˚C with a material to liquor ratio of 1:50 (g:ml). 1% citric acid and sodium hydroxide solutions were prepared using the Equation (1) and there pH are 3 for citric acid and 11 for sodium hydroxide.
Mass percent = weight of solute ( g ) × 100 weight of solute + weight of solvent ( g ) (1)
For aqueous extraction, 50 ml of distilled water was poured into a 100 ml beaker and placed in a water bath with the temperature set at 60˚C. As the temperature of the distilled water got to 60˚C, 1 g of the plant powder was added and stirred. The solution was stirred then allowed to stand for 45 minutes while maintaining the temperature at 60˚C. The supernatant liquid was drained off into a sample test bottle using a white synthetic fabric as the sieve. Same procedure was followed using 1% citric acid, 1% NaOH and iso-propanol solutions respectively. The results (shown in Figures 2-5) are presented below.
2) FTIR Spectroscopy
Transmittance method was used with wavenumber range of 4000 - 650 cm−1, Happ-Genzel apodization, 16 sample scans, 16 background scans and 8 times resolution
Infra-red (IR) spectroscopy of three samples were taken and their absorption spectra with peaks corresponding to certain frequencies (cm−1) (shown in Figures 6-8). Each of the spectra was also interpreted by identifying the possible functional group each peak with assigned number represents (presented in Tables 1-3).
By visual observation, only aqueous and alkali extraction methods gave a deep
coloured liquid after the extraction time (Figures 2-5). While alkali extraction gave a deep brown colour liquid, aqueous extraction gave a black colour liquid. Acid and isopropanol extraction methods gave a clear coloured liquid. In keeping with the objectives of this research, only the deep coloured liquids after extraction were characterized with the FTIR spectroscopy. This is because intense colour and solubility are some of the properties a compound that can function as a dye must possess [
It was observed that 5 ml of the supernatant liquid from the aqueous extraction when mixed with drops of 1% NaOH solution changed colour from black to deep brown. Whereas there was no change in the colour of 5 ml of deep brown colour liquid from the alkali extraction when mixed with drops of water. This perhaps indicates that the natural dye molecule in dry Rothmannia whitfieldii fruit does not dissolve in water but dissolves in alkali solution. A solute will not dissolve in a solvent if their solubility parameters and/or affinity are different [
An infrared spectrum represents a fingerprint of a sample with absorption peaks which correspond to the frequencies of vibrations between the bonds of the atoms making up the material. The fact that materials are a unique combination of atoms, no two compounds produces exactly the same infrared spectrum. Therefore, infrared spectroscopy can be used to positively identify (qualitative analysis) different kinds of materials. Also, the size of the peaks in the spectrum is a direct indication of the amount of material present [
Each of the peaks identified with a wavenumber in an IR spectrum represent a certain functional group in the compound being investigated. It should be noted that infrared spectroscopy is used majorly to confirm the presence of functional groups in a compound and not for determination of the structure of a compound. For the purpose of interpretation infrared spectrum can be split into four distinct regions [
1) 4000 - 2500 cm−1: absorption of single bonds to hydrogen, e.g. C-H, O-H, N-H
2) 2500 - 2000 cm−1: absorption of triple bonds, e.g. C ≡ C and C ≡ N
3) 2000 - 1500 cm−1: absorption of double bonds, e.g. C=C, C=O
4) 1500 - 400 cm−1: absorption owing to other bond deformations, e.g. rotating, scissoring and some bending.
There are some exceptions, e.g. N-H bending is observed at 1550 - 1620 cm−1. The region between 1500 - 400 cm−1 is the fingerprint region because it is unique to each compound. This region helps to identify particular molecules because no other compound will have the same pattern of absorptions.
The content of
Wavenumber (cm−1) | Bond | Functional group |
---|---|---|
3257.7 | O-H stretch, H-bonded | alcohols, phenols |
2094.8 | -C(triple bond)C-stretch or N=C=S stretching | Alkynes or Isothiocyanate |
1636.3 | C=C stretching or N-H bending or C=C stretching | Conjugated alkene or Amines or Cyclic alkene |
1390.3 | C-H bending or O-H bending or N-O symmetric stretch | Alkane or Phenol, alcohol or Nitro |
Wavenumber (cm−1) | Bond | Functional group |
---|---|---|
3265.1 | O-H stretch, H-bonded | alcohols, phenols |
2926 | C-H stretch | Alkanes |
2113.4 | -C(triple bond)C-stretch | Alkynes |
1718.3 | C=O stretching | Cyclo or aliphatic ketone |
1606.5 | N-H bending or C=C stretching | Amines or Cyclic alkene |
1438.8 | C-H bend or C=C stretch (in-ring) | Alkanes or Aromatics |
1379.1 | C-H bending | Alkanes |
1248.7 - 1036.2 | C-N stretching | Aromatic amines |
883.4 | =C-H bend or C-H bend | Alkenes or Aromatics |
Wavenumber (cm−1) | Bond | Functional group |
---|---|---|
3257.7 | O-H stretch, H-bonded | alcohols, phenols |
2927.7 | C-H stretch | Alkanes |
2113.4 | -C(triple bond)C-stretch | Alkynes |
1867.3 | C-H bending or C=O stretch | Aromatic compound |
1718.3 | C=O stretching | Cyclo or aliphatic ketone |
1606.5 | N-Hbending or C=C stretching | Amines or Cyclic alkene |
1438.8 | C-H bend or C=C stretch (in-ring) | Alkanes or Aromatics |
1379.1 | C-H bending | Alkanes |
1248.7 - 1036.2 | C-N stretching | Aromatic amines |
764.1 | C-H bend | Aromatics |
The IR spectra shown in
We can therefore conclude from the FTIR spectroscopy result that all functional groups found in
Similarly, from the FTIR spectroscopy, we have been able to ascertain that the dye component of dry Rothmannia whitfieldii fruit was only extracted by the alkali solution and not water. Visual observation of the supernatant liquid after extraction with alcohol and acid solution also confirmed that the dye component of dry Rothmannia whitfieldii fruit is not soluble in both and not extracted in both.
We have therefore succeeded to prove that dry Rothmannia whitfieldii fruit which hitherto is not considered useful is a good source of natural dye. It has also been established that to extract dye from dry Rothmannia whitfieldii fruit powder, alkali extraction method should be used. Unlike Jansen [
The authors declare no conflicts of interest regarding the publication of this paper.
Nnorom, O.O. and Onuegbu, G.C. (2019) Authentication of Rothmannia whitfieldii Dye Extract with FTIR Spectroscopy. Journal of Textile Science and Technology, 5, 38-47. https://doi.org/10.4236/jtst.2019.52004