Isolation, Identification And Antibacterial Activity Of Pigment From Naturally Brown Cotton

Naturally colored cottons (NCCs) has attracted wide attention for their security, ecology,environmental friendly and high economic efficiency properties, but some of their shortcomingshave restricted the further development of NCCs industry. One important drawback is theinstability of NCCs pigment to some factors in processing, such as acid, alkali, heat, oxidants,and led to the poor color fastness of NCCs products. Thus, the investigation of the pigmentcomponent is important to NCCs processing, because suitable procedure conditions can bechosen to avoid color change of NCCs products. In this paper, the pigment of brown NCC wasfirstly preliminary identified and then isolated by preparative Liquid chromatography, four purityproducts were obtained and analyzed by ESI-MS. Besides, the molecular weight distribution ofcrud pigment was also analyzed. Finally, the antibacterial activity of brown and green NCC fiberand their pigment extracts were tested.The diagnostic reagents, UV-VIS Spectrophotometer, infrared absorption spectra were usedto comparative analysis of the chemical compositions of the pigment extracted from brown NCCfiber and delinted white cottonseed hulls (DWCH). The results showed that they were similar inmain chemical constituents and all belonged to condensed tannins (CT). The normal phasehigh-performance liquid chromatography (NP-HPLC) method was developed to separate the twosamples, the results showed that there were four compositions with one overwhelming in NBCFpigments, and various kinds of constituents were separated in DWCH pigments, however,constituents with the same molecular structure were not found in two pigments.The polyamide column chromatography, reverse-phase high-performance liquidchromatography (RP-HPLC) and preparative liquid chromatography were used to separatebrown cotton pigment. The results showed that the pigment extract could be successfullyfractionated by polyamide column chromatography, the pigment consists of two fractions fortheir different colors and HPLC chromatograms of elution segments. Two colored compositionsand two colorless were isolated from water elution segment by preparative C18-Reversed-phasechromatography, but the other segment can not be isolated by this chromatography column,according to the retention action on chromatography columns, this part of pigment may belong toa series of polyphenol compounds with closely similar structure.The MADLI-TOF MS and ESI-MS were separately used to analyzed the crude pigment and the isolated products. The results showed that there were many ingredients in brown cottonextract, most of which were in the850-1250molecular-weight (MW) region. The two obtainedcolorless components were extremely similar in their ESI-MS features, a phenyl was the onlydifference between the structure of two components, and they probably belonged to lignans withmultiple aromatic rings. The obtained colored components were not the same class of substance,the yellow-brown product belonged to the other phenolic compounds with MW high than1000,while the orange product may be the trimer or tetramer of B type CT for their closely similarESI-MS features.The antibacterial activity of NCCs was evaluated though AATCC Test Method100-2004.Compared to the conventional white cotton, brown NCC was found to exhibit excellentantibacterial activity with a reduction rate of89.1%and96.7%, when contacting with twospecies of bacteria, Staphylococcus aureus and Klebsiella peneumonia, respectively, while theantibacterial effect of green NCC was faint. To investigate the antibacterial mechanism of NCCs,pigments have been extracted from NCC fibers for further determination of their antibacterialactivity using the disk diffusion method. The results are as follows: the pigment from browncotton fibers showed significant inhibition against the two challenge bacteria, while theresistance capacity of the pigment from green cotton fiber was insignificant, indicating that theantibacterial efficacy of NCC fibers was highly related to the chemical nature of the pigment.The effect of high temperature treatment on antibacterial activity of the pigment extracted frombrown cotton was also examined. It showed that the general textile high temperature curingconditions will decrease its antibacterial activity, but the antibacterial activity still has satisfiedretention, indicating durable naturally antibacterial performance of brown NCC to hightemperature curing technology. The antibacterial effect of pigment extract of brown cottonshowed an insignificant change under human body sweat condition.