Analysis of antibacterial properties of naturally colored cottons

The antibacterial activity of naturally colored cottons (NCCs) is evaluated. Compared to the conventional white cotton, brown NCC was found to exhibit excellent antibacterial activity with a reduction rate of 89.1% and 96.7%, when in contact with two species of bacteria, Staphylococcus aureus and Klebsiella pneumoniae, respectively, while the antibacterial 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 antibacterial activity using the disk diffusion method, and the chemical nature of extracted pigments was also analyzed. The results are as follows: the pigment from brown cotton fibers showed significant inhibition against the two challenge bacteria, while the resistance capacity of the pigment from green cotton fiber was insignificant, indicating that the antibacterial efficacy of NCC fibers was highly related to the chemical nature of the pigment. Diagnostic results indicated that the pigment from brown cotton belonged to condensed tannins, and the pigment from green cotton fiber was identified as flavonoids. The effect of high-temperature treatment on antibacterial activity of the pigment extracted from brown cotton was also examined. It showed that the general textile high-temperature curing conditions decrease its antibacterial activity, but the antibacterial activity still has a satisfactory retention, indicating a durable natural antibacterial performance of brown NCC to the high-temperature curing technology.