Comparison and validation of Fourier transform infrared spectroscopic methods for monitoring secondary cell wall cellulose from cotton fibers

The amount of secondary cell wall (SCW) cellulose in the fiber affects the quality and commercial value of cotton. Accurate assessments of SCW cellulose are essential for improving cotton fibers. Fourier transform infrared (FT-IR) spectroscopy enables distinguishing SCW from other cell wall components in a rapid and non-invasive way. Thus it has been used for monitoring SCW development in model plants. Recently, several FT-IR methods have been proposed for monitoring cotton fiber development. However, they are rarely utilized for assessing SCW cellulose from cotton fiber due to limited validation with various cotton species grown in different conditions. Thus, we compared and validated three FT-IR methods including two previously proposed methods analyzing entire spectra or specific bands as well as a new method analyzing FT-IR spectral regions corresponding to cellulose with various cotton fibers grown in planta and in vitro. Comparisons of the FT-IR methods with reference methods showed that the two FT-IR methods analyzing the entire spectra or cellulose regions by principal component analysis monitored SCW qualitatively, whereas the FT-IR method analyzing specific bands (708, 730, and 800 cm⁻¹) by a simple algorithm allowed the monitoring of SCW cellulose levels quantitatively. The quantitative FT-IR method is a potential substitute for lengthy and laborious chemical assays for monitoring SCW cellulose levels from cotton fibers, and it can be used for a better understanding of cotton fiber SCW development and as a part of the quality assessment tools used to guide choices for improving fiber quality.