Quantification of plant biomass composition via a single FTIR absorption spectrum supported by reference component extraction/isolation protocols

Abstract

A fairly simple yet efficient quantitative protocol was developed to investigate plant composition using Fourier-transform infrared spectroscopy (FTIR), through biomass analysis arising from the whole shoot system of Cardoon (Cynara cardunculus L.), Cannabis (Cannabis sativa L.) and Switchgrass (Panicum virgatum L.). An analytical compositional report of the biomasses, serving as a standard method to identify the different chemical groups present, was compared with relevant FTIR spectra and Thermogravimetric Analysis (TGA) thermographs. In order to interpret the highly convoluted absorption spectra, not only a series of reference materials were examined but also extraction protocols were implemented to sequentially isolate the compositional units allowing a spectroscopic monitoring of their progressive removal from the biomass. This approach enabled the assignment and distinction of a series of vibrational peaks and regions identified in the lower wavenumber region. These peaks/regions, were found to be capable of quantitating different chemical units, such as lignin, fats and lipids, even in the case of structural polysaccharides, like cellulose, hemicellulose and pectin, which are the primary constituents of plant cells. Fats and lipids were easily detected at the 3050–2800 cm⁻¹ region, with their concentration determined by the isolated 720 cm⁻¹ and the 728 cm⁻¹ peaks, when present. Lignin concentration was determined via the 1508 cm⁻¹ peak. Hemicellulose is contributing to the 1640, 1245 cm⁻¹ as well as the 1740 cm⁻¹ peak, with its concentration determined in the 850–750 cm⁻¹ region. Cellulose content was quantified via the 895 cm⁻¹ peak, while pectin appeared at the 915 cm⁻¹ peak and also contributed to the 1640 cm⁻¹ signal. Consequently, a better understanding of the vibrational convolution could thus be achieved when studying plant cells where multiple structural units contribute to the spectra. It is therefore expected that plant cellular composition can be adequately revealed with a single FTIR spectrum, without the need for intensive analysis methods, offering a faster and more efficient approach.