## 3 LCF Structure Analysis and Quality Control
### Chemometrics Used for Ligocellulose Feedstock Specification
To do so, the authors processed a broad variety of input parameters, including wood species, resulting in root-mean-square errors of less than 1.51% [129; 143; 142]. Due to the fact that genotype and cultivation conditions significantly influence the 3D chemical structure of any crop, it is of importance to have access to specific plants. It should be emphasized that we do have unique access to well-defined LCF raw materials--crops cultivated at Campus Klein-Altendorf University Bonn, one of the largest field labs for _Miscanthus_ cultivation in Europe (more than 30 genotypes), and further special biomasses, i.e., _Silphium perfoliatum, Paulownia_. In addition, there is also access to crops from specific harvesting seasons (i.e., September, December, April), specific years, and plant portions (leaf versus stem). Thus, in previous studies the correlation between crop genotype, harvesting time (year, season), plant portion and lignin amount, and 3D structure was investigated. For six different genotypes, the lignin content varies, as shown in Figure 11.  
Based on this information, a decision can be made regarding the harvesting time (season) in order to obtain highest yields. In general, there are various advantages of _Miscanthus_ cultivation: as a C\({}_{4}\) plant, the plants bind to four (instead of three) carbon atoms, resulting in an exceptional CO\({}_{2}\) fixation rate and high photosynthesis yields. Thus, _Miscanthus_ crops are intensively studied for industrial exploitation, including lignin generation. Recently, we reported a systematic study showing strong correlations of the lignin structure with the _Miscanthus_ genotype and plant portion (stem versus leaf) [26]. In detail, for lignins isolated via non-catalyzed organosolv, pulping the amount and linkages of the three monolignol building blocks (G, H, and S) was studied with different analytical methods (i.e., NREL protocol, FTIR, UV-Vis, HSQC-NMR, thermal gravimetric analysis (TGA), pyrolysis gas chromatography/mass spectrometry (GC/MS). The FTIR data have been processed using chemometric methods (i.e., principal component analysis). A comparison of beech wood and _Miscanthus_ lignins could show that the _Miscanthus_-derived lignins showed lower molecular weight and narrow polydispersities (<1.5, compared to >2.5 for beech), most probably due to an increased homogeneity. Figure 10: Plot of scores (samples) and loadings (\({}^{31}\)P NMR chemical data) on principal component 1 (PC1) and 2 (PC2). Reproduced with permission from [142], Elsevier 2019. The nature and ratio of different monolignol linkages has been studied in detail using heteronuclear single quantum correlation (HSQC) 2D-NMR. Results showed that leaves contain two-thirds of the G units, whereas in stems and mixtures the G content is rather low. Compared to G, H and S units were found to be highest in samples containing leaf and stem mixtures. Figure 12 shows the calculated ratio of the most abundant \(\beta\)-arylether (A) linkages (55-65%), followed by phenyl coumarane (B) and resinol (C) linkages. Stem-derived lignins mainly contain unsaturated esters (D) (ca. 30%). The concentration of residual carbohydrates was below the detection threshold, indicating the high purity of organosolv-derived lignins. PCA processing of FTIR data from lignin samples was performed to determine the structural differences of lignins obtained from different _Miscanthus x giganteus_ plant portions (stems, leaves, and their mixtures). Results are shown in Figure 13--the projections of IR spectra from lignin samples on the first three principal components (82% of variance). In particular, a differentiation of stem versus leaf-derived lignins was possible, since the aromatic in-plane deformation signals at 1160 cm\({}^{-1}\) do correspond to the monolignol substitution pattern (Figure 13) [27]. Figure 11: Leaf versus stem content of _Miscantthus_ genotypes: _M. x giganteus_ (Gig17, Gig34, Gig35), M. _nagana_ (NagG10), _M. sinensis_ (Sin2), and _M.