Fig. 6 PCA score scatter plots of peanut cell wall FT-IR spectra in the 1800-800 cm-1 region for pectin, hemicellulose, and cellulose under different extraction conditions.
(a: solid-liquid ratio; b: enzyme concentration; c: enzyme hydrolysis temperature; d: enzyme hydrolysis time)
The scores scatter plots PC1 (explained 81.59% of variability) and PC2 (explained 7.84% of variability) were used to obtain separation of each group of cell wall polysaccharides in 1800-800 cm-1 region at different solid-liquid ratios (Fig. 6a). The scores scatter plot PC1 vs. PC2 indicates that the cell wall polysaccharides are grouped along the PC2 axis and scattered along the PC1 axis. The tendency for the location of scores of cell wall polysaccharides was going from positive to negative values along the PC1 axis, indicating that the solid-liquid ratio exerted a strong effect on characteristic wave numbers of CDTA-soluble pectin, Na2CO3-soluble pectin, cellulose, and hemicellulose. The high coefficients of infrared wave values in the component matrix (Table 3) indicated that the corresponding group played a larger role in the enzymatic hydrolysis of the cell wall. The characteristic wave numbers of cellulose influenced by liquid-solid ratio were 997.2, 1008.7, 1010.7, 1313.5, and 1317.3 cm-1 and they were related to the C-O stretching, C-C stretching, and the CH2 symmetrical bending of cellulose. The characteristic wave numbers of hemicellulose were 960.5, 1037.7, and 1139.9 cm-1, and they were assigned to the C-O stretching, C-C stretching, and O-C-O asymmetrical bending of hemicellulose. Furthermore, the characteristic wave numbers of pectin were 1010.7, 1014.5, 1265.3, and 1267.2 cm-1, and they acted on the C-O stretching and C-C stretching of pectin.
The scores scatter plot shown in Figs. 6b-d allow the distinction of each group of cell wall polysaccharides in 1800-800 cm-1 region at different enzyme concentrations, enzyme hydrolysis temperatures, and enzyme hydrolysis times along the PC1 axis, which corresponds to 77.00, 63.42, and 76.01% of the variability contained in the FT-IR spectra, respectively. The scores scatter plot PC1 vs. PC2 indicates that the cell wall polysaccharides are grouped along the PC2 axis and scattered along the PC1 axis. The scores of cellulose and Na2CO3-soluble pectin lay on the positive side of PC1 scores, while CDTA-soluble pectin and hemicellulose were on the negative side of PC1. Clear grouping of cell wall polysaccharides was obtained under different enzyme concentrations, enzyme hydrolysis temperatures, and enzyme hydrolysis times, indicating that enzymatic conditions had strong effect on cell wall polysaccharides. The characteristic wave numbers of cellulose influenced by enzyme concentration were 997.2, 1010.7, 1313.5, 1317.3 cm-1, and they acted on the C-O stretching, C-C stretching, and CH2 symmetrical bending of cellulose; the characteristic wave numbers of hemicellulose were 960.5 and 1139.9 cm-1, and they acted on the O-C-O asymmetrical bending of hemicellulose; the characteristic wave numbers of pectin were 1010.7, 1230.5, 1265.3, and 1267.2 cm-1, and they acted on the C-O stretching and C-C stretching of pectin (Fig.6b and Table 3). The characteristic wave numbers of cellulose influenced by enzyme hydrolysis temperature were 997.2, 1008.7, and 1010.7 cm-1; they acted on the C-O stretching and C-C stretching of cellulose; the characteristic wave numbers of hemicellulose were 960.5, 1037.7, and 1139.9 cm-1, and they acted on the C-O stretching, C-C stretching, and O-C-O asymmetrical bending of hemicellulose; the characteristic wave numbers of pectin were 1010.7, 1230.5, 1265.3, and 1267.2 cm-1, and they acted on the C-O stretching and C-C stretching of pectin (Fig.6b and Table 3). As shown in Fig. 6d and Table 3, the characteristic wave numbers of cellulose influenced by enzymatic time were 997.2, 1010.7, 1313.5, and 1317.3 cm-1, which acted on the C-O stretching, C-C stretching, and CH2 symmetrical bending of cellulose; the characteristic wave number of hemicellulose was 1139.9 cm-1, which acted on the O-C-O asymmetrical bending of hemicellulose; the characteristic wave numbers of pectin were 1010.7, 1014.5, 1230.5, 1265.3, and 1267.2 cm-1, which acted on the C-O stretching and C-C stretching of pectin.