Two major residues are produced by the sugarcane industry, the fibrous fraction following juice extraction (bagasse), and the harvest residue (straw). The structures of the lignins from these residues were studied by pyrolysis coupled to gas chromatography-mass spectrometry (Py-GC/MS), nuclear magnetic resonance (NMR), and derivatization followed by reductive cleavage (DFRC). Whereas the lignin from bagasse has a syringyl-rich p-hydroxyphenyl:guaiacyl:syringyl (H:G:S) molar composition of 2:38:60, the lignin from straw is guaiacyl-rich (H:G:S of 4:68:28). The compositional differences were also reflected in the relative abundances of the different interunit linkages. Bagasse lignin was primarily β-O-4′ alkyl-aryl ether units (representing 83% of NMRmeasurable units), followed by minor amounts of β-5′ (phenylcoumarans, 6%) and other condensed units. The lignin from straw has lower levels of β-ethers (75%) but higher relative levels of phenylcoumarans (β-5′, 15%) and dibenzodioxocins (5-5/4-O-β, 3%), consistent with a lignin enriched in G-units. Both lignins are extensively acylated at the γ-hydroxyl of the lignin side-chain (42% and 36% acylation in bagasse and straw), predominantly with p-coumarates (preferentially on S-units) but also with acetates (preferentially on G-units) to a minor extent. Tetrahydrofuran structures diagnostically arising from β-β-coupling (dehydrodimerization) of sinapyl p-coumarate or its cross-coupling with sinapyl alcohol were found in both lignins, indicating that sinapyl pcoumarate acts as a monomer participating in lignification. The flavone tricin was also found in the lignins from sugarcane, as also occurs in other grasses.

The composition of lipophilic phytochemicals in sugarcane bagasse and straw, the two major residues of sugarcane processing, was investigated in detail by gas chromatography and mass spectrometry. The composition of the lipids from sugarcane bagasse and straw was completely different from each other. While the extracts of sugarcane bagasse were dominated by n-aldehydes (ca. 48% of all identified lipids) and n-fatty alcohols (ca. 23%) with lower amounts of n-fatty acids (10%) and steroid ketones (14%), the extracts from sugarcane straw were strongly dominated by n-fatty acids (accounting for ca. 60% of all identified compounds) with significant amounts of steroid compounds, particularly sterols (10%) and steroid ketones (14%). Tocopherols and triterpenols were also found, being particularly abundant among the extractives of sugarcane straw. Sugarcane bagasse and straw can thus be considered as promising feedstocks for obtaining highly valuable phytochemicals of nutraceutical or pharmaceutical interest.

AbstractCorn fibers are a significant residue of agriculture due to the huge amounts, which has fueled interest in a more rational use of its components, particularly regarding hemicelluloses. The impact of hemicellulose redeposition on printer and writing (P&W) paper grade pulp properties are discussed in this paper. Xylans extracted from corn fibers (16.9 % xylans) by cold caustic extraction (CCE) were added to commercial brown pulps (eucalypt and pine) in the oxygen delignification (O-stage) and further bleached to 90 % ISO brightness. Hemicelluloses deposition occurred at variable degree (up to 7 % on pulp weight). Pulp bleachability was not impaired by xylan deposition for eucalypt and pine pulps. Xylan deposition onto fibers was more efficient in eucalypt pulp than pine. Pulp beatability and strength properties were improved by xylan deposition for P&W paper grades.