A strategy for co-extracting hydroxycinnamic acids with hemicellulose, cellulose and lignin from wheat residues in an integrated biorefinery

Cross-linkages with polysaccharides and lignin compromise hydroxycinnamic acid yields and purity in integrated biorefineries. A two-stage-alkaline-based process was sequentially optimised in a wheat straw (WS) and wheat bran (WB)-based biorefinery setup for selective co-production of hydroxycinnamic acids (p-Coumaric acid & ferulic acid) with hemicellulose at the mild-alkaline stage (MAS), and with lignin & cellulose-rich residues at severe-alkaline stage (SAS). The optimum MAS biorefining conditions gave hemicellulose, lignin, and hydroxycinnamic acid yields of 35, 60, and 85 % for WS, and 37, 72, and 66 % for WB, respectively. The WS hydroxycinnamic acids contained p-Coumaric acid (64 %) and ferulic acid (29 %), whereas WB's contained ferulic acid (95 %). At the SAS optimum conditions, cellulose and lignin yields were 76 and 60 % for WS similar to 48 and 62 % for WB, respectively. The cellulose content and crystallinity of MAS WB residues increased by 111 and 100 %, respectively >55 and 14 % for WS. However, the SAS WS and WB residues' cellulose content and crystallinity increases were > 30 % and 10-20 %, respectively. Therefore, sequential optimization enabled selective hydroxycinnamic acid extraction and increased hemicellulose, lignin, and cellulose-rich residue yields. Furthermore, the optimal conditions for WS and WB at the two stages overlapped, allowing potential coprocessing in integrated biorefineries.