Integrated process for sequential extraction of saponins, xylan and cellulose from quinoa stalks (Chenopodium quinoa Willd.)

Abstract

World quinoa production is increasing due its high nutritional value. As a consequence, large quantities of stalks accumulate as unused byproducts. Here, we verify the presence of saponins in the stalks and present a biorefinery approach with quinoa stalks as feedstock, using an integrated processing scheme to separate saponins, xylan and cellulose. Saponins were extracted using pressurized hot water extraction (PHWE), optimized by a central composite experimental design (rotatable 22) with temperature and extraction time as factors. Xylan was extracted from the residual solid material after PHWE by an alkaline method using 0.5 M NaOH at 80 °C. Cellulose was purified from the remaining residuals using acetic and nitric acid at 120 °C, which resulted in recovery of white cotton-like cellulose, showing no need of further bleaching. The saponin yield was significantly increased at temperatures exceeding 110 °C, with highest amounts obtained at 195 °C (15.4 mg/g raw material). The yield in the following xylan extraction (maximum 120 mg/g raw material) was however significantly reduced when preceded by PHWE above 110 °C, indicating degradation of the polymer. Cellulose recovery (maximum 296 mg/g raw material) was less affected by variations in temperature and time in the preceding PHWE. The results obtained shows that tuning between saponin and xylan extraction is critical. This approach is foreseen to be applicable to the valorisation of residual fiber-rich biomass from various types of crops, besides quinoa.