Biorefining of buckwheat (Fagopyrum esculentum) hulls by using supercritical fluid, Soxhlet, pressurized liquid and enzyme-assisted extraction methods

Dehulling of buckwheat seeds produces high amounts of processing by-product, the hulls. Soxhlet, supercritical carbon dioxide (SFE-CO2), pressurized liquid (PLE) and enzyme assisted extraction (EAE) schemes were applied for the biorefining of hulls into higher added value soluble fractions. The highest total yield (on dry hull weight basis) of soluble solids in Soxhlet extraction using hexane, acetone and methanol was 5.2%, while at optimal SFE-CO2 parameters (55 MPa, 60 degrees C, 90 min) in the selected interval of independent variables 1.47% of lipophilic constituents were isolated. Addition of 5% co-solvent ethanol in SFE-CO2 increased the yield to 1.86%. Extract yields were highly dependent on powder particle size. Extraction process was continued by applying to SFE-CO2 residues PLE (at 10.3 MPa) and EAE using 'green' solvents, ethanol ant water and commercial xylanolytic enzyme preparation Viscozyme L These methods enabled to increase the yields of soluble fractions 4-5-fold. The extracts and residues of extractions were evaluated using antioxidant activity and total phenolic content assays. The study shows that buckwheat hulls may be biorefined into strong antioxidants and other functional ingredients, which may find various applications, primarily in foods and nutraceuticals. (C) 2017 Elsevier Ltd. All rights reserved.