Removal of 5-hydroxymethylfurfural from brewer's spent grains hydrolysates obtained by subcritical water hydrolysis: An approach using liquid-liquid extraction

Abstract

This study evaluated the use of a semi-continuous subcritical water hydrolysis (SWH) process followed by liquid-liquid extraction to produce a concentrated hydrolysate with a low content of 5-hydroxymethylfurfural (5-HMF). The SWH was operated at 15 MPa, 180 °C, 5 mL min−1, and a solvent-to-feed ratio of 22.5 g g−1. The hydrolysate was subjected to liquid-liquid extraction at different pH (2.5–6.5), temperatures (25–45 °C), and volumetric ratios between hydrolysate and ethyl acetate (1:2–2:1 v/v) using the Box–Behnken design followed by response surface methodology. The optimal conditions for removing 5-HMF (73.85 %) were pH 6.5, 35 °C, and a volumetric ratio between hydrolysate and ethyl acetate of 1:2 (v/v). The hydrolysate presented a final composition of 14.82 g L−1 cellobiose, 10.83 g L−1 glucose, 6.36 g L−1 xylose, 3.61 g L−1 arabinose, 2.47 g L−1 formic acid, 3.75 g L−1 acetic acid, and 1.04 g L−1 5-HMF.