Production of Furfural Compounds from Dextran under Different Acid Hydrolysis Conditions

In this study, a method for the simultaneous detection of 5-hydroxymethyl-2-furfural (HMF), 5-methyl furfural (MF) and furfural (FF) was established by ultra-high performance liquid chromatography (UPLC) after enrichment of furfurals in the acid hydrolysate of dextran by solid phase extraction (SPE) using a hydrophilic-lipophilic balance (HLB) column. The effect of different degrees of acid hydrolysis of dextran on the production of HMF, MF and FF was analyzed. The results showed that the proposed UPLC method was rapid, accurate and sensitive. Under incomplete acid hydrolysis conditions (0.5 mol/L H₂SO₄, 60 ℃), the recovery of monosaccharides from dextran was low and the three furfural compounds were undetectable in the hydrolysate. Under the optimal hydrolysis conditions (2 mol/L H₂SO₄, 100 ℃), the content of monosaccharides in dextran hydrolysate increased, the formation rate and content of HMF increased significantly, and FF was detected; however, the formation rate and content of FF were lower than those of HMF. Under excessive hydrolysis conditions (4 mol/L H₂SO₄, 120 ℃), the recovery of monosaccharides was lower than that under the optimal hydrolysis conditions. Meanwhile, the contents of HMF and FF were higher, and MF was not detected during the whole hydrolysis process. The above results show that during the hydrolysis of dextran, the yield of furfural compounds is closely related to the monosaccharide content in the hydrolysate. In addition, more vigorous acid hydrolysis conditions will promote the formation of HMF and FF in dextran hydrolysate, HMF being the easiest to form, followed by FF. The formation of MF requires more vigorous catalytic conditions.