Complete conversion of agarose into water soluble agaro-oligosaccharides by microwave assisted hydrothermal hydrolysis

This study aims to produce oligosaccharides by microwave-assisted hydrothermal hydrolysis of agarose, which is a more environmentally friendly and green economical approach than acid or enzymatic hydrolysis. Under the optimized condition of 160 °C and 25 min, total liquefaction of agarose was achieved, the dominant products in the hydrolysate are agaro-oligosaccharides (AOs), with only a small portion of d-galactose and 5- hydroxymethylfurfural (5-HMF). This approach can produce even and odd number AOs simultaneously, which is due to the random hydrolysis of α-1,3 glycosidic linkage at first and subsequent hydrolysis of the β-1,4 glycosidic linkage at the reducing end. The yield of AOs of a low degree of polymerization (DP) can reach about 57% of the theoretical maximum, while the total yield of AOs is over 90%. In conclusion, microwave-assisted hydrothermal hydrolysis is a way of producing oligosaccharides from agarose with extra-high efficiency and practical significance.