Production of protein-rich galactomannan oligosaccharides from Gleditsia sinensis Lam. seeds via two-step hydrolysis mediated by organic acid and enzyme

The growing demand for healthier living has spurred the production of bioactive ingredients from lignocellulosic biomass. However, the enzymatic production of galactomannan oligosaccharide (GMOS) as a functional additive using β -mannanase is challenged by low yields and a broad molecular weight distribution of hydrolysis products. In this study, a novel two-step hydrolysis strategy was developed for producing protein-rich GMOS from Gleditsia sinensis Lam. seeds. This approach involved a primary organic acid hydrolysis followed by a secondary enzymatic hydrolysis. Results showed that the organic acid hydrolysis (0.5 M acetic acid at 150 °C for 50 min) yielded 79.1 % of incompletely degraded galactomannan (IDGM) and 30.9 % of protein. More importantly, the two-step hydrolysis remarkably improved the GMOS yield to 57.3 %, which was 2.6-fold higher than that achieved by the one-step enzymatic hydrolysis method. Correspondingly, the ratio of GMOS to IDGM in hydrolysis products increased to 76.3 %. The increased GMOS yield and GMOS to IDGM ratio demonstrate that the organic acid hydrolysis effectively promoted the subsequent enzymatic preparation of GMOS. This study gives valuable insights into the development of an efficient and sustainable process for producing GMOS from GM-rich lignocellulosic biomass. • Protein-rich GMOS was produced from Gleditsia sinensis Lam. seeds. • Primary acid hydrolysis promoted the secondary enzymatic hydrolysis of galactomannan. • Two-step hydrolysis achieved a GMOS yield of 57.3 % from G. sinensis Lam. seeds. • The percentage of GMOS in the degraded galactomannan products reached 72.5 %.