Green preparation of low-molecular-weight galactomannan from Gleditsia sinensis and mechanistic investigation on ameliorating nonalcoholic fatty liver disease.

Galactomannan comes from a wide range of plant resources and has some biological activities, but its bioavailability is limited due to its large molecular weight and complex structure. In this study, three degradation methods (H2O2, ultrasound, and β-mannanase) combined with ethanol fractional precipitation (25 %, 50 %, and 75 %) were used to degrade and separate Gleditsia sinensis galactomannans (GSG), and the physicochemical properties and biological activities of GSG after degradation were analyzed. Comprehensive comparison indicates that H2O2 exhibits had a better degradation effect. After 4 h of degradation using 4 % H2O2, the yield of GSG precipitated with 50 % ethanol was 37.06 % (the yield of undigested GSG is 1.80 %). Simultaneously, the molecular weight (reduced from 225.25 to 36.87 kDa) and viscosity were significantly reduced under this condition, while the solubility was increased. In addition, the low-molecular-weight GSG (LGSG) obtained by 4 % H2O2/50 % ethanol showed the strongest free radical scavenging activity in vitro. Furthermore, the results of in vivo antioxidant assays showed that LGSG inhibited Aflatoxin B1-induced developmental toxicity by regulating gene expression in the Keap1/Nrf2 pathway. LGSG also promoted Nrf2-mediated expression of the lipid metabolism genes ppar-α and cpt1, while suppressing expression of the fatty acid synthesis genes fas and scd-1. Therefore, the liver recovered from lipid peroxidation induced nonalcoholic fatty liver disease (NAFLD). The present study introduces a method for green and efficient preparation of LGSG, indicates its potential as a nutritional product.