Structural and bioactive characterization of purified polysaccharide from deep-freeze pretreated Sorghum bicolor L. leaf sheath

This study determined the effect of deep-freeze pretreatment of sorghum leaf sheath on the extraction yield of ultrasound-extracted purified polysaccharides (DFUP-1), and confirmed the physicochemical, structural and bioactive characteristics of DFUP-1. Deep-freeze pretreatment induced breaks in the cell walls and resulted in a higher yield (14.35%) of crude polysaccharide extract than without pretreatment (9.23%). The crude extract was purified using DEAE-52 cellulose ion exchange and Sephadex G-100 gel-filtration chromatography to obtain DFUP-1. The H-1 and C-13 NMR spectra of DFUP-1 showed the presence of beta-glycosidic linkages and a substitution at C6 of the sugars which may be O-methyl substitution or due to beta (1-6) linkages. Peaks for alpha-anomeric linkages were not detected. The FTIR spectrum of DFUP-1 confirmed its carbohydrate functional groups. Periodate oxidation and formic acid analysis of DFUP-1 showed 1-, 1-6, 1-2, 1-3 and 1-4 linkages. GC-MS analysis of monosaccharide residues of DFUP-1 showed presence of glucose, galactose, arabinose, mannose and xylose. Congo red assay showed that DFUP-1 was not of triple-helix configuration. The ABTS+ and DPPH radical scavenging assay showed an IC50 of 0.10 mg/mL and 1.19 mg/mL for DFUP-1 respectively. At 0.2 mg/mL DFUP1 showed anti-inflammatory (anti-egg denaturation) activity of 41.52%. The DFUP-1 sample showed lower inhibitory effect against proliferation of leukemia cells at an IC50 of 37.43 mu g/mL compared to curcumin with IC50 of 0.98 mu g/mL. Taken together, deep-freeze pretreatment coupled with ultrasound extraction increases yield of sorghum leaf sheath polysaccharides with potential nutraceutical and pharmaceutical applications.

Automated summary

This study investigated the effect of deep-freeze pretreatment on the extraction yield of sorghum leaf sheath polysaccharides using ultrasound extraction. The results showed that deep-freeze pretreatment increased the yield of crude polysaccharide extract. The purified polysaccharides, DFUP-1, exhibited certain physicochemical, structural and bioactive characteristics, making them potentially useful in nutraceutical and pharmaceutical applications.