To produce manno-oligosaccharides from cassia gum, a mutated glycoside hydrolase family 134 β-mannanase gene (mRmMan134A) from Rhizopus microsporus var. rhizopodiformis F518 was expressed in Pichia pastoris and a high expression level (3680 U mL-1) was obtained through high cell density fermentation. mRmMan134A exhibited maximum activity at pH 5.5 and 50 °C. It was then subjected to hydrolyze cassia gum with 70.6% of overall yield of manno-oligosaccharides. From the hydrolysate, seven components (F1-F7) were separated and identified as mannose, mannobiose, galactose, mannotriose, mannotetraose, 61-α-d-galactosyl-β-d-mannobiose, and mannopentaose, respectively. According to in vitro fermentation, the manno-oligosaccharides were able to promote the growth of three Bifidobacterium strains and six Lactobaillus strains with 3.0-fold increment in culture absorbance, and these strains preferred manno-oligosaccharides with degree of polymerization (DP) 2-3 rather than those with DP 4-5. Novel manno-oligosaccharides from cassia gum with promising prebiotic activity were provided in the present study.
Keywords: Cassia gum; Characterization; Manno-oligosaccharides; Prebiotic activity; β-Mannanase.
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