Abstract:The effect of the preparation process of konjac oligoglucomannan（KOGM）after β-mannanase hydrolysis on the degree of polymerization（DP）was studied by using konjac glucomannan（KGM）as raw material.The differences of physicochemical properties and microstructure between KOGM with different DPs and raw material KGM were investigated.Their effects on the proliferation，acid production，total sugar utilization and short-chain fatty acids of five kinds of lactic acid bacteria were also discussed.The results showed that the technology steps of monosaccharides removal method by yeast fermentation，subsequent centrifugation and sterilization had no significant effects on the DP of KOGM.The DPs of the prepared three kinds of KOGMs were 16.74，12.74 and 11.13，respectively.The backbone structure of these KOGMs was similar to that of the raw material KGM，and the two low polymerization konjac oligoglucomannan KOGM-L（the DP of KOGM-L1 was 12.74，and that of KOGM-L2 was 11.13）had lower viscosity characteristics and similar microscopic morphology，showing more obvious fragmentation and pore structure.Compared with KGM and medium polymerization konjac oligoglucomannan（KOGM-M，DP was 16.74），KOGM-L was more conducive to promoting the proliferation of lactic acid bacteria，acid production and total sugar decomposition，but there was no significant difference between the two KOGM-L（P>0.05）.KOGM-L2 cultivated with Bifidobacterium longum reached the maximum colonies in total count（OD600=2.13），but KOGM-L1 cultivated with Lactobacillus rhamnosus had the highest proliferative ratio values（4-5 times）.The total output and each component content of short-chain fatty acids showed that KOGM-L was significantly higher than KOGM-M，raw material KGM and inulin（P<0.05）.In summary，KOGM with different DPs had significant differences in prebiotic functions，in which KOGM with low DP gained the best effect.KOGM with similar DPs had similar probiotic functions，and the DP 11-13 had better probiotic effects on B.longum and L.rhamnosus.