Production of Konjac Oligo-glucomannan and Their Effect on the Gut Microbioca

Abstract

Konjac glucomannan (KGM) is neutral polysaccharide that can be produced by extraction from the tuber of Amorphophallus konjac. Degradation product of konjac glucomannan is konjac oligo-glucomannan (KOG). KOG can be produced by enzymatic hydrolysis of KGM using ẞ-mannanase. Response surface methodology (RSM) was used to optimize the hydrolysis temperature, time, pH and enzyme to substrate ratio (E/S) to obtain high yield of KOG with the variations performed with design of experimental using Box-Behnken design (BBD). The highest content of oligosaccharide from hydrolysis of KGM analyzed by HPSEC was 9.21 mg/mL under the conditions of 48°C, 4h hydrolysis time, pH 5.5 and E/S of 0.05%. The result showed that KOG was produced successfully by ẞ-mannanase from KGM. In order to increase the purity of KOG, purification step was performed by ultrafiltration (UF) membrane. The oligosaccharide content in KOG after purification was analyzed by high performance size exclusion chromatography (HPSEC). The final product after purification step with UF pore size of 3,000 NMWC produced two groups of KOG with different fraction from permeate and retentate. Low molecular weight fraction (LKOG) was found in permeate with the concentration of oligosaccharides was 9.54 mg/mL and high molecular weight fraction (HKOG) was found in retentate with the concentration of oligosaccharides was 8.49 mg/mL. The effect of KOG on changes in human fecal bacterial populations and short chain fatty acids (SCFAs) production were evaluated. Bacterial populations of bifidobacteria increased significantly (P<0.05) after 24h and lactobacilli was slightly increased after 6h during LKOG fermentation. Population numbers of bacteroides and clostridia after 24 and 6h, respectively, decreased significantly. Prebiotic index (PI) of LKOG was 0.76, lower than KGM (1.26), inulin (0.97) and PGM (1.23). SCFAs analysis results showed that LKOG can enhance the production of butyric acid in the colon. The concentration of butyric acids was increased as the time fermentation increased with 8.24 mM was the highest concentration and found at 72h fermentation. Positive PI value of LKOG and its ability to support the growth of beneficial bacteria especially bifidobacteria are indicated that LKOG has potency as a prebiotic and it may have specific health function related with butyric acid production. Further study of LKOG might be needed to investigate its beneficial effect in human.