| Konjac glucomannan oligosaccharides are a new type of prebiotics,and it mainly composed of glucose and mannose linked by β-1,4 bonds.Prebiotics themselves cannot be utilized by the human body,which need to be catabolized by probiotics.The secondary metabolites produced by probiotics were absorbed and utilized by the human body,which could regulate the intestinal environment,lower blood sugar and blood lipids,resist oxidation and enhance human immunity.In this study,a comparative analysis of the stability of glucomannan oligosaccharides(GMOS)and fructo-oligosaccharides(FOS)was carried out,including gastrointestinal simulation,high temperature and high pressure,different p H environment,and thermal decomposition characteristics.It was found that FOS was extremely unstable under gastric acid conditions and was easily decomposed into monosaccharides.The content of FOS dropped to less than 20% after 2 hours under gastric acid environment.While,GMOS showed high stable.Then,the activation energy(E),pre-exponential factors(ln A),thermodynamic parameters ΔG,ΔH and ΔS,and the determination of the pyrolysis mechanism of two oligosaccharides were analyzed,and calculated with three analytical methods Kissinger,Kissinger-Akahira-Sunose and Flynn-WallOzawa at non-isothermal heating rates.Results showed that there are three pyrolysis processes include water evaporation,the second and third decomposition stages for these two oligosaccharides,and the decomposition peak temperature was 200～300℃.According to the thermal decomposition analysis,glucomannan oligosaccharides was more stability than fructo-oligosaccharide.To improve the stability of FOS in gastric acid conditions,microencapsulated experiment with konjac glucomannan as wall material was performed.Results showed that encapsulation ratio was about 73%,and the particle size distribution was within 1～5 μm,which belonged to the Quasi-nanoscale microcapsule.The surface morphology showed irregular spherical shape with surface shrinkage and depression was observed by SEM.Infrared spectrogram analyzes the way the fructo-oligosaccharidewas encapsulated.The release ratio of microcapsulte reached about 85% after 2 hours,which improved the acid stability of the fructooligosaccharide microcapsules under gastric acid conditions.Lactobacillus plantarum was one of the probiotics in human intestine.It was often used as a probiotic additive in food and medical applications.In order to improve the bacterium’s resistance to adverse environments,konjac glucomannan was used to microencapsulate L.plantarum with wall material: core material(1:1and 1:1.5).Analysis was carried out on the basic physical properties,encapsulation ratio,infrared analysis,thermogravimetric analysis,storage stability and gastrointestinal simulation digestion test analysis.The results showed thatthe encapsulation ratio was all above 80%,and the thermal stability of L.plantarum after embedding was improved on the two both 1:1 and 1:1.5microcapsules.Under the conditions of 4℃ and 25℃,1:1.5 microcapsules had the best protective effect on L.plantarum during storage.The 1:1 and 1:1.5microcapsules increase the number of viable bacteria by 1.78 and 1.63 times respectively,under gastric acid conditions.Comparison of the utilization of different oligosaccharides by Enterococcus faecium and L.plantarum were performed,and the microbial metabolism mechanism were analyzed.With glucose as a carbon source control,it was found that GOS and FOS had the best growth-promoting effect on E.faecium and L.plantarum,respectively.Subsequent study showed that the growth-promoting effect of different concentrations of oligosaccharides on E.faecium and the bacteria’s utilization of the oligosaccharide components,and found that the bacteria can fully utilized oligosaccharide polymerization degree DP ≤ 3,but the utilization of the components with DP ≥ 4 is below 10%.Finally,transcriptional analysis of lactic acid bacteria with different oligosaccharides feedstocks showed that differential gene expression.It was found that the enriched metabolic pathways included the PTS system and the ABC transport system.Also,the results showed some enzyme genes was up-regulated,Including β-glucosidase and β-galactosidase.The differences in the transmembrane transport of glucomannan oligosaccharides on different lactic acid bacteria could provide a mechanism explanation for the interaction between intestinal flora and different prebiotics. |
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