Effectsof Oligosaccharides On The Bioactivity Of Lactobacillus

Microbial modulators can effectively modify intestinal microbiota, to restore balance or improve its composition. Microbial modulators can be classified into three categories according to their mechanism, namely, probiotics, prebiotics and synbiotics, among which prebiotics are especially most widely used. Common prebiotics include fructo-oligosaccharides, inulin, galacto-oligosaccharides, soybean oligosaccharides, etc. Oligosaccharides can exert prebiotic effects via different mechanisms, such as enhancing the viability of probiotics in the digestive tract and facilitating the growth of beneficial microorganisms as metabolic substrates. In this work, three Lactobacillus strains (Lactobacillus rhamnosus, Lactobacillus bulgaricus and Lactobacillus casei) were selected to evaluate the prebiotic effects of various oligosaccharides. Tested oligosaccharides included galacto-oligosaccharide, raffinose, stachyose, fructo-oligosaccharide, isomalto-oligosaccharide, and xylo-oligosaccharide. The comprehensive comparative results could provide a theoretical basis for further product development of oligosaccharides.1Growth-promoting effect of oligosaccharides on LactobacillusObjective To investigate the growth-promoting effects of oligosaccharides with various concentrations on Lactobacillus.Methods Different concentrations of the six oligosaccharides, i.e.,0,0.3%,0.6%, and1.2%(w/v), were added to MRS medium without glucose. Strains of Lactobacillus were inoculated into the mMRS-oligosaccharide medium and OD630was measured continuously for42h to obtain growth curves.Results Galacto-oligosaccharide, isomalto-oligosaccharide, xylo-oligosaccharide and fructo-oligosaccharide supported the growth of tested strains better than other oligosaccharides. At the concentration of1.2%, galacto-oligosaccharide and isomalto-oligosaccharide had the best effect on supporting Lactobacillus growth and achieved a similar effect to that of glucose, whereas raffinose and stachyose performed the worst.Conclusion Various growth-promoting effects of different oligosaccharides were observed. Galacto-oligosaccharide and isomalto-oligosaccharide (1.2%, w/v) had the best growth-promoting effect on tested strains.2Effects of oligosaccharides on the activity preservation of LactobacillusObjective To investigate the effects of the oligosaccharides on the activity preservation of Lactobacillus during common laboratory or production preservation processes.Methods Oligosaccharides of2%or20%were tested for the protective effects on Lactobacillus during various treatments, including silica gel desiccation, freezing, and freeze-drying. Viable cells counts and pH curves in milk were determined to show the viability and activity of remained cells. Freeze-dried powder was stored for two weeks at room temperature and the dying rate was measured. LC-MS was used to analyze the composition and changes of oligosaccharides during the freeze-drying and preservation period.Results All tested oligosaccharides with a concentration of2%protected Lactobacillus well in freezing storage. With a concentration of20%, fructo-oligosaccharide and xylo-oligosaccharid showed a better protective effect than that of others. In the silica gel desiccation and freeze-drying preservation tests, raffinose and stachyose performed the best. After2weeks storage at room temperature, viable counts remained high in freeze-dried form with raffinose or stachyose. Further LC-MS analysis showed that raffinose or stachyose was not absorbed into cells and degraded in the freeze-drying storage, indicating an extracellular physical protecting mechanism.Conclusion When preserving probiotics, different oligosaccharides should be selected according to preservation methods in order to achieve better preservation effect.3Effects of oligosaccharides on the adhesion of bacteria to mucus Objective To investigate effects of oligosaccharides on the adhesion of bacteria to mucus.Methods Bovine serum albumin and porcine gastric mucin were immobilized to simulate the intestinal mucus layer. Recombinant Escherichia coliwith enhanced expression of green fluorescent protein was selected for the adhesion assay. The E. coli cells were allowed to adherefor1h, and then excessive non-adherent cells were removed. Laser confocal microscope was used to visualize the adherent cells and the cell numbers were counted for analysis.Results Raffinose could significantly increase the adhesion of recombinant E. coli on polystyrene; isomalto-oligosaccharide could significantly reduce the adhesion of E. coli on BSA; stachyose, galacto-oligosaccharide and fructo-oligosaccharide could significantly increase the adhesion of E. coli on mucin, whereas raffinose could significantly reduce the adhesion of E. coli on mucin.Conclusion Different effects of various oligosaccharides on the adhesion of E. coli were observed, indicating that the adhesion of bacteria to oligosaccharides required certain structure specificity.