Preferential growth stimulation of probiotic bacteria by galactan exopolysaccharide from Weissella confusa KR780676.

Many microbial exopolysaccharides (EPS) are reported to have prebiotic properties. This study reports the prebiotic properties of a galactan exopolysaccharide produced by Weissella confusa KR780676 of fermented food origin. We have reported potential techno-functional properties of this EPS earlier. We have studied the parameters such as enzymatic hydrolysis, growth proliferation effect on probiotic bacteria and in vitro fecal fermentation to demonstrate the prebiotic property of the galactan. The galactan showed strong resistance to simulated human digestive juices such as α-amylase (99.1%), gastric (98.4%) and intestinal fluid hydrolysis (98.8%). It also encouraged the growth of probiotic bacteria viz, Lactobacillus plantarum MTCC9510 (recently reclassified as Lactiplantibacillus plantarum) and L. fermentum MTCC903 (recently reclassified as Limosilactobacillus fermentum) from 6.69 to 9.45 log CFU/mL and 7.13 to 9.05 log CFU/mL respectively in 72 h of fermentation. Carbohydrate utilization also exhibited the same pattern. Fecal fermentation of galactan for 48 h through in vitro studies exhibited significant changes in microbial population and short chain fatty acids (SCFAs) production. Bifidobacterium sp. and Lactobacillus sp. showed significantly (p ≤ 0.05) higher growth when compared to Enterococcus sp. (9.62 log CFU/mL, 8.45 log CFU/mL and 8.31 log CFU/mL respectively from 6.54 log CFU/mL) at the end of fermentation. SCFAs (acetic acid, butyric acid and propionic acid production) increased significantly (p ≤ 0.05) from 4.53 to 69.12 mM/L, 1.27 to 5.47 mM/L and 0.68 to 42.11 mM/L respectively. These results clearly prove the potential prebiotic property of the galactan EPS and could be used as an effective prebiotic to positively modulate the gut microbiome homeostasis.

Characterization of α-D-glucan produced by a probiont Enterococcus hirae KX577639 from feces of south Indian Irula tribals.

Exopolysaccharide (EPS) producing probiotic strain Enterococcus hirae KX577639 were isolated from the feces of South Indian Irula tribes. EPS yield was 18.57 g/L (dry weight) at 48 h in 2% sucrose supplemented MRS medium. TLC and GC-MS analysis confirmed the presence of predominant glucose monomer indicating the homopolysaccharide nature of EPS. FTIR and NMR studies revealed that the EPS were branched α-D-glucan polymer with α-(1 → 6) and α-(1 → 3) linkages. SEM analysis of glucan-EPS revealed porous and starch like cracked granules of aggregation. AFM studies proved spherical lumps and dense, grainy like network. The thermal behavior of glucan-EPS showed degradation temperature of 315.98 °C and melting point of 296.67 °C. The XRD analysis confirmed the amorphous nature of EPS with a crystalline index of 0.48. The water solubility index and water holding capacity of glucan-EPS showed 46.5% and 202.04%. These distinctive features of the glucan EPS could find its potential application in functional food products as the α-(1 → 3) linkage are resistant to human digestive enzymes and can serve as a nutrient to gut bacteria. This the first study reporting the EPS production by Enterococcus hirae.