Thavaratnam Vasanthan

Supplementation of the Diet with High-Viscosity Beta-Glucan Results in Enrichment for Lactobacilli in the Rat Cecum

ABSTRACT BBn (BioBreeding) rats were fed casein-based diets supplemented with barley flour, oatmeal flour, cellulose, or barley β-glucans of high [HV] or low viscosity [LV] in order to measure the prebiotic effects of these different sources of dietary fiber. The dietary impact on the composition of the cecal microbiota was determined by the generation of denaturing gradient gel electrophoresis (DGGE) profiles of PCR-amplified 16S rRNA gene sequences. The DGGE profiles produced from the cecal microbiota of rats within each dietary group were similar, but consensus profiles generated from pooled bacterial DNAs showed differences between rat groups. Animals fed HV glucans (HV-fed rats) had DGGE consensus profiles that were 30% dissimilar from those of the other rat groups. A 16S rRNA gene fragment that was more conspicuous in the profiles of HV-fed animals than in those of cellulose-fed rats had sequence identity with Lactobacillus acidophilus. Measurements of L. acidophilus rRNA abundance (DNA-RNA hybridization), the preparation of cloned 16S rRNA gene libraries, and the enumeration of Lactobacillus cells (fluorescent in situ hybridization) showed that lactobacilli formed a greater proportion of the cecal microbiota in HV-fed rats. In vitro experiments confirmed that some lactobacilli utilize oligosaccharides (degree of polymerization, 3 or 4) present in β-glucan hydrolysates. The results of this study have relevance to the use of purified β-glucan products as dietary supplements for human consumption.

β-Glucan from Two Sources of Oat Concentrates Affect Postprandial Glycemia in Relation to the Level of Viscosity

Objective: Soluble dietary fiber has been shown to attenuate the postprandial rise in blood glucose levels and reduce the risk of type 2 diabetes and cardiovascular disease. This effect seems to be related to its rheological properties including viscosity. We examined the intra-fiber variability between two different processing methods of concentrating β-glucan from oats (aqueous vs. enzymatic) in relation to the level of viscosity of β-glucan and its effect on postprandial glycemia in healthy individuals. Design: In an acute, randomized, double-blind, crossover study, 11 healthy subjects (gender: 5M:6F; age: 34 ± 5 years; BMI: 23 ± 0.8 kg/m2) were randomly assigned, on three separate occasions, to consume one of three fiber-matched treatments along with a 75g oral glucose drink. The enzymatically processed β-glucan (Oat-A) differed from β-glucan processed through the aqueous method (Oat-B) solely with regard to viscosity. Finger-prick capillary blood samples were obtained at fasting and at 15, 30, 45, 60, 90 and 120 min after the start of the test drink. The viscosities of the fiber drinks were determined (Paar Physica UDS200 viscometer). Results: Rheological measurements demonstrated that Oat-A had a significantly higher viscosity than Oat-B and control at 5, 15, 30, 60, and 120 min (p < 0.001). The incremental area under the glucose curve (AUC) on Oat-A was 19.6% and 17% lower than that of Oat-B and control, respectively (p < 0.01). Conclusions: This study shows that processing oat β-glucan through enzymatic, rather than by aqueous methods, preserves the viscosity and improves postprandial glycemic control.

Dietary Oat β-Glucan Reduces Peak Net Glucose Flux and Insulin Production and Modulates Plasma Incretin in Portal-Vein Catheterized Grower Pigs

Net glucose and SCFA flux and insulin secretion into the portal vein might be associated with the incretins glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). Our objectives were to clarify this association and study the impact of 2 doses of dietary oat beta-glucan on the variables. Three 35-kg portal vein-catheterized pigs were fed 3 diets containing 0, 3, or 6% oat beta-glucan concentrate (BG0, BG3, and BG6) for 7 d in a repeated 3 x 3 Latin square. On d 7, blood was sampled for 12 h postprandially. Net glucose flux and apparent hormone production were calculated from plasma portal-arterial differences x flow. Postprandially, pigs fed BG6 had lower (P < 0.05) portal glucose at 15, 30, and 45 min and a lower (P < 0.05) net glucose flux during the first hour. Pigs fed BG6 tended to have lower (P < 0.10) portal C-peptide without lowering insulin, indicating that pigs fed BG6 had lower actual insulin release combined with a higher prehepatic retention of insulin. Pigs fed BG6 had lower (P < 0.05) portal GIP and GLP-1, which in turn were correlated (R(2) = 0.81 and 0.88, respectively; P < 0.01) with portal glucose. Pigs fed BG3 and BG6 had a higher (P < 0.05) net SCFA flux than pigs fed BG0, indicating increased fermentation. In conclusion, dietary supplementation of 6% oat beta-glucan concentrate decreased net glucose flux, increased net SCFA flux, and decreased peak apparent insulin production, changes that were associated with GIP and GLP-1 mediation.

Effects of viscosity and fermentability of dietary fibre on nutrient digestibility and digesta characteristics in ileal-cannulated grower pigs

Relative contributions of two functional properties, viscosity and fermentability of dietary fibre, on apparent ileal digestibility (AID), apparent total tract digestibility (ATTD), digesta passage rate, N retention and SCFA concentration have not been established. Thus, eight ileal-cannulated pigs randomised in a double 4 × 4 Latin square were fed four diets based on maize starch and casein supplemented with 5 % of actual fibre in a 2 × 2 factorial arrangement: low-fermentable, low-viscous cellulose (CEL); low-fermentable, high-viscous carboxymethylcellulose (CMC); high-fermentable, low-viscous oat β-glucan (LBG); high-fermentable, high-viscous oat β-glucan (HBG). Viscosity and fermentability interacted to affect (P < 0·001) digesta viscosity and AID and ATTD of nutrients. These properties tended to interact to affect (P < 0·10) digesta passage rate and butyrate. Pigs fed the CMC diet had the lowest (P < 0·05) digesta passage rate and the highest (P < 0·001) AID of energy, crude protein and DM, and ATTD of energy and DM. Post-ileal DM digestibility was highest (P < 0·001) for pigs fed the CEL and HBG diets. Post-ileal DM digestibility had a negative, curvilinear relationship with the AID of energy and crude protein (R2 0·85 and 0·72, respectively; P < 0·001). Digesta viscosity had a less strong relationship with the AID of energy and crude protein (R2 0·45 and 0·36, respectively; P < 0·001). In conclusion, high-viscous, low-fermentable dietary fibre increases the proportion of a diet that is digested in the small intestine by reducing digesta passage rate.

In situ identification and quantification of starch-hydrolyzing bacteria attached to barley and corn grain in the rumen of cows fed barley-based diets

Cereal grains rich in starch are widely used to meet the energy demands of high-producing beef and dairy cattle. Bacteria are important players in starch digestion in the rumen, and thus play an important role in the hydrolysis and fermentation of cereal grains. However, our understanding of the composition of the rumen starch-hydrolyzing bacteria (SHB) is limited. In this study, BODIPY FL DQ starch staining combined with fluorescence in situ hybridization (FISH) and quantitative FISH were applied to label, identify and quantify SHB possessing active cell-surface-associated (CSA) α-amylase activity in the rumen of heifers fed barley-based diets. When individual cells of SHB with active CSA α-amylase activity were enumerated, they constituted 19-23% of the total bacterial cells attached to particles of four different cultivars of barley grain and corn. Quantitative FISH revealed that up to 70-80% of these SHB were members of Ruminococcaceae in the phylum Firmicutes but were not Streptococcus bovis, Ruminobacter amylophilus, Succinomonas amylolytica, Bifidobacterium spp. or Butyrivibrio fibrisolvens, all of whose amylolytic activities have been demonstrated previously in vitro. The proportion of barley grain in the diet had a large impact on the percentage abundance of total SHB and Ruminococcaceae SHB in these animals.