Background: Older people are more susceptible to deterioration of the gut microbiota. Prebiotics help improve the gut microbiota. Inulin, a major prebiotic, stimulates the growth of Bifidobacterium; however, it produces a large amount of gas, which leads to abdominal symptoms. Methods: In this study, in vitro fecal fermentation was performed using fecal samples from seven older people (mean subject age, 73.4 years; five men and two women) to examine whether combining inulin with another prebiotic material, resistant dextrin, could lead to decreased gas production and show prebiotic effects. Results: The Bifidobacterium counts and short-chain fatty acid production did not differ significantly between the inulin 0.5% group and the inulin 0.25% plus resistant dextrin 0.25% combination group. However, the inulin 0.25% plus resistant dextrin 0.25% combination group had lower gas production than the inulin 0.5% group (p < 0.10). Furthermore, compared with the inulin 0.5% group, the 0.25% combination group showed significantly greater gut microbiota diversity and tended toward a lower pH in the fermentation medium at the end of fermentation (p = 0.09). These effects are believed to be due to the combination of inulin, which is highly selective for Bifidobacterium and rapidly utilized by the gut microbiota, and resistant dextrin, which is slowly utilized by various bacterial genera. Conclusions: These findings suggest that the inulin plus resistant dextrin combination has superior prebiotic effects in older people and causes less gas production than inulin alone.

Xanthan gum-based thickeners are commonly used to treat dysphagic patients. Their rheological properties, such as shear-thinning, extension, and thixotropy, contribute to swallowing safety. However, the influence of rheological variations on swallowing dynamics remains unclear. This study investigated the impact of variations in the rheological properties of xanthan gum-based thickeners on swallowing dynamics, specifically tongue pressure, suprahyoid muscle activity, and swallowing sounds. Shear rheology, extensional viscosity, and 3-interval thixotropy tests were conducted on three commercial thickener solutions standardized to a 400 mPa·s viscosity at a 50 s⁻¹ shear rate. Twenty healthy volunteers (11 females, 24.6 ± 2.4 years) participated in this study, during which tongue pressure, suprahyoid muscle activity, and swallowing sounds were measured while swallowing 15 mL samples. The first thickener exhibited reduced shear viscosity at 300 s⁻¹, higher thixotropy, and shorter swallowing sound duration, suggesting a shortened pharyngeal transit time. The second showed prolonged filament breakage time and higher tongue pressure in the posterior-median region of the palate, leading to increased tongue activity during swallowing. The third exhibited lower extensional viscosity, different muscle activity than the second, and longer duration of swallowing sound than the first. These results suggest that rheological property variations in xanthan gum-based thickeners influence swallowing dynamics in healthy individuals.

The emptying rate of specific nutrients in enteral formulas is poorly understood, despite the importance of controlling the emptying rate in tube-fed patients. Because of their viscosity, thickened formulas are widely used to avoid gastric reflux and reduce the burden on caregivers. This study examined how thickeners in enteral formulas affected the gastric emptying rates of proteins and carbohydrates. A semi-dynamic gastric model was used to prepare and digest test enteral formulas that contained either no thickeners or agar (0.2%). The amounts of protein and carbohydrates in each emptied aliquot were determined, and the emptying rate was calculated. We found that agar accelerated protein emptying, and an exploratory experiment with agar (0.5%) suggested the possibility of concentration dependence. Additionally, experiments using gellan gum (0.08%), guar gum (0.2%), or carrageenan (0.08%, 0.2%) suggested that protein emptying could vary depending on the thickener type and that carrageenan might slow it. These results could help with the appropriate selection of thickeners added to liquid foods based on the patient’s metabolic profile to manage nutrition, not only for tube-fed patients but also for those with oropharyngeal dysphagia or diabetes.