Background: The gut microbiota in healthy older individuals typically show a decrease in beneficial bacteria like Bifidobacterium and Lactobacillus, alongside an increase in pro-inflammatory microbes such as Enterobacteriaceae and Clostridia. These changes contrast with younger and middle-aged individuals and appear to correlate with cognitive status. Although there is extensive research on gut microbiota and cognitive functions in cognitively impaired elderly individuals, its impact on cognitively healthy elderly populations has not been extensively studied. Method: A comprehensive literature search was conducted across PubMed, EBSCO, Web of Science, and Scopus databases to identify studies exploring the relationship between gut microbiota composition and cognitive functioning in healthy older adults. During the literature screening process, each record was initially assessed by its title, abstract, and keywords to exclude articles that did not align with the scope of this review. Three authors independently screened and retrieved the records. The inclusion criteria included: (1) publication in peer-reviewed journals; (2) studies involving neurologically, cognitively, and medically healthy populations; (3) participants identified as older adults, defined for this review as individuals aged 45 years and older due to the limited number of records; (4) analysis of gut microbiota; and (5) assessment of cognitive function. Subsequently, full texts were analyzed to determine eligibility. The exclusion criteria encompassed: (1) incorrect publication type; (2) inappropriate sample population; (3) unsuitable study design; (4) absence of one or more inclusion criteria; and (5) studies based on animal research. A risk of bias assessment was performed for each included study using the Joanna Briggs Institute (JBI) checklist, ensuring all selected studies met established quality standards. Results: A total of 6 eligible research articles from a possible 1752 published until March 2024 were identified and included. We categorized the included studies into two groups based on their focus: the taxonomic composition of gut microbiota and the alpha diversity, which is the variety of organisms within a sample. Additionally, two methods were identified for assessing cognition: neuropsychological tests and physiological measurements, notably electroencephalography (EEG). The studies show varying results regarding the abundance of specific bacterial taxa and their cognitive associations. Notably, the relationship between certain bacteria and cognition may vary when analyzed at different taxonomic levels, such as phylum versus family. Conclusions: Changes in gut microbiota composition in the elderly, even without a cognitive impairment diagnosis, could potentially serve as early biological markers for Alzheimer’s disease or other dementias before mild cognitive impairment appears.

In recent years, new plant-based foods and drinks have been developed to meet the growing demand for animal-derived alternatives, particularly dairy products. This study investigates the impact of lactic acid fermentation on the organic acids and sugars in oat and buckwheat beverages developed using Lactobacillus johnsonii K4 and Lacticaseibacillus rhamnosus K3, which are potential probiotics. The fermented samples were analyzed for pH changes, bacterial viability, and the concentration of organic acids and sugars over 15 days. The results indicated significant variations in bacterial colony counts, with L. johnsonii K4 showing the highest initial growth. Over 15 days, pH levels decreased, with the most acidic conditions observed in buckwheat beverages. Notably, fermentation led to a significant increase in acetic acid concentration and a reduction in malic acid levels, particularly in buckwheat samples. These findings highlight the dynamic nature of fermentation in enhancing the nutritional profile and shelf-life of plant-based beverages.

Background/Objectives: With increasing knowledge of the role of the microbiota in health and disease, the need for the reliable simulation of its behavior in response to various factors, such as diet and probiotic administration in in vitro conditions, has emerged. Although many studies utilize developed systems, data on how accurately these systems represent individual microbiota responses are scarce. Methods: In the present study, the Simulator of Human Intestinal Microbial Ecosystem (SHIME^®) was exposed to experimental conditions mimicking the application of probiotics and dietary changes in the study participant. Next-generation 16S rRNA sequencing was used to reveal the structure of the microbial communities in the analyzed samples. Results: Analysis of 17 samples revealed that predominantly diet and, to a lesser extent, probiotics had a divergent effect on the microbiota’s fluctuations dependent on the culture environment. Despite this, results from both in vitro and in vivo conditions aligned well with previously published data on the expected impact of dietary changes on the intestinal microbial community. Conclusions: The anecdotal evidence presented in this study suggested that current in vitro technology enables the reproduction of some of the microbiota responses that are well known from in vivo research. However, further work is required to enable simulations of an individual microbiota.

Background/Objectives: The microbiota–gut–brain axis (MGBA) plays a pivotal role in cognitive function, making psychobiotics a promising strategy for managing neurodegenerative diseases. Lactic acid bacteria (LAB) from traditional fermented foods represent a valuable source of candidate strains, and multi-strain consortia may offer enhanced therapeutic efficacy through synergistic effects. This study evaluated the functional and psychobiotic potential of three lactic acid bacteria (LAB) strains isolated from fermented foods, assessed as monocultures and a multi-strain consortium (MIX). Methods: The research encompassed an initial screening of the individual strains and the MIX, assessing their adhesion to mucin, stability in a static in vitro digestion model, and amino acid profiling. Subsequently, the LAB MIX underwent long-term evaluation in a dynamic gastrointestinal model (SHIME^®) inoculated with microbiota from a patient with Alzheimer’s disease, during which alterations in gut microbiota composition and amino acid metabolism were analyzed. Results: The LAB MIX demonstrated high stability under digestive stress and effective mucoadhesive properties. Furthermore, the consortium demonstrated a distinct metabolic signature, driving enhanced functional effects that complemented or exceeded those observed in individual monocultures. In the SHIME^® model, the MIX induced significant, site-specific shifts in microbial composition, notably increasing lactobacilli abundance. These taxonomic changes correlated with an enriched metabolic profile, including elevated levels of GABA precursors and amino acids with antioxidant potential, which are crucial for MGBA modulation. Conclusions: These results identify the LAB consortium as a compelling psychobiotic candidate. Further in-depth in vivo and clinical studies are required to validate its therapeutic potential for MGBA modulation.

Background: The transfer of human intestinal microbiota from in vivo to in vitro conditions alters its structure. This transition may trigger functional changes in the microbial community, such as its ability to produce short-chain fatty acids (SCFAs) and lactate. Methods: This study evaluated SCFAs and lactate profiles in the dynamic simulator and in the feces of a human volunteer who donated a sample for the inoculation of the system. Changes in SCFA and lactate levels were monitored over a 28-day dietary intervention and a parallel 14-day probiotic supplementation. Results: Microbial and dietary variation were not significant predictors of variability in SCFA and lactate profiles. In contrast, culturing environment and probiotic intervention exerted significant effects on SCFAs and lactate. The probiotic intervention appeared to influence SCFA and lactate profiles under in vitro conditions, whereas no similar effect was observed in vivo. Furthermore, the abundance of individual microbial genera was mostly weakly correlated with SCFA and lactate levels, and the direction of these correlations was inconsistent across two microbiota culturing environments. Conclusion: Our findings suggest that structural changes in the microbiota during its transfer from in vivo to in vitro conditions are accompanied by alterations in microbial functions, such as SCFA and lactate levels or response to interventions. However, these responses align with data from other human studies, supporting the ability of dynamic in vitro models to simulate key functions of the intestinal microbiota. Further optimization is required to accurately model personalized microbiota responses.