An in vitro batch fermentation protocol for studying the contribution of food to gut microbiota composition and functionality

Knowledge of the effect of foods on gut microbiota composition and functionality is expanding. To isolate the effect of single foods and/or single nutrients (i.e., fiber, polyphenols), this protocol describes an in vitro batch fermentation procedure to be carried out after an in vitro gastrointestinal digestion. Therefore, this is an extension of the previous protocol described by Brodkorb et al. (2019) for studying in vitro digestion. The current protocol uses an oligotrophic fermentation medium with peptone and a high concentration of fecal inoculum from human fecal samples both to provide the microbiota and as the main source of nutrients for the bacteria. This protocol is recommended for screening work to be performed when many food samples are to be studied. It has been used successfully to study gut microbiota fermentation of different foodstuffs, giving insights into their functionality, community structure or ability to degrade particular substances, which can contribute to the development of personalized nutrition strategies. The procedure does not require a specific level of expertise. The protocol takes 4-6 h for preparation of fermentation tubes and 20 h for incubation.

Bioactivity of food melanoidins is mediated by gut microbiota

Melanoidins are an important component of the human diet (average consumption 10 g/day), which escape gastrointestinal digestion and are fermented by the gut microbiota. In this study melanoidins from different food sources (coffee, bread, beer, balsamic vinegar, sweet wine, biscuit, chocolate, and breakfast cereals) were submitted to an in vitro digestion and fermentation process, and their bioactivity was assessed. Some melanoidins were extensively used by gut microbes, increasing production of short chain fatty acids (mainly acetate and lactate) and favoring growth of the beneficial genera Bifidobacterium (bread crust, pilsner and black beers, chocolate and sweet wine melanoidins) and Faecalibacterium (biscuit melanoidins). Quantification of individual phenolic compounds after in vitro fermentation allowed their identification as microbial metabolites or phenolics released from the melanoidins backbone (specially pyrogallol, 2-(3,4-dihydroxyphenyl)acetic and 3-(3,4-dihydroxyphenyl)propionic acids). Our results also showed that antioxidant capacity of melanoidins is affected by gut microbiota fermentation.

Modifications in bacterial groups and short chain fatty acid production in the gut of healthy adult rats after long-term consumption of dietary Maillard reaction products

Bread crust (BC) is one of the major sources of Maillard reaction products (MRPs) in the Western diet. This work was designed to analyze the impact of diets containing important levels of MRPs from BC on intestinal bacterial growth and short chain fatty acids (SCFAs) production in adult rats. Additionally, the pools of compounds excreted in feces attending to their molecular weights were analyzed. Rats were fed for 88days a control diet or diets containing BC or its soluble high molecular weight (HMW), soluble low molecular weight (LMW) or insoluble fractions, respectively. Intestinal (cecum) microbiota composition was determined by qPCR analysis. Consumption of the BC diet lowered (P<0.05) Lactobacillus spp. and Bifidobacterium spp. log₁₀ counts (8 and 14%, respectively), an effect for which soluble LMW and HMW fractions of BC seemed to be responsible. In these same animals, Escherichia/Shigella counts increased by around 45% (P<0.05), a fact which correlated with a higher production of formic acid in feces (r=0.8197, P=0.0458), and likely caused by the combined consumption of all MRPs contained in the BC. A significant 5-fold increment (P<0.05) was detected in the fecal proportion of propionic acid in the BC group, one of the products that have largely been associated with anti-inflammatory actions. Regarding the distribution of MRPs in feces, only the LMW fed group exhibited a predominance of those ranging between 90,000-1000Da, whereas the rest of the groups presented higher amounts of products above 90,000Da. It is concluded that dietary Maillard reaction products are in vivo fermented by the gut microbiota, thereby changing both the pattern of SCFAs production and the microbiota composition.

Green Tea and Its Relation to Human Gut Microbiome

Green tea can influence the gut microbiota by either stimulating the growth of specific species or by hindering the development of detrimental ones. At the same time, gut bacteria can metabolize green tea compounds and produce smaller bioactive molecules. Accordingly, green tea benefits could be due to beneficial bacteria or to microbial bioactive metabolites. Therefore, the gut microbiota is likely to act as middle man for, at least, some of the green tea benefits on health. Many health promoting effects of green tea seems to be related to the inter-relation between green tea and gut microbiota. Green tea has proven to be able to correct the microbial dysbiosis that appears during several conditions such as obesity or cancer. On the other hand, tea compounds influence the growth of bacterial species involved in inflammatory processes such as the release of LPS or the modulation of IL production; thus, influencing the development of different chronic diseases. There are many studies trying to link either green tea or green tea phenolic compounds to health benefits via gut microbiota. In this review, we tried to summarize the most recent research in the area.

Antioxidant, ACE-inhibitory and antimicrobial activity of fermented goat milk: activity and physicochemical property relationship of the peptide components

Increasing evidence on goat milk and the health benefits of its derived products beyond its nutritional value show its potential as a functional food. In this study, goat milk fractions were tested for their total antioxidant capacity using different methods (ORAC, ABTS, DPPH and FRAP), as well as their angiotensin-I-converting-enzyme inhibitory and antimicrobial (against Escherichia coli and Micrococcus luteus) activities. Different whey fractions (whey, cation exchange membrane permeate P and retentate R) of two fermented skimmed goat milks (ultrafiltered goat milk fermented with the classical starter bacteria or with the classical starter plus the Lactobacillus plantarum C4 probiotic strain) were assessed. Additionally, P fractions were divided into two sub-fractions after being passed through a 3 kDa cut-off membrane: (a) the permeate with peptides of MW <3 kDa (P < 3); and (b) the retentate with peptides and proteins of MW >3 kDa (P > 3). No differences in biological activities were observed between the two fermented milks. However, the biological peptides present in the P < 3 fraction showed the highest total antioxidant capacity (for the ORAC assay) and angiotensin-I-converting-enzyme inhibitory activity. Those present in the R fraction showed the highest total antioxidant capacity against ABTS˙⁺ and DPPH˙ radicals. Some antimicrobial activity against E. coli was observed for the fermented milk containing the probiotic, which could be due to some peptides being released by the probiotic strain. In conclusion, small and non-basic bioactive peptides could be responsible for most of the angiotensin-I-converting-enzyme inhibitory and antioxidant activities. These findings reinforce the potential benefits of the consumption of fermented goat milk in the prevention of cardiovascular diseases associated with oxidative stress and hypertension.

Ulcerative Colitis and Crohn's Disease Are Associated with Decreased Serum Selenium Concentrations and Increased Cardiovascular Risk

The incidence of inflammatory bowel disease (IBD) and associated oxidative stress is increasing. The antioxidant mineral selenium (Se) was measured in serum samples from 106 IBD patients (53 with ulcerative colitis (UC) and 53 with Crohn’s disease (CD)) and from 30 healthy controls. Serum Se concentrations were significantly lower in UC and CD patients than in healthy controls (p < 0.001) and significantly lower in CD patients than in UC patients (p = 0.006). Se concentrations in patients were significantly influenced by sex, body mass index (BMI), the inflammatory biomarker α-1-antitrypsin, surgery, medical treatment, the severity, extent, and form of the disease and the length of time since onset (p < 0.05). Se concentrations in IBD patients were positively and linearly correlated with nutritional (protein, albumin, prealbumin, cholinesterase and total cholesterol) and iron status-related (hemoglobin, Fe and hematocrit) parameters (p < 0.05). A greater impairment of serum Se and cardiovascular status was observed in CD than in UC patients. An adequate nutritional Se status is important in IBD patients to minimize the cardiovascular risk associated with increased inflammation biomarkers, especially in undernourished CD patients, and is also related to an improved nutritional and body iron status.

Green and white teas as health-promoting foods

Tea is one of the most consumed beverages around the world and as such, it is constantly the object of novel research. This review focuses on the research performed during the last five years to provide an updated view of the current position of tea regarding human health. According to most authors, tea health benefits can be traced back to its bioactive components, mostly phenolic compounds. Among them, catechins are the most abundant. Tea has an important antioxidant capacity and anti-inflammatory properties, which make this beverage (or its extracts) a potential aid in the fight against several chronic diseases. On the other hand, some studies report the possibility of toxic effects and it is advisable to reduce tea consumption, such as in the last trimester of pregnancy. Additionally, new technologies are increasing researchers' possibilities to study the effect of tea on human gut microbiota and even against SARS CoV-2. This beverage favours some beneficial gut microbes, which could have important repercussions due to the influence of gut microbiota on human health.

Effect of in vitro digestion-fermentation on green and roasted coffee bioactivity: The role of the gut microbiota

Coffee is one of the most consumed beverages and has been linked to health in different studies. However, green and roasted coffees have different chemical composition and therefore their health properties might differ as well. Here, we study the effect of in vitro digestion-fermentation on the antioxidant capacity, phenolic profile, production of short-chain fatty acids (SCFAs), and gut microbiota community structure of green and roasted coffee brews. Roasted coffees showed higher antioxidant capacity than green coffees, with the highest level achieved in fermented samples. Polyphenol profile was similar between green and roasted coffees in regular coffee brews and the digested fraction, but very different after fermentation. Production of SCFAs was higher after fermentation of green coffee brews. Fermentation of coffee brews by human gut microbiota led to different community structure between green and roasted coffees. All these data suggest that green and roasted coffees behave as different types of food.

Spent Coffee Grounds Extract, Rich in Mannooligosaccharides, Promotes a Healthier Gut Microbial Community in a Dose-Dependent Manner

Coffee is one of the most consumed beverages around the world, and as a consequence, spent coffee grounds are a massively produced residue that is causing environmental problems. Reusing them is a major focus of interest presently. We extracted mannooligosaccharides (MOS) from spent coffee grounds and submitted them to an in vitro fermentation with human feces. Results obtained suggest that MOS are able to exert a prebiotic effect on gut microbiota by stimulating the growth of some beneficial genera, such as Barnesiella, Odoribacter, Coprococcus, Butyricicoccus, Intestinimonas, Pseudoflavonifractor, and Veillonella. Moreover, short-chain fatty acids (SCFA) production also increased in a dose-dependent manner. However, we observed that 5-(hydroxymethyl)furfural, furfural, and polyphenols (which are either produced or released from the spent coffee grounds matrix during hydrolysis) could have an inhibitory effect on other beneficial genera, such as Faecalibacterium, Ruminococcus, Blautia, Butyricimonas, Dialister, Collinsella, and Anaerostipes, which could negatively affect the prebiotic activity of MOS.

Spent coffee grounds improve the nutritional value in elements of lettuce (Lactuca sativa L.) and are an ecological alternative to inorganic fertilizers

The element concentration in lettuces grouped in 5 categories (baby variety, cultivated in agricultural soils with low or high percentages of spent coffee grounds-SCG, without SCG and with NPK) were measured. Lettuces cultivated in agricultural soils amended with SCG had significantly higher levels of several essential (V, Fe, Co, V, and probably Mn and Zn) and toxic elements (Al and probably As), without reaching their toxicological limits. Additionally, blocking of N uptake and therefore plant biomass, and probably Cd absorption from agricultural soil was observed. Organic farming with SCG ameliorates element concentrations in lettuces vs. NPK fertilization. The linear correlations among element uptake and the amendment of SCG could be related with their chelation by some SCG components, such as melanoidins and with the decrease in the soil pH. In conclusion, the addition of SCG produces lettuces with higher element content.

High Antioxidant Action and Prebiotic Activity of Hydrolyzed Spent Coffee Grounds (HSCG) in a Simulated Digestion-Fermentation Model: Toward the Development of a Novel Food Supplement

Spent coffee grounds are a byproduct with a large production all over the world. The aim of this study was to explore the effects of a simulated digestion-fermentation treatment on hydrolyzed spent coffee grounds (HSCG) and to investigate the antioxidant properties of the digestion and fermentation products in the human hepatocellular carcinoma HepG2 cell line. The potentially bioaccessible (soluble) fractions exhibited high chemoprotective activity in HepG2 cells against oxidative stress. Structural analysis of both the indigestible (insoluble) and soluble material revealed partial hydrolysis and release of the lignin components in the potentially bioaccessible fraction following simulated digestion-fermentation. A high prebiotic activity as determined from the increase in Lactobacillus spp. and Bifidobacterium spp. and the production of short-chain fatty acids (SCFAs) following microbial fermentation of HSCG was also observed. These results pave the way toward the use of HSCG as a food supplement.

Enrichment of Food With Tannin Extracts Promotes Healthy Changes in the Human Gut Microbiota

Food and food bioactive components are major drivers of modulation of the human gut microbiota. Tannin extracts consist of a mix of bioactive compounds, which are already exploited in the food industry for their chemical and sensorial properties. The aim of our study was to explore the viability of associations between tannin wood extracts of different origin and food as gut microbiota modulators. 16S rRNA amplicon next-generation sequencing (NGS) was used to test the effects on the gut microbiota of tannin extracts from quebracho, chestnut, and tara associated with commercial food products with different composition in macronutrients. The different tannin-enriched and non-enriched foods were submitted to in vitro digestion and fermentation by the gut microbiota of healthy subjects. The profile of the short chain fatty acids (SCFAs) produced by the microbiota was also investigated. The presence of tannin extracts in food promoted an increase of the relative abundance of the genus Akkermansia, recognized as a marker of a healthy gut, and of various members of the Lachnospiraceae and Ruminococcaceae families, involved in SCFA production. The enrichment of foods with tannin extracts had a booster effect on the production of SCFAs, without altering the profile given by the foods alone. These preliminary results suggest a positive modulation of the gut microbiota with potential benefits for human health through the enrichment of foods with tannin extracts.

An extended reconstruction of human gut microbiota metabolism of dietary compounds

Understanding how diet and gut microbiota interact in the context of human health is a key question in personalized nutrition. Genome-scale metabolic networks and constraint-based modeling approaches are promising to systematically address this complex problem. However, when applied to nutritional questions, a major issue in existing reconstructions is the limited information about compounds in the diet that are metabolized by the gut microbiota. Here, we present AGREDA, an extended reconstruction of diet metabolism in the human gut microbiota. AGREDA adds the degradation pathways of 209 compounds present in the human diet, mainly phenolic compounds, a family of metabolites highly relevant for human health and nutrition. We show that AGREDA outperforms existing reconstructions in predicting diet-specific output metabolites from the gut microbiota. Using 16S rRNA gene sequencing data of faecal samples from Spanish children representing different clinical conditions, we illustrate the potential of AGREDA to establish relevant metabolic interactions between diet and gut microbiota.

Evaluating the effects of a standardized polyphenol mixture extracted from poplar-type propolis on healthy and diseased human gut microbiota

INTRODUCTION

A large body of evidence suggests that propolis exerts antioxidant, anti-inflammatory, and antimicrobial activities, mostly ascribed to its polyphenol content. Growing evidence suggests that propolis could modulate gut microbiota exerting a positive impact on several pathological conditions. The aim of this study was to determine the in vitro impact of a poplar-type propolis extract with a standardized polyphenol content, on the composition and functionality of gut microbiota obtained from fecal material of five different donors (healthy adults, and healthy, obese, celiac, and food allergic children).

METHODS

The standardized polyphenol mixture was submitted to a simulated in vitro digestion-fermentation process, designed to mimic natural digestion in the human oral, gastric, and intestinal chambers. The antioxidant profile of propolis before and after the digestion-fermentation process was determined. 16 S rRNA amplicon next-generation sequencing (NGS) was used to test the effects on the gut microbiota of propolis extract. The profile of the short-chain fatty acids (SCFA) produced by the microbiota was also investigated through a chromatographic method coupled with UV detection.

RESULTS

In vitro digestion and fermentation induced a decrease in the antioxidant profile of propolis (i.e., decrease of total polyphenol content, antiradical and reducing activities). Propolis fermentation exhibited a modulatory effect on gut microbiota composition and functionality of healthy and diseased subjects increasing the concentration of SCFA.

CONCLUSIONS

Overall, these data suggest that propolis might contribute to gut health and could be a candidate for further studies in view of its use as a prebiotic ingredient.

Effect of Cooking Methods on the Antioxidant Capacity of Plant Foods Submitted to In Vitro Digestion-Fermentation

The antioxidant capacity of foods is essential to complement the body's own endogenous antioxidant systems. The main antioxidant foods in the regular diet are those of plant origin. Although every kind of food has a different antioxidant capacity, thermal processing or cooking methods also play a role. In this work, the antioxidant capacity of 42 foods of vegetable origin was evaluated after in vitro digestion and fermentation. All foods were studied both raw and after different thermal processing methods, such as boiling, grilling roasting, frying, toasting and brewing. The cooking methods had an impact on the antioxidant capacity of the digested and fermented fractions, allowing the release and transformation of antioxidant compounds. In general, the fermented fraction accounted for up to 80-98% of the total antioxidant capacity. The most antioxidant foods were cocoa and legumes, which contributed to 20% of the daily antioxidant capacity intake. Finally, it was found that the antioxidant capacity of the studied foods was much higher than those reported by other authors since digestion-fermentation pretreatment allows for a higher extraction of antioxidant compounds and their transformation by the gut microbiota.

Phytotoxicity and chelating capacity of spent coffee grounds: Two contrasting faces in its use as soil organic amendment

Spent coffee grounds (SCG) are a bioresidue generated in large amounts worldwide, which could be employed as either fresh or transformed organic soil amendment, by means of different treatments in order to improve its agronomic qualities. An in vitro experiment was conducted in order to evaluate the effect of using different bioamendments derived from spent coffee grounds (SCG) on biomass and Zn, Cu and Fe content of lettuces. Application of 7.5% (w/w) fresh SCG, vermicompost, compost, biochars (at 270 and 400 °C; pyrolysis), SCG washed with ethanol and water, and hydrolysed SCG was carried out in an agricultural soil (Cambic Calcisol). In order to compare with conventional agriculture, the addition of NPK fertilizer was also assessed. Only vermicompost and biochar at 400 °C overcome the growth limitation of SCG. However, these treatments diminished Zn, Cu and Fe concentrations in lettuce probably due to the destruction (microbial degradation/thermal treatment) of natural chelating components (polyphenols). Increase in mineral content was observed in those treatments that did not completely eliminate polyphenols. NPK fertilizer gave rise to lettuces with higher biomass but lower micronutrients content. The results lead us to the possible solution for the use of SCG as organic amendment by vermicomposting and biocharization in order to eliminate toxicity.

Effect of roasting conditions on cocoa bioactivity and gut microbiota modulation

Cocoa is a highly consumed food with beneficial effects on human health. Cocoa roasting has an important influence on its sensory and nutritional characteristics; therefore, roasting could also play a role in cocoa bioactivity. Thus, the aim of this paper is to unravel the effect of cocoa roasting conditions on its antioxidant capacity and modifications of gut microbiota after in vitro digestion-fermentation. HMF and furfural, chemical markers of non-enzymatic browning, were analyzed in unroasted and roasted cocoa powder at different temperatures, as well as different chocolates. The antioxidant capacity decreased with roasting, most probably due to the loss of phenolic compounds during heating. In the case of the evaluated chocolates, the antioxidant capacity was 2-3 times higher in the fermented fraction. On the other hand, HMF and furfural content increased during roasting due to increasing temperatures. Moreover, unroasted and roasted cocoa powder have different effects on gut microbial communities. Roasted cocoa favored butyrate production, whereas unroasted cocoa favored acetate and propionate production in a significant manner. In addition, unroasted and roasted cocoa produced significantly different gut microbial communities in terms of composition. Although many bacteria were affected, Veillonella and Faecalibacterium were some of the most discriminant ones; whereas the former is a propionate producer, the latter is a butyrate producer that has also been linked to positive effects on the inflammatory health of the gut and the immune system. Therefore, unroasted and roasted cocoa (regardless of the roasting temperature) promote different bacteria and a different SCFA production.