The intestinal microbiome plays an important role in the metabolism of chemical compounds found within food. Bacterial metabolites are different from those that can be generated by human enzymes because bacterial processes occur under anaerobic conditions and are based mainly on reactions of reduction and/or hydrolysis. In most cases, bacterial metabolism reduces the activity of dietary compounds; however, sometimes a specific product of bacterial transformation exhibits enhanced properties. Studies on the metabolism of polyphenols by the intestinal microbiota are crucial for understanding the role of these compounds and their impact on our health. This review article presents possible pathways of polyphenol metabolism by intestinal bacteria and describes the diet-derived bioactive metabolites produced by gut microbiota, with a particular emphasis on polyphenols and their potential impact on human health. Because the etiology of many diseases is largely correlated with the intestinal microbiome, a balance between the host immune system and the commensal gut microbiota is crucial for maintaining health. Diet-related and age-related changes in the human intestinal microbiome and their consequences are summarized in the paper.

Background COVID-19 is a pandemic disease that has paralyzed social life and the economy around the world since the end of 2019, and which has so far killed nearly 600,000 people. The rapidity of its spread and the lack of detailed research on the course and methods of transmission significantly impede both its eradication and prevention. Scope and approach Due to the high transmission rate and fatality resulting from COVID-19 disease, the paper focuses on analyzing the current state of knowledge about SARS-CoV-2 as well as its potential connection with food as a source of pathogen and infection. Key findings and conclusions There is currently no evidence (scientific publications, WHO, EFSA etc.) that COVID-19 disease can spread directly through food and the human digestive system. However, according to the hypothesis regarding the primary transmission of the virus, the source of which was food of animal origin (meat of wild animals), as well as the fact that food is a basic necessity for humans, it is worth emphasizing that food can, if not directly, be a carrier of the virus. Particular attention should be paid to this indirect pathway when considering the potential for the spread of an epidemic and the development of prevention principles.

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This review presents the comprehensive knowledge about the bidirectional relationship between polyphenols and the gut microbiome. The first part is related to polyphenols’ impacts on various microorganisms, especially bacteria, and their influence on intestinal pathogens. The research data on the mechanisms of polyphenol action were collected together and organized. The impact of various polyphenols groups on intestinal bacteria both on the whole “microbiota” and on particular species, including probiotics, are presented. Moreover, the impact of polyphenols present in food (bound to the matrix) was compared with the purified polyphenols (such as in dietary supplements) as well as polyphenols in the form of derivatives (such as glycosides) with those in the form of aglycones. The second part of the paper discusses in detail the mechanisms (pathways) and the role of bacterial biotransformation of the most important groups of polyphenols, including the production of bioactive metabolites with a significant impact on the human organism (both positive and negative).

The chemical structure of 5-hydroxymethyl-2-furfural (HMF), its physicochemical properties and reactions that lead to the synthesis of HMF were discussed. Special attention was paid to HMF formation in food during processing. The potential applications of this compound in industry were described as well. Moreover, this review outlines the most important sources of HMF in human diet and estimates the potential daily intake of HMF by consumers. The known and suggested metabolic pathways, as well as the impact of HMF and its metabolites on human health are also discussed.

We studied how the selection of the growth medium influences the antioxidant properties and synthesis of bioactive compounds (β-carotene, C-phycocyanin, allophycocyanin, and phycoerythrin) in six selected species of cyanobacteria of Arthrospira genus. For this purpose, cyanobacteria cultures were cultivated on a typical Zarrouk medium and on a cheaper substitute – RM6 medium. Significant differences were observed in the efficiency of synthesis of the studied compounds depending on the strain of cyanobacteria. The quantitative and qualitative composition of Zarrouk medium was more beneficial for β-carotene synthesis in the cells of all strains of cyanobacteria studied. This medium also allowed for the antioxidant potential of the studied strains to be increased. On the other hand, the RM6 medium, deprived of some mineral ingredients, enabled more efficient synthesis of phycobiliproteins in all studied strains except A. platensis SAG 85.79.  

The aim of this study was to determine the influence of different factors such as fruit processing, pectinolytic enzyme application, strain of yeast (Johannisberg-Riesling, Steinberg), cell immobilization on the alginate, and type of fermentation on the antioxidant profile and volatile composition of apple wines. Champion and Idared apples were used during experiments. The factors used influenced significantly (p < 0.05) antioxidant capacity, polyphenol profile, and volatile composition of apple wines. Pulp fermentation caused formation of higher amounts of ethanol and favorably influenced the antioxidant activity of wines. Procyanidins B2 and C1 as well as epicatechin and catechin prevailed among polyphenols in these samples. Cell immobilization positively affected the ethanol content, but decreased the antioxidant activity, of wines. Volatile composition of wines was mainly influenced by strain of yeast and type of fermentation. Apple wines fermented spontaneously were characterized by more esters and methanol and fewer higher alcohols compared to inoculated samples.

Phenolic compounds play an important role in the defense system of the human organism against reactive oxygen species. They are present mainly in fruit and vegetables, but their bioavailability is the key factor determining their concentration in blood and tissues. The aim of this article was to study the transformations that apple polyphenols undergo during digestion. An in vitro model with dialysate membranes simulating the human alimentary tract was used for evaluating the composition and antioxidant properties of fresh apples and products of their digestion in dialysates. Epicatechin, chlorogenic acid, and procyanidins were the main antioxidant compounds in the whole fruits and flesh of the two varieties of apples analyzed. In the apple peel additionally quercetin glycosides were present. As a result of in vitro digestion both polyphenolic compounds concentration and the antioxidant activity of the dialysates increased as compared to the raw materials (from 35% to 95% and from 50% to 236%, respectively). In the simulated alimentary tract, it was proved that procyanidins disintegrate to (+)catechin, which is well absorbed from the small intestine, while chlorogenic acid and quercetin glycosides were characterized by a low bioavailability.