Page 16 - Petelin, Ana. 2020. Ed. Zdravje delovno aktivne populacije / Health of the Working-Age Population. Proceedings. Koper: University of Primorska Press.
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avje delovno aktivne populacije | health of the working-age population 14 Introduction
Dietary polyphenols represent a large class of naturally occurring chem-
ical compounds characterized by the presence of multiple phenol structural
units. As secondary metabolites, they are found widely in plant foods provid-
ing colour, flavour and astringency, and defence against exogenous stresses,
like reactive oxygen species (ROS), ultraviolet radiation (UV) and plant path-
ogens. Due to the electron-donating phenolic groups polyphenols are well
known antioxidants that prevent stress-related cellular and extracellular dam-
age. In humans, they have been found to possess important biological activi-
ties, including anti-inflammatory, anticarcinogenic and antimicrobial activi-
ties (Zhang, 2015). Several epidemiologic studies have shown that consumption
of food rich in polyphenols has beneficial effects on human health. Their an-
tioxidant and anti-inflammatory properties have preventive effects on differ-
ent chronic diseases such as cardiovascular diseases, diabetes, obesity, neu-
rodegenerative disorders and cancer (Fraga et al., 2019; Li et al., 2014). Most
polyphenols pass through the small intestine without being absorbed, thus en-
countering the gut microbiota (Ozdal et al., 2016). This has led to the devel-
opment of a two-way mutual relationship between polyphenolic compounds
and gut microbiota. First, polyphenols are biotransformed by gut microbio-
ta that results in the increased bioavailability of their metabolites. The micro-
biota is responsible for the extensive breakdown of the original polyphenolic
structures into low-molecular-weight phenolic metabolites that can be easily
absorbed and may actually be responsible for the health effects derived from
polyphenol-rich food consumption (Cardona et al., 2013). Second, polyphenols
modulate the composition of the gut microbial community mostly through the
inhibition of pathogenic bacteria and the stimulation of beneficial bacteria. The
last is supported by their prebiotic properties enriching the beneficial bacteria
(Valdés et al., 2015). Therefore, the interactions of dietary polyphenols and gut
microbiota may impact human health.
Polyphenols characterization and bioavailability
Polyphenols are classified into a range of structurally related groups, with over
9000 different structures identified in various plant species. This heterogeneous
group of molecules, divided into four main classes according to their chemical
structure: flavonoids (including flavonols, flavanols, flavanones, flavones, an-
thocyanidins, chalcones, dihydrochalcones, dihydroflavonols and isoflavones),
lignans, stilbenes and tannins. Phenolic acids (hydroxybenzoic, hydroxycin-
namic, hydroxyphenylacetic, hydroxyphenylpropanoic and hydroxyphenylac-
tic acids) are also frequently included in this category (Abbas et al., 2017).
Most dietary polyphenols exists as polymers or in glycosylated forms, in
which one or more sugar moieties are bound to phenolic or a hydroxyl group at
the C-3 position (Manach et al., 2004). The basic structure of flavonoids, mean-
ing the structure of the aglycon form, and which type of sugar moiety is at-
Dietary polyphenols represent a large class of naturally occurring chem-
ical compounds characterized by the presence of multiple phenol structural
units. As secondary metabolites, they are found widely in plant foods provid-
ing colour, flavour and astringency, and defence against exogenous stresses,
like reactive oxygen species (ROS), ultraviolet radiation (UV) and plant path-
ogens. Due to the electron-donating phenolic groups polyphenols are well
known antioxidants that prevent stress-related cellular and extracellular dam-
age. In humans, they have been found to possess important biological activi-
ties, including anti-inflammatory, anticarcinogenic and antimicrobial activi-
ties (Zhang, 2015). Several epidemiologic studies have shown that consumption
of food rich in polyphenols has beneficial effects on human health. Their an-
tioxidant and anti-inflammatory properties have preventive effects on differ-
ent chronic diseases such as cardiovascular diseases, diabetes, obesity, neu-
rodegenerative disorders and cancer (Fraga et al., 2019; Li et al., 2014). Most
polyphenols pass through the small intestine without being absorbed, thus en-
countering the gut microbiota (Ozdal et al., 2016). This has led to the devel-
opment of a two-way mutual relationship between polyphenolic compounds
and gut microbiota. First, polyphenols are biotransformed by gut microbio-
ta that results in the increased bioavailability of their metabolites. The micro-
biota is responsible for the extensive breakdown of the original polyphenolic
structures into low-molecular-weight phenolic metabolites that can be easily
absorbed and may actually be responsible for the health effects derived from
polyphenol-rich food consumption (Cardona et al., 2013). Second, polyphenols
modulate the composition of the gut microbial community mostly through the
inhibition of pathogenic bacteria and the stimulation of beneficial bacteria. The
last is supported by their prebiotic properties enriching the beneficial bacteria
(Valdés et al., 2015). Therefore, the interactions of dietary polyphenols and gut
microbiota may impact human health.
Polyphenols characterization and bioavailability
Polyphenols are classified into a range of structurally related groups, with over
9000 different structures identified in various plant species. This heterogeneous
group of molecules, divided into four main classes according to their chemical
structure: flavonoids (including flavonols, flavanols, flavanones, flavones, an-
thocyanidins, chalcones, dihydrochalcones, dihydroflavonols and isoflavones),
lignans, stilbenes and tannins. Phenolic acids (hydroxybenzoic, hydroxycin-
namic, hydroxyphenylacetic, hydroxyphenylpropanoic and hydroxyphenylac-
tic acids) are also frequently included in this category (Abbas et al., 2017).
Most dietary polyphenols exists as polymers or in glycosylated forms, in
which one or more sugar moieties are bound to phenolic or a hydroxyl group at
the C-3 position (Manach et al., 2004). The basic structure of flavonoids, mean-
ing the structure of the aglycon form, and which type of sugar moiety is at-
