The pomegranate ( Punica granatum L.) is an ancient plant belonging to the Lythraceae family (previously Punicaceae ) native to Asia and , in particular , of China, the Indian subcontinent, Afghanistan and Iran , whose cultivation today extends from Iran, to the Mediterranean region, to the Turkish borders of Europe and the American Southwest , whose fruits are consumed as food throughout the world .
Numerous extracts are obtained from the pomegranate starting from flowers, fruits, pericarp and seeds which boast countless health properties attributable to their bioactive components such as vitamin C, amino acids (proline, valine, glutamic acid , aspartic acid and methionine) , mineral salts (sodium, calcium, potassium and iron salts) and polyphenols . Pomegranate fruits are , in fact, rich in polyphenols, including there are hydrolysable tannins ( such as gallotannins and ellagitannins ) , which are polyphenolic compounds most quantitatively represented , followed by hydroxycinnamic acids , flavanols ( epigallocatechin ), flavanones ( naringenin and hesperidin ), flavonols (myricetin, quercetin and kaempferol ), flavones ( apigenin and luteolin), anthocyanins (delphinidin, cyanidin and pelargonidin ) and dihydrochalcones ( phloridzin ).
This rich and complex polyphenolic component is able to justify over 90% of the antioxidant activity associated with pomegranate juice , which in vitro studies have shown to be higher than that determined for other drinks rich in polyphenols such as orange juice, red wine, green and black tea , blueberry juice, black cherry juice and açaí juice . Among the pomegranate polyphenols , ellagitannins have recently attracted the interest of researchers as these polymeric compounds are hydrolyzed in the intestine to ellagic acid , which is metabolized by the microorganisms of the colonic microbiota to urolithins , which, in turn, are absorbed and distributed in various organs where they perform their anti-inflammatory action .
Recent studies published in the scientific literature demonstrate That the extracts obtained from the by-products of the agri-food industry producing pomegranate juice , rich in hydrolyzable tannins , incubated with fecal bacteria cause the formation of urolithin which improves the growth of microbial species belonging to the genus Bifidobacterium and Lactobacillus . In another study, such pomegranate extracts high in ellagitannins significantly improves the growth of Bifidobacterium brevis and Bifidobacterium the infants , while They inhibit the growth of some pathogenic bacteria, including Pseudomonas aeruginosa , Staphylococcus golden and some species of the genus Clostridium. It is interesting to note that the effects of individual pomegranate ellagitannins are evident, but less pronounced than the mixture of tannins present in the plant extract . It is also known that ellagitannins in addition to promoting growth, they can improve the functionality of the microorganisms intestinal eubiotics which , following the interaction with these polyphenols, increase the synthesis of short chain fatty acids ( Short Chain Fatty Acids ) - SCFA ) such as acetate, propionate and butyrate , which , after intestinal absorption , in addition to providing energy to the enterocytes, can be transported to different organs and influence numerous metabolic pathways associated with both in the state of health both in a state of illness .
In vivo studies conducted on experimental animals have demonstrated that SCFAs induce the activation of proliferator -activated receptors peroxisomal ( Peroxisome P roliferator - Activated Receiver - PPAR) , belonging to the superfamily of nuclear receptors , which are activated by high concentrations of lipids, are involved in the metabolism, storage or movement of lipids to intracellular organelles or are implicated in their elimination , and which play an essential role in the regulation of cellular differentiation, carbohydrate , lipid and protein metabolism , and in the carcinogenesis of higher organisms .
By activating PPARα, SCFAs can prevent the expression of pro-inflammatory mediators according to the mechanism reported below:
1 ) reduction in the expression of activator proteins (AP) -1 , signal transducer and activator of transcription (STAT) and nuclear factor kappa B (NF- κB ) leading to
2) to reduce the genetic transcription of tumor necrosis factor (TNF-α), interleukins (IL-1 and IL-6) and cyclooxygenase (COX) , thus reducing the inflammatory state .
Since growing evidence suggests that polyphenols could modulate the intestinal microbiota and , consequently , its functionality and therefore the synthesis of short-chain fatty acids , exerting a positive impact on the health and well-being of the human organism , at the University of Naples Federico II an in vitro study was conducted which aimed to determine the impact of the digestion and fermentation process on the total concentration of polyphenols and on the antioxidant capacity of the extract . standardized pomegranate fruit and evaluate the effect of the digested and fermented extract on the functionality of the human intestinal microbiota isolated from the fecal material of healthy, obese or celiac subjects obtained both from a adults both from pediatric subjects , by determining the concentration of SCFA released by the microbiota in the culture medium . In more detail, the extract obtained from the pomegranate fruit was subjected to a simulated digestion in vitro , using a predefined protocol that mimics the digestive process in its different phases (oral, gastric and intestinal) , following which the antioxidant profile of the extract was determined through :
1) measurement of the concentration of total polyphenols with Folin – Ciocalteu reagent , by spectrophotometric assay ,
2) the evaluation of the reducing power using the FRAP method ( Ferric Reducing Antioxidant Power ) which is based on the ability of the antioxidants present in the extract to reduce the colorless complex ferric tripyridyltriazine (TPTZ-Fe3+) in its ferrous form characterized by an intense blue color (TPTZ - Fe2+) whose absorbance , measured at 593 nm , is proportional to the reducing power of the antioxidants present in solution ,
3) the determination of the anti - radical activity by means of the DPPH assay which is based on the spectrophotometric measurement of the radical decay diphenylpicrylhydrazyl (DPPH) which in solution it has a purple colour which changes to yellow-colourless when this radical passes to the reduced form DPP HH which is proportional to the anti - radical activity of the extract , and
4) the determination of the anti - radical activity by means of the ABTS assay , which consists in the determination of the cationic radical 2,2'-azino- bis( 3-ethylbenzothiazoline-6-sulfonic acid , a chromogenic substance which can be converted into its radical monocationic form ABTS+ (coloured) if treated with an oxidising agent.
The digested sample , After evaluation of the antioxidant profile, it was subjected to fermentation induced by the intestinal microbiota isolated from the fecal material of six different types of donors (i.e., healthy adults and children, obese adults and children , and adults and children celiac disease ). Then, the digested and fermented samples of pomegranate were tested to evaluate the ability to modulate the functionality of the intestinal microbiota in terms of SCFA production , quantified by a chromatographic method coupled to UV detection . To evaluate the statistical significance of the effect of pomegranate extract, the results of these experiments were compared with those obtained from control samples , prepared using the same digestion and fermentation protocols in the absence of the pomegranate extract . The results showed that oral, gastric and intestinal digestion processes in vitro led to a significant increase in the concentration of total polyphenols of the pomegranate extract , while the antioxidant capacity ( expressed as radical scavenging activity and reducing properties ) of the pomegranate extract was significantly reduced. These results are in line with those obtained by other researchers who have studied the variation in the concentration of the total polyphenol component following digestion , observing a significant increase , both with studies on other fruits in which , After in vitro digestion , an increase in total polyphenols occurred , probably induced by the hydrolysis of phenolic glycosides in their cones . and from the release of phenolic compounds from the fibres present in the food matrix , making the polyphenols more bioavailable and more easily metabolised by the intestinal microbiota .
With regard to the decrease in antioxidant activity following simulated digestion in vitro , it can be concluded that the antioxidant capacity of pomegranate extract does not appear to be correlated with the total polyphenol content present in the extract after digestion . On the other hand , it is known that the antioxidant activity of plant extracts does not depend only on the amount of polyphenols, but also on their structure, i.e. on the number of hydroxyl groups, and on the degree of polymerization .
A further result of this in vitro study concerned the modulatory effect exerted by the pomegranate extract on the functionality of the intestinal microbiota isolated from the faeces of healthy and sick adult and pediatric subjects , demonstrated by the significant increase in the concentration of lactic acid produced by the microbiota isolated from the fecal material of the subjects. celiac and especially obese adults , compared to healthy subjects. Comparing the effect of pomegranate extract with the control sample, slight effects on acetic and succinic acids were observed when the intestinal microbiota of healthy subjects was treated with digested pomegranate extract. Furthermore, following the fermentation of pomegranate with the microbiota derived from celiac subjects , a statistically significant increase was demonstrated propionic acid , while following the fermentation of pomegranate with the microbiota derived from healthy or obese adult subjects , a slight increase in the concentration of butyric acid was recorded . Fermentation of pomegranate extract with the microbiota isolated from obese children resulted in a significant increase in the production of lactic, succinic and propionic acids . The concentration of acetic acid increased only when pomegranate extract was fermented with the microbiota isolated from healthy subjects, while no significant effects on butyric acid were observed. The improvement of the functionality of the microbiota which translates into a greater release of SCFA as metabolites of eubiotic microorganisms, if confirmed in vivo in humans, could justify the beneficial effects on immunity, metabolism and gastrointestinal physiology recognized by the polyphenolic component , and in particular by ellagitannins. of the pomegranate .
In conclusion :
The results obtained from this latest in vitro investigation will be confirmed in man, pomegranate fruit extract with a high content of ellagitannins , which are ascribed to numerous beneficial properties for the body , will be able to boast positive activities also on intestinal health and could be used as a prebiotic ingredient , clearing the concept that in addition to dietary fiber, which consists of non-digestible polysaccharides, whose prebiotic properties have been known since the last century, polyphenols represent a new class of prebiotics that satisfy the criteria to be classified as such, such as resistance to digestion at the duodenal level , the ability to be fermented by the intestinal microbiota and to modulate its functionality.
Readings recommended
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