The Significant Antioxidant Effect Exerted by Pomegranate (Punica granatum): The Hidden Polyphenols

Background: Although the definition of dietary fibre is complex and constantly evolving, today we can identify it as "carbohydrate polymers with at least 10 monomeric units, which are not hydrolysed in the small intestine of humans". In addition to the numerous and well-known benefits of dietary fibre for human health, our attention is drawn to its antioxidant properties, achieved through polyphenolic compounds linked to polysaccharide complexes. This study investigated the antioxidant effects of an extract from the fruit of Punica granatum (PUN), particularly rich in polyphenols, fibre, flavonoids, vitamins, organic acids, minerals, amino acids, and alkaloids. Furthermore, these effects were evaluated in two human nervous system cell lines under oxidative stress induced by hydrogen peroxide. Methodology: After examining the fibre composition, some polyphenols present in the extract were identified and quantified by HPLC. Furthermore, the antioxidant power of PUN was measured using the DPPH method, the chelating activity assay, the reducing power test, the ORAC method, the measurement of reactive oxygen species accumulation, the quantification of lipid peroxidation, and the detection of mitochondrial superoxide in cell cultures. Results: The results were consistent, and PUN demonstrated a strong antioxidant potential, justified not only by the high content of easily extractable polyphenols (EPPs) but also by a further addition of these more difficult to identify compounds (NEPPs), indicated as "hidden polyphenols"; therefore, the total polyphenol content in the extract resulted from the sum of EPPs + NEPPs (71 ± 7.9 + 55 ± 6.4 mg = 126 ± 14.3 mg gallic acid equivalent (GAE)/g dry weight). The fraction of hidden polyphenols could therefore explain a mechanism by which the fibre exerts an antioxidant effect. Another important result was achieved by the cell lines used, both of which were significantly protected by PUN following oxidative damage generated by a pro-oxidant treatment. However, astrocytes were found to be more responsive and sensitive than were human neurons. At the same time, PUN mitigated the effects of oxidative damage, and it could be hypothesised that this extract could be used to extinguish the A1 phenotype. Conclusions: We can conclude that the fibrous component of pomegranate is related to the antioxidant property exerted, and the neurodegeneration caused by oxidative stress could be slowed following the intake of Punica granatum. It is possible to identify the pomegranate as a "superfood" or "functional food", with excellent nutritional characteristics and chemical composition.