Abstract
Pomegranate peel is a natural source of phenolics, claimed to possess healing properties, among which are antioxidant and antidiabetic. In the present study, an ethyl acetate extract, obtained by Soxhlet from the peel of Dente di Cavallo DC2 pomegranate (PGE) and characterized to contain 4% w/w of ellagic acid, has been evaluated for its hypoglycemic, antiglycation, and antioxidative cytoprotective properties, in order to provide possible evidence for future nutraceutical applications. The α-amylase and α-glucosidase enzyme inhibition, interference with advanced glycation end-products (AGE) formation, and metal chelating abilities were studied. Moreover, the possible antioxidant cytoprotective properties of PGE under hyperglycemic conditions were assayed. Phenolic profile of the extract was characterized by integrated chromatographic and spectrophotometric methods. PGE resulted able to strongly inhibit the tested enzymes, especially α-glucosidase, and exerted chelating and antiglycation properties. Also, it counteracted the intracellular oxidative stress under hyperglycemic conditions, by reducing the levels of reactive oxygen species and total glutathione. Among the identified phenolics, rutin was the most abundant flavonoid (about 4 % w/w). Present results suggest PGE to be a possible remedy for hyperglycemia management and encourage further studies to exploit its promising properties.
Highlights
Fruit and vegetable waste are defined as the inedible parts of vegetables, discarded during collection, handling, transportation, and processing [1]
Spectrophotometric analysis showed that PGE contained high levels of total phenolics and tannins, expressed as microgram equivalents of tannic acid (TAE) per milligram of extract (Table 1): These data are in agreement with the previous characterization that highlighted PGE to contain the greatest amount of phenolics with respect to the ethanolic and methanolic pomegranate peel extracts [30]
In regard to the minor components of PGE, the contribution of punicalagins seems to be of lower relevance, taking into account that previous data highlighted the ethanolic extract from the peel of Dente di Cavallo DC2 pomegranate, characterized by a high amount of punicalagins with respect to ellagic acid (14:1 ratio) [30], was ineffective as an α-glucosidase inhibitor. This evidence supports our hypothesis about the possible contribution of rutin to the PGE activity. These results suggest that PGE may contain a pool of phenolics able to differently affect several targets involved in the control of carbohydrate metabolism: the high potency against glucosidase seems to be ascribable to the combined contributions of rutin, catechin, ellagic acid, and gallic acid, while rutin and syringic acid could contribute to the amylase inhibition
Summary
Fruit and vegetable waste (i.e., seeds, peel, rind, and pomace) are defined as the inedible parts of vegetables, discarded during collection, handling, transportation, and processing [1]. Waste could be reduced by applying targeted prevention strategies, among which are reduction, reuse, and recycling [2]. Several crop waste, from both vegetable, cereals and fruits, are known to be source of bioactive phytochemicals, among which are polyphenols, anthocyanins, carotenoids, terpenoids, lactones, glucosinolates, lectins and dietary fibers [4,5,6,7,8,9,10,11] and to possess interesting pharmacological activities [5,6,7,8,9,10,11,12,13,14,15,16], becoming attractive materials for further uses in drug discovery and nutraceutical fields
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