Avaliação de extratos ricos em polissacarídeos, obtidos a partir de cebolas amarelas e roxas (Allium cepa, Linn), quanto ao seu potencial antioxidante e modulatório da cristalização de oxalato de cálcio (CaOx)

Abstract

The onion (Allium cepa Linn.), plant of the Amaryllis family (Amaryllidaceae), is one of the most important vegetable species in the world, standing out for being the second with greater added value. Its structure is mostly made up of carbohydrates, whose pharmacological applications have been studied and verified for a long time. Thus, the objective of this work was to obtain extracts rich in polysaccharides, from yellow (YAC) and red onions (PAC), characterize them chemically - through the quantification of sugar, protein, sulfate, and phenolic compounds - and structurally - by procedures such as HPLC and infrared chromatography - in search of compounds that can provide greater added value and applicability to these plants. Following this search, tests were carried out to evaluate the extracts as to the antioxidant potential and potential modulator of the formation of calcium oxalate crystals (CaOx). It was observed that the extracts obtained are mainly composed of heteropolysaccharides, which have the following monosaccharides in their structures: glucose, galactose and uronic acids (PAC) and glucose, galactose, uronic acids and arabinose (YAC). In addition to the carbohydrate portion, the presence of sulfates and low levels of proteins and phenolic compounds were also identified in the extracts. However, despite the considerable amount of sulfate found in the samples, there is no evidence that onions synthesize sulfated polysaccharides. To evaluate the antioxidant potential of YAC and PAC extracts, five tests were performed: total antioxidant capacity (CAT), reducing power, copper chelation, iron chelation and hydroxyl radical scavenging. In three of the five tests performed, better results were obtained for the YAC extract. These best values were identified specifically in the tests: CAT (110.8 mg of AA per gram of the extract), reducing power (48% of activity) and iron chelation (80.01% of chelating activity). Regarding the modulatory activity of CaOx, positive results were found for the YAC extract, which was effective in directing crystallization to the formation of small-sized dihydrate calcium oxalate crystals (COD), which could, in biological systems , facilitate the process of excretion of the crystals in the urine and decrease the ability of the crystals to bind to the epithelial cells of the renal tubules causing damage. The results found in this work are promising and open the way for further studies that can evaluate and confirm such potentials in vivo.