Caracterização físico-química e avaliação da atividade antioxidante de extratos hidrossolúveis do perídio maduro do cogumelo Calvatia bicolor

Abstract

Macrofungi, including mushrooms, are full of diversity of bioactive compounds such as polysaccharides and fungal glucans have already been described with several pharmacological activities. In this scenario, the influence of the volume of NaCl was verified to obtain extracts containing polysaccharides from the peridium of the mushroom Calvatia bicolor, and to analyze the chemical composition, purify these polysaccharides and evaluate their antioxidant action. The delipidated peridium were subjected to different extraction processes with different volumes of 0.25M NaCl (1v, 3v and 5v). Crude extracts (EB-CB1v, EB-CB3v, EB-CB5v) were solubilized in distilled water at 10 mg/mL for separation of water-soluble extracts (CB1v, CB3v, CB5v) by centrifugation. The yield, chemical composition and electrophoretic profile of CB1v, CB3v, CB5v were evaluated, and these were subjected to two different purification processes with 90% trichloroacetic acid (TCA) (CB1v-TCA, CB3v-TCA, CB5v-TCA) and by molecular mass (MM) separation with 3kDa filters (CB1v-MM, CB3v-MM, CB5v-MM). The purified extracts were physicochemically characterized and evaluated for total antioxidant capacity (CAT), reducing power and iron and copper chelation. The average dry mass yield of the crude extracts ranged from 79 to 91 mg, while that of the water-soluble extracts ranged from 50 to 60 mg (63.3%) in relation to the EB mass. The content of sugars, proteins, phenolic compounds and sulphate of CB1v, CB3v, CB5v was from 8 to 15%, from 6 to 7%, from 0.3% to 0.4% and from 4 to 5%, respectively. CB1v, CB3v, CB5v showed a polydispersed electrophoretic profile with discrete metachromasia indicating the presence of negatively charged polysaccharide groups (sulfated and carboxylated). The yield of CB1v-TCA, CB3v-TCA, CB5v-TCA ranged from 5 to 8.6%, while that of CB1v-MM, CB3v-MM, CB5v-MM was from 60 to 77.5% in relation to dry mass of each extract before purification. As for the chemical composition, the purified extracts showed a percentage of sugar between 22 and 49% and proteins between 1 and 11%. In CB5v-TCA and CB-5v-MM were found 0.1 and 0.4% of phenolic compounds and 12.65% and 19.27% of sulfate, respectively. CB1v-MM, CB3v-MM, CB5v-MM showed an electrophoretic profile similar to that of the water-soluble extracts and CB1v-TCA, CB3v-TCA, CB5v-TCA showed less polydispersed electrophoretic profiles, however, negatively charged groups were verified. Results of the monosaccharide composition and infrared data (FTIR) indicate that the purified extracts are composed of β-glucan type heteroglucans with galactose and glucuronic acid and sulfate traces, an uncommon finding in fungi. Antioxidant activity was observed in CB5v-MM, in the CAT tests (79.4 mg of ascorbic acid/g of sample), reducing power (21% to 130%), copper chelation (46.2%) and iron chelation (63.64%). Based on the data, the best condition to obtain water-soluble extracts with a high sugar/protein ratio of C. bicolor peridium was from the extraction with 5v of NaCl and the best way to purify these extracts for acquisition of antioxidant compounds is by purification by molecular mass. For this reason, CB5v-MM is a possible candidate as an antioxidant compound of fungal origin.