Elemental Composition, Antioxidant and Antibacterial Properties of Some Wild Edible Mushrooms from Romania
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agronomy Article Elemental Composition, Antioxidant and Antibacterial Properties of Some Wild Edible Mushrooms from Romania 1 2 2 3 Melinda Fogarasi , Zorit, a Maria Diaconeasa , Carmen Rodica Pop , Szabolcs Fogarasi , 1 2 1, Cristina Anamaria Semeniuc , Anca Corina Fărca¸s , Dorin T, ibulcă *, 1 2 2, Claudiu-Dan Sălăgean , Maria Tofană and Sonia Ancut, a Socaci * 1 Department of Food Engineering, University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, Calea Mănăstur 3–5, 400372 Cluj-Napoca, Romania; [email protected] (M.F.); [email protected] (C.A.S.); [email protected] (C.-D.S.) 2 Department of Food Science, University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, Calea Mănăs, tur 3–5, 400372 Cluj-Napoca, Romania; [email protected] (Z.M.D.); [email protected] (C.R.P.); [email protected] (A.C.F.); [email protected] (M.T.) 3 Faculty of Chemistry and Chemical Engineering, Babe¸s-BolyaiUniversity, 11 Arany Janos Str., 400028 Cluj-Napoca, Romania; [email protected] * Correspondence: [email protected] (D.T.); [email protected] (S.A.S.); Tel.: +40-264-596388 (S.A.S.); Fax: +40-264-593792 (S.A.S.) Received: 13 November 2020; Accepted: 14 December 2020; Published: 15 December 2020 Abstract: Five selected wild edible mushrooms from Romania (Agaricus bisporus, Pleurotus ostreatus, Cantharellus cibarius, Boletus edulis, and Lactarius piperatus) were investigated for their antioxidant potential using an ABTS spectrophotometric assay. Among the selected mushrooms, B. edulis displayed the highest radical scavenging activity and the greatest phenolic content, measured by the Folin–Ciocalteu reagent method. The total flavonoids were quantified using the aluminum chloride colorimetric method, with the extract of B. edulis being the richest. L. piperatus and B. edulis mushrooms exhibited the strongest antibacterial activity against S. aureus and E. coli. The content of trace elements was determined using an atomic absorption spectrometer, and it was found that K and Mg were the main metals present in all the selected mushroom species. The obtained results suggest that the studied wild edible mushrooms are natural functional matrices, and may have potential to be used as natural antioxidants if they are introduced into the daily diet. Keywords: antioxidant; antimicrobial properties; bioactive compounds; elemental composition; mushrooms 1. Introduction Today, the attention of consumers is focused more and more on healthier and safer food products, rich in bioactive compounds that can provide the body’s necessary nutrients, and the energy required for the modern lifestyle. For this reason, globally there can be witnessed a growing demand for functional foods due to significant changes in dietary habits [1]. In order to fulfill this modern necessity of a balanced diet, many researchers have pointed out the importance of plants and different food products fortified with vegetable sources, among which an important category is represented by edible mushrooms [2]. In consequence, edible mushrooms have received the attention of consumers because, in addition to the fact that they are tasty, they also possess remarkable nutritional value due to their high protein, carbohydrate, vitamin, and mineral content, as well as their associated low-fat content [3–5]. Agronomy 2020, 10, 1972; doi:10.3390/agronomy10121972 www.mdpi.com/journal/agronomy Agronomy 2020, 10, 1972 2 of 9 Due to their nutritional components, many researchers consider edible mushrooms as the next generation food, with potential benefits not only from a nutritional point of view but also from a medical one; considering that for their unique properties they could be used for the treatment of different diseases like tumors and nervous disorders [6,7]. In fact, edible mushrooms are characterized by antifungal, anti-inflammatory, antiviral, antibacterial, hepatoprotective, antidiabetic, hypolipidemic, hypotensive, and cytotoxic properties, as well as by a diversified composition, involving the presence of some relevant biomolecules, such as phenolic compounds, tocopherols, ascorbic acid, and proteins/enzymes [8–10]. Novel approaches in the bio-medical and biotechnological fields have appeared because mushrooms produce many bioactive peptides or proteins, such as lectins, fungal immunomodulatory proteins, antimicrobial proteins, ribonucleases, ribosome inactivating proteins, and ribotoxins [11,12]. Edible mushrooms also contain many traces and minor elements, like chromium, cobalt, copper, iron, manganese, and zinc which are essential for the development and function of the human body [13]. It is also important to note that, depending on climate and soil conditions, wild edible mushrooms could also have a negative effect on human health through the accumulation of toxic heavy metals like mercury, lead, cadmium, and organic substances resulting from human industrial activities [14]. Romania’s mountains, such as the Carpathian Mountains, are recognized as a significant source of wild edible mushrooms for Europe, which could supply different species of wild edible mushrooms. However, despite their great potential, there have only been a few published studies regarding the bioactive compounds and antimicrobial activity of Transylvanian wild edible mushrooms [4,13,15,16]. Thus, in order to emphasize the potential benefits of some Transylvanian wild edible mushrooms, the present study aims to determine the antioxidant and antimicrobial activity, total phenolic and total flavonoid contents, and the elemental profile of the selected mushrooms species. 2. Materials and Methods 2.1. Mushrooms Material and Preparation of Extracts Fruiting bodies of the selected mushroom species (Agaricus bisporus, Pleurotus ostreatus, Cantharellus cibarius, Boletus edulis, and Lactarius piperatus) were collected between September–November 2018, from Mese¸sMountain, Sălaj County, Transylvania region, Romania. The clean fruiting bodies of the fresh mushrooms were dried at 45 ◦C using a laboratory plant dryer, followed by their being ground (using a laboratory mill) into a fine powder. All the samples were kept at 4 ◦C, for further analysis. The methanolic mushroom extracts were prepared as reported in a previous publication [17]. Briefly, the powdered material was extracted with methanol (1:10, w/v) until the extraction solvent became colorless (the total used solvent volume was 60 mL). The obtained filtrates were dried at 40 ◦C with a vacuum rotary evaporator, and then redissolved in 8 mL of methanol and stored at 20 C − ◦ until analyzed. 2.2. Total Phenolic Content The total phenolic content of each mushroom methanolic extract was quantified by a slightly modified Folin–Ciocalteu method, and expressed as mg of gallic acid equivalents (GAE)/100 g dry weight (DW) [18,19]. Briefly, an aliquot of the extract (25 µL) was initially mixed with 1.8 mL of distilled water, followed by the addition and homogenization with 120 µL of Folin–Ciocalteu reagent. Five minutes later, 340 µL of 7.5% Na2CO3 aqueous solution were added to the mixture. The samples were incubated for 90 min at room temperature in the dark, and then their absorbances were read at 750 nm against the blank, using a microplate reader (BioTek Instruments, Winooski, VT, USA). Each extract was analyzed in triplicate. Agronomy 2020, 10, 1972 3 of 9 2.3. Total Flavonoid Content The content of total flavonoid of each methanolic mushroom extract was determined using an aluminum chloride colorimetric assay, as described previously in other studies [20]. Briefly, after the dilution of the methanolic extracts with distilled water to a final volume of 5 mL, a volume of 300 µL 5% NaNO2 was added. After 5 min incubation, 300 µL AlCl3 (10%) were added and then 2 mL NaOH 1 M. The absorbance was recorded at 510 nm using a spectrophotometer (JASCO V-630 series, International Co., Ltd., Tokyo, Japan). The results were expressed as mg quercetin equivalents (QE)/100 g dry weight (DW). Each extract was analyzed in triplicate. 2.4. ABTS Radical Cation Decolorization Assay (ABTS+) The antioxidant activity of the mushrooms extracts was determined according to the procedure described by Arnao et al. [21], with some modifications. The blue-green, ABTS+ solution was prepared by mixing a 7 mM aqueous solution of ABTS+ and 2.45 mM potassium persulfate. The reaction was carried out in the dark at room temperature for 12–16 h before use. ABTS+ working solution was obtained by diluting the stock solution with ethanol, having the absorbance of 0.70 0.02 AU at 734 nm. ± After obtaining the working solution, 20 µL Trolox at different concentrations of mushroom extracts were added to 170 µL ABTS+ solutions, incubated for 6 min at room temperature, in the dark, and the absorbance measured using a microplate reader. Results were expressed as µmol Trolox/100 g DW. 2.5. Bacterial Strains The following microorganisms were tested: Salmonella typhimurium (ATCC 14028), Staphylococcus aureus (ATCC 49444), Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 25922), and Bacillus cereus (ATCC 11778) (Microbiologics Inc., St. Cloud, MN, USA). Each strain was grown in 10 mL sterile nutrient broth at 37 ◦C for 24 h, except B. cereus, which was grown at 30 ◦C for 24 h. The purity of the inoculum was confirmed by microscopic examination of the Gram-stained smear. A loopful of inoculum was transferred onto selective medium: (i) XLD agar for S. typhimurium; (ii) Baird–Parker agar base supplemented