Introduction
Food spoilage bacteria and oxidative process are the major contributors to decreasing the nutritional and sensory quality of meat and meat products, which consequently reduce consumers´ acceptability (Papuc, Goran, Predescu, Nicorescu & Stefan, 2017). For this reason, the use of antimicrobial and antioxidant agents are widely used for inhibiting or delay the growth of microorganism and oxidation reactions (Kumarasamy et al., 2010; Papuc et al., 2017; Poljsak, Šuput & Milisav, 2013). However, there are evidence of a growing number of microorganisms that are resistant to antibiotics, mainly caused by their uncontrolled use, and consequently causes a public health problem (Kumarasamy et al., 2010). In addition, the utilization of synthetic antioxidants (i.e., butylated hydroxyanisole, BHA; butylated hydroxytoluene, BHT; among others) have been also limited due to several studies have provided evidence of the potential risk in human health (Poljsak et al., 2013).
In order to avoid the uncontrolled use of antimicrobial drugs and solve the disadvantages of synthetic antioxidant, several investigations have been reported in natural sources (edible and wild mushrooms, green tea, grape, apple, bee products and olive) the presence of antibacterial and antioxidant compounds. Polyphenols like catechin, ellagic acid, epicatechin, epicatechin gallate, gallic acid, tannic acid, caffeic acid, ferulic acid, protocatechuic acid, quercetin, among others, are commonly found in the above mentioned sources (Carneiro et al., 2013; Khatun, Mahtab, Khanam, Sayeed & Khan, 2007; Mazzutti et al., 2012; Moure et al., 2001; Papuc et al., 2017; Soares et al., 2009). Recently, edible mushroom has been proposed as an important source of bioactive compound to be employed as potential functional ingredient for food industry (Ma et al., 2018).
In this context, the food industry requires the use of appropriate and standard methods to extract active compounds from natural sources, i.e., using conventional (Soxhlet, maceration or hydrodistillation extraction) and non-conventional methods (ultrasound-assisted, pulsed-electric field, enzyme and microwave, pressurized liquid and supercritical fluid extraction) (Azmir et al., 2013). However, several factors such input parameters like temperature, pressure, time, and solvent used can affect the efficiency of the extraction process (Azmir et al., 2013; Cowan, 1999).
Therefore, the aim of this study was to determine the effect of the solvent extraction used on the chemical composition, physicochemical properties, as well as its antioxidant and antimicrobial activity of edible mushrooms extracts (Agaricus brasiliensis, Ganoderma lucidum and Pleurotus ostreatus).
Materials and methods
Materials and chemicals
The edible mushrooms powder (AB, Agaricus brasiliensis; GL, Ganoderma lucidum; and PO, Pleurotus ostreatus) were obtained from Aloha Medicinals, Inc. (USA). All chemicals were of analytical grade. Folin-Ciocalteu’s reagent, sodium carbonate (Na2CO3), potassium persulfate (K2S2O8), aluminum chloride (AlCl3), methanol, ethanol, 1,1-diphenyl-2-picrylhydrazyl (DPPH•), 2,2’-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS•+), ammonium persulfate [(NH4)2S2O8], trichloroacetic acid (C2HCl3O2), iron chloride (FeCl3), brain hearth infusion agar (BHI, Difco TM), and Mueller Hinton agar were purchased from Sigma-Aldrich (St. Louis, MO, USA).
Proximate composition
Edible mushrooms powder was analyzed for proximate composition (AOAC, 2005). Moisture content was obtained in dried samples (Yamato DX402 drying oven, Tokyo, Japan) at 105 °C for 12 h (method 934.01). Total protein content was determined by Kjeldahl method, using a conversion factor of N x 4.38 (method 968.06). The crude fat content was extracted with petroleum ether in a Goldfish apparatus (method 985.01), while ash content was determined by incineration in dried samples (method 920.153) at 550 °C for 5 h (Felisa muffle furnace FE-361, Jalisco, Mexico). The total carbohydrate content was estimated in percentage as follow: 100 - [moisture content (%) + protein content (%) + crude fat content (%) + ash content (%)].
Obtaining extracts
The bioactive compounds from edible mushrooms powder (20 g) were obtained with 180 mL of a polar (water) and reduced polar (ethanol and water-ethanol, 1:1 ratio) as solvent, using an ultrasound-assisted equipment (Branson 3800 Ultrasonic bath, Brason, Germany) at 25 °C/40 KHz for 1 h. The resultant mixture was filtered (Whatman #1 filter paper) under vacuum (MVP 6 vacuum pump, Jeju, Korea) and concentrated in a rotaryevaporator at 65 °C (Yamato RE301BW, Tokyo, Japan). The edible mushrooms extracts (EME) were lyophilized (Yamato DC401 Freeze Dryer, Tokyo, Japan) and stored at -20 °C in the dark, until analysis (Soares et al., 2009).
Physicochemical properties
The pH value of EME (50 mL, 5 mg/mL) was measured using a potentiometer (Hanna Multiparameter HI3512, Rhode Island, USA) with automatic temperature compensation (method 943.02) (AOAC, 2005). The total solids content of EME were determined according to the AOAC, 2005. An aliquot of each EME (5 mg/mL) was placed in a refractometer equipment and the results were expressed as °Brix (%) (method 932.14). The color evaluation of EME was carried out according to the CIElab parameters (L*, a*, and b*) (Robertson et al., 1977).
Briefly, EME (5 mg/mL) were placed in a 40 mL quartz cell, and determined with a spectrophotometer (Konica Minolta, CM508d, Tokyo, Japan), using D65 illuminant with 10° observer angle.
Phenolic composition
The total phenolic content (TPC) was determined by the Folin-Ciocalteu method (Ainsworth & Gillespie, 2007), with slight modifications. Briefly, each EME (50 µL, 5 mg/mL) was homogenized with 800 µL of distilled water, 200 µL of Folin-Ciocalteu’s reagent (0.25 N), and 300 µL Na2CO3 (7%, w/v). The reaction mixture was incubated at 25 °C for 1 h, under dark, and the absorbance was measured at 750 nm in a spectrophotometer (Thermo Scientific Multiskan FC UV-Vis, Vantaa, Finland). The results were expressed as mg of gallic acid equivalents/g of dried extract (mg GAE/g).
The total flavonoid content (TFC) was determined based on aluminum chloride complex formation (Popova et al., 2004). Each EME (50 µL, 5 mg/mL) was homogenized with 650 µL of methanol and 50 µL of AlCl3 (2.5%, w/v). The reaction mixture was incubated at 25 °C for 30 min, under dark, and the absorbance was measured at 412 nm. The results were expressed as mg quercetin equivalents/g (mg QE/g).
Antimicrobial activity
The antimicrobial activity was evaluated according to the disc diffusion method (Wiegand, Hilpert & Hancock, 2008). Staphylococcus aureus ATCC 29213B, Listeria innocua, Salmonella typhimurium ATCC 14028 and Escherichia coli ATCC 25922 were inoculated in BHI agar and incubated at 37 °C for 24 h. Afterwards, the cellular suspension (McFarland 0.5, approximately 1.5 x 108 UFC/mL) was cultivated on Muller-Hinton agar plates and incubated at 37 °C for 24 h. After, each EME (5 µL, 100 μg/mL) was added to the surface of the discs, using ethanol, water, a mixture of water-ethanol, and gentamicin as controls. The results were expressed as halo inhibition zones (mm).
Antioxidant activities
Reducing power and antiradical activity
The reducing power ability (RPA) was determined based on ferricyanide/prussian blue method (Berker, Güçlü, Tor, Demirata & Apak, 2010). Briefly, each EME (200 µL, 100 µg/mL) was homogenized with 500 µL of phosphate buffer (50 mM, pH 7.0) and 500 µL of potassium ferrocyanide (1%, w/v). The reaction mixture was incubated at 50 °C for 20 min (Yamato BM500 water bath, Tokyo, Japan), mixed with 250 µL of trichloroacetic acid (10%, w/v), and centrifuged at 3,900 g for 10 min (Thermo Fisher Scientific Sorvall ST16R, IL, USA). After, 500 µL of supernatant was homogenized with 100 µL of distilled water and 100 µL FeCl3 (0.1%, w/v). The absorbance was measured at 700 nm and results expressed as absorbance at the same wavelength.
Antiradical activity was measured by the DPPH• radical scavenging method (Molyneux, 2004). All EME (500 µL, at 100 µg/mL) were homogenized with 500 µL of DPPH• solution (300 µmol) and incubated at 25 °C for 30 min, under dark. The absorbance was measured at 517 nm. The results were expressed as inhibition (%) = [1 - Abs(S)/Abs(0)] x 100, where Abs(S) is the absorbance of the antioxidants at 30 min, and Abs(0) the absorbance of control at 0 min.
Antiradical activity was also measured by the ABTS•+ radical cation scavenging method (Re et al., 1999). Each EME (10 µL, 100 µg/mL) was homogenized with 990 µL of ABTS•+ solution (adjusted to an absorbance of 0.8 nm). The samples were incubated at 25 °C for 30 min, under dark. The absorbance was measured at 730 nm. The results were expressed as inhibition (%) = [Abs(0) - Abs(S)/Abs(0)] x 100, where Abs(S) is the absorbance of the antioxidants at 30 min, and Abs(0) the absorbance of control at 0 min.
Antioxidant activity in a meat system
Lipid oxidation was measured by the TBARS method (Pfalzgraf, Frigg & Steinhart, 1995), with slight modifications. The meat extract was obtained homogenizing (4,500 rpm/5 °C/1 min) pork meat with distilled water (1:10, w/v) and the respective antioxidants at 500 ppm (50 µL of BHT or 1 mL of EME), using an Ultraturrax (T25, IKA®, Staufen, Germany). The resultant solution was incubated (37 °C, at different periods for 16 h) in a water bath. Then, meat homogenates (0.5 mL) were mixed with 1 mL of TCA solution (10%, w/v) in a vortex mixer at 10,000 rpm for 1 min (Analog vortex mixer, Fisher Scientific TM, Nueva Jersey, USA). After, 1 mL of the resultant filtered solution (Whatman 4 filter paper) was homogenized with 1 mL of TBA solution (0.02 M) and placed in a water bath (97 °C for 20 min), and subsequently cooled. The absorbance was measured at 531 nm and results expressed as mg of malondialdehyde per kg of meat (mg MDA/kg).
Statistical analysis
All measurements were conducted in triplicate with at least three independent experiments, and the results were expressed as mean ± standard deviation. An analysis of variance (ANOVA) was used to analyze the data, and the Tukey-Kramer method was used to compare the averages (p < 0.05). Furthermore, a principal component analysis (PCA) was performed to evaluate the relationships among the analyzed variables (SPSS, version 21).
Results and discussion
Proximate composition of edible mushrooms
The results showed significant differences (p < 0.05) between the carbohydrates > protein > ash > moisture > fat content of all analyzed mushrooms (Table I). According to these results, G. lucidum and P. ostreatus powders presented (p < 0.05) the lowest moisture (< 4%) and lipids contents (< 2%), and the highest carbohydrates contents (> 80%). Also, P. ostreatus powder showed the lowest ash and the highest protein contents (p < 0.05). In agree with our results, it has been reported an ash and carbohydrates content between 2.8-8.9% and 78.2-81.5%, respectively, for G. lucidum (Stojkovic et al., 2013). However, in the same study were reported highest values for protein (9.911.3%) and fat content (2.8-8.9%). In another work (Vargas-Sánchez et al., 2018), using P. ostreatus was found a protein (12.3%), fat (3.3%), and carbohydrate content (64.4%), results in disagree with our study. Similarly, it has been reported for A. brasiliensis a different proximate composition with protein (31.3%), fat (1.8%), ash (7.5%), and carbohydrates (59.4%) content (Carneiro et al., 2013).
Table I
Proximate composition of the edible mushroom powders (%).
In addition, it has been reported that edible mushrooms composition varies between species which can also be associated with several factors such as maturation stage, the content of exopolysaccharides in the fruiting body, cultivation method (solid or liquid medium and substrate), environmental conditions, and conservation treatment (pH and temperature) (Carneiro et al., 2013; Lin & Sung, 2006; Stojkovic et al., 2013). Based on proximate composition, the carbohydrates and crude protein are the two main components (Kalač, 2009); thus, a variation of protein and carbohydrate content can affect the physicochemical and biological activity of the mushrooms (Pan, Jiang, Liu, Miao & Zhong, 2013; Yan et al., 2019).
Solvent effect on physicochemical properties
The results showed significant differences (p < 0.05) between the extraction yield, pH, and color of the analyzed samples by solvent effect (Table II). The highest extraction yields (> 40%) were obtained by P. ostreatus water extract, followed by ethanolic and aqueous-ethanolic extracts (p < 0.05). This higher extraction yield indicates a high solubility of the mushroom powder compounds, which is improved by increasing the solvent polarity (Azmir et al., 2013; Cheung, Cheung & Ooi, 2003). In agreement with our findings, it was reported an extraction yield of Pleurotus eous extract was higher (> 40%) using a polar solvent extraction (water > methanol > ethyl acetate) (Sudha, Vadivukkarasi, Shree & Lakshmanan, 2012). In addition, a similar extraction yield (34.2%) was showed for P. ostreatus water extract (Vargas-Sánchez et al., 2018). In disagree with our work, it has been reported higher extraction yields for A. brasiliensis water extract (45.2-46.6%) and G. lucidum water extract (26.4-28.8%) (Kozarski et al., 2011).
Table II
Effect of solvent extraction on physicochemical properties of EME.
Moreover, the highest pH value (> 5.0) was obtained in P. ostreatus ethanol and aqueous-ethanolic extracts, while the lowest pH values were found in A. brasiliensis water and aqueous-ethanolic extracts (p < 0.05). No significant differences (p > 0.05) were found in pH values of G. lucidum extracts, when compared between extraction solvents. The results also showed highest °Brix values (>16) in all samples extracted with the polar solvent; however, no significant differences (p > 0.05) were found between EME obtained with the same solvent. In addition, it has been reported that acidic compounds presented in EME can reduce the pH values; while an increase in total soluble solid (TSS) is associated with the maturity stage of the wall of the mushrooms, and consequently, with the increase of the °Brix value (Jafri, Jha, Bunkar & Ram, 2013).
Regard color measurements, the highest L* values were obtained in all water extracts, and G. lucidum ethanol and aqueous-ethanolic extracts showed the lowest L* value (p < 0.05). P. ostreatus water extract presented the highest a* values, and the lowest a* values were found in A. brasiliensis and G. lucidum water extract (p < 0.05). The highest b* values was obtained in P. ostreatus extracts, and the lowest values were found in A. brasiliensis and G. lucidum ethanol and aqueous-ethanolic extracts (p < 0.05). The color is an important factor that influences the quality of edible mushrooms, which can be affected by the maturity or substrate supplementation received during the production, and by the presence of compounds such as polysaccharides and polyphenols (Mami, Peyvast, Ziaie, Ghasemnezhad & Salmanpour, 2014; Pan et al., 2013). It has been demonstrated that the color of edible mushrooms can be influenced by the cooking method (steaming, pressure cooking, microwave, frying or boiling), as well as by the method used to obtain the powder (sun or oven dried) (Sun, Bai & Zhuang, 2014). In addition, phytochemicals as polysaccharides and phenolic compounds are responsible for the brown color of EME, and an increase in the dark-brown color can be associated with high levels of these compounds (Siu, Chen & Wu, 2014).
Solvent effect on phenolic composition
Phenolic compounds are secondary metabolites widely distributed in plants and mushrooms, which can be used as nutraceutical ingredients (Papuc et al., 2017). The results of TPC and TFC of EME analyzed are display in Table III. The highest TPC (> 30 mg GAE/g) was showed in P. ostreatus ethanol and aqueous-ethanolic extracts (p < 0.05), and the lowest values (p < 0.05) were found in A. brasiliensis and G. lucidum water extract. In addition, the highest TFC (mg QE/g) value (p < 0.05) was found in P. ostreatus water extract, and lowest values (p < 0.05) were reported in A. brasiliensis ethanol and aqueous-ethanolic extracts. Regardless the mushroom species, the TFC was enhanced by the polar solvent.
Table III
Effect of solvent extraction on chemical composition and antibacterial activity of EME.
In agreement with our work, a study reported that the highest TPC was obtained with the polar reduced solvent (ethanol > water) for Ganoderma spp. extracts. While, in another work, it was demonstrated that highest TPC were obtained with ethanol > water for P. ostreatus extracts (Vamanu, 2013). Also, it has been reported that the highest TFC was reported for Agaricus spp. obtained with the polar solvent (water > ethanol) (Abugri & McElhenney, 2013). On the other hand, in disagree it was reported the highest TPC and TFC in Agaricus spp. extracts obtained with the polar (water > 60% water-ethanol) and reduced polar (60% water-ethanol > water) solvent extraction, respectively (Gan, Amira & Asmah, 2013). As well, in another work Pleurotus eous showed a high TPC values in polar solvent extraction (water > methanol), while high TFC values were obtained in reduced polar solvent (methanol > water) (Sudha et al., 2012).
Solvent effect on antimicrobial activity
Furthermore, data of antimicrobial activity (Table III) indicate that EME showed different rates of bacterial inhibition. Regardless of the extraction solvent, the higher effect was obtained in Gram-positive (L. innocua > S. aureus) than Gramnegative bacteria (E. coli > S. typhimurium). Also, G. lucidum and P. ostreatus ethanol and aqueous-ethanolic extracts showed the highest inhibition of Gram-positive and Gram-negative bacteria than water extracts (p < 0.05). In addition, water, ethanol, and a solvent mixture (1:1) were used as controls and results indicate that both solvents showed lowest or negative antimicrobial effect (< 5 mm), while the standard gentamicin exert the highest antimicrobial effect. In agree with our results, G. lucidum extracts showed the high inhibition zone against S. aureus, E. coli and S. typhi in methanol > ethanol > water (Quereshi, Pandey & Sandhu, 2010). Also, it has been reported that Pleurotus spp. extracts obtained with the polar reduced solvent (ethanol), showed the highest inhibition against S. aureus > E. coli > S. typhimurium (Kalyoncu, Oskay & Kayalar, 2010).
In disagree, it has been reported that Pleurotus squarrosolus water extract showed highest antimicrobial activity against S. aureus, when compared with the polar reduced extract (ethanol) (Nwachukwu & Uzoeto, 2010). Also, it has been reported that A. brasiliensis aqueous-ethanolic extracts did not exert antimicrobial activity against S. aureus and E. coli (Ye & Lin, 2001). It has been demonstrated that solvent polarity is a key factor in the type of compound to be extracted from natural sources, e.g., in aqueous extracts compounds such as polyphenols (phenolic acids and flavonoids), tannins, saponins and terpenoids can be extracted; while in ethanolic extracts flavonoids, tannins, terpenoids and alkaloids can be extracted (Abugri & McElhenney, 2013; Papuc et al., 2017). Whereas, in methanolic extracts has been found anthocyanins and flavonols, terpenoids, saponins and tannins (Azmir et al., 2013).
In addition, the antimicrobial activity of EME can be associated with the specie and differences in their phenolic constituents (Nowacka et al., 2014). These compounds can follow different action mechanism: (1) inhibition of cellular division; (2) destruction of the cytoplasm and cellular membrane causing cellular components exit and create changes in the fatty acids and phospholipids of the membrane; (3) bacteriolysis; (4) inhibition of protein synthesis and finally; (5) inhibition of DNA and RNA synthesis (Martínez & Sánchez, 2007).
Solvent effect on antioxidant activities
Regardless of the extraction solvent, the highest antioxidant values (Table IV), i.e., RPA (> 0.40 abs) and antiradical DPPH• and ABTS•+ activity (> 80 and 50%, respectively), were showed in P. ostreatus extracts. In all analyzed EME, a high RPA was found in samples obtained with water (p < 0.05). While a high DPPH• inhibition was observed in treatments obtained with ethanol and aqueous-ethanol than water. The results of ABTS•+ inhibition showed no significant differences (p < 0.05) between extractions solvent analyzed in A. brasiliensis, G. lucidum and P. ostreatus extracts. In addition, according to the Figure 1 the highest MDA formation inhibition (45.1%) was found in meat samples stored (at 37 °C during 16 h), and treated with G. lucidum and P. ostreatus ethanolic and aqueous-ethanolic extracts (p < 0.05).
Table IV
Effect of solvent extraction on antioxidant activity of EME.
[i] Data are mean ± standard deviation (n = 6). TPC, total phenolic content (mg GAE/g); TFC, total flavonoid content (mg QE/g); RPA, reducing power ability (absorbance at 700 nm); antiradical assays are expressed as inhibition percentage. Different superscripts (a-e) in each row indicate significant differences between samples (p < 0.05).
In agree with our results, it has been reported a highest reducing power activity for Agaricus spp. extracts obtained with water > 60% water-ethanol. While the highest DPPH• inhibition was found in the extract obtained with the 60% water-ethanol > water (Gan et al., 2013). Also, reported the highest RPA for A. brasiliensis extracts obtained with water > ethanol (Tsai, Tsai & Mau, 2007). On the other hand, it was reported the highest DPPH• inhibition for G. lucidum was showed in extract obtained with water > ethanol (Kalyoncu et al., 2010). In another work Pleurotus eous showed the highest DPPH• and ABTS•+ inhibition using methanol > water (Sudha et al., 2012). Additionally, it has been demonstrated the use of edible mushrooms in the development of meat products to reduce lipid oxidation process (Montes, Rangel-Vargas, Lorenzo, Romero & Santos, 2020).
Multivariate analysis
A principal component analysis was carried out to evaluate the differences between treatments and analyzed variables (Figure 2). The first and second component showed a variance of 49.4 and 21.9%, respectively; thus, an accumulative 71.3% of the total variation was explained by the two components. Also, the results showed a separation of analyzed treatment and biological activity (p < 0.05); for example, P. ostreatus ethanol and aqueous-ethanolic extracts showed the highest antioxidant and antimicrobial activity, which was associated to the solvent extraction, yield, color (a* y b*), TPC, TFC and pH of the samples. The above suggest that principal component analysis could be used as a good predictive for antimicrobial and antioxidant activity of EME for their application in food industry.
Conclusions
Edible mushrooms (A. brasiliensis, G. lucidum and P. ostreatus) are an important source of nutriments (protein, fat, ash, and carbohydrates). However, the solvent used for obtaining edible mushrooms extracts exert an effect on phenolic components (flavonoids content) and physicochemical properties (extraction yield, pH, TSS and color). Respect antibacterial activity, G. lucidum and P. ostreatus ethanol and water-ethanol extracts showed the highest antimicrobial effect against Staphylococcus aureus > Listeria innocua > Escherichia coli > Salmonella typhimurium. While antioxidant assays revealed that P. ostreatus extracts showed the highest reducing power and antiradical activity, and G. lucidum and P. ostreatus ethanol and water-ethanol extracts showed the highest lipid oxidation inhibition. Therefore, EME can be used to reduce the growth of pathogenic microorganisms and as stabilizers of oxidative reaction.
