Determination of Antioxidant and Oxidant Potentials of Pleurotus citrinopileatus Mushroom Cultivated on Various Substrates

Many mushroom species have been used by people for different purposes, from past to present. Cultivated mushrooms may show different biological effects depending on the content of the substrate they grown on. The present study aimed to determine the total antioxidant status (TAS), total oxidant status (TOS) and oxidative stress index (OSI) of Pleurotus citrinopileatus Singer mushroom cultivated on five different substrates. The cultivated mushrooms were extracted with ethanol in a Soxhlet device. TAS, TOS and OSI of extracts were determined with Rel Assay kits. The highest TAS (3.125±0.038 mmol/L), TOS (10.786±0.313 μmol/L) and OSI (0.345±0.014) values were determined in the mushrooms grown on 90% beech sawdust+10% bran. The lowest TAS (2.316±0.042), TOS (1.246±0.044) and OSI (0.054±0.001) values were obtained from the mushrooms grown on 100% poplar sawdust. Research Article Article History Received : 30.09.2019 Accepted : 09.01.2019


INTRODUCTION
Reactive oxygen species (ROS) increase in living organisms as a result of environmental and metabolic activities. In response to this increase, the endogenous antioxidants produced in the organisms play an active role and suppress the oxidant ROS. In cases where endogenous antioxidants are inadequate against ROS, the molecular structure of the organism may degrade.
Exogenous antioxidants, which are supplemented when endogenous antioxidants produced in humans are inadequate against oxidant compounds, are very important in preventing oxidative damage. Being one of the several natural sources of exogenous antioxidants, mushrooms play an important role in human diet. Edible mushrooms are collected from their natural environment and consumed by humans throughout the history. However, especially after the second half of the 20th century, mushroom cultivation became popular and turned into an industry of billions of dollars turnover annually (Pilz et al., 2001;Yılmaz et al., 2017). In addition to the strong nutritional properties, mushrooms are also important medicinal natural resources because of containing the secondary metabolites. Research demonstrated that mushrooms are also important natural sources used in the treatment of AIDS (Acquired Immune Deficiency Syndrome) patients in Africa, as well as wound healing, immune system strengthening and tumorinhibiting properties (Dai et al., 2009;Baba et al., 2012;Cheung, 2013;Zhang et al., 2014).
It is important to analyze mushroom species in order to identify and offer as new natural medical sources. Previous studies have reported pharmacological effects of P. citrinopileatus such as antioxidant, antibacterial, anticancer and antihyperlipidemic (Hu et al., 2006;Lee et al., 2007;Chomcheon et al., 2013;Yıldız et al., 2017). There are no studies in the literature determining the oxidative stress status of the P. citrinopileatus. In the present study, TAS, TOS and OSI values of Pleurotus citrinopileatus cultivated on various substrates were determined. The study also aimed to examine which compost medium is more suitable for the medical usages of P. citrinopileatus mushroom.

Substrates
No trees were cut down throughout the study. The sawdusts were obtained from sawmill located in the Karadeniz Technical University Campus (KTU) (Trabzon/Turkey). The substrates used in this study are presented in Table 1. Mycelium was supplied from a commercial firm.

Mushroom cultivation
The sawdusts were soaked to 70-80% humidity and stored for one day. Next day, to ensure homogeneity, moisture and autoclavable bags filled with sawdust were mixed and sterilized in the autoclave at 121 ° C for 1.5 hour. After sterilization, they were moved to the fume cabinet for cooling. Substrates were inoculated with spawn of 3% of the sawdust weight (Küçükomuzlu and Pekşen, 2005). The bags were counted in the Mushroom Culture Laboratory (KTU) and allowed to incubate. The mycelium colonizations were completely wrapped within 10 days, and the harvest was initiated on the 17th day. Harvested mushrooms ( Figure 1) were prepared for the extraction process. TAS results were shown mmol Trolox equiv./L. TOS results were shown μmol H2O2 equiv./L (Erel, 2004;Erel, 2005). The following Equation 1 was used to calculate the OSI (AU: Arbitrary Unit) values obtained by dividing the TOS value to TAS value (Erel, 2004).    wheat bran substrate. was found higher when compared to the mushrooms reported in those studies. There were some differences between the literature results. These differences may be due to the different antioxidant production capacity of different mushroom species growing in different substrates. Mushrooms produce endogenous antioxidant compounds as a defense mechanism against oxidative damage (Ramírez-Anguiano et al., 2007). Thus, the high antioxidant capacity of P. citrinopileatus exposed that the mushroom had high tolerance to oxidative damage. It was also considered that the mushroom could be used as a supplementary antioxidant source to decrease the oxidative damage in human body.  (Akgul et al., 2017;Sevindik et al., 2017;Sevindik et al., 2018). These mushrooms were wild and collected from the nature unlike our study. The differences in TOS values can be due to the differences in growth conditions and metabolic processes. It was reported that natural products which have antioxidant activity such as mushrooms may help the endogenous defense system (Ferreira et al., 2009 (Akgul et al., 2017;Sevindik et al., 2017;Sevindik et al., 2018). These findings indicated that oxidative stress induced by endogenous oxidant molecules produced by P. citrinopileatus was better inhibited by TAS that includes all enzymatic and none-enzymatic systems, and consequently, OSI values were lower.

CONCLUSION
Many natural antioxidants such as mushrooms are being widely investigated for their qualified capacity to defend cells and organisms from degradation brought on by oxidative stress.
In the study, antioxidant/oxidant potentials and oxidative stress status of P. citrinopileatus mushroom cultivated in different composts were determined. It was observed that the mixture of 90% beech+10% bran, exhibited the highest antioxidant potential. The lowest antioxidant potential was seen in the 100% poplar. The all test mushrooms cultivated on different synthetic composts exhibited a low oxidative potential. Therefore, it can be stated that cultivated P. citrinopileatus mushroom had a lower oxidative stress status. In conclusion, it was determined that P. citrinopileatus had antioxidant potential and this potential varied based on the substrate used. It was also found that P. citrinopileatus cultivated in culture medium was healthier due to the lower oxidant compound levels.

Statement of Conflict of Interest
Authors have declared no conflict of interest.

Author's Contributions
The contribution of the authors is equal. Edible mushroom cultivation for food security and rural development in China: bio-innovation, technological dissemination and marketing. Sustainability, 6(5): 2961-2973.