1 Introduction

Rapid developments in the agricultural food sector due to rapid population growth worldwide lead to generating a significant amount of lignocellulosic waste every year [1]. Most of these residues are rich in organic compounds and are suitable for recycling. It is used for energy production, biofertilizer, biofuel, and biogas production [2] and can also be used in producing ethanol, enzymes, essential oils, and additives with sustainable practices and different technological methods [3, 4]. While a tiny portion of these wastes are used in beneficial applications, a large portion cause serious environmental problems because they may require disposal costs or be incinerated [5, 6]. In particular, various methods such as stubble burning in the disposal of these wastes cause air pollution and negatively affect the soil’s physical, chemical, and biological structure [7]. Therefore, studies should be conducted to convert these agro-residues into profitable products using fungal biotechnology.

Considering that lignocellulosic residues are abundant in other countries and Turkey, it is one of the most remarkable issues that these products do not harm the environment and that there are different alternative ways to transform them into high-value-added products. Especially, growing microbial cells on agricultural wastes to synthesize biologically active compounds using different biotechnological innovations has gained interest [8]. In this sense, mushroom cultivation is a biotechnology that can transform waste plant materials into valuable foodstuffs and ensure food safety [9, 10]. Utilizing agricultural wastes in mushroom cultivation is thought to be beneficial both in the biological transformation of lignocellulosic wastes and in eliminating environmental pollution. Mushrooms are grown commercially using lignocellulosic waste through a biological process and are an economically important biotechnological industry. It is an environmentally friendly process that has gained excellent importance today owing to the increasing global demand for nutritious and natural foods [5].

Edible mushrooms have attracted attention for many years because of their nutritional content, various bioactivities, and ease of cultivation [11]. They are especially rich in proteins, amino acids, sugar alcohols, vitamins, unsaturated fatty acids, and mineral substances (Na, P, K, Ca, Ca, Mg, Na, Fe, Zn, Cu, and Li). They are also among the foods sought in the diet due to their low fat and dietary fiber ratio. For this reason, mushroom cultivation is increasing daily, and its production is increasing by 6–7% every year [10, 12]. Genus Pleurotus spp., also known as oyster mushroom, ranks second in the world in the edible mushroom cultivation [13]. Oyster mushrooms have an important place in the food industry because of their nutritional properties , and gastronomical and medicinal effects. They are also considered excellent lignocellulosic decomposers because of their high mycelial growth rate, enzymatic capacity, and ease of growth [14,15,16,17]. Oyster (P. ostreatus), king eryngii (P. eryngii), phoenix (P. pulmonarius), gold oyster (P. citrinopleatus), and also especially love mushroom-pink oyster mushroom (P. djamor) are popular and widely cultivated worldwide.

Pleurotus djamor (Rumph. ex Fr.) Boedjin is an edible, delicious tropical species native to Southeast Asia and Central America. It is an exotic species because of its pink color, fibrous texture, and nutritional and antioxidant properties [18, 19]. It can be grown more easily and in a shorter time than other edible species, through a process known as solid fermentation [18, 20,21,22,23,24]. It would be beneficial to produce different types of mushrooms that are not widely known by the public, are not produced, and are not among the mushroom varieties grown. At the same time, it would be beneficial for P. djamor to be included among other cultivated mushrooms in terms of ease of growing conditions and obtaining products in a short time. Therefore, to contribute to sustainable agro-food waste management, the use of quinoa stalk (QS), wheat straw (WS), and their mixtures, which are agricultural wastes found in Turkey, in P. djamor culture and their effects on vegetative growth days, yield and nutritive properties were investigated.

2 Material and methods

2.1 Mushroom cultivation

The mushroom samples used in the current study were obtained from previous studies [25]. The main culture of the P. djamor strain was obtained from Mushroom Box Company, Monmouth, England. The isolate was donated by Dr. M.N. Owaid from the Fungi and Plant Pathology Laboratory, College of Science, University of Anbar, Iraq, and maintained at 4 °C on malt extract agar (MEA) medium (Fig. 1a). Mycelium and spawn (Fig. 1b) were kept on MEA and wheat grain at 25 °C in the dark on average for 6 and 9 days (Fig. 1c), respectively. Other stages such as mycelium growth, spawn propagation, compost preparation, inoculation, and culture conditions were followed by the recommended methods [26].

Fig. 1
figure 1

Cultivation of Pleurotus djamor (a Pure mycelium. b–c Spawn. d–f Compost. g–h Spawn inoculation compost and colonization of compost. i–j Pirmordia. k–l Basidiocarp)

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Trial groups consisting of wheat straw (WS) (control group), quinoa stalks (QS), and their 1:1 (kg/kg) mixture (WS-QS) were kept in water for 48 h until they reached 70–75% humidity (Fig. 1d). The drained materials were poured onto a polyethylene sheet, and 35 g of gypsum and lime per kg of dry compost were added to obtain the desired pH (5.5–6.5). The prepared composts were placed in cloth bags and autoclaved at 121 °C for 30 min. and then allowed to cool to room temperature (Fig. 1e, f). A 5% spawn inoculated (Fig. 1g) compost (750 g) was placed in bags (20 × 30 cm) and stored in the dark at 25 ± 1 °C in the culture room (2.35 × 2.42 × 3.17 m) for 12 days. After the compost was completely covered with spawn (Fig. 1h), the culture room for primordium stimulation (Fig. 1i, j) was fixed at 18±1 °C, humidity at 80–85%, light at 500 lux (12 h per day) and ventilation for 3 h per day. Additionally, the cultures were watered twice a day by spraying water. Fruit bodies were harvested when they reached the characteristic maturity stage (Fig. 1k, l). Basidiocarps were dried at room temperature (25 °C) for subsequent analysis.

2.2 Nutritional properties

Selected nutritive properties of P. djamor cultured on various agro-residues including, moisture, crude protein, ash, mineral content, organic matter, energy, nitrogen-free extract, and dry matter were defined by appropriate methods [27], as described below. Dry matter was determined by drying in an oven at 55–60 °C for 48 h. The ash content was analyzed by weighing the samples before and after burning at 550 °C for 4 h. Organic matter and moisture were calculated by the difference: % dry matter—% crude ash or 100—dry matter. The fat content was determined by Soxhlet using petroleum ether as a solvent. Crude protein was estimated using the Kjeldahl method, and the calculated nitrogen was multiplied by 6.25. Crude protein and energy were calculated according to the following equations: crude protein (%) = [(0.1 N received HCI − 0.1 N spent NaOH) × 0.0014 × 6.25 × 100]/(amount of sample, g); energy (kcal) = 4 × (g protein + g carbohydrate) + 9 × (g lipid).

2.3 Vitamin A and E levels

Homogenized mushroom samples (1 g) were transferred into polyethylene tubes, and 2 ml of ethanol was added to the tubes. After 0.3 ml of n-hexane was filled into tubes for vitamin extraction, they were centrifuged. This step was repeated twice. n-hexane in tubes was evaporated using nitrogen. The residues were then solved in the mobile phase (methanol:acetonitrile:chloroform; 47:42:11, v/v). Chromatograms were monitored at 326 and 296 (vitamin A and E, respectively), and the injection volume was set 50 μL. Techsphere ODS-2 packed column (5-μm particle, 250 × 4.6 ID) was used and the flow rate was 1.0 mL/min [28].

2.4 Vitamin C and MDA levels

0.5 ml of HClO4 (0.5 M) and 4.5 ml of distilled water were added to an aliquot portion of (1.0 g) mushroom samples [28]. Then, the samples were centrifuged at 4500 rpm for 5 min, and the supernatants were injected into the HPLC system. The addition of acid was necessary to precipitate proteins and release the malondialdehyde (MDA) bound to the amino groups of proteins and other amino compounds. Acid addition was also required to maintain the stability of vitamin C. The mobile phase was 30 mM KH2PO4 -methanol (82.5+17.5, v/v%, pH 3.6), and the flow rate was 1.2 mL/min. Chromatograms were monitored at 250 nm and injection volume was 20 μL. A Wakosil II 5C18 RS 5 μm (150 × 4.6 mm SS, SGE, AUS) column was used at room temperature.

2.5 Elemental analysis

The mushroom samples air-dried at room temperature were re-dried at 105 °C overnight and crushed with a mortar and pestle. The digestion of mushroom samples was performed by using a mixture of HNO3:H2SO4:H2O2 (10:1:1, 12 ml for 1 g sample) and heating at 100 °C for approximately 10–15 min. After cooling, 50 ml of deionized water was added and then all was filtered. To determine all the materials, all the used glassware was cleared with deionized water [28]. Elemental analysis was performed in the Middle East Technical University Chemical Analysis Laboratory. Fe, Zn, Mn, Cu, Cr, Cd, Co, Ni, Pb, K, Ca, and Na mineral contents in the samples were determined by inductively coupled plasma optical emission spectrophotometer.

2.6 Statistical analysis

In the analysis software SPSS 25 and the data were summarized as mean ± standard deviation. Significant differences between the groups were obtained from Duncan‘s post-hoc test.

3 Results and discussion

3.1 Growth period and yield of Pleurotus djamor cultured on lignocellulosic residues

Spawn colonization period, primordia formation period, harvest days, and yield of Pleurotus djamor cultured on wheat straw, quinoa stalk, and their mixture in a 1:1 ratio are shown in Table 1. As seen in Table 1, although the spawn colonization periods of P. djamor grown on the three types of compost varied between 11.5 and 12.8 days, there was no statistical difference (p>0.05). In literature studies, shortest and longest spawn colonization periods of different Pleurotus species were reported to be 11.33–17.67 days [21], 11.5–12.3 [25], 20–30 days [29], 16.67–25.00 days [30], 8.0–12.6 days [31], 16–30 days [32], 9–20 days [33], 16.4–25.2 days [34, 35], 32.33–42.33 days [36], 14.7–17.7 days [37], 28.71 days [38], and 22.67–41.00 days [39], based on the biochemical properties of lignocellulosic material used, additive ratio, and type of mushroom. It was determined that spawn colonization periods of P. djamor (11.5–12.8 days) were lower than some literature studies [29, 30, 32, 34,35,36,37,38,39] and similar to some literature studies [21, 25, 31, 33]. As a result, it was observed that the factors affecting colonization in mushrooms depend primarily on the mushroom type and compost material. It has been observed that the spawn of P. djamor colonized the compost in a very short time; therefore, there is no risk of infection.

Table 1 Growing period and yield of P. djamor grown on various agro-residues
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The primordium formation period of P. djamor grown on various lignocellulosic residues (WS, WS-QS (1:1), and QS) varied from 20.3 to 26.0 days, but the earliest was observed in QS at 20.3 days (shown Table 1). The shortest and longest primordium formation periods of oyster mushrooms grown on lignocellulosic residues are generally reported as 16.67–22 days [21], 21–29 days [29], 24.00–30.33 days [30], 26.2–44.2 days [31], 13–25 days [33], 19.3–25.2 days [34], 38.33–55.66 days [36], 24.0–34.7 days [37], 32.36–48.10 [38], 26.67–48.33 days [39], and 25.8–36.5 days [25]. It was determined that the primordium formation times (20.3–26.0 days) of P. djamor cultured on wheat straw, quinoa stalk, and their mixture in a 1:1 ratio were similar to those of some of the studies in the literature [21, 25, 29, 30, 33, 34, 37] and were lower than those of others [31, 36, 38, 39]. The results varied depending on the mushroom species, growing medium, and method used. Primordium formations were observed 10 days after opening compost bags in P. djamor. This shows that this species is an early species among different cultivated mushrooms.

P. djamor culture lasted approximately 90 days, during which an average of three crops were harvested, but the earliest harvest occurred at 50.0 days in QS (see Table 1). It was observed that the suitable substrate at the point of early harvesting and earliness in P. djamor culture was QS (50.0 days). The shortest and longest total harvest periods of oyster mushrooms in different studies have been reported as 35 days [29], 27.00–35.00 days [30], 14.0–25.6 days [31], 15–35 days [33], 23.8–50.2 days [34], 25.8–54.8 days [35], 21–26 days [21], 72–87 days [37], 29.67–51.67 days [39], and 61.8–90.5 days [25]. The total harvest times of P. djamor obtained from three different composts may differ based on substrate type, cultivation techniques, and mushroom isolate, as noted by the researchers above [21, 25, 29,30,31, 33,34,35, 37, 39].

The lowest yield per 100 g of material (70% moisture) was 12.0 g on WS, and the highest yield was 23.5 g on QS (Table 1). The results showed that QS medium (23.5%) was the best substrate in point of yield in P. djamor culture (Table 1). Quinoa stalk (QS) may be a suitable substrate for the cultivation of P. djamor because its yield is comparable to that of other wastes. In studies conducted by different researchers, the minimum and maximum total yield of Pleurotus species cultured in different compost materials were ~23–41 g [29], 24.3 to 33.3 g [37], 10–17 g [39], 29.6 g [25], 32.87–41.27 g [40], 24.76 g [41], 30.0–44.5 g [42], 46.7–62.9 g [38]. It was stated that pure or mixtures of various agricultural residues can be easily used in mushroom cultivation, and the interaction between the biochemical structure of plant residues and the fungal isolate has significant effects on yield. The total yield of Pleurotus spp. grown on different combinations of agro-residues reported by previous researchers was 10.0–90.7 g [25, 29, 37,38,39,40,41,42]. Our reports (23.5 g/100 g) were observed to be different from what some researchers observed [39], lower than some studies [25, 38,39,40,41,42], and consistent with results in some studies [29]. As stated in the aforementioned report, various results can be obtained based on the biochemical properties of plant materials, different growing techniques, and isolate types.

As a result, it was determined that quinoa stalk (QS) was the best culture medium in terms of primordium formation period (20.3 days), total harvest period (50.0 days), and yield (23.5 g/100 g). Regarding earliness and high yield, it will be beneficial to use quinoa stalks pure or as additives in the cultivation of edible fungi.

3.2 Nutritional analysis of Pleurotus djamor grown on various lignocellulosic wastes

The selected proximate compositions of Pleurotus djamor grown on some agro-residues are shown in Table 2.

Table 2 Nutritional properties of P. djamor cultured on various agricultural wastes (%, dry weight)
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In P. djamor obtained from different compost materials, 89.9–91.4% dry matter, 8.6–10.1% moisture, 250.8–277.5 kcal energy, 22.0–41.2% protein, 1.1–1.7% fat, 5.8–9.6% ash, 82.0–84.1% organic matter, and 20.3–38.2% nitrogen-free extract were determined (shown Table 2). The nutritional contents of P. djamor grown on different compost media (wheat straw, quinoa stalk, and their mixture in a 1:1 ratio) were found to be statistically significant (p<0.05, see Table 2). The organic matter, moisture, and dry matter of P. djamor from WS and WS-QS (1:1) did not differ statistically (p>0.05), but there were significant differences from QS in both media (p<0.05, shown in Table 2). Additionally, significant differences were found between the protein, carbohydrate, ash, and energy ratios of the samples obtained from different materials (p<0.05, see Table 2). The highest crude protein was detected in WS-QS (1:1) (41.2%). When the agro-residues used as culture media were examined, it was seen that the energy and crude protein ratio of P. djamor obtained from those residues was quite high (shown in Table 2). As shown in Table 2, a significant increase was observed in the analysis of the nutritional contents of P. djamor obtained from quinoa straw and quinoa-added compost media.

In previous reports [24, 29, 36, 40, 43, 44], most fresh mushrooms contained approximately 90% moisture and 10% dry matter. The dry matter ratio of P. djamor obtained from QS, WS-QS (1:1), and WS was determined as 89.9–91.4, and the moisture ratio was 8.6–10.1% (see Table 2). These results are consistent with the previously aforementioned studies. The energy amounts of P. djamor grown on various agricultural wastes were calculated as 250.8 kcal in WS, 259.9 in WS-QS (1:1), and 277.5 kcal in QS (shown in Table 2). It was observed that the energy value of P. djamor obtained from QS and WS-QS (1:1), where quinoa stalk was used as pure or as an additive, increased (see Table 2).

It is seen in Table 2 that the protein ratios of P. djamor grown on wheat straw, quinoa stalk, and their mixture in a 1:1 ratio were 22.0%, 41.2%, and 37.5%, respectively. In the analysis of the mushrooms obtained in the quinoa stalk and quinoa-supplemented trial group, it was observed that the protein ratio increased (see Table 2). Crude protein contents of P. djamor cultured in experimental groups created from pure and different mixtures of various lignocellulosic wastes were reported as 21.61–25.63% in P. djamor [18], 31.48–35.50 g in P. djamor [21], 24.84 g in P.djamor [40], 23.5–30.4% in P. djamor [41], 15.6% in P.djamor [43], 33.30–35.50 g in P. djamor [45], 24.51% [46], 26.55 g in P. djamor [47], 11.37–32.37% in P. djamor [48], and 44% in P. djamor [49]. Protein contents in different Pleurotus species (P. sajor-caju, P. citrinopileatus, P. platypus) and Agaricus bisporus vary between 25.63 and 44.3% [29, 35, 39, 50, 51]. Our reports (41.25% in QS) were higher than those of other researchers reports [18, 21, 35, 39,40,41, 43, 45,46,47,48, 50, 51], lower than those reported by others [29, 49, 51], but appeared homogeneous with the outcome in the report [29]. The composition of the substrates in compost significantly affects the protein content of mushrooms. It has been stated in the aforementioned studies that the protein content of mushrooms depends on the chemical composition of the substrate, C/N ratio, and the type of mushroom grown. In addition, the protein content of mushrooms has an important place in nutrition. It is known that the proteins of Pleurotus species are more digestible than those of plants and have important biological activities. It contains all nine essential amino acids that humans need and can be used as a meat substitute [52,53,54]. In this sense, the high protein content of P. djamor is very important when evaluated in terms of human health.

As shown in Table 2, the crude fat ratio in P. djamor grown on wheat straw, quinoa stalk, and their mixture in a 1:1 ratio varied between 1.1% and 1.7%. Similar studies [18, 21, 24, 33, 36, 39,40,41, 43, 45,46,47,48, 50, 51] reported that the fat ratio of mushrooms and Agaricus bisporus grown in different culture environments may vary, but the amounts are low (0.13–6.7). Our reports (1.1–1.7%) are lower than those observed by other researchers [21, 33, 40, 41, 45, 47, 48, 50, 51], higher than those reported by others [18, 24, 36, 39, 45, 46]; however, they are compatible with the data in some studies [21, 39, 41, 43]. Macrofungi have low crude fat content and rich unsaturated fatty acid content. Therefore, these foods, which have low fat content, are suggested as good dietary foods in the mentioned reports. Pleurotus species contain low lipids and excellent sources of fatty acids such as linoleic acid and oleic acid. Considering that these fatty acids have anticancer effects, especially on breast, colon, and prostate cancer, they are important foods for human health [54, 55].

As shown in Table 2, the highest ash ratio of P. djamor was observed in QS (9.6%) and the lowest in WS (5.8%). The crude ash contents obtained from various lignocellulosic wastes were previously reported as 5.9–8.40% in P. djamor [21], 4.1% in P. djamor [33], 8.35% in P. djamor [40], 5.83% in P. djamor [43], 7.55–8.64% in P. djamor [47], 9.5% in P. djamor [41], 8.9% in P. djamor [50], 4.03–8.40% in P. djamor [45], and 6.7–7.9% in P. djamor [48]. Our reports (5.8–9.6%) differ from those observed by other researchers [33, 43, 45], but are compatible with the data in some reports [21, 40, 41, 47, 48, 50]. The ash ratio of mushrooms varies depending on the substrate material used, which part of the mushroom is used, the species, and the technique used.

Organic matter ratios of P. djamor obtained from various compost media were calculated as 82 to 84.1% (see Table 2). The organic matter contents obtained from various agro-residues were previously reported as 81.1–83.8% in P. citrinopileatus [25], and 76–84% in Agaricus and Pleurotus spp. [44], and 84–88.2% in P. ostreatus [56]. The organic matter amounts of P. djamor obtained from different environments (Table 2) are compatible with the findings of other studies.

It was determined that the highest nitrogen-free extract ratio of P. djamor was 38.2% on WS, while the lowest was 20.3% on WS-QS (1:1) see Table 2. Nitrogen-free extracts were previously reported as 46.8% in P. pulmonarius [37], 46.8% in P. citrinopileatus [25], and 26.7–36.8% in Agaricus and Pleurotus spp [44]. The nitrogen-free extract of P. djamor may vary with the findings of other researchers, depending on the mushroom type, compost environment, and culture method.

The importance of elements that have regulatory properties in human nutrition and metabolic functions should not be ignored. The “love mushroom-pink oyster mushroom” P. djamor contained reasonable amounts of sodium, potassium, calcium, iron, zinc, manganese, and copper (see Table 3). All the aforementioned elements exist in varying amounts in P. djamor; the mineral levels can vary, but they are available at nutritious and nontoxic levels as seen in Table 3. The fruiting bodies of Agaricus spp. and Pleurotus spp. (P. eryngii, P. djamor, P. ostretus, P. pumonarius, P. citrinopetus, etc.) contained varying quantities of micro-macro elements such as sodium, potassium, calcium, iron, zinc, manganese, and copper [21, 25, 29, 43, 44, 47, 48, 57]. It has been stated in the aforementioned studies that many factors such as the lignocellulosic materials used in mushroom cultivation, their different combinations, element contents, the type of mushroom, and the ability of the mushroom to accumulate each element affect the element level of the mushroom. It was observed that the mushrooms obtained in the quinoa stalk and quinoa-supplemented trial group showed an increase in element levels. In addition, it was determined that the element levels of the mushrooms obtained especially from the quinoa stalk were the highest, not at toxic levels and nutritious levels (see Table 3).

Table 3 Mineral element concentration of P. djamor grown on various agro-residues (mg/L)
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There are many essential vitamins that are required in our diet daily. Mushrooms are important nutritional sources, especially of group B, K, C, and E vitamins [58, 59]. Vitamins A, C, and E have important activities on the metabolic functions of humans. The first one plays a role in hormone synthesis, immune responses, and regulation of cell growth and differentiation; the second one is a vital micronutrient for humans. It can prevent heart, chronic inflammation, and neurodegenerative diseases; and the third one protects DNA, low-density lipoproteins, and polyunsaturated fatty acids against oxidative damage, and also plays a role in biosynthesizing hemoglobin, modulating immune responses and stabilizing membrane structure. The mentioned vitamins prevent free radical damage, reducing the risk of chronic disease [60]. The highest vitamin A, E, C, and MDA contents were found to be 0.73% on WS-QS (1:1), 59% on WS, 732.4% on QS, and 354.9% on WS-QS (1:1), respectively (shown in Table 4). It was determined that P. djamor grown on different compost media (wheat straw, quinoa stalk, and their mixture in a 1:1 ratio) did not differ statistically in point of vitamin A and E contents, but they did differ in terms of vitamin C and MDA. It was previously reported that the vitamin level of edible mushrooms varies depending on the genetic structure of the species, physical and chemical differences in the growing environment and their combination, and the analysis methods used [58, 59, 61,62,63,64]. It was determined that the results showed variability depending on the compost material used, fungus species, and method.

Table 4 Vitamin level of P. djamor grown on various agro-residues (mg/kg)
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4 Conclusion

As a result, “love mushroom or pink oyster mushroom” can be easily cultured on various local agro-residues. It helps to valorize local agro-wastes and transform them into protein-rich foods. Quinoa stalk (QS) was observed as a suitable compost medium at the point of vegetative growing periods. In terms of earliness and high yield, it will be beneficial to use quinoa stalks pure or as additives in the cultivation of edible mushrooms. The highest crude protein content was detected in WS-QS (1:1) (41.2%). It is also noteworthy that it contains different levels of vitamins and elements. The most suitable plant material for mineral content was QS. It can be consumed as a good nutritional source for low fat and energy ratios, nutritious protein, carbohydrates, regulatory vitamins, and non-toxic element levels. We think that P. djamor, which has an attractive color and aroma, can be cultured on different lignocellulosic residues and contribute to other studies with this study. In addition, this species needs to be grown on different compost materials, and the bioactive substances it contains should be studied in more detail. Because we know that the carbohydrates contained in mushrooms can be used in adjuvant treatment for human health, especially in cancer, which is a disease of our age. Therefore, the nutritional contents of P. djamor should be included in more detail in the literature.