Nutritional composition of the substrates

P. ostreatus mushroom is proficient in decomposing lignocellulosic components, i.e., cellulose, hemicellulose, and lignin, as a carbon source for its mycelium growth and fruiting body development (Grimm and Wosten 2018), which makes them ideal for mushroom cultivation (Doroški et al. 2022). Nitrogen-rich compounds are used as supplements to mushroom cultivation substrates and result in higher mushroom yields with increased metabolic activities triggered by the presence of extra nitrogen according to the study of Rodriguez Estrada and Royse (2007), which contradicts the claim that higher nitrogen is the cause of mycelial growth interruption (Doroški et al. 2022). On the other hand, the addition of excess nitrogen-rich substrates may also lead to higher contamination risks by competitor microorganisms (Yildiz et al. 2002). The ideal nitrogen content of the substrate is reported to range between 0.5 and 2% Naraian et al. (2009), the value of which agreed with the results of the present study (Table 2). Moreover, the factors significant for mycelial growth, yield, and efficiency of mycelium production include the range of the C/N ratio, pH, and moisture contents (Nwanze et al. 2005). In addition, P. ostreatus requires inorganic compounds such as K, Ca, Mg, Na, and Zn to enhance yields and biological efficiency (Golian et al. 2021). Supplemented substrates with carbon or nitrogen compounds are important to shorten the spawn run time and increase the harvesting cycles of mushrooms (Ulziijargal et al. 2013; Cogorni et al. 2014).

Spawn running, pinhead formation and fruiting body formation

The shortest spawn run time of 10 and 12 days was obtained from P. ostreatus grown on S7 substrate, followed by that of S6 substrate, in which the C: N ratio was 40.15 and 50.98% respectively (Table 2). The spawn run time recorded from the current study was faster (shorter) than that of Hoa et al. (2015), who reported that the spawn run period took three weeks for Pleurotus ostreatus grown on pure sugarcane bagasse substrate without any supplements. The current result is also in agreement with that of Musieba et al. (2012), who reported short colonization time and high mycelium density of mushroom cultivated on straw substrate. The current result is also in agreement with that of Atila (2017), who verified that safflower hay supplemented with wheat bran and Gypsum substrate supported fast colonization of 16.4 days for P. djamor. The finding of Albores et al. (2006) revealed that there was a positive correlation between the C/N ratio of substrate and mycelium growth rate.

Substrate with a lower C/N ratio supported fruiting body formation better than substrate with a high C/N ratio. This is supported by Naraian et al. (2009), who demonstrated that mycelium growth and primordial development of Pleurotus florida were dependent on the C/N ratio.

The result of the current study was similar to that of Yang et al. (2013) who showed that a higher C/N ratio favored mycelium growth, but a lower C/N ratio favored fruiting body growth, thereby reducing the final maturity to harvest time. Yang et al. (2013) also determined that oyster mushroom P. ostreatus grown on substrate with 80% cotton seed hull with C/N = 34.87 needed longer to complete colonization period than that cultivated on substrate of 80% rice straw and 80% wheat straw with C/N = 49.19 and C/N = 64.63, respectively. Hoa et al. (2015) reported that sugarcane bagasse provided 51.71% of C: N with early spawn run completion for P. ostreatus mushroom. This is due to the high nitrogen content, which commonly inhibits mushroom growth in excessive amounts (Bellettini et al. 2019). In addition, an excess nitrogen content in the growth substrates is known to delay the formation of the fruiting body and suggested that the C/N ratio that would favor the primordial and fruiting body formation is about 22–30:1 (Yang et al. 2013). Generally, the results of the current study confirmed that a higher C/N ratio favors mycelial growth and a lower C/N ratio favors fruiting body growth. According to the results of the current study, S1, S6, and S4 substrates were found to be richer in hemicellulose content compared to the others. Obodai et al. (2003) reported a negative relationship between yield and hemicellulose content of a substrate, which agrees with the results of the present study. However, there was a positive relationship between yield and hemicellulose during the first flushes (Table 2; Fig. 4), the results of which were in agreement with those of Atila (2017). Hemicellulose is mainly utilized during the active growth phase Bellettini et al. (2019), and the growing macro-fungi cannot immediately benefit from the lignin and cellulose content of a substrate Wang et al. (2006). Moreover, reported that nitrogen-rich materials increase the degradability of the lignocellulosic material to enhance the accessibility of essential nutrients. In the present study, mycelial growth may be accelerated by the increased utilization of lignocellulosic content such as hemicellulose, cellulose, and lignin in parallel with the nitrogen content. It appears reasonable to assume that the high hemicellulose content associated with the high nitrogen concentration exerts a positive effect on mycelial growth.

The fastest mycelial growth may or may not correspond with the appearance of pinhead formation (Table 5). Hence, the days of pinhead formation ranged between 2 and 6.67 days, the duration of which was shorter than that of Hoa et al. (2015) and Ahmad Zakil et al. (2022), who reported pinhead formation within 5.50–8 and 6–7 days. The fast growth and pinhead formation of mushrooms were attributed to the addition of supplements such as wheat bran and other nitrogen-rich substrates (Das and Mukherjee 2007). In this study, the addition of cow dung, horse manure, and chicken manure as nitrogen sources enhanced the mycelium growth of P. ostreatus.

The earliest first harvest (3 days) of P. ostreatus was recorded from S1 substrate (Table 6), the results of which were contrary to those of Mondal et al. (1970), who found that the first fruiting and harvesting of mushrooms cultivated on banana leaves and rice straw was 11.25 days. The result of the present study was similar to that of Atila (2017), who demonstrated the harvest date for Pleurotus spp. to be 4 to 5 days after pinheads’ formation. This difference is due to the difference in total C, total N, and C/N ratios of the substrate, which had more effects on mycelium growth, pinheads’ formation, and the development of the fruiting body.

Cap diameter and stipe length

There were variations in stipe length and cap diameter of mushrooms cultivated on different substrates (Table 6). Hence, the stipe length of the products varied as shown in Table 5, which is very close to that of 100% rubber tree sawdust substrate, which gave a mean height of 9.12 to 7.75 cm for the best yield and the least yield, respectively Ahmad Zakil et al. (2020), while the cap diameter gave the highest value at 7.80 cm. The physical quality of oyster mushrooms depends on the length of stipe and it is suggested that in the case of yield, the larger the cap size, the higher the yield (Ahmed et al. 2013). Kortei et al. (2018) noted that the higher the stipe length and the smaller the mushroom cap diameter, the less desirable the quality of the marketable product. A similar result was reported by Yang et al. (2013) that the supplement of wheat bran and cotton seed hull to rice straw or wheat straw could shorten mushroom stipe length (3.1 cm) but increase mushroom cap diameter (9.2 cm), which confirmed the quality of mushrooms. Therefore, large-sized fruit bodies with shorter stipe are widely perceived to be of superior quality with high-ranking mushroom cultivation. Mushrooms with a relatively bigger pileus (cap), a higher thickness, and shorter but wider stipes are preferred for their marketable quality. This could be attained under optimum environmental conditions such as aeration, temperature, relative humidity, and substrate moisture holding capacity during the various growth stages (Vega et al. 2022). The results of the present study are in agreement with those of (Sánchez 2010; Onyango and Palapala 2011; Yang et al. 2013) indicated that locally available substrates with supplementation have been reported to boost the nutritional contents, yield, biological efficiency, mycelium growth, and quality of the fruiting bodies of the cultivated mushrooms.

Weight, total yield, and biological efficiency

A higher yield of P. ostreatus was obtained from the first flush and gradually decreased during the subsequent flushes (Fig. 4). Significantly higher (P < 0.05) total yield and biological efficiency (744.20 g/bag and 148.80%) were recorded from the mushroom cultivated on S2 substrate (Fig. 4). The biological efficiency of P. ostreatus mushroom species in the present study was higher in comparison to the results of other studies Hoa et al. (2015) involved in the cultivation of mushrooms on corncob and sugarcane bagasse substrates that resulted in biological efficiencies of 66.08 and 65.65%, respectively. Khan et al. (2021) reported a higher total yield of 388.40 g/bag and biological efficiency of 77.68% from oyster mushrooms cultivated on a substrate comprising 50% office scrap paper and 50% poultry manure, the results of which were lower than those of the current study. In contrast, Bhattacharjya et al. (2013) observed that the biological efficiency of P. ostreatus ranged from 187.0 to 213.2%, the values of which were higher than those of the current study. The current results agree with that of Das and Mukherjee (2007), who indicated a biological efficiency of 139.0% of the mushroom cultivated on the combined substrates of rice straw and weed plants. This is significantly affected by the application of different substrates and supplements, like cow dung, to the main substrates (Kortei et al. 2018). Also, Siwulski et al. (2017) described that pure sawdust is not very effective for mushroom growth and produces poor products. However, sawdust mixed with different nutrient supplements had significant effects on mushroom yield and productivity.

The result of the present study shows that the C/N ratio of the substrate formulas used in this experiment is negatively correlated with the total yield and biological efficiency of P. ostreatus mushrooms. The current result was in agreement with that of Philippoussis (2009) who reported that there is a strong negative correlation between mushroom yield (mushroom number and BE) and the C/N ratio of the substrate. The optimum C/N ratio (40.42%) was found for biological yield and biological efficiency of the mushroom cultivated on S2 substrate, the values of which were in agreement with those of Atila (2017), who suggested an optimum C/N ratio of 35.7 and 40.6% for P. ostreatus and P. florida, respectively. The values were within the range of the C/N ratio of 32/1 ~ 150/1 reported by Chang and Miles (2004) to be effective for pinhead formation in Pleurotus species. On the other hand, Wang et al. (2006) showed that there was a positive correlation between biological efficiency and the degradation of cellulose and hemicellulose but reported a negative relationship between biological efficiency and lignin degradation. Hoa et al. (2015) indicated that organic substances rich in cellulose were one of the best substrates for the cultivation of oyster mushrooms. Substrates with high lignin content decreased the activity of cellulose, but less lignin would enhance enzyme activity and thus ensure higher mushroom yield and biological efficiency (Atila 2017).

Nutritional composition of the harvested fruiting bodies

Protein insufficiency is one of the world’s most critical human dietary issues (Elkhateeb 2020). The protein content obtained in this study seems to be sufficient to solve this common problem. The high protein content of 13.27–21.53% obtained from mushrooms in this study could be due to the richness of carbon, nitrogen, and crude protein in the supplements added, as verified by the study of Odunmbaku, and Adenipekun (2018) which is essential for good health since protein helps in body growth, repair, and body tissue maintenance. Generally, the result obtained in this study is in agreement with that of Li et al. (2017), who cultivated P. ostreatus using cotton seed hull and perilla stalk with protein content ranging from 20.45 to 26.12%. Likewise, Cogorni et al. (2014) documented that the protein content of mushroom fruiting bodies cultivated on various substrates ranged from 20.33 to 25.33%. The results of which were similar to those of (Ashraf et al. 2013). The protein content obtained in this study is higher than the 5.2–10.85 reported by Das and Mukherjee (2007). Likewise, the protein and ash contents of the mushrooms obtained in the present study are comparable with that of Mintesnot et al. (2014), which may depend on the content of the growth substrates. Therefore, the protein content of the mushrooms depends on the selection and optimization of agro-industrial byproducts to enhance the dietary values of mushrooms.

The carbohydrate content achieved in this study indicated that mushrooms are a good source of energy, the result of which agrees with that of Li et al. (2017) and Tolera and Abera (2017), who reported carbohydrate contents ranging from 38.75 to 42%. The crude fiber content of P. ostreatus cultivated on different substrates ranged from 31.03 to 34.38%, which is higher than that of P. ostreatus cultivated on palm oil waste and sawdust supplemented with wheat and rice bran (Grimm et al. 2021; Elkanah et al. 2022). However, the fiber contents of the oyster mushroom are the same as those of P. ostreatus cultivated on sugarcane bagasse mixed with acacia sawdust (Adebayo et al. 2013). The current result is expected since sugarcane bagasse is a highly fibrous substrate and increases with proper formulation of the respective supplements.

The fat content obtained from P. ostreatus in this study is higher than that of (Onyeka and Okehie 2018; Grimm et al. 2021). Nevertheless, the low-fat content observed from P. ostreatus cultivated on all the substrates used in this study showed a lower caloric value (Elkanah et al. 2022). Low fat content makes mushrooms one of the most suitable dietary sources for patients with hypertensive problems. The moisture content of P. ostreatus cultivated on different substrates (6.14–8.82%) was generally lower, and the differences could be attributed to the drying level of mushroom samples (Adebayo et al. 2014). High water activities could increase microbial growth since they affect nutritional quality and chemical composition of P. ostreatus (Tolera and Abera 2017; Elkanah et al. 2022).

In the last three decades, human awareness of the promotion of good health through dietary intervention has increased, and eating edible mushrooms as sources of essential nutrients in diets is important for promoting human health (Oyetayo et al. 2013).

Mineral composition of the harvested fruiting bodies

The mineral element composition of P.ostreatus harvested from all the substrates showed variation in concentration as reported elsewhere (Manzi et al. 2001; Mleczek et al. 2021). Potassium has an important role in metabolism Keskin et al. (2021) and in maintaining an osmotic balance between cells and the intestinal fluid in the animal system. According to Raman et al. (2020), the presence of potassium in P. ostreatus showed that oyster mushrooms would be good at lowering blood pressure, reducing the risk of osteoporosis, and maintaining bone health (Bilal et al. 2010). A mushroom-based diet is recommended for those suffering from hypertension and heart disease due to its high potassium-to-sodium ratio (Elkanah et al. 2022). According to the results of this study, the content of potassium in the harvested P. ostreatus cultivated on different substrates was variable, as suggested by the results of previous studies (Alaimo et al. 2018; Mleczek et al. 2020; Golian et al. 2021). Hence, based on these values, it was concluded that the obtained values are compatible with the literature data. As indicated in Table 6, sodium was the highest mineral element found in the mushroom fruiting bodies, with different concentrations based on different substrates (Zhou et al. 2023). According to (Cogorni et al. 2014; Gao et al. 2020) the sodium content in the samples of P. ostreatus in the stipe and in the cap showed different values, the results of which were consistent with the results of the present study.

There is a good balance between the high content of K and the low content of Na in mushrooms that can be implicated in curing high blood pressure (Manzi et al. 2001). The results of this study showed that Pleurotus mushroom species have nutritive potential endowed with medicinal importance. Calcium is an essential mineral and is important in the prevention and development of osteoporosis and in the formation of strong bones and teeth (Arnold et al. 2021). The calcium content determined in this study was generally higher compared to that of the previous studies (Adebayo et al. 2018; Zhou et al. 2023). On the contrary, lower concentrations of calcium were observed in the current study compared to the previous studies (Cogorni et al.