Effects of exogenous nutrients on the growth of mycelial biomass materials and its characterization

Abstract: Biodegradable materials have been drawn great attention to reduce carbon emissions under the concept of carbon neutrality and serious environmental pollution. A mycelium material has been widely developed as a new type of green biomass for these requirements. A completely degradable porous material can be prepared as follows. Some agricultural wastes (rich in cellulose, hemicellulose, and lignin, and mycelium) are degraded to penetrate or wrap the substrate for better binder function. As such, the nutrients of mycelium can be obtained by secreting cellulase, lignin peroxidase, and laccase. Therefore, it is very necessary to clarify the mycelial growth during preparation, in order to obtain a mycelial material with excellent performance. In this study, exogenous nutrients were added to promote mycelial growth in the process of traditional edible fungus culture. The mycelial growth rate was also taken as the response index. The best exogenous nutrients were first screened out using a single factor experiment. Then, a Plackett-Burman experiment was used to determine the main influencing factors on the growth of Pleurotus ostreatus, such as glucose, yeast powder, and KH2PO4. The steepest climbing test and Box-Behnken response surface method (RSM) were also used to obtain the best combination of exogenous nutrients. The results showed that the glucose, yeast powder, and potassium dihydrogen phosphate presented a significant effect on the growth rate of mycelium. Specifically, the model determination coefficient was 0.987 9, and the correction determination coefficient was 0.972 2, indicating an excellent performance and high reliability of the model. An optimal combination of parameters was also achieved, where 4.7% mass fraction glucose, 1% mass fraction yeast powder, and 0.3% mass fraction KH2PO4. The experiment showed that the average growth rate of mycelium was 10.28 mm/d, which was consistent with the predicted value. In addition, the structure and properties of mycelial materials were characterized in the control and nutrient groups. It was found that there was no significant difference in the density between 240-260 kg/m3. However, the Scanning Electron Microscope (SEM) images showed that the morphology of mycelium material with exogenous nutrients presented dense and tangled with each other, where the pores between the hyphae were reduced, compared with the control group. The shape was also the dense hyphal membrane structure in the nutrition group. Specifically, the average diameter of the hyphae in the nutrition group (1 730 nm) increased by 460 nm, compared with the control group (1 270 nm). The compression strength of the material in the nutrition group was 114 kPa, which increased by 43.7% over that in the control group. In terms of rebound rate, the material in the nutrition group (61.4%) was also slightly higher than that in the control group (55.3%). The mechanical properties demonstrated that the addition of exogenous nutrients promoted the growth of Pleurotus ostreatus mycelium, whereas, the increase in silk led to the increase in the strength and resilience of mycelial material. This finding can also provide a strong reference for the preparation and properties optimization of mycelial biomass materials.