Quantitative Changes in the Biochemical and Mineral Composition of the Substrate in Solid-State Cultivation of Enoki Mushroom

This study, for the first time, investigated the pattern of changes in a range of macromolecules and minerals of a lignocellulosic substrate utilized for cultivation of Enoki mushroom. Five different phases of a lignocellulosic substrate (consisting of 40% wheat straw + 40% sawdust + 18% wheat bran) were examined, including raw, mycelia-filled, pinning, fruiting, and the spent substrates. A well-authenticated native strain of Enoki mushroom, Flammulina velutipes, was used for cultivation in the substrate. The results exhibited a significant 1.35-fold, 1.18-fold, and 1.30-fold increase in nitrogen, soluble carbohydrates, and ash contents of the spent substrate, respectively, compared to the raw substrate. Conversely, a remarkable reduction was observed in holocellulose (27%), insoluble lignin (27%), insoluble carbohydrates (33%), and C:N ratio (33%) in the spent substrate, compared to the raw substrate. Soluble lignin increased by 23% in the mycelia-filled phase compared to the raw substrate, but it returned to its initial level in the spent substrate. Further HPLC coupled with GC–MS confirmed the lignin changes and demonstrated that the ratio of syringyl to guaiacyl (as lignin monolignols) increased towards the fructification phases. There was also a significant increase in the contents of elements in the spent substrate compared to the raw substrate. The data presented here provide evidences for understanding how biochemical changes in macromolecules of a lignocellulosic substrate could lead to optimum vegetative growth and fructification of Enoki mushroom, leaving a high-value non-toxic spent substrate.