Three-phase structure analysis of sawdust cultivation substrates and rapid detection of the optimal water environment for Lentinula edodes growth based on LF-NMR

The three-phase structure of the solid fermentation substrates is composed by the solid, liquid and gas phases, adjusting the ratio of the three-phase structure has proven to be a strategy that can better serve the growth of microorganisms. In this study, the effect of the three-phase structure of the cultivated substrate on the growth of Lentinula edodes was evaluated. Our results showed that the liquid phase was most impacted by the particle size and moisture content among the three-phase. Further analysis of the three-phase structure index (TPSI) showed that the highest efficiency of L. edodes growth was achieved at TPSI value of 23.3, and the liquid phase was the most affected variable on the TPSI of cultivated substrates among the three phases. Further, to determine the optimal water environment for L. edodes in the substrates, three types of water containing four proton components in the cultivation substrate were identified based on distributed exponential curve fitting of transverse relaxation (T-2), namely, bound water T-2b, free water T-21a and T-21b, and bulk water T-22. L. edodes exhibited the best growth efficiency on elm (59% moisture content), peanut shell (52% moisture content) and apricot (56% moisture content) substrates, all of which were filled with free water and without bulk water, respectively. The same conclusion was also obtained in the mixed material cultivation substrate. In overview, L. edodes had the best growth efficiency in substrates filled with free water and not containing bulk water, which enabled proton analysis based on LF-NMR spectroscopy to provide new insights into the moisture content of wood-rot fungal cultivated substrates.