The Method Of Monitoring Substrate Moisture Based On Low-field Nuclear Magnetic Resonance Technique And Its Application In Water-supply Solid-state Fermentation

Solid state fermentation is a kind of fermentation with gas phase as continuous phase,and there is no or almost no free water in the fermentation substrate.The water plays an important role in the process of solid-state fermentation,including the nutrients transportation and heat emission.During the process of fermentation,the moisture content of the’ substrate always gradually decrease due to the microial growth and the water evaporation,which in turn affects the fermentation efficiency of solid-state fermentation.In this study,the water detection method of fermentation substrate water was constructed by low-field nuclear magnetic resonance(LF-NMR)technique,and the effect of super absorbent polymers on water-supply solid-state fermentation was studied.The results of this study are as follows:(1)In this study,the determination method of substrate was established based on the soil physics and other research theories.The main physical parameters included water content,specific gravity,bulk density,specific surface area,total porosity and specific heat capacity,etc.The specific gravity was determined by pycnometer.The bulk density was measured by ring knife.The specific surface area was determined by the gas adsorption instrument.The specific heat capacity was measured by differential scanning calorimetry and so on.(2)The moisture standard curve of substrate was drawn by LF-NMR technology and can accurately reflect the moisture content and the different types of water of the substrate.The moisture standard curve of fermentation substrate with different particle sizes and the packing densities were also studied.For different sizes,the smaller the particle size,the shorter the retention time of the main peak of the substrate.When the water content was 70%,the retention time of the main peak of the 60 mesh substrate 59.13 ms,and the retention time of the main peak of the 5 mesh substrate was 90.78 ms.The retention time of 5 mesh substrate was larger than the 60 mesh by 34.86%.At different stacking densities,the greater the stacking densities,the greater the relaxation peak area of the substrate at the same water content.Detection by LF-NMR technology found that the water content in the fermentation substrate was mainly capillary water.With the growth and utilization of microorganisms and the water evaporation,the water content of the fermentation substrate reduced gradually,and the lost water was mainly capillary water.While the relaxation peak area of the adsorbed water did not change obviously,and the proportion of water in the substrate was also getting higher and higher.The lateral relaxation time of the fermentation substrate reduced gradually,indicating that the force between the substrate and the water was enhanced.(3)Addition of super absorbent polymers can realize the on-line water supply of capillary water for fermentation substrate.The optimum amount of super absorbent polymers was 7.5 g saturated super absorbent polymers/24.93 g wet substrate(water content 70%).The filter paper(FPA)and carboxymethyl cellulase(CMC)activities of Trichoderma reesei were the highest,reaching 376.840 U/g and 1025.968 U/g,respectively.The FPA and CMC activities and the biomass of Trichoderma reesei were improved by 2.327,1.646 and 1.6 times,respectively.The relaxation peak area of the fermentation substrate was shortened by LF-NMR technique,which indicated that the water content of the fermentation substrate decreased gradually,but the relaxation peak area of the water supply solid-state fermentation was larger than that of the substrate in static solid-state fermentation.Addition of the super absorbent polymers can effectively supply the water to the fermentation.By comparing the relaxation retention time for the main peak for the substrate in cold model solid-state fermentation(non-inoculation),static solid-state fermentation(inoculation)and water supply solid-state fermentation(inoculation and super absorbent polymers added),it was found that the.relaxation retention time of the main peak for water-supply solid-state fermentation was lower than that of the substrate in static solid-state fermentation and cold model solid-state fermentation at the same water content,which reflected the change in the physical structure of the fermentation substrate.It showed that addition of super absorbent polymers had a positive effect on solid-state fermentation.The physical parameters of static solid-state fermentation and water-supply solid-state fermentation substrates were measured and compared.It was found that the surface area,porosity and specific heat capacity of water supply solid-state fermentation substrate were larger than those of the substrate in static solid-state fermentation,and increased by 15.14%,1.66%,16.74%,respectively.The results showed that water supply solid-state fermentation was more favorable for the mass transfer,heat transfer and microbial growth.