| With the continuing development of the fermentation industry,liquid fermentation has become the trend of microbial industrial production.At present,the improvement of microbial fermentation efficiency is still focused on the screening mutagenesis and the optimization of culture conditions.However,these specific methods can only be applied for a specific species.Therefore,they are not universally applicable.Additionally,they are time-consuming and come with high research costs.Previous studies have found that microbial fermentation aided by low intensity alternating magnetic field can promote microbial growth or microbial metabolites synthesis.Therefore,the application of magnetic field(low intensity alternating magnetic field)into food processing provides a universally applicable new idea to further improve edible fungus industrial production rate.Grifola frondosa,an edible fungus with rich nutritional value and wide bioactivity,is chosen as the research subject to study the effect of alternating magnetic field on liquid fermentation.A single factor experiment is first conducted step-by-step in order to attain optimal flask condition of aided Grifola frondosa fermentation,along with a comparison of fermentation product(mycelia)under optimal and conventional conditions.Based on the results,a 5 liter fermentation tank expansion test is then carried out to demonstrate the possibility of its industrial use.Meanwhile,through the study of mycelia in magnetic aided groups and conventional fermentation groups on molecular levels,this paper also intends to explore the assistive mechanism of low intensity alternating magnetic field on liquid fermentation of Grifola frondosa.The main research work and its results are as follows:(1)Flask culture and fermentation of Grifola frondosa: Using mycelium biomass promotion rate of Grifola frondosa as the evaluation index,the enhancing effect of low intensity alternating magnetic field on the liquid fermentation of Grifola frondosa was studied.The results indicate that magnetic induction,magnetic treatment intervention time,magnetic treatment time and treatment times,as well as other conditions will affect the results of magnetic aided treatment.The optimal treatment conditions were as follows: the first magnetic intervention time was 1h after inoculation,the magnetic induction intensity was 35 Gs,and the magnetic treatment was carried out for 3h at the same time from the first day to the fourth day of fermentation,the biomass promotion rate was more than 11.43%.In the experimental group,when the magnetic treatment time was 3h and 5h,the "biological window effect" of the magnetic field took place.The effect of alternating magnetic field aided fermentation on the mycelium was most significant at the first 48 h of the fermentation period.The content of fiber and total sugar in the test group were increased by 14.29% and 28.05% respectively compared with the control group,the crude protein content(%)decreased by 3.18%,the crude fat content and the ash content(%)indicated no significant changes.There was no significant difference in the type of polysaccharide produced.The output of amino acid species was consistent,the content difference,however,was comparatively larger.Among them,the contents of Met,Val,Thr,Tyr and Ala in the experimental group were significantly higher than those in the control group,and the essential amino acid content percentage of the total free amino acid(47.7%)was significantly higher than that in the control group(37.8%).Using SEM and LSCM to observe the G.frondosa: SEM discovered that magnetic aided treatment apparently changed mycelial morphology,increased the number of mycelial branches,and contributed to a more loose mycelial body.LSCM discovered magnetic aided treatment also impacted the mycelial nuclei,since it may have accelerated the nucleus splitting rate.(2)Magnetic field promoting growth of G.frondosa expand training test: Choosing the optimal flask test conditions for fermenter culture,the experimental group biomass promotion rate reached 12%..In the process of liquid fermentation,the pH value of the fermentation broth decreased first but increased later.The content of polysaccharide in the fermentation broth was steadily decreasing,after fermentation test group content of polysaccharide(97.1 g/100 mL)higher than the control group(87.2 g/100 mL),and the fermentation broth relative dissolved oxygen in the test group was higher than that of the control group.(3)Transcriptome sequencing: After the magnetic auxiliary processing,amino acid metabolism related gene expression increased,conform to the increased of many kinds of amino acid content in mycelium in early experiment.And the cell repair and stress response gene expression quantity increased after magnetic auxiliary treatment,this may cause the mycelium biomass increase. |
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