Physico-chemical Properties Of Solid Medium And Novel Solid-state Fermentation Process

Solid-state fermentation has advantages of energy-saving,water-saving and environment-friendly.It should be the important strategy for releasing the bottleneck problems in current fermentation industry,including large amount water discharge and serious environment pollution.Physico-chemical properties of solid medium in solid-state fermentation were firstly studied,as well as its effect on solid-state fermentation.Secondly,suitable processes were developed based on biological characteristics of aerobic and anaerobic microorganism.The main results were listed as follows:(1)Solid medium in solid-state fermentation medium usually contains organic macromolecule which cannot be directly used by microorganism.Proper pretreatment of the solid medium is beneficial to microbial growth.In this thesis,steam explosion was employed to pretreat wheat bran.Results showed that total free sugars increased from 9.83 mg/g to 30.75 mg/g in wheat bran after steam explosion at 0.5 MPa,5 min.Monascus pilosus was employed to perform solid-state fermentation for esterifying enzyme production.Biomass in steam-exploded wheat bran increased from 30.5 mg/g to 63.6 mg/g while esterifying capability increased from 0.99 U/g to 1.72 U/g.Additionally,steam explosion can also get solid medium sterilized while pre-hydrolyze macromolecule in solid medium.Steam-explosion sterilization where the solid medium moves along with the gas flow and in-situ steam-explosion sterilization were compared.The two methods can sterilize the solid medium at 128?,5 min and 133 ?,10 min,respectively.In-situ steam-explosion sterilization showed lower efficiency but cannot overgrind the solid medium.Therefore,the two sterilization methods were suitable for different solid medium.(2)Physical characteristics of solid medium were studied,as well as its effect on conglomeration and loading coefficient.Hollow and solid cylindrical solid medium were obtained in granulation experiments of wheat bran.Compared with raw material,displacement of hollow and solid cylindrical solid medium reduced 9.5%and 20.7%respectively,indicting better anti-conglomeration capability of solid medium after granulation.Both of the raw and granulated solid medium were used to perform solids-state fermentation.In 100 mL working volume,loading coefficient of raw matrix,hollow and solid cylindrical solid medium were 21.2 g,62.7 and 67.5 respectively,and total biomass were 1.60 g,2.97 g and 2.22 g after solid-state fermentation.The results indicated granulation of wheat bran contributed to improving loading coefficient and biomass accumulation.(3)A two-steps gas double-dynamic solid-state aerobic fermentation process of Conithyrium minitans was developed.Gas double-dynamic solid-state fermentation increased biomass from 98.9 mg/g to 147 mg/g at 240 h while air pressure was set at 0.2 MPa,20s and normal pressure was kept for 20 min periodically,indicating gas-double dynamic contributed microbial growth.However,rapid microbial growth led to temperature accumulation,hindering pycnidia differentiation and formation of Conithyrium minitans and inhibiting conidia production radically.The two-steps gas-double dynamic refer to the process that cultivating Conithyrium minitans in gas double-dynamic environment at initial stage and transfer into low temperature when pycnidia began to differentiate.In the two-steps gas double-dynamic solid-state fermentation process,conidia were 1.53×1010/g dry mass.(4)Effect of tween-20,polyethylene glycol and sodium lignosulfonate on high-solid enzymatic hydrolysis of steam-exploded cornstalk.Results showed that 3%tween-20 and polyethylene glycol both contributed to glucan conversion.At 72 h,glucan conversion ratio reached to 73.85%in tween-20 assisted enzymatic hydrolysis.Additionally,a diffusion-reaction kinetic model which described the relationship between glucan conversion ratio and time was established.The model revealed that tween-20 increased relative diffusion rate by 7.3%.Additionally,low field nuclear magnetic resonance was employed to characterized water variation in enzymatic hydrolysis process of the steam-exploded cornstalk.The result revealed that less water restraint in tween-20 assisted enzymatic hydrolysis which provided a favorable environment for enzyme diffusion.(5)In order to solve the problems of high oxygen partial pressure and CO2 accumulation which go against sold-state anaerobic fermentation,nitrogen periodic pulsation sold-state anaerobic fermentation was invented.39.9 g/L ethanol was obtained at 24 h while high pressure was set at 0.2 MPa,20 s and normal pressure was kept for 180 min.21.7 g/L and 22.2 g/L ethanol was obtained at 24 h in nitrogen protection group and control group.CO2 concentration maintained at a low level(less than 5000 ppm)in nitrogen periodic pulsation sold-state anaerobic fermentation while that in control group accumulated to 38080 ppm at 21 h,indicating enhanced mass transfer by periodic pulsation.Nitrogen provided a desired anaerobic environment and periodic pulsation accelerated CO2 removal,thus improving solid-state anaerobic fermentation ethanol performance of Saccharomyces cerevisiae.