When the new stirrer was installedand used in a 5-L fermenter, P. ostreatus grew better thanwith the Rushton turbine. Glucose consumption was rela-tively faster, and the maximum dry weight of myceliumwas increased by 47 % to 7.4 g/L relative to the Rushton turbine. The maximum laccase activity is also increased by15 % up to 2,277 U/L.Analysis of the viscosityThe viscosity of the fermentation broth has some impact onthe metabolism of fermentation products. In most cases, ahigh viscosity of fermentation broth is detrimental to theproduction process of target metabolites from microor-ganism. As shown in Figs. 5 and 6, the viscosity changesare corresponding to the accelerated growth. The viscosityof the culture medium was increased exponentially duringthe cultivation time from 25 to 125 h. At the same time, thecell growth rate was also increased exponentially. There-fore, the relationship between cell growth and viscosityvalues is very regular. However, compared to the Rushtonturbine, the new stirrer can reduce the shear stress onbiological cells, which is beneficial to the accumulationand secretion of laccase, but is disadvantageous to accu-mulation and secretion of exopolysaccharides. Therefore,the viscosity of the fermentation broth of the new paddlewas lower than the conventional paddle throughout theprocess. In the logarithmic growth phase, the viscosity wasslightly higher, which may be due to the rapid myceliumgrowth. The lower viscosity of the fermentation promotesthe transfer of dissolved oxygen and complete mixing ofnutrients, all of which facilitate cell growth, and lead tomore products. Therefore, when the cellular activity andbiomass concentrations were getting similar in two fer-mentation runs, the viscosity courses were also different inthe late fermentation phase.Analysis of the pHIn general, the fermentation broth pH gradually increasedfor the secretion of alkaline metabolites. The pH gap isFig. 6 Time profiles of vsicosity during fermentation with differentstirrers. Rushton turbine (open triangle), straight diagonal-pitchedblade stirrer (closed triangle) small at the beginning of fermentation. In the fermentationprocess with the new impeller, the fermentation broth pHgradually increased and reached a stable value (Fig. 7),which was different from pH profile in the fermentationprocess using the Rushton turbine. When using the Rushtonturbine, at the latter stages of fermentation process, the pHdeclined and the mycelia began to autolyse. The mainreason for different pH profiles is the fact that myceliummorphologies are very different in two fermentation runs.Mycelium morphologies are mainly affected by the shearstress of stirrer. Compared to the Rushton turbine, the newstirrer can reduce the shear stress on biological cells, whichis beneficial to the intracellular accumulation of metabo-lites. At the same time, the lower shear stress cannotfacilitate the extracellular secretion of metabolites in shortperiod and change the fermentation broth pH greatly andrapidly. This is also the reason that the fermentation brothpH gradually increased and reached a stable value in thefermentation process with the new impeller.ConclusionsIn this work, a straight diagonal-pitched blade stirrer wasdesigned, built and characterized in a 5-L fermenter. At thesame time, the new stirrer was installed in a 5-L bioreactorand evaluated in submerged fermentation of the ediblefungus Pleurotus ostreatus. The results showed that,comparing with submerged cultivation using the Rushtonturbine, the maximum dry weight of mycelium is increasedby 47 % and reached 7.47 g/L, and the maximum laccaseactivity is increased by 15 % up to 2,277 U/L. Glucoseconsumption was also found to be relatively faster. Finally, the power consumption of this new stirrer is 2.8 % lowerthan that of the Rushton turbine. In submerged fermenta-tion of higher fungi, the straight diagonal-pitched bladestirrer should improve the production of mycelia andmetabolites and reduce production costs.
The informationobtained in this study may be a reference for other newstirrer designs.Acknowledgments We thank Robert K. Thomas FRS from Uni-versity of Oxford for his contribution in improving the manuscript.This work was financially supported by the Natural Science Foun-dation of China (No. 41276135, 31172010 and 30800775), Programfor New Century Excellent Talents in University (NCET-13-1031)and the Fundamental Research Funds for the Central Universities(13CX02063A).References1. Delabona Pda S, Farinas CS, Lima DJ, Pradella JG (2013)Experimental mixture design as a tool to enhance glycosylhydrolases production by a new Trichoderma harzianum P49P11strain cultivated under controlled bioreactor submerged fermen-tation. Bioresour Technol 132:401–4052. Bari SM, Balachandar S, Adrian RJ, Ha MY, Yoon H-S, Hill DF(2005) Reynolds number scaling of flow in a Rushton turbinestirred tank: part I-mean flow, circular jet and tip vortex scaling.Chem Eng Sci 60:3169–31833. Milly PJ, Toledo RT, Kerr WL, Armstead D (2008) Hydrody-namic cavitation: characterization of a novel design with energyconsiderations for the inactivation of Saccharomyces cerevisiaein apple juice. J Food Sci 73:298–3034. Li MZ, White G, Wilkinson D, Roberts JK (2005) Scale up studyof retreat curve impeller stirred tanks using LDA measurementsand CFD simulation. Chem Eng J 108:81–905. Xia JY, Wang YH, Zhang SL, Chen N, Yin P, Zhuang YP, Chu J(2009) Fluid dynamics investigation of variant impeller combi-nations by simulation and fermentation experiment. Biochem EngJ 43:252–2606. Wang SJ, Zhong JJ (1996) A novel centrifugal impeller biore-actor. I. Fluid circulation, mixing, and liquid velocity profiles.Biotechnol Bioeng 51:511–5197. Wang SJ, Zhong JJ (1996) A novel centrifugal impeller biore-actor. II. Oxygen transfer and power consumption. BiotechnolBioeng 51:520–5278. Zhang ZY, Zhong JJ (2004) Scale-up of centrifugal impellerbioreactor for hyperproduction of ginseng saponin and polysac-charide by high-density cultivation of panax notoginseng cells.Biotechnol Prog 20:1076–10819. Qian KX, Zeng P, Ru WM, Yuan HY (2007) An improved designof axially driven permanent maglev centrifugal pump withstreamlined impeller. J Med Eng Technol 31:170–17410. Arjunwadkar SJ, Saravananb K, Pandit AB, Kulkarnia PR (1998)Optimizing the impeller combination for maximum hold-up withminimum power consumption. Biochem Eng J 1:25–3011. Mounir B, Michel R (2001) Power consumption, mixing time andhomogenisation energy in dual-impeller agitated gas–liquidreactors. Chem Eng Process 40:87–95 直立式斜叶桨搅拌器英文文献和中文翻译(5):http://www.751com.cn/fanyi/lunwen_26369.html