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There-fore, the oxygen transfer performance of the new stirrer ispoorer than the Rushton turbine, consistent with the lowershear stress of the new stirrer. Although the dispersioncapacity is lower, the new stirrer is more suitable for theefficient top-to-bottom mixing of the viscous shear-thin-ning fermenting broths.In fact, all these KLa values were relatively low becausethe dynamic method was used in measuring KLa.In general, there are many measuring methods of KLa, mainlyincluding chemical method, sodium sulfite oxidationmethod and dynamic method. The chemical method cangive values higher than the real ones because the absorp-tion rate may be enhanced by fast chemical reactions in theliquid phase, if the experimental conditions are not keptwithin certain limits. The sodium sulfite oxidation methodalso has the limitation that, because some of its physico-chemical properties are very different from those of fer-mentation broths, the hydrodynamics of the solution ischanged, mainly due to the influence of those properties onbubble size. These changes cause the KLa values obtainedto be bigger than those obtained by other techniques, andnon realistic.The dynamic method, which is based on the measure-ment of dissolved oxygen concentration in the medium byabsorption or desorption of oxygen, is by far the mostcommonly used in the last decades to evaluate KLa, due toits simplicity. The accuracy of this method will be guar-anteed only when both the absorption and desorptionmeasurements give equal values of KLa under identicalhydrodynamics conditions. Furthermore, the dynamicresponse of the electrode must be taken into account fordetermining correct values of KLa if the characteristic time for oxygen electrode is of the same magnitude as thecharacteristic time for the oxygen transfer process (1/KLa).However, scientists generally do not consider this correc-tion, which results in relatively low KLa values. Therefore,compared to chemical method and sodium sulfite oxidationmethod, all these KLa values obtained are relatively low.The research also showed that the mixing power ratio ofthe Rushton turbine declined at low ventilation speedbecause a certain amount of gas gathered in the disc fol-lowing cavitation in the rear of the impeller [11]. Thestirring power of the straight diagonal-pitched blade stirreris relatively stable, indicating that there is no cavitation.When the gas flow rate was relatively large, the gasdestroyed the original cavitation behind the leaves expos-ing the back of the leaves to the liquid. This increases theflow resistance of the impeller and the mixing power.Flow pattern comparison of different impellersThe Re numbers of Rushton turbine and the new impellerare 30,759.0 and 32,036.0 respectively. If Re is larger than104, the fluid is in a turbulent state in the fermenter for bothstirrers. The top and bottom of the Rushton turbineimpellers form two areas of circulation and the overallmixing effect is relatively poor, but the new impellerproduces a central vortex pattern having mixed radial axialflow characteristics and a high mixing efficiency. Theoperating speed of the new impeller (ut = 0.888 m/s) istypically lower than that of the Rushton turbine(ut = 1.256 m/s), leading to a lower shear stress, reducingthe shearing of mycelium, and hence aiding mushroomgrowth and metabolite secretion.Pleurotus ostreatus fermentation using straightdiagonal-pitched blade stirrerPleurotus ostreatus was cultivated in submerged fermen-tation in a 5-L fermenter equipped with a straight diagonal-pitched blade stirrer. As shown in Fig. 5, the glucoseconsumption was slow in the initial stage of growth, thegrowth rate was also slow, and there is little differencebetween the two types of impellers. There was almost nodifference in laccase activity. As the rate of glucose con-sumption began to increase, mycelia grew rapidly andlaccase activity accumulated rapidly in the logarithmicphase. At this stage, the rate of glucose consumption withthis new stirrer is faster than that of the Rushton turbine,mycelia grew faster, and laccase activity was higher. Whenthe rate of glucose consumption decreased, mycelium dryweight began to decline, and laccase activity achieved astable value in the stable phase. In the declining phase,glucose was consumed gradually, mycelium dry weightcontinued to decline, and laccase activity began to decline. In the whole process, the growth of Pleurotus ostreatuswith this new stirrer was better than that with the Rushtonturbine and the mycelium can secrete metabolites in a moremoderate environment.