Fermentations of the yeast Saccharomyces cerevisiae were carried out in a 90 to 250-L working volume concentric tube airlift fermentor. Measurements of liquid circulation velocity, gas hold-up, and liquid mixing were made under varying conditions of gas flowrate, vessel height, and top-section size. Both liquid circulation velocity and mixing time increased with vessel height. Liquid velocity varied approximately in proportion to the square root of column height, supporting a theoretically based relationship. The effect of vessel height on gas hold-up was negligible. The height of the top-section had a significant effect on liquid mixing. Mixing time decreased with increasing size of the top-section up to a critical height. As the top-section was expanded beyond this height, little improvement in mixing was seen. This indicated the presence of a two-zone flow pattern in the top-section. Liquid velocity and gas hold-up were essentially independent of top-section height. (c) 1994 John Wiley & Sons, Inc.

Yeast alcohol dehydrogenase (ADH) solutions (approximately 1 mg/ml, pH 7) were sheared in a coaxial cylindrical viscometer. This was fitted with a lid sealing the contents from the atmosphere and preventing evaporation. At 30 degrees C after a total of 5 hr intermittent shearing at 683 sec-1 no losses of activity were observed. No losses were found after 5 hr continuous shearing and in a no-shear control. At 40 degrees C and 683 sec-1 there were only small activity losses in 5 hr. Shearing at 3440 sec-1 no measurable losses of activity were found with a 1.03 mg/ml solution in 5 hr at 30 degrees C, a 1.03 mg/ml solution in 8 hr at 5 degrees C, and with a 3.89 mg/ml solution in 3 hr at 5 degrees C. In all these cases, however, a white precipitate formed that was not observed in zero shear control experiments. The sheared 3.89 mg/ml solution was clarified by centrifugation. It was shown that there were no ADH aggregates in the supernatant and that the precipitate was less than 2% of the original protein. At 30 degrees C under adverse pH conditions (pH 8.8) there was no significant difference in activity losses of an approximately 1 mg/ml solution sheared at 65 and 744 sec-1. An approximately 0.5 mg/ml ADH solution, pH 7, was agitated in a small reactor with no free air-liquid interface. Peak shear rates near the impeller were estimated to be about 9000 sec-1. Only a small decrease in specific activity was observed until over 15 hr total running at 5 degrees C.

SummaryIntermittent shear was applied to approximately 1 mg/ml solutions of bovine liver catalase in a coaxial cylindrical viscometer at temperatures from 20 to 60°C and shear rates up to 683 sec-I. The viscometer was sealed to prevent evaporation. Up to 40°C there were no activity losses during 3 hr total shearing. Above 40°C shearing reduced losses due to thermal inactivation, possibly by interfering with precipitation. At 3440 sec-l and 40°C fine precipitates formed but little activity was lost. No activity losses were found with experimentai conditions under which Taylor vortexing occurred, nor when shear stresses were increased up 57 times by adding glycerol to raise the viscosity. There were no significant losses in a capillary rheometer at shear rates up to 106 sec-*. When low concentration (6 pgiml) catalase solutions were sheared there was little loss in sealed systems, but there were losses in "open" systems even in low-temperature nonshear experiments. Although there were no losses with 1 mg/ml solutions, 6 pgiml catalase solutions from an alternative source did lose activity in sealed systems but much less than expected from previously published work. Approximately 1 mg/ml jack bean urease solutions were sheared in the sealed system at 23°C and 683 sec-I for 3 hr. N o losses were found. No evidence of temporary or permanent inactivation was found with 28 pgiml solutions sheared in the presence of urea. Shear forces alone were not found to be as effective in causing enzyme inactivation as is generally believed and alternative mechanisms for damage are discussed.

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