Microorganism cell disruption using a three-phase fluidized bed with agitator

Abstract

In this study, for the disruption of baker's yeast cells (Saccharomyces cerevisiae) to recover useful intracellular protein, a three-phase fluidized bed with agitator has been utilized as a new type cell disrupter. The three-phase system consists of yeast suspension, air bubble and glass beads employed as liquid phase, gas phase and solid phase, respectively. The operating parameters for the yeast cell disruption, which are impeller speed, the existing of draft tube in the fluidized bed column, superficial gas velocity, and superficial liquid velocity as well as bead size have been investigated extensively. The efficiency of disruption is evaluated by the yeast cell size distribution, and measuring total crude soluble protein released as well as using microscopic observation. The results show that in the case of presence of glass beads, an increase in the impeller speed between inthe range of 500 rpm and 3000 rpm does not affect on yeast cells disruption whether the gas bubbles are introduced into the system or not. On the other hands, with the presence of glass beads, the rate constant of yeast cells disruption increases with the increasing the impeller speed. The existing of the coaxial draft tube does not affect the yeast cell disruption compared with the single-phase mixing without the draft tube. Introduction of the gas bubbles into the bubble column also does not affect on yeast cells disruption whether the agitation is employed or not. Increasing the superficial gas velocity between 10 to 40 cm/min decreases the rate constant of yeast cell disruption but contributes the better heat transfer. The circulation of yeast suspension using centrigugal pump at the feed rate between 10 and 30 cm/min provides insignificant effect on the yeast cell disruption. Increasing the superficial liquid velocity decreases the rate constant of yeast cell disruption in the three-phase fluidized bed system. Glass beads with a diameter of 1000 mu m contribute to the higher efficiency of yeast cell disruption compared with those of 2000 mu m. The yeast cell rupture becomes less efficient at low impeller speed (25 rpm) although the direct contact between glass beads and impeller blades is employed.