Impacts of temperature, pH, divalent cations, sugars and ethanol on the flocculating of SPSC01

Abstract

The pilot plant running demonstrated that the flocculating control of SPSC01, a self-flocculating ethanol fermentation yeast strain, is a prerequisite for both yeast cell immobilization through retention during fermentation and yeast floc recovery through sedimentation after fermentation. The impacts of fermentation process parameters including temperature, pH, divalent cations, sugars, and ethanol on the flocculating of SPSC01 were quantitatively investigated using recently established floc size distribution on-line monitoring technology. It was found that the flocculating of SPSC01 was thermo-stable when temperature was below 60 °C, but the deflocculating of SPSC01 occurred when temperature was higher than this criterion. The change of pH from 3.5 to 6.0 did not exert significant impact on the flocculating of SPSC01. The roles of divalent cations, Ca 2+ and Mg 2+, in the flocculating of SPSC01 depended on their concentrations. The optimum concentration of Ca 2+ was experimentally measured to be 1 mmol/L, almost the same level as that naturally existed in the industrial mash of starch materials, while no optimum concentration for Mg 2+ was observed in its concentration range of 0–100 mmol/L. Mannose showed deflocculating ability, which indicated that the flocculating of SPSC01 is MS phenotype. Glucose and sucrose showed weak deflocculating ability, which indicates industrial sugar or mash from starch materials for ethanol fermentation is suitable for this self-flocculating yeast strain. Ethanol exerted positive impact on the flocculating of SPSC01 when its concentration was below 15% (v/v), which indicates that better flocculating can be achieved in those rear fermentors in cascade fermentation systems where higher ethanol concentrations present. The negative impact of ethanol on the flocculating of SPSC01 was observed when ethanol concentration was higher than 15% (v/v).