Establishment of a Sterilization Regime for Sugarcane Molasses Used in Baker's Yeast Production

Abstract

Background and Objective: Geobacillus stearothermophilus is a major contaminant of sugarcane molasses which withstand the traditional primary heat treatment of crude molasses and compete with baker’s yeast in sugar fermentation. Present work aims to study the thermal death kinetics of G. stearothermophilus and to establish a heat treatment regime for the molasses used in baker’s yeast production. Methodology: Thermal inactivation studies were carried out on spores of G. stearothermophilus strain-isolated from Egyptian sugarcane molasses and populated on TSB as well as diluted molasses (10E Brix) adjusted to pH 4.7. Thermal death kinetics were calculated using TDT-tubes at temperatures ranging from 90-130EC. The thermal death experiments were done after 1 h from primary preheating the spore suspensions at 80EC for 10 min to eliminate the vegetative cells and induce heat shock for the spores. Results: Survival curves of spores are linear following first-order kinetic pattern for spore heated at temperatures >115EC. Obtained decimal reduction time (D-values) were 23.71, 8.07, 4.68, 0.834, 0.473 and 0.174 min for spore suspensions heated in molasses media at 100, 110, 115, 120, 125 and 130EC, respectively. Spore suspensions heated in TSB media showed higher D-values. The temperature range (Z-value) required to reduce the D-value by 1/10 was in the range of 14.05EC. The obtained D and Z-values were used to establish a continuous sterilization regime for molasses to achieve a reduction of G. stearothermophilus spores of 7 logarithmic cycles to insure molasses sterility. The proposed sterilization system is based on steam injection, holding the molasses in a sterilization tube for the necessary time and flashing to reduce the molasses temperature. Calculated sterilization time was 73.08, 32.11 and 14.11 sec for sterilization temperatures 130, 135 and 140EC, respectively. The corresponding length of necessary holding tube was 89.16, 39.17 and 17.21 m, respectively. Conclusion: The pump power required to force the flow of molasses through sterilization system was in the range of 1.37-1.7 HP and the steam pressure needed for sterilization was 4-5 bar. The steam requirement is of 1 kg steam for each 10 kg molasses.