Mobilization of endogenous glycogen and trehalose of industrial yeasts

Abstract

The fermentation of yeast reserve carbohydrates, glycogen and trehalose is a procedure to increase protein level of yeast cells and improve ethanol production. This work studied on the degradation kinetics of glycogen and trehalose carried out with two industrial strains of Saccharomyces cerevisiae (PE-2 and SA-1) and the effect of different temperatures (38°, 40°, 42° and 44°C) on degradation rate. Endogenous fermentation was carried out in a yeast suspension at 20% (w/v) based on wet weight, suspended in fermented media with 3.0 to 4.5 % (v/v) of ethanol. The degradation of the carbohydrate reserves at 40°C followed first-order kinetics, showing that its rate is mainly dependent on the carbohydrate concentration in the cell. The degradation rate (k) ranged from 0.0387 to 0.0746 h-1. Analyzing other parameters at 40°C, it was observed that viability and dry and wet yeast biomass were reduced while cell protein, ethanol, glycerol and nitrogen in the medium increased. Glycogen and trehalose degradation at different temperatures (38°, 40°, 42° e 44°C) showed that at 38°C the degradation rate was slow and from 42°C on the degradation of glycogen stopped after few hours of incubation. Thus, from a practical point of view, the best incubation temperature is around 40°C. The application of the Arrhenius equation showed that activation energy from 40° to 42°C was 165.90 and 107.94 kcal.°K-1.mol-1 for trehalose and glycogen respectively for PE-2 strain, and 190.64 and 149.87 kcal.°K -1.mol-1 respectively for SA-1 strain.