Sachie Fujii

Drying of Yeasts—Factors Affecting Inactivation During Drying

The inactivation behavior of bakers yeasts during low-temperature hot air drying and freeze drying was investigated. The activity was determined by measuring the fermentative abilities. Inactivation was observed during the falling drying rate period even at low temperature (30°C). As their fermentation activities in suspensions at 30°C are maintained up to a few hours, this decrease was found to be due to dehydration inactivation. Similar dehydration inactivation was also observed during freeze drying. The dehydration inactivation became more significant when the drying rate was increased. The stability of dried yeasts increased with decreasing water content. The addition of sorbitol before drying further improved the stability of dried yeasts.

Enzyme Retention During Drying of Amorphous Sugar and Carbohydrate Solutions: Diffusion Model Revisited

Enzyme retention during drying of amorphous sugar and carbohydrate solutions was investigated based on the diffusion model. As the water diffusion coefficient decreases sharply with decreasing water content, there is a period where the water content decreases slowly while the sample temperature is high. The enzyme activity is lost in this period. However, as enzymes become stable at lower water contents, high enzyme retention is possible when the drying condition is tuned. The diffusion model with the heat balance equation and the inactivation rate equation was able to describe the experimental data reasonably. Various sugars tested (glucose, xylose, sucrose, trehalose, maltose, maltodetrin) showed similar enzyme retention behavior except for maltodextrin. Lower enzyme retention of maltodextrin is found to be due to lower drying rates.